Fabian Klenner
email: f.klenner@fu-berlin.de

Muhammad Umair

Sebastian H G Walter

Nozair Khawaja

Jon Hillier

Lenz Nölle

Zenghui Zou

Maryse Napoleoni

Arnaud Sanderink

Wilhelm Zuschneid

Bernd Abel

Frank Postberg

Illia Zymak
email: illia.zymak@eli-beams.eu

Ján Žabka

Miroslav Polášek

Jean-Pierre Lebreton

Bertrand Gaubicher

Barnabé Cherville

Anna Zymaková

Christelle Briois

Developing a Laser Induced Liquid Beam Ion Desorption Spectral Database as Reference for Spaceborne Mass Spectrometers

Keywords: high-resolution mass spectrometer, Orbitrap, continuous ion source, no C-trap, ion optics

Chapitre I

Le premier chapitre de cette thèse replace dans son contexte la recherche de la vie telle que nous la connaissons. Il y a eu de nombreuses tentatives pour définir le vivant, mais aucune définition ne parvient à faire l'unanimité dans la communauté. Malgré cela, les prérequis pour l'émergence de la vie sont connus : des éléments chimiques (CHNOPS), une source d'énergie et un solvant. La vie sur Terre a utilisé l'eau comme solvant, et la recherche de présence d'eau dans des corps planétaires est devenue la pierre angulaire de l'exobiologie, et plus largement de l'exploration spatiale. Les corps célestes avec un fort potentiel d'habitabilité sont les cibles privilégiées des agences spatiales. L'eau liquide peut se trouver à différent endroits dans un système solaire. D'abord, et comme c'est le cas pour la Terre, dans la "zone habitable", qui représente la zone autour d'une étoile où l'énergie stellaire est dans les bonnes proportions pour maintenir une température permettant d'abriter de l'eau liquide à la surface d'une planète. En dehors de cette zone habitable, de l'eau liquide peut également subsister grâce à d'autres sources d'énergies. C'est le cas pour les lunes des géantes gazeuses. L'excentricité des orbites des lunes induit un réchauffement de celles-ci par effet de marée. Encore une fois cette énergie doit être dans les bonnes proportions, trop d'énergie résulte en un volcanisme très intense et trop peu en une lune entièrement glacée. Dans notre Système Solaire, on trouve plusieurs lunes se trouvant dans une zone pouvant permettre l'apparition d'un océan de sous-surface. Les exemples les plus notables étant les lunes de Jupiter et Saturne, respectivement Europe et Encelade. Ces deux corps ont la particularité d'être à la bonne distance de leur planète hôte, mais également relativement petits, induisant de plus faibles pressions dans leur hydrosphère (i.e. la couche de glace en surface et la couche d'eau liquide). Ces pressions limitées empêchent la formation de glaces de hautes pressions, qui pourraient s'interfacer entre l'océan liquide et le noyau rocheux. Un tel cloisonnement pourrait empêcher des réactions hydrothermales, qui peuvent être à l'origine de l'enrichissement de l'océan liquide en élément chimique nécessaire à l'apparition de la Vie. C'est en raison de l'existence de ces réactions hydrothermales qu'Encelade et Europe sont les cibles privilégiées des missions spatiales avec une forte composante exobiologique. Parmi ces missions, on retrouve la mission NASA/ESA Cassini-Huygens, qui a étudié Saturne et ces lunes durant 14 ans, ainsi qu'Europa-Clipper, future mission NASA visant à étudier Europe.

Au pôle sud d'Encelade se trouvent des geysers éjectant des matériaux provenant des réservoirs d'eau liquide de sous-surface. Ces matériaux, généralement sub-micrométrique, sont sous forme de grains de poussière minérale ou de glace. Ces grains glacés sont tout particulièrement intéressant car ils contiennent des informations sur la composition de l'océan, révélé être riche en molécules organique. Cette composition a été mesurée par le Cosmic Dust Analyser (CDA) à bord de Cassini. CDA est un spectromètre de masse de type temps de vol, utilisant une méthode d'ionisation par impact hypervéloce (> 1 km/s), analysant ainsi la matière se trouvant autour d'Encelade. Les mesures de CDA ont permis de nombreuses découvertes, mais la faible résolution en masse de l'instrument (20 -50 m/Δm à mi-hauteur de 1 à 200 u) limite les possibilités d'interprétation des données. Un nouvel instrument bénéficiant de l'héritage de CDA, le SUrface Dust Analyser (SUDA) est actuellement en phase de développement et partira à bord d'Europa Clipper en 2024. Sa résolution en masse sera supérieure à celle de CDA (200-300 m/Δm de 1 à 500 u) mais celle-ci reste limitée et de nombreuses interférences isobariques seront présentes. Pour pallier à cela, Il est possible de reproduire en laboratoire la même technique d'ionisation que CDA ou SUDA en couplant un accélérateur de poussière à un analyseur masse, permettant ainsi de mesurer la composition de poussières hypervéloces avec de meilleures performances. Cependant, en raison de limitations techniques il n'est pas encore possible d'accélérer des grains de glaces avec un accélérateur de poussière. Afin de pouvoir reproduire les données de CDA, LILBID (Laser Induced Liquid Beam Ion Desorption), une technique d'ionisation analogue est utilisée. La technique LILBID consiste à ioniser un faisceau d'eau liquide micrométrique avec un laser pulsé infrarouge. Malgré la différence de phase entre l'eau liquide et les grains glacés, les spectres de masses sont similaires. Couplé à un analyseur en masse de type temps de vol (formant donc un LILBID-TOF), il est possible de reproduire les données de CDA en laboratoire, avec même une résolution en masse presque 20 fois supérieur (~800 m/Δm). Cette augmentation de résolution en masse permet de mieux comprendre les données, et d'aller plus loin dans leur CHAPTER IV FRENCH CHAPTER SUMMARIES comporte un module C-trap. Les conséquences de cette absence sont multiples et sont discutées dans ce chapitre. Enfin, la méthode de traitement de données ainsi que les outils de traitement qui ont été développés tout au long de la thèse sont présentés. Ceux-ci sont essentiels pour extraire des informations pertinentes des données brutes et des spectres de masse, permettant par la suite l'optimisation du banc de test.

Chapitre III

Le Chapitre 3 de la thèse présente les améliorations techniques entreprises sur l'instrument OLYMPIA. OLYMPIA a vu le jour en 2018 à Orléans, et ma thèse a débuté en Octobre 2019. Les premiers spectres d'OLYMPIA ont été obtenus peu de temps avant cette date. Ces résultats préliminaires présentaient une résolution en masse maximale d'uniquement quelques milliers avec une précision en masse parfois supérieur à 100 ppm, ces valeurs étant loin des performances attendues d'un spectromètre de masse intégrant une cellule Orbitrap. À cette époque, le couplage pérenne d'OLYMPIA à l'installation LILBID de Berlin était prévu pour l'été 2020. Le temps disponible avant le déménagement a donc été mis à profit pour améliorer différents sous-systèmes d OLYMPIA, afin d'accroître sa fiabilité et ses performances.

Nous avons identifié plusieurs sous-systèmes nécessitant des améliorations, comme l'optique ionique, l'efficacité du vide ou la stabilité de la tension dans la cellule Orbitrap. Cette dernière était très probablement responsable des résultats à faible résolution de masse. Comme ces modifications ont eu lieu à Orléans au LPC2E, elles ont été effectuées avec une configuration d'OLYMPIA utilisant de l'Impact Electronique (IE) comme ionisation. L'optimisation s'est faite en différentes phases. Une première phase a consisté en des améliorations techniques, afin de rendre le setup plus fiable et l'ionisation plus stable. Chaque sous-système fût alors démonté et nettoyé en profondeur. À la suite de cela, il a été très difficile de mesurer à nouveau des spectres en masse. Beaucoup de temps a été consacré pour trouver ce qui empêchait les ions d'être mesurés, et à améliorer chaque étape du processus. Le vide, un paramètre crucial pour obtenir de haute performances, a été amélioré en changeant des brides et plusieurs pompes. Divers connecteurs, assurant une meilleure stabilité pour les hautes tensions ont également été installés. OLYMPIA fut de nouveau fonctionnelle durant l'été 2020.

La deuxième phase d'optimisation commença afin d'atteindre la haute résolution en masse attendue. Les performances obtenues avec différentes alimentations haute tension des électrodes de la cellule Orbitrap (l'électrode centrale et l'électrode de déviation) pointèrent que nous ne pouvions nous passer de l'utilisation d'une haute tension commerciale Thermo Fisher pour significativement augmenter le temps de vie des ions capturés dans la cellule, et ainsi d'atteindre de très haute résolution en masse.

Après cela, il a été possible d'entreprendre des améliorations à plus grande échelle. Dans la configuration initiale, le préamplificateur d'OLYMPIA était la version également utilisée dans les Orbitrap™ commerciaux. Un nouveau préamplificateur compatible avec le vide a été construit par nos collaborateurs tchèques. La comparaison de mesures confirma le choix du préamplificateur tchèque, car sa capacité à pouvoir être placé sous vide permet d'obtenir un meilleur signal, celui-ci étant alors protégé de l'environnement radio extérieur.

Fort des hautes performances de mesures de l'instrument, nous avons ensuite entrepris la détermination de la valeur optimale de l'électrode de déflection. Une mauvaise valeur de tension appliquée sur cette électrode peut induire de nombreux biais lors des mesures. Par exemple des variations de temps de vie entre différents isotopes ou de pics de masse asymétriques. Une méthode d'optimisation ainsi que des routines MATLAB pour le traitement de données ont été développées. Malheureusement, il n'a pas été possible de conclure sur une valeur précise, les résultats pointant plutôt sur un gamme de tension assez grande. Cependant la méthode développée peut être utilisée pour des configurations futures d'OLYMPIA, ou d'autres instruments basés sur une cellule Orbitrap. Le fait que la tension appliquée sur l'électrode de déflection ne soit que peu impactant sur nos données actuelles, soulève certaines questions sur la méthode d'injection des ions. En effet, comme le setup ne comporte pas de module C-Trap pour gérer l'injection, celle-ci est directe et continue. Une injection continue peut être assimilée à l'injection de charges pendant les mesures, qui peuvent donc déstabiliser les ions capturés dans la cellule Orbitrap. Afin de vérifier que cette insensibilité à l'électrode de déflection est bien liée à l'injection continue, des tests devront être effectués avec une injection pulsée, et ce, en utilisant la technique LILBID.

First and foremost, I extend my deepest gratitude to Christelle for her tireless efforts in securing funding, both in France and abroad. It was her unwavering belief in me that led to the proposal of this PhD subject and allowed me to embark on this remarkable journey. I would also like to express my heartfelt appreciation to Frank in Berlin, who took a chance on a candidate with minimal chemistry background for a mass spectrometry-focused topic. It is not uncommon for PhD students to struggle in their relationships with their supervisors. However, I could never relate to such difficulties as you both proved to be exceptionally supportive and dedicated to the project.. Additionally, I extend my thanks to Valéry for his invaluable advice and proofreading assistance throughout these three years.

My thanks also go to the CNES for the funding, and in particular, I would like to express my gratitude to Francis Rocard for his consistent support in the development of the Orbitrap in Orléans. Jano, you not only created OLYMPIA but also made this PhD possible. I am grateful for your contributions and the pieces of advice you provided. Collaborating with you has been a truly enjoyable experience, both on OLYMPIA and HANKA. Thank you for allowing me to be a part of this incredible space adventure.

I would like to express my gratitude to all my colleagues in Orléans. Bertrand, it was an absolute pleasure working with you. Your meticulousness and your 'eagerness not to rush' were crucial when dealing with such a delicate instrument. I am also thankful for all the trips you made to Berlin to assist me in the lab. Jean-Pierre, I couldn't have wished for a better partner in data processing and our engaging discussions on spacecraft and space missions. A special thanks also goes to Laurent and Fabrice for your valuable expertise. Laura, organising the session at EPSC was a fantastic experience, that I am looking forward to renew.

In Berlin, I would like to extend my sincere thanks to Fabian for his invaluable support in navigating the complexities of LILBID. Your guidance and expertise have been crucial with this demanding technique. I am also grateful for the enriching scientific discussions we shared and for your assistance in proofreading. Additionally, I want to express my gratitude to my officemates as well as Maryse, Pietro, and Lucia.

A heartfelt thank you to Ales and Bernd in Leipzig for their invaluable help throughout my thesis and for generously lending us their laser, which saved us hours on optical realignment. Your support and expertise have been truly appreciated.

Marie-Helène, thank you for meticulously checking the English in my entire thesis. It is already a long read for those in the field, it must have been even longer since you are not familiar with it.

Thanks to all the members of the jury defence. To the rapporteurs, Gabriel and Peter, and to the examiners, Morgan and Ralf. It has been an honor to be able to present you my work, and your challenging questions brought the PhD to a beautiful end. Morgan, thanks a lot for giving me the opportunity to present this project at the AGU Fall Meeting in New Orleans, it was a truly wonderful experience, especially after a challenging year of the pandemic. Big thanks to the two reviewers of my publication, your feedback came during the writing of this manuscript and allowed me to delve deeper into the interpretation and understanding of the data.

Pour finir merci à toute ma famille et mes amis, ces lignes sont les dernières que j'écris en tant qu'étudiant et beaucoup d'entre vous savent que ça n'a jamais été un long fleuve tranquille. Merci à tous d'avoir été là toutes ces années.

Et enfin ma chère Raphaëlle, merci de m'avoir épaulé pendant toute cette thèse, de m'avoir permis d'en relever les défis, et de m'avoir appris à être fier de ce que j'avais accompli.

CHAPTER II

FRENCH CHAPTER SUMMARIES interprétation. Cependant, et malgré cette augmentation significative, de nombreuses interférences isobariques sont toujours présentes.

C'est dans ce contexte que ces travaux de thèse ont été conduits. Afin d'approfondir notre compréhension de la composition des océans de sous surface des lune glacées, il est nécessaire d'améliorer nos capacités analytiques avec une meilleure résolution en masse. Pour ce faire, un tout nouvel instrument a été construit, utilisant une méthode d'analyse capable d'atteindre des résolutions en masse ultra haute, la technologie Orbitrap™, qui sera présentée dans le chapitre suivant. L'objectif de cette thèse est de développer ce nouvel instrument, et de le coupler à la méthode d'ionisation LILBID, créant un setup unique au monde. Les hautes performances de ce nouvel instrument permettront d'enrichir la base de données de SUDA (et par la même de CDA) créée avec le LILBID-TOF, en la complétant avec des données à très haute résolution en masse.

Chapitre II

Le deuxième chapitre de cette thèse présente l'histoire du développement et le fonctionnement de la technologie Orbitrap™, inventée par Alexander Makarov en 1999. Un Orbitrap™ est un analyseur en masse de type piège à ions. La cellule est composée d'une électrode centrale, de deux électrodes externes et d'une électrode de déflection. Les ions étudiés sont injectés dans la cellule et capturés en orbite autour de l'électrode centrale grâce à un champ électrostatique. Ce champ est défini par l'électrode centrale, sur laquelle une haute tension est appliquée. L'oscillation harmonique des ions d'un côté à l'autre de la cellule est mesurée par le courant d'image induit par ceux-ci sur les deux électrodes externes. Chaque masse à sa propre fréquence d'oscillation, qui peut alors être retrouvée via une Transformée de Fourier. Le grand avantage de cette méthode d'analyse est qu'il est possible de mesurer de très faible variation de fréquences, et donc d'obtenir une résolution en masse très élevée. La résolution en masse augmente avec le temps d'acquisition. La stabilité du champ électrostatique à l'intérieur de la cellule est donc cruciale pour des mesures de qualité.

Depuis 2005, Alexander Makarov travaille pour la société Thermo Fisher avec laquelle il a commercialisé la technologie Orbitrap qui est largement utilisée dans de nombreux domaines de recherche, notamment en biologie, en chimie ou en géologie. Afin d'améliorer les capacités analytiques de l'instrument, de nombreux sous systèmes ont été ajoutés à la version commerciale. L'amélioration technique la plus notable est le système d'injection des ions, le C-trap. Le C-trap est en quelque sorte un réservoir qui stocke les ions et les injecte dans la cellule Orbitrap avec une énergie cinétique très définie, et dans un temps très court (~100 ns). Cette méthode permet un piégeage optimal des ions, ceux-ci orbitent ainsi à l'intérieur de la cellule dans un « anneau » très défini. Les ions sont alors très stables à l'intérieur de la cellule, permettant de long temps d'acquisition, et ce avec une intensité mesurée maximale.

Depuis 2009, le LPC2E pilote un Consortium visant à adapter la technologie Orbitrap™ à l'environnement spatial, afin d'amener ses hautes performances d'ultra résolution en masse pour les futures missions d'exploration spatiale. C'est lors de discussions préparant de futures missions spatiales, en 2010, qu'une collaboration avec l'équipe allemande/américaine (R. Srama, F. Potsberg, S. Kempf) et le LPC2E pour l'étude des poussières du Système Solaire a germé. Comme mentionné au précédent chapitre, l'instrument SUDA (PI : S. Kempf, LASP, Univ. Colorado) fait partie de la charge utile de la mission NASA/Europa-Clipper. En couplant un dispositif d'analyseur/détecteur en masse de type Orbitrap au dispositif LILBID nous accéderons à une plus grande résolution en masse (LILBID opérant comme SUDA, actuellement avec un TOF (Time-Of-Flight)). Ces travaux seront essentiels pour l'interprétation des contaminants organiques complexes intégrés dans la croûte de glace d'Europe. Ce développement permettra d'établir une bibliothèque de spectres de haute résolution en masse pour l'environnement d'Europe.

Dans ce cadre en 2017 une collaboration entre le LPC2E et l'institut de Physique Chimie J.Heyrovský à Prague, dans le but de construire un nouvel instrument entièrement dédié au couplage avec le système d'ionisation LILBID. Lors d'un séjour d'une année en tant que chercheur invité, Jan Zàbka a designé et initié la construction de ce nouveau banc de tests baptisé OLYMPIA (Orbitrap anaLYser MultiPle IonisAtion). OLYMPIA a été construit avec une majorité d'éléments sur étagère, principalement pour la chaîne d'acquisition et le système d'ultra-vide. La cellule Orbitrap, constituant la partie analyseur de l'instrument est une cellule commerciale D30 utilisé pour les Orbitrap™ commerciaux de Thermo Fisher. Certains sous-systèmes ont été conçu spécialement pour le setup, notamment l'optique ionique. Afin de pouvoir travailler indépendamment du système LILBID, situé en Allemagne, les premiers travaux de calibration d'OLYMPIA ont été effectué avec une source d'impact électronique. Cette méthode d'ionisation a pour avantage d'être relativement simple à mettre en oeuvre, hautement reproductible et peu coûteuse. Grâce à cette configuration, il a été possible de travailler à Orléans sur ce nouveau banc de test, afin de s'assurer de son bon fonctionnement avant le couplage avec LILBID. Ce chapitre présente en détail chaque sous système d'OLYMPIA, leur fonctionnement ainsi que la méthode pour les optimiser. Le design d'OLYMPIA étant inspiré du CosmOrbitrap, lui-même conçu pour des applications spatiales, aucun des deux instruments ne

Chapitre IV

Grâce à tous les travaux d'optimisation présentés dans le chapitre précédent, OLYMPIA est maintenant capable d'enregistrer des spectres à haute résolution de masse pour des composés gazeux en utilisant la technique d'ionisation par impact électronique. Après cette phase d'optimisation, l'objectif était de démontrer les capacités nouvellement acquises du setup dans un contexte d'exploration spatiale en analysant des gaz pertinents pour l'études des atmosphères planétaires. Les résultats de ce chapitre font l'objet d'une publication, consultable en Annexe II.

CHAPTER V FRENCH CHAPTER SUMMARIES

Pour ce faire, nous avons mesuré un mélange de gaz composé de trois gaz ayant un rapport m/z très proche : le monoxyde de carbone CO (27,9949 u), l'éthylène C 2 H 4 (28,0313 u) et diazote N 2 (28,0061 u). La quantification de l'abondance de N 2 dans les corps célestes donne des informations sur les conditions dans lesquelles ils se sont formés, cependant, en raison de sa proximité en m/z avec la molécule de CO, le rapport est rarement quantifié, et ce à cause de la faible résolution en masse des spectromètres de masse spatiaux. Seul le spectromètre de masse ROSINA à bord de la sonde européenne Rosetta a été capable de quantifier ce rapport autour de la comète 67P. L'étude de ce mélange de gaz a été un succès, et les trois pics de masses ont pu être séparés. La résolution en masse atteinte, pour une transformée de Fourier de 250 ms, est d'environ 50 000. Malgré une concentration volumique initiale égale, l'amplitudes des trois espèces chimiques est bien différentes dans le spectre en masse, C 2 H 4 étant deux fois plus haut que CO et N 2 . Cela est dû à des différences de section efficace d'ionisation, ionisant plus efficacement les molécules les plus grandes (ici C 2 H 4 ) que les plus petites (CO et N 2 ). De plus, les espèces avec l'énergie d'ionisation la plus faible seront également amplifiées par transfert de charge. Enfin, l'ionisation par impact électronique produit de nombreux fragments, pouvant réduire l'amplitude du pic de la molécule mère.

Pour d'autant plus caractériser les performances d'OLYMPIA, un échantillon de Krypton pur a été analysé. Le Krypton est un gaz noble composé de six isotopes stables, et leur détection permet donc une estimation de la précision de l'abondance isotopique relative (RIA) du setup. La détermination de cette précision a été effectuée sur des spectres en masse avec une durée pour la transformée de Fourier de 50 et 250 ms. Afin de calculer plus précisément, et en retirant les biais expérimentaux, la valeur en amplitude de chaque isotope, l'aire sous la courbe de chaque pic est prise en compte, et ce à 10% de la hauteur totale. La précision du RIA est calculée sur une trentaine de fichiers de données afin de pouvoir quantifier la variabilité de celle-ci. Les résultats de cette étude ont montré une très forte variabilité dans les valeurs d'amplitude de chaque isotope, ainsi qu'une surestimation (jusqu'à plus de 4 fois la valeur théorique) des ions peu abondants. Cette surestimation peut également être interprétée comme une sous-estimation de l'amplitude de l'ion majoritaire, sur laquelle les autres isotopes sont calibrés. Cette sous-estimation montre une fois de plus que le comportement des ions n'est pas optimal à l'intérieur de la cellule. L'hypothèse la plus probable pointe à nouveau vers l'injection continue des ions, qui ne permet pas, d'une part, la création d'un paquet d'ions défini afin d'optimiser la capture en orbite autour de l'électrode centrale, et d'autre part, d'assurer une stabilité des ions pendant la mesure. Il est cependant également difficile de conclure sans faire des mesures avec une injection pulsée.

Enfin, afin d'estimer le nouveau temps de vie maximal des ions dans la cellule Orbitrap, le signal brut a été coupé en tranche afin de suivre l'évolution du rapport signal sur bruit pendant la mesure. Grâce à une meilleure définition et stabilité du champ électrostatique dans la cellule, le signal est maintenant détectable jusqu'à plus de 500 ms, soit dix fois plus qu'au début de ces travaux. Une comparaison entre la résolution en masse mesurée et théorique a été faite, celle-ci atteignant environ 85% pour l'ion majoritaire. En revanche, les autres ions, moins abondants, n'atteignent qu'environ 40% de la valeur théorique.

OLYMPIA a été conçue pour être couplée avec LILBID, mais sa capacité à mesurer des gaz reste un grand avantage. Ainsi, dans l'hypothèse ou le setup serait de nouveau utilisé en configuration impact électronique, des perspectives sont également présentées. Les fortes contraintes de pressions dans la cellule Orbitrap sont antagonistes avec l'injection d'un échantillon gazeux. Un nouveau design pour la source d'ionisation est en cours afin de rendre celle-ci plus efficace, et de réduire le volume de gaz nécessaire pour une ionisation optimale. Cela permettrait un meilleur vide dans la cellule Orbitrap, et donc un temps de vie des ions à l'intérieur de celle-ci étendue. De plus, comme l'injection continue semble induire de nombreux biais il est envisagé d'utiliser une vanne capable d'injecter l'échantillon gazeux pendant un temps très court, se rapprochant ainsi d'une injection pulsée.

Chapitre V

Le chapitre V présente le couplage d'OLYMPIA avec la technique d'ionisation LILBID. Même si l'ionisation entre le LILBID-TOF et LILBID-OLYMPIA est similaire, certaines adaptations ont dû être apportées afin de pouvoir interfacer LILBID avec un analyseur en masse de type Orbitrap™. Pour bien comprendre ces différences, le fonctionnement du temps de vol est décrit. Celui-ci utilise le principe d'extraction retardée. Cela consiste en une ionisation sans champ électrostatique, suivie d'une accélération par commutation rapide de la tension des électrodes situées proche de la source. Le délai entre l'ionisation et l'accélération des ions permet de sélectionner des ions plus ou moins lents, et donc plus ou moins lourds. Ces ions lourds sont des marqueurs de vitesses d'impact analogues faibles. En effet, il est possible en sélectionnant différents sets de paramètres de reproduire des spectres en masse mesurés par CDA à différentes vélocités. De fortes vélocités (>15 km/s) impliquent une forte énergie d'ionisation qui fragmente totalement les molécules d'intérêt. À l'inverse, des vélocités plus faibles (~5 km/s) préservent l'intégrité des molécules et créent des clusters d'eau de la forme (H 2 O) n H 3 O + . La possibilité de reproduire différentes vitesses analogues est un atout, cependant les vitesses les plus intéressantes scientifiquement sont celles préservant l'intégrité des molécules organiques. En effet, pouvoir détecter la molécule mère et non ses CHAPTER V FRENCH CHAPTER SUMMARIES fragments permet de mieux caractériser la chimie organique présente dans l'océan.

Ce chapitre présente également les résultats obtenus lors de la campagne de couplage LILBID-OLYMPIA d'octobre 2019. Cette campagne a eu lieu au tout début de ces travaux de thèse, et est donc antérieur aux phases d'optimisation présentée dans le chapitre III. Elle a permis de mesurer pour la première fois des ions issus de l'interaction entre le laser pulsé et de l'eau liquide. Ces ions ne sont cependant pas « des ions LILBID » à proprement parler, car la longueur d'onde du laser a dû être abaissée de 2840 nm à 1064 nm. Ceci a pour effet d'augmenter l'énergie du laser, s'éloignant ainsi du régime de désorption caractéristique de LILBID. Avec une énergie d'ionisation plus importante, le nuage ionique créé est plus important, facilitant les mesures. Cependant, même s'il a été possible de mesurer des ions d'eau avec cette configuration, ceux-ci ne sont pas applicables pour l'objectif scientifique de ces travaux, à savoir l'étude des organiques présent dans les océans de sous-surface des lunes glacées. En effet le régime de désorption est nécessaire afin de pouvoir interpréter les données dans ce contexte.

Vient ensuite la description des travaux entrepris à Berlin. Le départ à Berlin, et le couplage plus pérenne entre OLYMPIA et LILBID était initialement prévu en août 2020. Cependant, dû à la pandémie et à l'impossibilité de se déplacer à l'international, le déménagement a été repoussé à février 2021. Contrairement aux intégrations mécaniques précédentes (lors des 3 campagnes à Leipzig, en 2018 et 2019, et celle de Berlin en août 2020) où OLYMPIA avait été placée à la place du TOF, l'intégration c'est cette fois-ci faite en parallèle, afin d'être toujours en mesure d'utiliser le temps de vol. En effet, l'objectif n'est pas de remplacer le TOF, celui-ci ayant ses propres avantages. Le nouveau couplage LILBID-OLYMPIA a pour but de complémenter ceux-ci. Les deux modes d'analyses en masse sont quasiment indépendants et le changement de configuration est réalisable en un temps très court.

Après l'intégration mécanique, la première étape était de contrôler la justesse de l'alignement entre la source, l'optique ionique et la cellule Orbitrap. Pour ce faire, les premières mesures ont été effectuées en ionisant un fil d'étain. Tirer sur un métal permet d'obtenir une ionisation bien plus efficace que sur un film d'eau liquide, et facilite donc la calibration de l'instrument. La mesure des isotopes de l'étain a rapidement été possible et a permis de comparer les performances du dispositif avec une injection pulsée et continue. Les performances d'OLYMPIA avec ce nouveau mode d'ionisation sont bien plus élevées que pour l'impact électronique. Le temps de vie des ions dans la cellule est bien plus élevé, un signal très fort (> 400 de rapport signal sur bruit) étant encore observé à 850 ms. Tous les isotopes stables de l'étain sont détectés, même le plus faible ( 115 Sn) qui n'est abondant qu'à 0.34%. La résolution en masse théorique à mi-hauteur du pic pour une durée de signal de 300 ms pour les isotopes de l'étain est de 99%, indiquant une stabilité optimale dans la cellule Orbitrap. Enfin, la détermination de la précision de l'abondance isotopique a été effectuée avec la même méthode que pour l'étude sur le Krypton. Les résultats sont également bien meilleurs, avec une déviation de seulement quelques pourcents. A l'inverse de l'étude en configuration impact électronique, une sous-estimation de l'intensité des isotopes les moins abondants (< 1%) est observée. Ce phénomène est cependant connu et également observé dans les Orbitrap™ commerciaux. Cela est dû à des effets de charge induit par les ions majeurs sur les ions mineurs, les déstabilisant à l'intérieur de la cellule.

L'étude sur l'étain ayant été un succès, l'ionisation du faisceau d'eau liquide caractéristique de LILBID a débuté. Cette fois-ci avec une longueur d'onde laser de 2840 nm et donc sous un régime de désorption, des ions H 3 O + and H 2 O + ont été mesurés. Cette mesure est une première : jamais auparavant des ions issus de désorption laser sur un faisceau d'eau n'avaient été mesurés avec une cellule Orbitrap. L'apparence des spectres en masse est similaire à ceux mesurés par CDA à des vélocités entre 15 et 18 km/s. Ce régime correspond à celui où aucun cluster d'eau n'est observé, ni d'espèce observable à plus haute énergie tel que OH + . Ces résultats font l'objet d'une publication dans Analytical Chemistry, présentée en Annexe III. Avec un temps court pour la transformée de Fourier de 50 ms, la résolution en masse mesurée (à mi-hauteur du pic) est à 95% de celle obtenue par la théorique, et la précision en masse est de quelques ppm. Des mesures ont été faites avec une durée de 500 ms pour la transformée de Fourier, on observe alors une duplication des pics. Globalement, la durée de vie des ions d'eau est inférieure à ceux de l'étain. Ceci est dû à une pression plus élevée dans la chambre, l'eau liquide dégazant à l'intérieur et détériorant donc le vide.

Afin de pouvoir à nouveau effectuer une estimation de l'exactitude de l'abondance relative isotopique, une solution d'eau avec 2% de deutérium a été analysée. Sur un grand nombre de spectres, l'erreur d'estimation de l'intensité du pic DH 2 O + par rapport au pic d'H 3 O + est de seulement 1%.

Suite à ce premier succès, l'objectif suivant était de pouvoir mesurer des clusters d'eau. Ceci s'est avéré être le plus grand challenge de ces travaux. Malgré des variations d'énergie laser, il n'a pas été possible de mesurer les clusters d'eau. Les mois qui ont suivi ont donc été dédiés à la recherche de ce qui empêchait la mesure de ces clusters d'eau. Parmi tous les tests effectués, le plus notable a été de caractériser l'impact de la haute tension dans la source sur leur création/distribution. Pour ce faire, la buse du jet d'eau d'OLYMPIA, sur laquelle peut être appliquée une haute tension a été placée sur le dispositif LILBID-TOF. Des mesures ont été réalisées à différents délais d'extraction et différentes valeurs de haute tension. La conclusion de cette étude a permis d'être certain qu'appliquer une tension dans la source n'empêchait pas la formation des clusters d'eau. Cela dit, leur distribution COMPARISON CHAPTER & CONCLUSION FRENCH CHAPTER SUMMARIES est grandement affectée. En effet, avec une haute valeur dans la source (>1000 V) les clusters n'ont plus la distribution typique de CDA ou du LILBID-TOF, passant d'une distribution en gaussienne à une distribution plate sur toute la gamme de masse.

Sachant cela, il est donc nécessaire de limiter les valeurs en tension dans la source pour le dispositif LILBID-OLYMPIA. En effet, même si l'objectif est de mesurer des clusters d'eau, ceux-ci doivent être analogues à ceux obtenus avec CDA (et par conséquent SUDA). Des adaptations ont donc été apportées sur les paramètres de la source d'OLYMPIA. De nombreux tests ont été réalisés pour focaliser les ions dans la cellule Orbitrap tout en tentant de réduire la valeur en tension dans la source. Finalement, les tests sur la fin 2022 ont été dédiés à essayer de faire une extraction retardée comme pour le LILBID-TOF. Malheureusement, le design initial de la source ne permettant pas une accélération efficace, ces tests ont également été infructueux.

Le chapitre se conclue sur la présentation des perspectives pour le futur, pour finalement être en mesure de détecter les clusters d'eau avec le nouveau dispositif LILBID-OLYMPIA. Un nouveau design pour la source ionique est présenté, celui-ci étant directement inspiré du LILBID-TOF. Il devrait permettre de pouvoir accélérer les ions en un paquet spatialement bien défini, et avec une énergie cinétique optimale pour la cellule Orbitrap.

Chapitre Comparaison des Résultats & Conclusion

Des mesures avec un grande variété d'échantillons, de types d'injections et de gammes de pressions dans la cellule Orbitrap ont été faites pendant ces travaux. Cette section permet de comparer l'ensemble de ces données afin de conclure sur l'impact de chaque paramètre.

Les mesures sur le Krypton en impact électronique ont été réalisées avec une injection continue, à des pressions relativement hautes dans la cellule (1.10 -8 mbar). L'étude de l'étain était au contraire avec une injection pulsée, et le métal ne dégazant pas, le vide était proche des valeurs optimales pour l'Orbitrap™ (3.10 -9 mbar).

Dû aux différences de pression, le temps de vie des ions pour ces trois échantillons est très différent. Les ions d'étain ont pu être détectés à plus de 850 ms, l'isotope majeur du Krypton jusqu'à environ 500 ms et les ions H 3 O + jusqu'à 300 ms. Une plus haute pression réduit donc le temps de vie des ions dans la cellule. Ceci est bien sûr attendu, puisque les ions sont perturbés par les espèces chimiques neutres. Il est intéressant de noter que l'injection continue ne semble pas avoir d'impact significatif sur la durée de vie des ions dans la cellule.

Des mesures d'abondance isotopique relative ont été faites avec chaque technique d'ionisation. L'étude en impact électronique a montré une surestimation pour les espèces peu abondantes, avec des erreurs de l'ordre de plusieurs dizaines de pourcents, indiquant une sous-estimation du principal isotope du krypton. Pour les mesures de l'étain et du D 2 O, les erreurs d'abondance relative sont nettement plus faibles. Les isotopes peu abondants de l'étain ont même été sous-estimés (d'environ -20 %). La détection et la quantification de DH 2 O + ont été effectuées à une pression plus élevée que pour les mesures en impact électronique. Malgré cela, l'amplitude du pic se situait dans la fourchette de ce que l'on attendait, avec une différence de seulement 1%. Ceci indique que la surestimation/le manque d'amplitude pour le calibrant est effectivement dû à l'injection continue. Cela confirme l'idée que les ions injectés pendant la mesure déstabilisent l'anneau ionique de l'isotope majeur du krypton, ce qui entraîne une diminution de son amplitude. De plus, le fait qu'aucun paquet d'ions ne soit préparé avant injection peut aussi mener à un anneau ionique très peu défini dès le début de la mesure.

La conclusion reprend les objectifs scientifiques de ces travaux et présente un bref résumé chapitre par chapitre, suivi des perspectives à long terme. Les pistes pour la mesure des clusters avec OLYMPIA ont déjà été présentées dans le chapitre V, cette section vise à explorer dans quels autres projets l'utilisation d'OLYMPIA pourrait se révéler bénéfique. L'instrument pourrait par exemple être couplé à une nouvelle méthode d'ionisation, comme l'ionisation par impact, en étant directement couplé avec un accélérateur de poussière. Des développements sont également en cours pour être en mesure d'accélérer des particules glacées à des vitesses compatibles avec l'ionisation par impact. Avec une nouvelle source ionique étant capable de focaliser les ions issus de ces impacts vers la cellule Orbitrap, il serait possible de mesurer la composition de poussière hypervéloces sans utiliser la technique analogue LILBID. Enfin, et dans l'objectif de directement mesurer la composition des poussières cosmiques avec une haute résolution, un développement est en cours pour spatialiser une cellule Orbitrap couplée avec une source par impact de poussière. Cet instrument, HANKA, est actuellement en cours de sélection pour une mission en orbite terrestre basse. Le fonctionnement d'un tel instrument en orbite autour de la Terre permettrait de démontrer la maîtrise de cette technologie, qui pourrait alors être sélectionnée pour des missions d'agences spatiales tel que l'ESA ou la NASA, afin d'étudier directement les lunes glacées avec une cellule Orbitrap. The different subsystems of a Mass Spectrometer (from Arevalo et al., 2020). . . . . . . . . . . I.9

CONTENTS

List of Tables

List of Figures

The same mass spectrum with different mass resolution. A : 5 000, B : 8 000, C : 15 000, D : 24 000 m/ ∆m (Credit : ScienceDirect). .

LIST OF FIGURES LIST OF FIGURES

V.1 Schematic of the LILBID-TOF setup. For illustration reason, the laser has been placed on top, but the laser beam hits the water beam perpendicularly to the direction of the ion flight. After ionisation, the ions fly in field free environment through a skimmer that allows a differential pumping.

Foreword

Space exploration is one of the few subjects that fascinates everyone, although it is not the easiest to understand. I am often asked if I always wanted to work in this field, and I guess the answer is that the passion has always been there, but the belief that it was actually possible came quite late. This was during my bachelor's degree in Earth sciences, and by the end of it, I realised that the same phenomenon taking place on Earth seemed much more interesting when it occurred on another planet. From there, learning how to do physics and math was only a small step for a man, and I joined the "Planetology and Space Exploration" master's degree in Paris. This is where I also realised that the exploration part is also particularly exciting, as in fact even Mars is even a bit too well-known for my taste, I would rather go further away in the Solar System. I think that is when I started dreaming about being in a mission control room, looking at the launch of a spacecraft embedding the instrument I developed. I therefore looked for a PhD with a strong instrumentation focus, and was lucky enough to find Christelle Briois' proposal on the French space agency (CNES) website. Although not all the words in the title were immediately meaningful to me (hypervelocity dust in cryogenic environment ?), all the ingredients were there to keep the passion going. The cryogenic environments are the moons of Jupiter and Saturn, and what better exploration subject than the ocean of a distant world, and the potential life that could appear there. The journey started in October 2019 in Orléans, under the supervision of Christelle Briois and Frank Postberg. I hopped on a train named OLYMPIA that was born a year before, and was starting to gain momentum. The project aims to develop a new instrument for the calibration of spaceborne mass spectrometers. Space science is all about collaboration, and four laboratories from three different countries are involved in the development. During the PhD, I made some stops in Prague, Leipzig and a two-year stay in Berlin.

This manuscript follows the evolution of OLYMPIA (Orbitrap anaLYser MultiPle IonisAtion), and is therefore written chronologically throughout the different steps of development. Chapter I provides an introduction to the context and purpose of this work. It begins by discussing the quest to find life as we know it and puts into context the astrobiological relevance of the icy moons of our solar system. Then, the method used in this work, mass spectrometry, and different spaceborne mass spectrometers are presented. Finally, the chapter outlines the objectives of this work.

Chapter II explains the functioning of the Orbitrap™ technology, and presents the new laboratory testbench OLYMPIA. I made the choice to present the setup as it was at the beginning of my PhD, to better highlight the further improvements and parametrisations, which are presented in Chapter III. Before going to Berlin and coupling OLYMPIA with the LILBID technique, I started with electronic impact ionisation for the first calibrations of the setup. The results of this study are shown in Chapter IV, and the associated publication in Appendix II. The long term coupling of OLYMPIA and LILBID only occurred in February 2021. This is why the LILBID (Laser Induced Liquid Beam Desorption and Ionisation) method is presented at the beginning of the Chapter V, followed by the results of this unique setup. Those are also the subject of a publication that can be seen in Appendix III.

Chapter I Introduction

The word Science originates from the Latin word scientia, which literally means "knowledge", or "understanding". From this early definition, Science describes all the knowledge that is possessed by an individual, or that the latter can acquire through study, reflection or experience. This knowledge is mainly characterised by four words : objectivity, reproducibility, demonstrability and exactness. Those words define the ethic each scientific researcher strives to respect. When reproducibility and demonstrability are more about method and the way to present this new knowledge, objectivity and exactness are more delicate matter. On a larger scale, the purpose of Science is to build and organise knowledge to describe our surrounding universe. But as objective as researchers might try to be, the way we describe this universe will always be through the prism of our "Science", or in other words, the anthropological biases inherent in our human nature.

Those biases do not necessarily lead to a lack of exactness, but they definitely steer our building of knowledge towards major scientific questions. Those questions are in every scientific field, and are widely known as they usually tend to describe, explain or discover aspects that could change our ways of thinking or living. Some are directly connected to us : Is it possible to cure cancer ? What is consciousness ? Why do we dream ? Others to our surroundings, from the smallest to the largest scale : What is at the centre of a black hole ? What is dark matter ? And some fall somewhere in the middle of these two categories : How did life appear on Earth ? Are we alone in the universe ? Could life appear on another planet ? The work presented in this thesis is a part of the latter. The search for life has always been a major question, and not only for scientists. The sky and space are some of the few objects that everyone, at all times, has been able to observe with their eyes. Such an intriguing vastness naturally raises questions, which Science tries to answer, with as much objectivity and exactness as possible. The answers to these questions, whether positive or negative, would drastically change the way we place ourselves in the universe.

In this introductory chapter, I will present where Science stands at the moment, regarding the search for life in our Solar System, and what is done to pursue the objective of answering this major question.

The Search for Life as we Know it

Life as we know it, is the main anthropological bias of astrobiology, as it means focus on markers of life we know on Earth, leaving aside the ones we do not know about. However this reduces the scope of the research and helps put some constraints on where to look for, and what to look for. Through studies of life on Earth, we know what life needs to emerge and thrive. And what the markers that leave biotic species are. But even with this, the definition of Life itself is subject to debate. Numerous definitions have been proposed over the last decades (e.g. [START_REF] Schrödinger | What Is Life?[END_REF][START_REF] Sagan | In Encyclopaedia Britannica[END_REF][START_REF] Monod | Chance and Necessity[END_REF][START_REF] Feinberg | Life beyond Earth: The Intelligent Earthling's Guide to Life in the Universe[END_REF][START_REF] Dyson | Origins of Life[END_REF][START_REF] Fleischaker | Origins of Life: An Operational Definition[END_REF][START_REF] Shapiro | Extraterrestrials Where Are They?[END_REF][START_REF] Rizzoti | Defining Life the Central Problem in Theoretical Biology[END_REF][START_REF] Koshland | The Seven Pillars of Life[END_REF][START_REF] Cleland | Defining "Life[END_REF]..) but none managed to embrace the whole biosphere without including other non living-entities, thus facing strong counterexamples, such as crystals or fire [START_REF] Cleland | Defining "Life[END_REF]. This absence of a proper definition for "life" points out a missing brick in our understanding of life. This would be tantamount to to trying to define a plasma, without knowing the existence of electrons.

A commonly accepted and widely used definition was proposed by NASA in the frame of its Astrobiology program : "Life is a self-sustained chemical system capable of undergoing Darwinian evolution" [START_REF] Joyce | Origins of Life: The Central Concepts[END_REF]. Even though not perfect, in particular regarding the Darwinian evolution part [START_REF] Chyba | The Origin of Life in the Solar System: Current Issues[END_REF][START_REF] Cleland | Defining "Life[END_REF], and especially considering the timescales necessary for Darwinian evolution to happen [START_REF] Chyba | Possible Ecosystems and the Search for Life on Europa[END_REF], this definition is still useful to fix some requisites for life. There is a consensus on several attributes that a life form needs to have : growth, evolution, response to stimuli, exhibit organisation on several levels, relevant chemicals etc. Even if some areas are still grey (e.g. the case of the viruses, are they alive or not ?)

THE SEARCH FOR LIFE AS WE KNOW IT CHAPTER I. INTRODUCTION

this does not prevent Science from advancing in the field, notably through the listing of the different requisites for life, even if it is only the one as we know it.

The Conditions for Life

Even if the definition is subject to debate, the three basic requirements that life needed to appear on Earth are well known : essentials chemicals, an energy source and liquid water as a solvent. The chemicals are the famous CHNOPS, Carbon-Hydrogen-Nitrogen-Oxygen-Phosphorus-Sulfur. The first four are the major component of every living being and compose what we called Organic Matter (OM). The Phosphorus composes the structure of cells membrane (Phospholipids) or the RNA/DNA helix (De Duve, 1991; [START_REF] Karl | Phosphorus, the Staff of Life[END_REF], and Sulfur is a part of some amino acids, with two, i.e. methionine and cysteine, entering the composition of proteins. [START_REF] Brosnan | The Sulfur-Containing Amino Acids: An Overview[END_REF]. On Earth the main energy source is coming from the solar flux. It brings enough energy at the surface for ice to melt and for liquid water to be permanent. The majority of life forms on Earth depends on the solar flux via the photosynthesis of the plants or algae that are the beginning of their food chain [START_REF] De Marais | Evolution. When Did Photosynthesis Emerge on Earth?[END_REF]. Knowing the ingredients that life needs to appear, the first step was to define where such environments could naturally be, and characterise if life could also appear there or not, with a new criterion : habitability.

Habitability

The first concept of habitability has been introduced by [START_REF] Huang | The Problem of Life in the Universe and the Mode of Star Formation[END_REF][START_REF] Huang | Life Outside the Solar System[END_REF]. Later taken up by [START_REF] Dole | Habitable Planets for Man[END_REF] who uses the term "ecosphere". The definition of the habitable zone differs depending on the author, Dole directly refers to an alternative planet for human life, with temperature between 0 and 30°C. With time, the concept has grown less anthropocentric and new definitions have been proposed such as that of [START_REF] Fogg | An Estimate of the Prevalence of Biocompatible and Habitable Zone[END_REF], which distinguishes habitable from biocompatible. The latter is more the meaning behind habitable nowadays : the habitability of a celestial body represents its ability to support the emergence of life, as well as to sustain it. These two are not necessarily compatible, for example with the current atmosphere of the Earth, the last universal common ancestor could not have survived due to the oxidising conditions (Di Giulio, 2007; [START_REF] Weiss | The Physiology and Habitat of the Last Universal Common Ancestor[END_REF]. A body with a strong habitability potential would therefore contain the three ingredients necessary for life. The organic matter is believed to be quite common in the universe. Some complex organic molecules have been discovered in protosolar nebula or in the interstellar medium [START_REF] Pardo | Molecular Line Survey of CRL 618 from 80 to 276 GHz and Complete Model[END_REF][START_REF] Herbst | Complex Organic Interstellar Molecules[END_REF], and even in diffuse clouds [START_REF] Liszt | Comparative Chemistry of Diffuse Clouds: V. Ammonia and Formaldehyde[END_REF]. Closer to Earth in our Solar System, the small bodies (i.e. asteroids & comets) are rich not only in carbon, but also in complex prebiotic organics. Glycine, the simplest amino acid, has been detected in comets, in particular in the tail of 81P/Wild 2 [START_REF] Sandford | Organics Captured from Comet 81P/Wild 2 by the Stardust Spacecraft[END_REF][START_REF] Elsila | Cometary Glycine Detected in Stardust-Returned Samples[END_REF], or on 67P/Churyumov-Gerasimenko (Altwegg et al., 2016). On the surface of Mars, sulfured and chlorinated OM have been detected [START_REF] Freissinet | Organic Molecules in the Sheepbed Mudstone, Gale Crater, Mars[END_REF][START_REF] Eigenbrode | Organic Matter Preserved in 3-Billion-Year-Old Mudstones at Gale Crater[END_REF]). Saturn's icy moons are also rich in organic matter; a complex organic chemistry has been detected on Titan forming hydrocarbons and complex nitrogen compounds [START_REF] Waite | The Process of Tholin Formation in Titan's Upper Atmosphere[END_REF]. In Saturn's E-ring and in the vicinity of Enceladus a complex organic chemistry with macromolecular organic compounds has also been detected (Postberg et al. 2008, 2018,Khawaja et al. 2019).

With this quick overview of the organic matter across the universe, it is quite clear that the limiting factor in the three ingredients for life is not the organic chemicals compounds. For that reason, astrobiology and space exploration in general is currently driven by the saying : "Follow the water". To simplify, the organics chemicals are expected to be there, and if water is at a liquid state then there might also be enough energy to initiate the chemical reactions necessary for organic chemistry. Continuing the search for analogous forms of life, research naturally went towards the direction of planets with liquid water on the surface.

The Habitable Zone

With the same bias of Earth-like life, the characterisation of the circumstellar Habitable Zone (HZ) around a star emerged [START_REF] Kasting | Habitable Zones around Main Sequence Stars[END_REF], to find Earth-like planets. This zone is characterised by two boundaries, mainly fixed by the solar flux of the system's star. Figure I.1 shows an artist view of the HZ. The inner boundary is the limit where the flux is high enough to vaporise and photodissociate water. This would, in our Solar System place the HZ between 0.95 and 1.37 AU, with the outer boundary determined by the condensation of CO 2 [START_REF] Doyle | Circumstellar Habitable Zones: An Overview[END_REF]. Those limits are, if not anthropocentric, geocentric, as planets bigger than Earth and with different atmospheric composition would enlarge this HZ [START_REF] Kasting | Habitable Zones around Main Sequence Stars[END_REF]. Anyway, the concept is to be applied outside of our Solar System, on different stars and to help assessing the habitability potential of exoplanets. If at first the concept was essentially for sun-like relatively massive stars, studies later included an HZ around M dwarves stars (i.e. the coldest stars, with a surface temperature as low as 2500 K), which represents ~70% of all stars [START_REF] Heath | Habitability of Planets Around Red Dwarf Stars[END_REF].

Habitability Outside the Habitable Zone

Surface Habitability With the expansion of the scope of the HZ, it has somehow become a sub-part of the habitable concept, with terminology such as "surface habitability" appearing (Hand et al., 2007). According to the same authors, life "requires just two forms of energy : thermal energy for melting water and chemical energy for maintaining and regulating processes considered essential for life.". This definition is more inclusive towards unusual places and different energy sources. There is obviously still the concept of liquid water, but this energy can be provided by any means powerful enough to melt water, as for example, radiogenic or tidal energy, and not only solar illumination.

Subsurface Habitability Complementary to the surface habitable zone, [START_REF] Mcmahon | Circumstellar Habitable Zones for Deep Terrestrial Biospheres[END_REF] introduced the term "subsurface-habitability zone" (SSHZ). In their work, they model the boundaries of the SSHZ for Earth-like planet. The limiting factor of the distance from the star of the classical HZ is being complemented by a depth factor. The idea is that deep biospheres could develop, as temperature increases with depth. Thus, the solar flux is not the only source of energy, and the planet itself can sustain its own biosphere. A biosphere that is therefore not based on photosynthesis, as the solar flux being either too low or nonexistent. Such ecosystems do exist on Earth and at least three have been discovered. Two are methanogenic and use H 2 from the rock-water interactions [START_REF] Stevens | Lithoautotrophic Microbial Ecosystems in Deep Basalt Aquifers[END_REF][START_REF] Chapelle | A Hydrogen-Based Subsurface Microbial Community Dominated by Methanogens[END_REF]. The third one is a sulfur-reducing bacteria that uses redox couples originating from radioactive decay [START_REF] Lin | Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome[END_REF]. Numerous other subsurface microbial ecosystems thrive on Earth, (e.g. deep-sea hydrothermal vents, petroleum reservoirs, terrestrial sedimentary aquifers or subseafloor sediments). However these indirectly rely on products from photosynthesis. If we take the example of the famous hydrothermal vents, the chemical energy is coming from the reaction of H 2 S and O 2 , which again comes from the surface photosynthesis.

The model from McMahon et al. ( 2013) is intended to characterise circumstellar SSHZ of terrestrial bodies (even though they propose adaptions to icy bodies). Reynolds et al. proposed in 1987 that habitable zones could also be circumplanetary, introducing the term "Tidally-heated habitable zone". Moons with enough eccentricity could benefit from the induced tidal heating and bear liquid water [START_REF] Scharf | The Potential for Tidally Heated Icy and Temperate Moons around Exoplanets[END_REF]). If we take the example of the Jovian system, the four largest moons are Io, Europa, Ganymede and Callisto. Io's semi-major axis is 421 700 km, which is so close to Jupiter that the tidal heating actually initiated active silicate and sulfur volcanoes [START_REF] Mcewen | High-Temperature Silicate Volcanism on Jupiter's Moon Io[END_REF], leading to a young surface. Europa, 670 900 km away from Jupiter, benefits from a moderate tidal heating that leads to an active cryovolcanism resurfacing [START_REF] Schmidt | Active Formation of 'Chaos Terrain' over Shallow Subsurface Water on Europa[END_REF]. Going even further away from Jupiter, Ganymede (1 071 600 km) and Callisto (1 882 700 km) receive less and less energy, with the age of the surface increasing with distance. Io in this case is considered too close to Jupiter to be able to harbour a subsurface ocean, due to an excess of energy. The other three on the contrary, are at the proper distance, and evidence of a 2. ICY MOONS CHAPTER I. INTRODUCTION subsurface ocean could be detected. For this reason, the habitability potential of these icy moons is high and they are extensively studied. The following section, and more broadly this work will focus on the icy moons of the Solar System.

Going even further away from the host star, [START_REF] Abbot | The Steppenwolf: A Proposal for a Habitable Planet in Interstellar Space[END_REF] proposed that subsurface oceans maintained by radiogenic heating could exist, and be detected, on rogue planets in the interstellar medium.

Super Habitability Earth is the only place known to host life, and can therefore easily be considered the most habitable world of all. But this would again be a strong bias. As we have just seen, habitable zones could exist far away from the classical circumstellar habitable zone. But those effects could be coupled, and a body with illumination energy could at the same time benefit from a significant tidal heating. This has been introduced by Heller and Barnes (2013) and Heller and Armstrong (2014) with the concept of "Superhabitable Worlds".

I presented numerous places where life could appear in environments other than on Earth, widely opening up the possibilities and places to look for traces of life. This is of course still life as we know it. But as explained, it is a tedious thing to recognise "something" as life, if it is radically different from what we know. "Follow the water" is a useful tool to give a direction to our research and to prioritise and narrow the range of planetary bodies we need to explore. A broader approach would be to "Follow the energy" [START_REF] Hoehler | A "Follow the Energy" Approach for Astrobiology[END_REF], and to consider alternative solvents for biochemistry [START_REF] Bains | Many Chemistries Could Be Used to Build Living Systems[END_REF][START_REF] Benner | Is There a Common Chemical Model for Life in the Universe?[END_REF][START_REF] Baross | The Limits of Organic Life in Planetary Systems[END_REF].

But for the time being, we have no choice but to look for life like the one who has lost their keys and only looks under the lamp post, where there is light, and in our case, liquid water. This is however the best place to start, and is complex enough to occupy us for a few decades.

Icy Moons

Overview

For this work, we will leave the circumstellar habitable zone and go in the outer Solar System, where water is naturally frozen due to the distance from the Sun. There are multiple icy moons in the Solar System, mainly orbiting gas giant planets. An icy moon is by definition covered by a layer of ice, the thickness of which can vary from one moon to another. Icy moons are orbiting Jupiter, Saturn, Uranus and Neptune or even Pluto (Figure I.2). The sizes can be very different, Jupiter's moon Ganymede being the biggest with a radius of 2634 km and Mimas the smallest with 198 km of radius. Among those icy moons, some are of particular interest for astrobiology, with a liquid ocean below the surface, sometimes suspected, sometimes confirmed. NASA defines an ocean world "as a body with a current liquid ocean (not necessarily global)" [START_REF] Hendrix | The NASA Roadmap to Ocean Worlds[END_REF]. That of course includes the Earth and its surface oceans, but also subsurface oceans that lie under the ice crust of some icy moons. As explained above when discussing the circumplanetary habitable zone, moons orbiting at the proper distance from their host planet can benefit from tidal heating [START_REF] Reynolds | Europa, Tidally Heated Oceans, and Habitable Zones around Giant Planets[END_REF][START_REF] Scharf | The Potential for Tidally Heated Icy and Temperate Moons around Exoplanets[END_REF] which considerably increases their habitability potential. Several space missions were dedicated to the study of the gas giants and their moons. The discoveries of subsurface oceans was mainly from the data of NASA's Galileo spacecraft (O'neil and Mitchell, 1983) orbiting Jupiter and Cassini-Huygens (NASA/ESA, Matson et al., 2003) orbiting Saturn. The two missions confirmed the strong habitability potentials of the icy moons, and even more space missions are now in preparation. The JUpiter ICy Moon Explorer (JUICE, Grasset et al. 2013) of the European Space Agency (ESA), and the Europa Clipper NASA mission (Howell and Pappalardo, 2020) will both orbit Jupiter and perform fly-bys above the Jovian icy moons. JUICE will especially focus on Ganymede, even going into orbit around it at the final mission phase, whereas Europa Clipper will study Europa in detail. Both missions are planned to enter Jupiter's orbit in the early 2030s. Being able to collect data in situ, it was possible for Galileo and Cassini to characterise the vicinity of each moon. The measurements of the magnetic field induced by Jupiter's own field around Europa (Figure I.3) and Callisto led to the conclusion that there have to be layers with strong electrical conductivity below the surface, and that is the subsurface oceans (Khurana et al., 1998). The same method has been used for Ganymede [START_REF] Kivelson | The Permanent and Inductive Magnetic Moments of Ganymede[END_REF], however complicated by the presence of Ganymede's intrinsic magnetic field. Nevertheless, the observations have been complemented by the assessment of the age of the surface which indicates that the moon is warm enough to sustain a liquid ocean [START_REF] Vance | Ganymede's Internal Structure Including Thermodynamics of Magnesium Sulfate Oceans in Contact with Ice[END_REF]. In the Saturnian system, an ocean has been detected below Titan and Enceladus (Figure I.4) surface. The strong deformations observed by Cassini in the gravity field of Titan indicates a deformable, low-viscosity layer below the surface. Convincing evidence for Enceladus ocean has first been detected by analysing the composition of emitted grains (Postberg et al., 2009) by the method that is the topic of this thesis, mass spectrometry and will be discussed in detail in the Section 3.

Discovery

Ice Thickness

Obviously measuring the composition of ice grains coming from the ocean cannot allow to determine the thickness of Enceladus ice crust. However, the measurements have later been complemented by libration measurements. Librations are modulations of a body's rotation along its orbit, and represent the most direct remote sensing technique to assess a global subsurface ocean. The libration measurements at Enceladus were far exceeding the expected values for a solid body, confirming not only the presence of a liquid water reservoir, but of a global ocean decoupling 2. ICY MOONS CHAPTER I. INTRODUCTION the ice crust from the solid core (Thomas et al., 2016). The estimation of Enceladus ice shell thickness is between 20 and 40 km [START_REF] Iess | The Gravity Field and Interior Structure of Enceladus[END_REF][START_REF] Mckinnon | Effect of Enceladus's Rapid Synchronous Spin on Interpretation of Cassini Gravity: Enceladus: Global Ocean, Thick Ice Shell[END_REF][START_REF] Cadek | Enceladus's Internal Ocean and Ice Shell Constrained from Cassini Gravity, Shape, and Libration Data[END_REF]. This value is largely reduced at the south pole, gravity and librations measurements [START_REF] Cadek | Enceladus's Internal Ocean and Ice Shell Constrained from Cassini Gravity, Shape, and Libration Data[END_REF] along with thermal anomalies (Le Gall et al., 2017) estimate a thickness as thin as 5 km.

The thickness of Europa's ice shell has been intensely debated. Radio Doppler experiments could assess the thickness of the hydrosphere (i.e. the liquid ocean and the ice shelf combined) in the range of 80 to 170 km [START_REF] Anderson | Europa's Differentiated Internal Structure: Inferences from Four Galileo Encounters[END_REF]. To constrain only the ice shelf, tidal dissipation rates were modelled by using the heattransfer rate through the ice layer. The results are imprecise due to the various parameters that the ice can adopt, such as various viscoelastic properties, different grain size or even a conductive or convective model. The accepted range for Europa's ice shell is a few km to more than 50 km [START_REF] Ojakangas | Thermal State of an Ice Shell on Europa[END_REF][START_REF] Hussmann | Thermal Equilibrium States of Europa's Ice Shell: Implications for Internal Ocean Thickness and Surface Heat Flow[END_REF][START_REF] Moore | Thermal Equilibrium in Europa's Ice Shell[END_REF].

In the case of larger moons, such as Titan, Ganymede or Callisto, the hydrosphere is much thicker. Titan's is expected to be between 500 to 700 km (Castillo-Rogez and Lunine, 2010; Vance et al., 2018), Ganymede's 800 km [START_REF] Vance | Ganymede's Internal Structure Including Thermodynamics of Magnesium Sulfate Oceans in Contact with Ice[END_REF]) and Callisto's around 250 km [START_REF] Vance | Geophysical Investigations of Habitability in Ice-Covered Ocean Worlds[END_REF]. Such a thick layer of water and ice induces much higher pressure at the bottom, that will lead to other high pressure phases for the water ice. It is expected to find successive layers of different ices, interfaced with liquid water. A direct way to assess the thickness of the icy moon ice shelf would be to perform close flybys with ice penetrating radars such as REASON onboard Europa Clipper [START_REF] Blankenship | REASON for Europa[END_REF] or RIME onboard JUICE [START_REF] Bruzzone | IEEE International Geoscience and Remote Sensing Symposium -IGARSS[END_REF]. The two radars are designed to scan the subsurface up to 30 km and 9 km, respectively. Finally, a method that would unveil the deep structure of the icy moons would be to place a seismometer at the surface.

Though not yet planned nor funded, a Europa lander mission definition is already under development and the payload includes such an instrument, based on SEIS [START_REF] Lognonné | SEIS: Insight's Seismic Experiment for Internal Structure of Mars[END_REF], the seismometer onboard the Insight NASA mission that landed on Mars in 2018.

Interaction with Rocky Core

As mentioned above, the light elements CHNOPS are a prerequisite for life. However, heavier elements such as iron or magnesium are also required. By assessing the bulk densities of the icy moons, it is possible to estimate the availability of such heavy elements (Hand et al., 2020). The more a moon is denser than liquid water and water ice (916.8±5 kg/m -3 ), the more heavy elements should be available. Europa is the densest icy moon with 3013±5 kg/m -3 , Ganymede (1942±5 kg/m -3 ), Callisto (1834±5 kg/m -3 ) and Titan (1880±5 kg/m -3 ) all show a significant silicate fraction. Enceladus has the lowest density with 1608±5 kg/m -3 which would tend to indicate a depletion in heavy elements, indicating the smallest rock fraction (~60%) of all currently known ocean moons. The reason why Europa and Enceladus are much more targeted and interesting from an astrobiology point of view is because of their relative small size. The pressure is not high enough to produce the high pressure ices, and therefore it is likely that their ocean lies directly on the silicate mantle (Figure I.5).

This water-rock interface can allow a circulation of seawater in the presumably permeable rocky layer. This would initiate exchanges between the mantle and the habitable ocean, and produce chemical energy gradients. For example, on Earth, much of the phosphorous is found in the composition of silicates, and hydrothermal systems located at the seafloor allow exchanges between the two compartments. The water-rock interaction could therefore enrich the icy moons ocean with this key element for life. Global hydrothermal activities have been confirmed on Enceladus from measurements taken in its vicinity (Hsu et al., 2015;[START_REF] Waite | Cassini Finds Molecular Hydrogen in the Enceladus Plume: Evidence for Hydrothermal Processes[END_REF]. This, and the abundance of dissolved salts (Postberg et al., 2009) indicate that the ocean does largely interact with the seafloor, but also that 2. ICY MOONS CHAPTER I. INTRODUCTION materials from the bottom of the liquid ocean can be transported all the way to the moon's surface.

The succession of ice and water layers for bigger icy moons, and a possible ice-rock interaction at the seafloor could minimise, if not prevent, an efficient exchange and enrichment of the ocean.

Hydrothermal Vents The liquid-water interaction at the bottom of the ocean could take the form of hydrothermal vents as they can be observed on terrestrial oceans seafloor. Cracks in the oceanic crust allow an infiltration of seawater that will provoke a transition of the ultramafic rocks (iron and magnesium rich silicates) into serpentine. This reaction is called serpentinisation. The chemical reaction of serpentinisation produces, via the reaction of ultramafic rocks with H 2 O and Carbon, dihydrogen (H 2 ) and methane (CH 4 ). Above mid-oceanic ridge, those hydrothermal vents can take the shape of black smokers, which can heat the water at temperature reaching more than 400°C [START_REF] Kelley | Volcanoes, Fluids, and Life at Mid-Ocean Ridge Spreading Centers[END_REF]. Away from the ridge, carbonate precipitation creates vents such as the ones at the Lost City site (

Plumes

In the prime 4-year Cassini mission, four Enceladus fly-bys were planned. During the second flyby, the magnetometer measured an anomaly and the trajectory of the third flyby was changed to investigate this phenomenon. Consequently, during the third fly-by, Cassini flew only 168 km above the south polar region, revealing its morphology with various instruments and detected the cryovolcanic plume, the camera ISS (Imaging Science Subsystem) also took high-resolution images (as fine as 4 m/pixel) of the south polar region. Those images revealed a youthful geology and tectonic patterns such as the "tiger stripes", a complex of several 130 km fractures (Porco et al., 2006) in which high temperature anomalies have been detected by infrared spectroscopy [START_REF] Spencer | Cassini Encounters Enceladus: Background and the Discovery of a South Polar Hot Spot[END_REF]. Those results were so intriguing that during several mission extensions, a total of 23 flybys above Enceladus were performed. The plumes are originating from cryovolcanic processes. The surface of the liquid water at 273 K (or slightly below) is close to open space. At such low-pressures, the liquid boils and evaporates, then rises through cracks in the crust undergoing temperature and pressure gradients. When reaching the surface, the temperature has 2. ICY MOONS CHAPTER I. INTRODUCTION dropped to about 200 K. Some active fissures have been characterised and can be only 9 m wide [START_REF] Goguen | The Temperature and Width of an Active Fissure on Enceladus Measured with Cassini VIMS during the 14 April 2012 South Pole Flyover[END_REF]. Most of the particles going out of the cracks do not reach sufficient velocities to escape Enceladus' gravity and eventually fall back on the surface [START_REF] Kempf | How the Enceladus Dust Plume Feeds Saturn's E Ring[END_REF]. There is still a significant fraction (5 -10%) that leaves Enceladus' Hill sphere and populates Saturn's E-ring [START_REF] Spahn | E Ring Dust Sources: Implications from Cassini's Dust Measurements[END_REF]Hillier et al., 2007;[START_REF] Kempf | How the Enceladus Dust Plume Feeds Saturn's E Ring[END_REF]. With the upcoming Europa Clipper mission, the question of whether there are plumes or not on Europa is a hot topic. Far UV imaging with the Hubble Space Telescope has revealed the presence of hydrogen and oxygen at altitude as high as 200 km above Europa's south pole which is consistent with water vapour plumes. The detection occurred during a maximum tidal stress period that could have led to surface cracking (Roth et al., 2014a(Roth et al., , 2014b) ) but repeated observation did not find anything [START_REF] Roth | A Stable H 2 O Atmosphere on Europa's Trailing Hemisphere From HST Images[END_REF]. Still with the Hubble Space Telescope, [START_REF] Sparks | Probing for Evidence of Plumes on Europa with HST/STIS[END_REF]2017) used occultation of the gas through the limb of Europa and detected absorption areas whose emission are consistent with the study from Roth et al. (2014aRoth et al. ( , 2014b) ) but at different location, and which were in rough agreement with surface thermal anomalies recorded by Galileo. Those results, although compelling are still heavily debated, in particular because of the very low Signal to Noise Ratio (SNR) of the data [START_REF] Saur | Hubble Space Telescope/Advanced Camera for Surveys Observations of Europa's Atmospheric Ultraviolet Emsission at Eastern Elongation[END_REF]. [START_REF] Jia | Evidence of a Plume on Europa from Galileo Magnetic and Plasma Wave Signatures[END_REF] re-analysed data from the Plasma Wave Spectrometer onboard Galileo and found that a significant increase in the plasma density has been recorded, in a region consistent with the previous studies, which would also indicate the presence of a plume. Despite these results, there is still no strong consensus on whether there are plumes on Europa or not, but no doubt that Europa Clipper and JUICE missions will be able to answer that question.

The presence of plumes on Europa is an important matter regarding the detectability of the compounds in the underlying ocean. However, hydrothermal activities, prebiotic or even biotic chemistry could still occur at the seafloor, even if there is no cryovolcanism or plumes at the surface. The great results on Enceladus come from a combination of the active and complex chemistry in the liquid ocean, and an actual access to this chemistry. We reach here a major challenge of space exploration in general : the tools used are extremely constrained. Instruments must be as light and small as possible to be integrated in a spacecraft, while ensuring sufficient protection to the hostile space environment and expected performances to allow discoveries. And though everything is functional in the end, the features of interest can remain hidden. But anyway we have no control on this, and all we can do is to develop the best tools to analyse what might be accessible. The following sections will be dedicated to the presentation of the methods and the tools used to characterise the Enceladus ocean composition, and the future exploration of Europa's.

INTRODUCTION TO MASS SPECTROMETRY CHAPTER I. INTRODUCTION 3 Introduction to Mass Spectrometry

Before taking a deep dive into Enceladus' ocean, we need to get back on Earth to better understand the techniques at our disposal to analyse the compositions of samples. In the previous section, a few techniques have been mentioned, such as gravitational measurements, radar sounding, plasma characterisation, spectroscopy etc. Among the techniques that have been used in space exploration, we will focus on mass spectrometry. Mass spectrometry is one of the few techniques (along with spectroscopy of electromagnetic radiation) that provides access to the chemical composition of samples. It is an in situ method, which therefore requires to access the samples of interest for analysis. The final results often enable the precise determination of the chemical formulas of the atoms and molecules constituting the studied materials, resulting in a thorough analysis and understanding of the sample as well as its formation and the chemical processes it has undergone.

Mass spectrometry is an analytical technique that measures the mass to charge ratio (m/z) of ionised elements and molecules in a sample. There are different types of Mass Spectrometers, (MS), but they are all constituted of the same sub-systems (Figure I.8), which are an ionisation source, a mass analyser, and a detector. Each subsystem has its own purpose, the ion source generates ions from the neutral sample that are required for mass analysis. Indeed, a mass analyser is not able to detect neutral (i.e. atoms, molecules or radicals). The ions are then accelerated to the mass analyser, which sorts the ions according to their m/z. The signal of each m/z is finally measured by the detector and digitised by an acquisition sub-system.

Performances

The performance of an MS is largely dependent on its mass analyser, while the spectral appearance (e.g. the ion yield and the degree of molecular fragmentation) is largely dependent on its ionisation method. There is a wide range of combination of ionisation sources and mass analysers, that vary according to the state of the sample (solid, liquid or gas) and the desired applications.

Mass resolution

The mass resolution of a mass spectrum represents its capacity to resolve different peaks with similar mass. The mass resolution is usually calculated as the Full Width at Half Maximum (FWHM) of a peak, following the equation m ∆m , with m the mass at the maximum of peaks and ∆m its width. The mass resolution can also be calculated at 1 or 10% of the peak height. Figure I.9 shows an example of the mass resolution effect. An increasing of mass resolution narrows a peak, which can eventually lead to resolving two different peaks that were at first merged into a larger one. To be able to agonistically identify which molecules is behind a peak the mass resolution must be sufficient.

Mass accuracy

The mass accuracy represents the difference between the theoretical mass of a sample and the one measured on the mass spectrum, i.e. the actual position of the peak along the m/z X-axis. Usually the mass accuracy is given in part per millions (ppm). This factor is linked with the mass resolution, as a precise mass must be measured to obtain a proper mass accuracy. A mass accuracy of few ppm greatly eases the reliability of the peak identification process, as the number of possible chemical compounds will be reduced.

Sensitivity The sensitivity represents the ability of a mass spectrometer to detect low concentration of specific compounds. With a low sensitivity, the detection limit of a mass spectrometer will be high, and low abundant ions could therefore stay hidden in the noise level. The perfect sensitivity would represent the ability to detect a single ion of a specific chemical species. Dynamic range The dynamic range represents the ratio between the highest and lowest intense peaks. This factor should be the highest possible in order to have a mass spectrum that is as representative as possible.

Quantification An MS is measuring the intensity of the charges induced by the ions in the mass analyser. The quantification factor represents the ability of an MS to measure those intensities properly, and have peaks with amplitudes corresponding to the abundance of each compound in the samples. This is especially important for quantitative compositional analysis or isotopic abundance quantification.

Mass range

The mass range is the difference between the lowest and highest measurable mass of a spectrum. Depending on the MS, the mass range can be adjustable, which means one spectrum will only go from one mass to another but with another acquisition the mass range could be shifted.

All those parameters define the performances and the reliability of an MS. Some factors are connected, for example a sufficient identifying power (i.e. a combination of good mass resolution and mass accuracy) is required for a proper isotopic quantification. Likewise, to analyse a chemical species with isotopes that are only in trace amounts, the sensitivity and dynamic range must be sufficient. As always, no technique excels in all these parameters and the MS technique must be chosen in consideration of the desired application.

A Diversity of Techniques

Because of the multiple physical properties, there are many different types of mass analysers, all of which have their own advantages and disadvantages. The mass analyser is measuring the charge induced by ions, and this signal is then measured by a detector. This subsection presents an insight of a few techniques of ionisation and mass analyser types.

Ionisation Since neutral compounds cannot be analysed, samples must be ionised in order to be measured by a mass analyser. The ionisation process is quite simple, if enough energy is brought to an atom or molecule, then the system will lose or gain an electron and becomes charged. And because there are many ways to bring energy to a system, there are many different ionisation methods, all of which can have different effects on the samples and the measured mass spectra. Therefore, the ionisation technique should be chosen according to the desired application. In this paragraph, I will present the most common techniques. Even before thinking of the results, the phase state of the sample is already a limiting factor. Some technique can be used only with gaseous materials and some only with liquid.

INTRODUCTION TO MASS SPECTROMETRY CHAPTER I. INTRODUCTION

Gaseous Gaseous samples can be ionised by Electron Ionisation (EI). This technique consists in bombarding the gas sample with a highly energetic electron beam, the resulting impact of which produce many cations. EI is considered as a hard technique, as the ionisation process will also produce a large quantity of fragments of the original sample. EI is one of the techniques used during this work, and will be detailed in the next chapter. The Chemical Ionisation (CI) is a method that allows a soft ionisation for gaseous sample. Using the CI, the production of fragment will be minimised. To perform a CI, a reactant gas must be introduced into the ionisation cell. This reactant gas undergoes EI, creating a reactive ion plasma of the reactant gas. Then, the gaseous molecules of interest are introduced and react with the ion plasma through collisions via ion-molecule reactions. There is a transfer of charge from the plasma to the molecules of interest, resulting in the observation of protonated ions.

Liquid To analyse a liquid sample, a soft ionisation process is the ElectroSpray Ionisation (ESI). In ESI, samples of interest are mixed with a solvent and ionized, primarily through protonation. A high voltage is applied into the liquid, itself placed in a capillary in the MS vacuum chamber. As the liquid comes into direct contact with the vacuum, it evaporates into droplets, which are then analysed. ESI is a popular technique as it allows to measure organic macromolecules (>1 000 m/ z) with minimised fragmentation. Liquid samples can also be directly analysed using laser ionisation. The ionisation can be either soft (laser desorption) or hard (laser ablation). The specific regime of laser ionisation depends on the laser energy and wavelength used.

Solid The laser ionisation can also be used on solid samples, with the same division for hard and soft ionisation. For the laser desorption, two techniques exist, the LDI (Laser Desorption/Ionisation) and MALDI (Matrix-Assisted Laser Desorption/Ionisation). Both techniques involve the use of a laser to desorb and ionise the sample. With LDI the sample is typically directly deposited onto a metal surface. For MALDI the sample is mixed with a suitable matrix which will be ionised by the laser shot. Similarly to the CI, those matrix ions collide with the molecules of interest and ionise them, mostly by protonation. The softness of the technique allows to study large biomolecules. Solid samples can also be analysed by Secondary Ion Mass Spectrometry (SIMS). SIMS uses a primary ion beam to ionise the surface of a sample. This will create secondary ions that will be ejected from the sample by sputtering. The SIMS method is generally used to map the composition the surface of a sample. Another example of ionisation is impact ionisation. With sufficient velocities (> ~1 km/s) microscopic solid samples that hit a surface will be at least partially ionised. Even though destructive, impact ionisation can lead to a relatively soft ionisation and thereby to the preservation of high-mass molecular materials. With the increase of velocity, the ionisation becomes harder and harder and can result in the measurement of only atomic compounds. This technique is not so common in laboratory mass spectrometry but is particularly interesting in space and for this work, as will be seen in the next section.

Mass Analysers

The mass analyser is the heart of the mass spectrometer and will define the overall performances of the instrument. Mass analysers will all determine the m/z of the ions delivered by the ionisation unit. Separating the ions per mass is usually related to their speed or trajectories. The list hereafter is not exhaustive but will present the most common mass analysers. Time of Flight Time of Flight (TOF) mass spectrometer, as the name suggests, are able to precisely measure the time that an ion will take to go from a point A to a point B. The ions are accelerated after their creation by a controlled electric field, to a kinetic energy that is a function of their m/z ratio. Therefore, heavier ions will be slower than lighter ions, and the mass can be retrieved with the time of flight measured at point B. TOFMS have a very good sensitivity, however their mass resolution can be low compared to some other techniques. This comes from the fact that ions with similar masses will tend to arrive at the same time, especially if the flight distance is short. Therefore, to increase the mass resolution of TOFMS, the flight path can be extended. The longer the flight path, the larger the difference in arrival times for the different m/z, and therefore the mass resolution. To keep instruments to a reasonable size and still increase the flight path, it is possible to deflect the ions and bend their trajectory with a Reflectron TOF (RTOF). A RTOF also corrects the possible energy differences for ions with the same m/z but with a different initial position. To go even further, it is possible to make the ions go back and forth in the same chamber with Multi Bounce TOF (MBTOF).

Sector Sector MS can work based on magnetic or electric current, or even both, when arranged in series. The principle of sector MS is to bend the trajectory of ions, using a magnetic or electric field. The field applied is similar for all ions, but because their speed is also dependent on their mass, the bending of the trajectory will also be a function of their mass. With a detector at the end of the system, the exact position of the ions can be determined, and gives their m/z ratio. Sector MS are particularly good regarding quantitative measurements, the

INTRODUCTION TO MASS SPECTROMETRY CHAPTER I. INTRODUCTION

other parameters are in the average range. Like for the RTOF, adding more length and bending areas will increase the performances. Two sectors system in series are usually called Double Focusing Mass Spectrometer (DFMS) Quadrupole Quadrupole MS are composed of four parallels rods on which a voltage is applied. The ions go between the four rods and oscillate along the created electrostatic field. During one measurement, specific voltages are applied and only ions with a corresponding m/z will be able to reach the end of the quadrupole and be detected, as the others ions collide with the rods. To measure other m/z, a new set of voltages is applied. The mass resolution and accuracy are very limited with quadrupoles. However, they are not only used as mass analysers, they can serve as mass filters if coupled with other mass analysers.

FT-ICR In Fourier Transform Ion Cyclotron Resonance (FT-ICR), the ions are trapped in a fixed magnetic field, and rotate at their specific cyclotron frequency. The cyclotron frequency of ions is dependent on their m/z ratio, and very small variation in the mass leads to measurable variation of frequency. The magnetic field induced by the superconducting magnets is much more stable than an electrostatic RF field. For those reasons, FT-ICR MS are the most precise instruments regarding mass accuracy and mass resolution, being able to reach several tens of millions at FWHM. However, these are usually very large and costly instruments. FT-ICR belongs to the family of ion traps MS.

Orbitrap™ Orbitrap™ mass analysers are also ion traps. The Orbitrap™ functioning will be described precisely in the next chapter. Briefly, the ions are trapped inside a cell by an electric field, orbiting around a central electrode. The oscillation frequency is dependent on the mass to charge ratio, which can be retrieved with a Fourier Transform. The mass resolution and mass accuracy of Orbitrap™ MS are its greatest asset, with several hundred thousands to a few millions (FWHM) and down to the ppm, respectively, but instruments are much smaller and less costly than FT-ICR.

With this brief overview of the common mass spectrometers, we can already sense that a lot of different techniques are possible, even for the same sample. As presented, a mass spectrometer is composed of an ionisation source, a mass analyser and a detector. The detector can be a separate subsystem, or in the case of ion traps, the mass analyser is also detecting the signal. To broaden the possibilities it is possible to mix the pairs and, for example, to analyse with an Orbitrap cell ions produced with ESI or laser ionisation. It is also possible to combine the techniques and create tandem mass spectrometry, also called MS/MS. As mentioned previously, quadrupoles are often coupled with other mass analysers as mass filters. Mass spectrometry is a powerful analytical technique that is widely used in laboratories to identify and quantify chemicals. MS is particularly useful for studying complex mixtures, and has a broad range of applications in fields such as chemistry, biology, and environmental science. In addition to its use on Earth, mass spectrometry is also an important tool for studying celestial bodies in space. Accessing the chemical composition of a Solar System object gives precious information about its formation, evolution and habitability potential. In the case of Enceladus, the two mass spectrometers on board Cassini have detected liquid water beneath the icy surface, complex organic chemistry and hydrothermal activity on the seafloor (Postberg et al., 2009;Hsu et al., 2015;[START_REF] Waite | Cassini Finds Molecular Hydrogen in the Enceladus Plume: Evidence for Hydrothermal Processes[END_REF]Postberg et al., 2018). However, mass spectrometry is an in situ technique and requires to be in the vicinity of the body of interest. This greatly reduces the possibility of measurements compared to remote sensing techniques, as only major missions can actually visit planets in the outer Solar System, or land on Mars to study specific samples. In addition, the constraints inflicted by the space environment are numerous and strong. An instrument must be able to withstand the space environment, which is very aggressive. Temperature differences can be several hundred degrees within a few minutes, radiation bombardment can damage electronic components and the instrument must be able to sustain the shocks and vibrations induced by lift-off. Also, the mass is a critical parameter for spacecraft. For example, Cassini-Huygens had a launch mass of 5683 kg, of which only 380 kg was devoted to the scientific payload. This represents only 7% of the total mass. With this ratio, it is clear that each kilogram of the instruments is very valuable, and that the payload mass must be reduced as much as possible. In addition to the ruggedised version, the instrument must be as light as possible. All of those limitations lead to performances much lower than what is usually achieved by laboratory instruments.

Among the different ionisation techniques and mass analysers presented in the previous subsection, only a few were adapted for the space environment as some are not compatible with such heavy constraints. The major milestones in the development of spaceborne mass spectrometers are gathered in Figure I.10. The first MS were onboard the Apollo missions, to analyse the composition of the lunar surface and atmosphere [START_REF] Hoffman | Lunar Orbital Mass Spectrometer Experiment[END_REF]. Analysis of the Martian atmosphere has been carried out since 1975, starting with the Viking lander (Klein, 1979). Onboard was a Gas Chromatograph Mass Spectrometer (GC-MS, which was able to separate volatile compounds before injection in the MS), using a DFMS (Anderson et al., 1972). Still on the Mars surface, NASA rover Curiosity carried a mass spectrometer using quadrupoles as a mass analyser [START_REF] Mahaffy | The Sample Analysis at Mars Investigation and Instrument Suite[END_REF]. Quadrupoles were also used around Saturn and onboard Cassini, with the Ion and Neutral Mass Spectrometer (INMS, [START_REF] Waite | The Cassini Ion and Neutral Mass Spectrometer (INMS) Investigation[END_REF], which studied the atmosphere composition of icy moons [START_REF] Waite | Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure[END_REF][START_REF] Waite | The Process of Tholin Formation in Titan's Upper Atmosphere[END_REF]. Another DFMS that has flown is the MS ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the ESA spacecraft Rosetta (Balsiger et al., 2007). TOF MS have also been sent to space, notably with the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. The results of CDA led to the work presented in this manuscript and will be presented in details in the following subsection.

The mass spectrometers presented hereabove are in some ways pioneers of mass spectrometry in space, and are even sometimes the first space version for the mass analyser. For that reason, the performances were not necessarily high, especially regarding the mass resolution. ROSINA DFMS is an exception, it is the first relatively high resolution mass spectrometer that has flown, reaching 9 000 m/ ∆m (FWHM, [START_REF] Schläppi | Influence of Spacecraft Outgassing on the Exploration of Tenuous Atmospheres with in Situ Mass Spectrometry[END_REF][START_REF] Rubin | Molecular Nitrogen in Comet 67P/Churyumov-Gerasimenko Indicates a Low Formation Temperature[END_REF]. Onboard the upcoming Europa Clipper mission, the MBTOF MASPEX (Mass Spectrometer for Planetary Exploration) is planned to be able to resolve the CO / N 2 interference at m/z 28 with a mass resolution of up to 7 000 (at 10% peak height) with 17 s integration time (Brockwell et al., 2016). To this date, ROSINA DFMS is still the only spaceborne High Resolution Mass Spectrometer (HRMS).

Hypervelocity Detectors

After this short insight of the spaceborne mass spectrometer, we will now focus on two specific MS. Both are hypervelocity instruments and are based on impact ionisation coupled with TOF MS. The process of impact ionisation has first been described by [START_REF] Friichtenicht | Micrometeroid Simulation Using Nuclear Accelerator Techniques[END_REF] and Auer and Sitte (1968) for micrometeroids applications, then by [START_REF] Friichtenicht | The Cosmic Dust Analyzer: Experimental Evaluation of an Impact Ionization Model[END_REF] for cosmic dust. Particles (i.e. dust or ice grains) with velocities higher than 1 km/s impact a target with a known composition. This impact produces neutral atoms, ions and electrons. The target materials can also be ionised, creating metallic ejecta which may be used as calibrant.

Cassini Cosmic Dust Analyser

Overview The Cosmic Dust Analyser (Figure I.11) orbited Saturn onboard the Cassini spacecraft for 13 years. The instrument was designed to characterise the micron and submicron dust environment in the Saturnian system (Srama et al., 2004). CDA is an impact ionisation instrument that is capable of measuring the properties of particles with velocities higher than 1 km/s. CDA weighed 17 kg and was composed of two independent subsystems : the High Rate Detector (HRD) and the Dust Analyser (DA). The former was used to detect particles impacts and their masses at very high counting rates (up to 10 4 s -1 ), while DA was analysing the dust properties usually at count rate from of less than 1 s -1 (i.e. electric charge, impact direction, speed, and composition of cations). The DA was composed of three main subsystems, the Entrance Grid (EG), the Impact Ionization Detector (IID) and the Chemical Analyser (CA). All subsystems gave complementary data and were functional at the same time. Overall, CDA could measure the properties of grains with masses between 10 -5 and 10 -9 g, speeds ranging from 1 to 100 km/s, and electric charges from 1 fC to 1 pC for individual particles.

The different subsystem of CDA are shown in the right panel of Figure I.11. The particles that entered the aperture of CDA first crossed the Entrance Grid. The EG was composed of two inclined grids that measured the electric charge of incoming particles. The charge induced by a particle on the grid is directly proportional to its electric charge. The time difference of the charge signal on the two grids is used to determine the speed of the particle, and their inclination indicates the particle direction in one plane. Following the grids, there were two different targets, the Impact Ionization Target (IIT) and the Chemical Analyser Target (CAT). The IIT is a 41 cm diameter golden plate and is a part of the IID. The IID were analogous to the dust detectors onboard Ulysses or Galileo (Grün et al., 1992a(Grün et al., , 1992b)). Those instruments could measure the properties of the whole grains (i.e. total mass, size and velocities) but were not able to measure the chemical composition of the grains. This is the role of the third subsystem of CDA, the Chemical Analyser. At the centre, surrounded by the IID target lies another target, the Chemical Analyser Target. The CAT is a 16 cm diameter rhodium plate. The plate was held at a potential of +1 kV and a grounded grid was placed 3mm away in front of it. This resulted in electron attraction and cation repulsion. The cation were directly focused toward the Ion Grid and the Multiplier detector behind it. The IG was kept at a potential of -350 V and accelerated the ions towards the Multiplier. There was a distance of 230 mm between the CAT and the Multiplier. This composed the TOF of CDA, with this flight path the ions with different masses arrived with tiny time differences that can be transformed into m/z spectra with a mass resolution of 20-50 m/ ∆m, the mass range going from 1 to ~200 u. The CDA subsystems are shown in Figure I.11.

Results Some CDA results have been briefly mentioned in the Icy Moons section. Thanks to the ability of CDA to actually measures the chemical composition of the ice and dust grains in the Saturnian system, a spectral classification of the different grain types was made. The dominant feature in CDA measurements is derived from water with clusters taking the form of (H 2 O) n H + (Hillier et al., 2007). The clustering of water molecules in the gas phase is well documented [START_REF] Searcy | Clustering of Water on Hydrated Protons in a Supersonic Free Jet Expansion[END_REF][START_REF] Shi | Water Clusters: Contributions of Binding Energy and Entropy to Stability[END_REF][START_REF] Wang | Investigations of Protonated and Deprotonated Water Clusters Using a Low-Temperature 22-Pole Ion Trap[END_REF][START_REF] Shi | Revisit the Landscape of Protonated Water Clusters H + (H 2 O) n with n = 10-17: An Ab Initio Global Search[END_REF], however clustering induced by an impact plasma has been far less explored [START_REF] Timmermann | In Origin and Evolution of Interplanetary Dust[END_REF]. Three different compositional types of ice grains have been defined from CDA measurements in the Enceladus plume and the E-ring, a CDA mass spectrum is shown for each type of grains in Figure I.12. Type I grains are quite homogeneous and are almost composed of pure water with only traces of sodium or potassium salts (Postberg et al., 2009). Type II grains contain organic compounds (Postberg et al., 2008). Additional analyses have revealed the presence of oxygen-, nitrogen-bearing and aromatic compounds (Khawaja et al., 2019), along with complex organic macromolecules (Postberg et al., 2018). Type III grains are dominated by salt ions, with inferred concentration of about 1% of the total ice grain mass and are thought to come from frozen parts of Enceladus' ocean (Postberg et al. 2009(Postberg et al. , 2011)). Impact Speed The composition of ice grains is not the only factor that can impact the pattern of CDA's mass spectrum. For the same composition but different impact speed the resulting mass spectra can be much different (Figure I.12). During an impact, the velocity of both the spacecraft and the particle must be added to obtain the actual impact speed. From CDA measurements of Enceladus' ice grains, impact velocities ranging from 4 to 21 km/s occurred. The mass spectra shown in Figure I.12 were recorded during the E5 flyby with velocities of 17.7 km/s. At such high velocities, the energy density of the impact is high enough to fragment larger molecules, resulting in measurements of Hydrogen, Sodium, Oxygen or Carbon (see also left spectrum of Figure I.13). With lower speed and impact energy density, water clusters start to appear in the mass spectra. Their concentration gradually increases with the diminution of the impact speed. This effect is attributed to the large difference in the post-ionisation kinetic energy between impact at 4 km/s and 20 km/s. In addition to the higher degree of fragmentation, for high velocities, the ion cloud is expanding faster after ionisation, thereby reducing the time available for clustering inside the impact cloud before the acceleration from the grid 3 mm away from the impact location. The right panel of Figure I.13 shows a low velocity impact mass spectra with the characteristic water clusters. Due to the vast amount of CDA data (about 1 000 000 mass spectra in total), the interpretation of CDA's data is still ongoing. The latest findings unveiled the presence of Phosphorous compounds (Na 3 PO 4 and Na 2 HPO 4 ) in some type III grains [START_REF] Postberg | Detection of Phosphates Originating from Enceladus's Ocean[END_REF]. From all the requisites for life listed hereabove, Phosphorous was the last missing brick in Enceladus. With this detection, the liquid water ocean, the chemical energy as well as all the CHNOPS compounds have been detected, making Enceladus one of the Solar System's body with the highest habitability potential.

Europa Clipper SUrface Dust Analyser

Overview The SUrface Dust Analyser (SUDA) is part of the payload of the upcoming Europa Clipper spacecraft. SUDA is built on the strong heritage left by CDA, but uses a RTOF instead of the linear ion path of CDA (Figure I.14, Kempf et al., 2014[START_REF] Kempf | The SUrface Dust Analyzer (SUDA): Compositional Mapping of Europa's Surface. Abstract[END_REF]. This feature extends the ion path and leads to a greater mass resolution, in the order of 150-300 m/ ∆m. SUDA mass range is 1-500 u, and unlike CDA, SUDA will be able to measure both cationic and anionic mass spectra (although not at the same time). The high sensitivity of the instrument will allow to detect trace compounds (< 1 ppm) in the sampled grains. Although SUDA is approximately half the size of CDA, it still weighs 14 kg because of the heavy shielding needed to protect the electronics from Jupiter's harsh radiation. Along with the RTOF, similar Entrance Grids to those in CDA can be found close to SUDA aperture. The grids are used for the same purpose as for CDA, characterising the mass and speed vector of the incoming particles, though with much better sensitivity (down to 0.3 µm particle size). Like CDA, a target (here made of Iridium) is placed at the bottom of the instrument and held at a potential of ±2.5 kV (depending on the studied ions polarity), the ions resulting from the impact are repelled from the target, then the reflecting grid (±3 kV) plays the role of an electrostatic mirror and focuses the ions towards the detector (Ion Sensor) placed in the centre of the impact target for detection via their time-of-flight.

Surface Composition Mapping

As its name suggests, SUDA is designed to analyse the surface composition of the Jovian moons. CDA could benefit from the Saturnian rings as well as Enceladus plumes to encounter samples from orbit. However, plumes on Europa are not confirmed yet, and even if they exist it is questionable if Europa Clipper can safely fly through it. One could ask how SUDA will be able to access surface samples by only performing flybys. This relies on the fact that airless bodies are surrounded by their own materials, lifted from the surface by micrometeoroid bombardment [START_REF] Krüger | A Dust Cloud of Ganymede Maintained by Hypervelocity Impacts of Interplanetary Micrometeoroids[END_REF][START_REF] Sremcevic | Impact-Generated Dust Clouds around Planetary Satellites: Model versus Galileo Data[END_REF][START_REF] Miljkovic | Models of Dust around Europa and Ganymede[END_REF]. Interplanetary meteoroids have typically masses in the range of 10 -8 kg and speed of around 9 km/s (Divine, 1993; V. [START_REF] Krivov | Impact-Generated Dust Clouds around Planetary Satellites: Spherically Symmetric Case[END_REF][START_REF] Sremcevic | Impact-Generated Dust Clouds around Planetary Satellites: Asymmetry Effects[END_REF]. When impacting surfaces, such micrometeoroids can uplift a significant number of particles, up to few thousand times their own masses [START_REF] Koschny | Impacts into Ice-Silicate Mixtures: Ejecta Mass and Size Distributions[END_REF]. Most of the ejected particles will take ballistic trajectories and will eventually fall back on the surface. It is this constantly fed dust clouds that SUDA is aiming for. With the particles information given by the Entrance Grids, combined with the attitude and position of the spacecraft, SUDA will be able to analyse the composition of samples with a constrained spatial origin, leading to a composition mapping of the surface [START_REF] Postberg | Compositional Mapping of Planetary Moons by Mass Spectrometry of Dust Ejecta[END_REF][START_REF] Goode | Detecting the Surface Composition of Geological Features on Europa and Ganymede Using a Surface Dust Analyzer[END_REF]. However, surface emitted particles do not necessarily have a trajectory perpendicular to the surface. A detection and a mass spectrum above a feature of interest is therefore not always linked to the feature. Figure I.15 [START_REF] Goode | Detecting the Surface Composition of Geological Features on Europa and Ganymede Using a Surface Dust Analyzer[END_REF] shows detection events and their origins modelisation depending on the spacecraft location and altitude. The dark blue points represent the detections from the chaos region Thera Macula. At a low altitude flyby, here 35 km, the detections are firstly much more frequent than at 100 km. Their origin can be well constrained and the composition can therefore be attributed to the proper area on the surface. This is especially important as chaos region are believed to be markers of shallow liquid water reservoirs [START_REF] Schmidt | Active Formation of 'Chaos Terrain' over Shallow Subsurface Water on Europa[END_REF]. In order to be able to characterise a chaos region both in cation and anion mode, it is planned in the Europa Clipper mission to perform flyby above the same feature twice.

Future Icy Moons Dust Detectors

RTOF The performances of a mass spectrometer and in particular its mass resolution, mostly defined by its mass analyser, can limit the science return of a mission. For this reason, developments are under way to increase the mass resolution of hypervelocity impact detectors. For example, SUDA is planned to reach 300 m/ ∆m (Kempf et al., 2019), which is approximately 10 times that of CDA. Even though higher, SUDA's mass resolution is still relatively low compared to HRMS. However, some dust impact ionisation MS have been designed and proposed for mission concept. ENIJA (ENceladus Icy Jet Analyser, also called ENIA, shown in Figure I.16) is the next generation of impact ionisation RTOF MS (Srama et al., 2015). Thanks to an extended flight path, ENIJA is planned to be able to measure impact ionisation mass spectra with a mass resolution above 1 000 m/ ∆m, a mass range between 1 and 2 000 u and a 50 Hz acquisition rate.

Next Generation Hypervelocity Dust Detectors I highlighted the fact that the ionisation and mass analyser are two independent subsystems of a mass spectrometer. The ionisation mostly impacting the spectral patterns, and the mass analyser constraining the performances. Therefore, and because only TOFMS has been used until now, the impact ionisation technique that we need for the study of dusty and icy grains orbiting icy moons could be coupled with a different mass analyser. Because of the high costs of space mission and the required high reliability of instruments, it is a tedious task to be selected on a future mission. For that reason, space agencies tend to select instruments with a strong heritage, like SUDA which is an improved version of CDA. However, each mass analyser has its pros and cons. The spatialisation of a new technique would greatly complement the reliable Impact Ionisation -TOF mass spectrometers, offering new opportunities for discovery.

Laboratory Calibration

Particles in space are either composed of ice, siliceous, metallic or organic components or mixtures of these. CDA mass resolution is very limited (20 -50 m/ ∆m), resulting in numerous mass interferences making peak identification on mass spectra often extremely challenging. For that reason, reproducing analogue experiments in laboratory can significantly help the interpretation of the mass spectra.

Dust Particles

The technical challenge in the laboratory calibration of dust impact ionisation is to reach relevant impact speed, which are in the range of 3 and 20 km/s for CDA. Micron and submicron dusty particles can be accelerated via electrostatic dust accelerators (Burchell et al., 1999b;Mocker et al., 2011;[START_REF] Shu | 3 MV Hypervelocity Dust Accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies[END_REF]. Such devices use power-supplies up to 2 or 3 Mega-volts to accelerate particle between 0.05 μm and 5 μm in size to speeds between 1 and 80 km/s. The particles must be able to carry on their surface the charges given by the high voltage source. For that reason, only conductive compounds like metals can be accelerated. For siliceous and organic materials, a coating can be applied to add a conductive layer. Organics have been accelerated thanks to a polymer coating (Burchell et al., 1999a;[START_REF] Srama | Mass Spectrometry of Hyper-Velocity Impacts of Organic Micrograins: MS Study of Hyper-Velocity Impacts of Organic Micrograins[END_REF], and minerals with a metallic coating such as platinum [START_REF] Hillier | The Production of Platinum-Coated Silicate Nanoparticle Aggregates for Use in Hypervelocity Impact Experiments[END_REF].

Icy Particles

Ice Grains Accelerator The acceleration of icy grains is even more challenging. Currently, there is no possibility to apply a conductive coating on ice for the use in electrostatic accelerators, and at the moment only ice analogue have been accelerated to relevant velocities [START_REF] New | Characterizing Organic Particle Impacts on Inert Metal Surfaces: Foundations for Capturing Organic Molecules during Hypervelocity Transits of Enceladus Plumes[END_REF]. However, recent efforts have succeeded in accelerating frozen water droplets created with ESI up to 1 km/s (Belousov et al., 2021). The icy grains of about 1 μm are accelerated by a linear accelerator. Further work is planned to increase the size of the linear accelerator and reach velocities of 5 km/s. According to the authors' simulation, this is theoretically possible with 0.5 μm particles [START_REF] Miller | Production and Impact Characterization of Enceladus Ice Grain Analogues[END_REF].

Analogue Experiment

The ice acceleration challenge could be circumvented thanks to a method usually used in the biochemistry field. The Laser Induced Liquid Beam Ion Desorption (LILBID) technique could be assimilated to MALDI, however in this case the matrix is liquid water [START_REF] Karas | Principles and Applications of Matrix-Assisted UV-laser Desorption/Ionization Mass Spectrometry[END_REF](Karas et al., , 2000)). The LILBID technique has numerous applications, such as the study of large biomolecules and protein identification [START_REF] Charvat | New Design for a Time-of-Flight Mass Spectrometer with a Liquid Beam Laser Desorption Ion Source for the Analysis of Biomolecules[END_REF][START_REF] Peetz | LILBID and nESI: Different Native Mass Spectrometry Techniques as Tools in Structural Biology[END_REF][START_REF] Young | LILBID Laser Dissociation Curves: A Mass Spectrometry-Based Method for the Quantitative Assessment of dsDNA Binding Affinities[END_REF] or the diagnoses of diseases (Patel, 2015;Sim et al., 2015). A detailed description of the LILBID technique can be found in the method section of Chapter V, which is dedicated to this technique. Briefly, LILBID is an ionisation technique that uses infrared (IR) laser desorption to ionise samples dissolved in an ultra thin micrometer-sized water beam (Figure I.17 right). Coupled with a mass analyser, it is possible to measure the chemical composition of the liquid sample. 13. This analogy opens a door to laboratory calibration of CDA's, with a large increase in mass resolution, depending on the mass analyser coupled with the ionisation apparatus. The setup used in Berlin is a LILBID-TOF, reaching a mass resolution of ~800 m/ ∆m. Thanks to this improvement, the interpretation of the mass interference of CDA's spectra could be mitigated. To give a concrete example, CDA's data showed spectral peaks at mass 81, which could be attributed to either NaOH(H 2 O)Na + or (NaCl)Na + . With the analogue samples measured with LILBID and its better mass resolution, it was possible to attribute the peak to the NaCl specie, highlighting the necessity of a liquid water reservoir to form such salt rich grains. Although the current LILBID setup that uses a TOF as mass analyser enables laboratory calibration with a better mass resolution, 800 m/ ∆m is still a rather low value and often mass interferences still prevent an non ambiguous chemical species identification.

OBJECTIVES OF THIS WORK. CHAPTER I. INTRODUCTION 5 Objectives of this Work

It is within the framework of the Europa Clipper mission that the work of my PhD has been carried out. More specifically, it intends to enhance the interpretation of SUDA's future data by proposing to couple a high resolution mass analyser based on the Orbitrap™ technology to the state-of-art SUDA's calibration experiment for icy materials, the LILBID experiment. The work of Postberg's team (Postberg et al., 2008(Postberg et al., , 2009(Postberg et al., , 2011(Postberg et al., , 2018;;Khawaja et al., 2019;Klenner et al., 2020a, 2020b, Dannenmann et al. 2022) has demonstrated the benefits of having a calibration setup with analogue ionisation patterns, but offering higher performances than the spaceborne instrument. However, the TOF used in the laboratory at the Freie Universität (FU) Berlin is still limited regarding its mass resolution, and the interpretation work could go even further with higher performances. From the ongoing development of a spaceborne Orbitrap-based mass spectrometer (Briois et al., 2016), the LPC2E has a strong experience regarding this type of mass analyser. Few years ago, the idea of coupling the LILBID technique to a customised new mass spectrometer composed of an Orbitrap cell rose between both teams. Such an instrument would be able to accurately mimic icy grains hypervelocity impact with LILBID, and measure the resulting ions with ultra-high mass resolution, in the order of tens of thousands FWHM at the mass of H 2 O, which is more than 500 times that of CDA, or 50 times that of the LILBID-TOF setup

To pursue this objective, the need for a new laboratory testbench fully dedicated to this project has been identified. Considering that the Orbitrap laboratory setup in Orléans is mainly dedicated to the space development, the choice has been made to build a new instrument for the collaboration with the team at the Freie Universität Berlin, and the coupling with the LILBID setup for measurements of the hypervelocity ice grains analogues.

The requirements and constraints of such a coupling have been identified, and a new mass spectrometer has been built, OLYMPIA. OLYMPIA is a custom-made mass spectrometer, designed to be versatile regarding its ionisation method, easily transportable and modular. OLYMPIA was designed and built by Ján Žabka (J. Heyrovsky Institute of Physical Chemistry, Prague, Czech Republic), during a one-year visit in Orléans in 2018, in the frame of the SMART LOIRE VALLEY GENERAL PROGRAMME of Le Studium. OLYMPIA stands for Orbitrap ana-LYser MultiPle IonisAtion, and as its name suggests, was designed to be adaptable to different ionisation method. In parallel, B. Abel, A. Charvat and F. Stolzat at the Leibniz Institute of Surface Engineering (IOM, Leipzig, Germany) adapted a duplicate version of LILBID to interface with OLYMPIA. Several short mechanical coupling campaigns have been organised between the different laboratories to assess the feasibility of the project (see Section 3 of Chapter II for more details).

My work starts during one of these campaigns, in October 2019 in Leipzig, the results of which are presented in Chapter V. The feedback from the campaign showed a need for improvements, which were the first step before a permanent coupling to FU Berlin LILBID setup. This was performed with OLYMPIA's electronic impact ion source in Orléans. This configuration helped to better handle the different parameters of OLYMPIA, that finally moved to Berlin in February 2021. The coupling of OLYMPIA and the LILBID ionisation was then possible.

For a few years, the team in Berlin has been building a database containing LILBID mass spectra for the calibration and data interpretation of SUDA (Klenner et al., 2022, Appendix I). The database currently includes over 12 000 mass spectra of more than 200 substances with different experimental parameters (see Chapter V for more details). All the spectra were recorded with the LILBID-TOF setup, and the objective of this PhD is to be able to complement this database with ultra-high mass resolution spectra recorded with the new LILBID-OLYMPIA setup.

Chapter II

A New Orbitrap-based Mass Spectrometer

This chapter will describe the functioning of a key part of the laboratory setup used for this thesis, OLYMPIA, an Orbitrap-based mass spectrometer. I will first describe the functioning of the Orbitrap™ technology and its performances, then each OLYMPIA sub-system as they were at the beginning of this work, as well as the method to optimise them. As mentioned in the first chapter, OLYMPIA is to be coupled with different ion sources, requiring some adaptation and specific parts for each configuration. To ease the reading, the parts specific to the Electron Impact ionisation and the LILBID setup will be described at the beginning of the respective chapters.

1 The Orbitrap ™ Mass Analyser

The Kingdon Trap

The concept of analysing ions by trapping dates back to 1923 with the first description of the concept by K.H Kingdon (Kingdon, 1923) giving the name of "Kingdon Trap" to the design. The Kingdon trap is composed of one cylindrical outer electrode with a wire in the centre and is closed on both end by two co-axial electrodes. By applying a DC voltage to the central wire, the potential creates an electrostatic field that can be described by this equation :

Φ = A ln r + B (II.1)
Where r is the radial coordinate, A and B the constants of the applied potential on the two electrodes. When introducing ions inside the trap with a velocity perpendicular to the wire, the electrostatic field Φ bends the trajectory of the ions and trapped them on stable orbits (Figure II.1). Equation II.1 makes the approximation that the electrodes are infinitely long. However, because the central wire alone does not confine the ions in the axial direction, they move all along it. To keep the ions from hitting the edges of the cylinder, a potential with the same polarity as the ions can be applied on the end-caps to repel back the ions inside the trap and revert their axial direction. This keeps the ions inside the trap but makes the electrostatic field non-ideal. The Kingdon trap has been used for numerous applications, mainly for particle physics, and coupled with various setups, such as Faraday cups, electron multipliers or photomultiplier for spectroscopic studies of trapped ions [START_REF] Prior | Hyperfine Structure of the 2s State of 3 He +[END_REF][START_REF] Vane | Electron Capture by Trapped Ne 10+ at Very Low Energies[END_REF]. As seen in the end view of around the central electrode is much alike the orbit of planets around their star. It is indeed the same principle, the gravitational energy of planets that trapped planets in orbit is just replaced by the electrical energy created by the electrostatic field in the trap. This analogy has even been used to describe plasma and dust interaction in planetary disks, as well as orbital mechanics [START_REF] Biewer | Electrostatic Orrery for Celestial Mechanics[END_REF][START_REF] Robertson | Collective Behavior of Non-neutral Plasma in a Kingdon Trap[END_REF][START_REF] Robertson | Experimental Studies of Charged Dust Particles[END_REF].

The Knight Trap

Due to the lack of harmonic oscillations induced by the end-caps, the Kingdon trap was not able to analyse the mass to charge ratio of the ions. By modifying its design, R.D. Knight was able to introduce the harmonic motion in the axial direction [START_REF] Knight | Storage of Ions from Laser-produced Plasmas[END_REF]. This new design (Figure II.2) is getting closer to the current shape of the Orbitrap cell. The Knight version of the Kingdon trap has later been qualified as an "ideal Kingdon trap" [START_REF] Gillig | Ion Motion in a Fourier Transform Ion Cyclotron Resonance Wire Ion Guide Cell[END_REF]Makarov, 2000;[START_REF] Perry | Orbitrap Mass Spectrometry: Instrumentation, Ion Motion and Applications[END_REF]. Thanks to this new shape, a new term in the electrostatic potential equation appears :

Φ = A z 2 - r 2 2 + B. ln r (II.2)
The z 2 term describes the harmonic motion of the ions along the axial axis, and implies that the frequency of this motion is m/z dependent, allowing mass analysis and mass spectrometry applications. However, Knight did not succeed in properly defining the electrostatic field inside the trap, resulting in distorted resonances (i.e. weakened, broadened or shifted frequencies). The central electrode is still a wire and the outer electrodes are quite simply designed with grids and not solid electrodes. Knight proposed that the central wire could distort the quadrupolar shape of the electrostatic field [START_REF] Knight | Storage of Ions from Laser-produced Plasmas[END_REF]. Despite this, the proof of concept of the mass analysis with an electrostatic field ion trap was demonstrated.

The Gillig Ideal Trap

With the development of software able to simulate the behaviour of ions in electrostatic fields such as SIMION [START_REF] Dahl | Simion for the Personal Computer in Reflection[END_REF]

THE ORBITRAP™ MASS ANALYSER CHAPTER II. A NEW ORBITRAP-BASED MS

This finding led to the understanding that to perfect the Knight trap one could create an electrode system and apply potential to match Equation II.2. This has been applied by the same team [START_REF] Solouki | Detection of High-Mass Biomolecules in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Theoretical and Experimental Investigations[END_REF][START_REF] Gillig | Ion Motion in a Fourier Transform Ion Cyclotron Resonance Wire Ion Guide Cell[END_REF], which proposed a modification of the ion cyclotron resonance (ICR) methods to enlarge both the mass range and mass resolution of the technique.

Another possibility to perfect the shape of the electrostatic field is to build a central electrode with the same shape as the field lines of the Knight trap. This was achieved by Alexander Makarov with the Orbitrap cell.

Makarov Orbitrap Cell 1.2.1 Cell Description

The first mention of an "Orbitrap" was in 1999 at an American Society for Mass Spectrometry conference. Makarov presented his own interpretation of the Kingdon Knight-style trap. The new design got rid of the central wire and replaced it with a spindle-shaped central electrode, and was composed of two symmetrical barrel-like outer electrodes, insulated from one another by a ceramic ring. The electrostatic potential distribution of the Orbitrap cell can be described with this equation (Makarov, 1999;Makarov, 2000) :

U (r, z) = k 2 z 2 - r 2 2 + k 2 (R m ) 2 ln r R m +C (II.3)
With r and z the cylindrical coordinates, R m is maximum radius at which ions can be captured, C a constant and k the axial restoring force that is dependent on the shape of the electrodes and the potential applied on them. This equation is composed of two main terms, the quadrupolar field :

k 2 z 2 -r 2 2
together with the logarithmic part

k 2 (R m ) 2 ln r R m .
This combination gives the name of the technique behind the Orbitrap™ ; a quadrologarithmic ion trap. The geometry of both the outer and central electrodes can be deduced from Equation II.3 as follow : The SIMION simulation of Figure II.4 presents an ideal shape for the electrodes obtained from Equation II.4 and the electrostatic field lines, that follows the shape of electrodes. However, one major point is omitted : the ions injection. Because ions must be injected inside the trap, an aperture must be placed in one outer electrode. This hole will however disturb the electrostatic field and lead to the destabilisation of the ions. To mitigate this disturbance, another electrode has been placed outside the cell : the deflection electrode. The deflection electrode (hereafter VDE) has two main purposes : (i) as the name suggests, to deflect the ions towards the Orbitrap cell, and (ii) to correct the field aberration caused by the aperture by applying the appropriate potential [START_REF] Grinfeld | Control of Aberration and Space-Charge Effects in the Orbitrap Mass Analyzer[END_REF]. The potential needed to deflect the ions and correct the electrostatic field is not the same, VDE must therefore be switched from one potential to another after the ion injection. Each Orbitrap cell has its own optimal value for VDE, and the search of OLYMPIA's optimal value has been undertaken during this work and will be presented in Chapter III.

z 1,2 (r) = ± r 2 2 - (R 1,2 ) 2 2 + (R m ) 2 ln R 1,2 r 1/2 (II.

THE ORBITRAP™ MASS ANALYSER CHAPTER II. A NEW ORBITRAP-BASED MS

Ion Trajectory

The left panel of Figure II.5 shows the ion path at injection. With a velocity perpendicular to the axial (z) axis, the ions are injected through the aperture, which is displaced from z=0 in order to give a potential energy in the z direction. This allows the ions to oscillate during the measurements from a +z to a -z position. This technique is called 'excitation by injection" (Makarov, 2000). The ions are stabilised at a distance r from the central electrode (VCE) and take the shape of a thin ring with ions distributed evenly along its circumference. The r distance is directly determined by the m/z ratio of the ions. This can be explain by the the radial oscillation around VCE equation :

r = 2 eV eE (II.5)
With r the radius of the outer electrodes as well as the radius of the ion trajectory, eV is the ion kinetic energy and eE is the electric field force experienced by the ions during its motion. Ions with a higher kinetic energy, and therefore mass will orbit the central electrode at a greater r distance than low kinetic energy ions. From Equation II.3 we can deduce the following equation that gives the ions coordinate inside the trap :

d 2 z dt 2 = - q m kz (II.6)
With m and q the mass and charge of ions, respectively. The solution for this equation is :

z(t) = z 0 cos (ωt) + 2E z k 1/2 sin (ωt) (II.7)
With z 0 the initial position of the ions (i.e. their position at injection) and E z the kinetic energy along the z axis, and ω as follow :

ω = q k m 1/2 (II.8)
which is the actual axial oscillations frequency of ions in rad/s. It is in equations II.7 and II.8 that the real strength of the Orbitrap™ lies. All the parameters of Equation II.7 are known and the oscillations of the ions are only depending on the m/z value and the potential applied on VCE (i.e. the k factor) which is held constant. Knowing this, it is expected that each ion will have a unique oscillation frequency and orbit around VCE. As shown in the right panel of Figure II.5, lower m/z ions will orbit closer from VCE than higher m/z ions, and with a higher frequency. The Orbitrap™ draws its ultra-high-resolution from this feature. However, if in theory the k factor is fixed, an extremely stable power supply is required for VCE. Indeed, as just demonstrated, the ions are sensitive to only one external parameter : VCE potential. This means that a tiny variation on the VCE potential during the trapping time (which lies in the order of 1 sec) will directly disturb the ions behaviour inside the trap and decrease the performance. With OLYMPIA, a trade-off had to be made for the selection of the power supply, as it can be a very expensive hardware. The results will be presented in Chapter III. It is important to understand that with a mass spectrometer using a Fourier Transform to process the data, longer measurement times will lead to better mass resolution. The mass resolution is directly linked to the frequency resolution, as described in Makarov (2000) :

1. THE ORBITRAP™ MASS ANALYSER CHAPTER II. A NEW ORBITRAP-BASED MS m/∆ m = 1 2 (ω/∆ ω) (II.9)
With ω/∆ ω the frequency resolution, that is equal to the inverse of the FFT duration. Figure II.6 is based on Equation II.9 and shows the evolution of the theoretical mass resolution as a function of the m/z ratio for different FFT duration. From the figure, it is obvious that a longer measurement time leads to higher performance. This is why it is crucial to keep the ions in the Orbitrap cell as stable as possible over time. As the frequency of ions is dependent on their m/z ratio (Equation II.8), the theoretical mass resolution decreases with increasing mass.

Ion Squeezing

As shown in the right panel of Figure II.5 and in Equation II.5 higher m/z ions will have an orbital radius bigger than lower m/z ions. This implies that there is a maximum m/z window during one measurement. To increase this window, a technique of electrodynamic squeezing is used (Makarov, 1999;Makarov, 2000;Hu et al., 2005). This consists in switching the DC voltage of VCE to a higher potential. The stronger electrostatic field will squeeze the ions closer to the central electrode (reducing the r value). The z amplitude will also be reduced, confining the ions further to the centre of the trap. Figure II.7 illustrates the variation in the ions path inside the trap for both VCE levels. Reducing the r value for a given m/ z will allow higher m/ z ions to be captured at the same time.

The VCE switch is another parameter that needs to be optimised. Usually, the potential level before squeezing is called VCE injection, whereas the potential during the measurements is called VCE measure. VCE measure is usually set at -3500 V for cations. In commercial instruments the value of VCE injection is -2500 V. The ramp (i.e the time to go from injection to measurement level) is usually between 20 -100 μs. Depending on the ramp, higher or lower m/z ions can be favoured (Hu et al., 2005). The switch of VCE must of course be synchronised with ions injection. An offset of just one μs from the optimal value can result in a capture failure.

Ion Detection

The ion detection is made by image current detection. As explained in Subsection 1.2.2 only the axial oscillations of an ion packet is independent from its m/z value or the injection parameters.By contrast, the radial and rotational oscillations are much impacted by such variations, and even if it is in theory possible to extract a mass spectrum from those frequencies the mass resolution will be very low [START_REF] Oksman | A Fourier Transform Time-of-Flight Mass Spectrometer. A SIMION Calculation Approach[END_REF]. However, by cutting the outer electrode in two symmetrical parts, Makarov was able to analyse the image current in the axial axis. The ion ring captured around VCE oscillates from a +z to a -z value, inducing therefore an opposite current on the two outer electrodes, which is then detected by differential amplification.

The axial dimension of the ion ring is at first rather small. However, through time its width can extend due to geometrical imperfections in the electrodes shape, space charge, or interaction with the neutral background (Hu et al., 2005). The broadening of the ion ring can ultimately lead to a size of the same order of the axial oscillations, The image current on the outer electrodes is measured by a preamplifier. All the ion frequencies are combined together and take the shape of the simulated signals on the right panels of Figure II.8. By applying a Fast Fourier Transform (FFT), the data go from a time-domain spectra to a frequency-domain spectra. As explained above, each frequency is linked to a single m/z ratio and the exact mass can be retrieved by using Equation II.8.

Ion Injection

As shown in Equation II.7 the kinetic energy of the ions is an important parameter that needs to be controlled. Considering the fixed value of -2500 V and -3500 V for both VCE levels, only ions with a certain range of Kinetic Energy (KE) will be able to be trapped by the electrostatic field of the Orbitrap cell. On the first version of the commercial Orbitrap cell, the reference KE is around 1620 eV (Hu et al., 2005). Ions injected with lower KE (~900 eV) will have a highly elliptical orbit with a perigee close to the central electrode. If the KE is even lower,

THE ORBITRAP™ MASS ANALYSER CHAPTER II. A NEW ORBITRAP-BASED MS

the ions will strike the central electrode. Ions with too much KE will not be captured by the electrostatic field and will either strike into the outer electrodes or simply go through the Orbitrap cell, its potential being too low to deflect the ions trajectory. For that reason, the ion packet at injection must have a defined KE, with a distribution as small as possible to create an ion-ring that is as thin as possible.

In addition, the injection time for similar m/z ions should be as short as possible. To ensure this, both the size and time distribution of the injected ion packet should be minimised. The ideal parameters for the ion packet are a few mm in space and between 100 to 200 ns in time [START_REF] Perry | Orbitrap Mass Spectrometry: Instrumentation, Ion Motion and Applications[END_REF].

During the Orbitrap™ development, three different techniques have been used, (i) Electrostatic Acceleration Lenses, (ii) a Linear Quadrupole Ion Trap and (iii) the C-trap. The principle of Electrostatic Acceleration Lenses will be described hereafter, as it is the technique used during this work with OLYMPIA. The Linear Quadrupole Ion Trap technique has quickly been replaced by C-trap for commercial instruments so only this technique will be described in detail here.

The C-trap module was invented by Makarov et al. (2006) to answer the specific needs of the KE distribution for the ion injection in the Orbitrap cell. A C-trap is a Radiofrequency-only (RF) quadrupole with a C-shaped central axis. It is used as an intermediate ion storage prior to the injection. After their ionisation from the ion source, the ions are injected into the C-trap, which is filled with Nitrogen at a pressure of 10 -2 mbar. Nitrogen has been chosen for its effective collisional cooling properties. After their transfer inside the C-trap, the ions are kept inside by the quadrupole RF field. During this time, they collide with the nitrogen background in order to cool down and lose their initial KE. Once this is done, the ions form a thin thread along the curved axis of the C-trap. To eject the ions, the quadrupole of the C-trap is quickly ramped to create a differential RF field that will accelerate ions towards the Orbitrap cell (Figure II.9). The ions are then accelerated to the proper KE with ion optics electrodes, and go through a three-stage differential pumping that ensures the ultra vacuum needed inside the Orbitrap cell (~2.10 -10 mbar).

Commercial Instruments

In 1999, Makarov obtained a patent (Makarov, 1999) ) the LTQ Orbitrap™ was able to benefit the high mass resolution and mass accuracy of the Orbitrap cell, but also the sensitivity, the precursor isolation and the fragmentation capabilities of the linear ion trap. The LTQ Orbitrap™ was a great commercial success in numerous fields of application. However, even though it was designed to be as versatile as possible, there were still some limitations, with a very low scan rate and a single ionisation/fragmentation method (the ion trap-base Collision-induced dissociation (CID)) that prevent the analysis of certain kind of peptides [START_REF] Eliuk | Evolution of Orbitrap Mass Spectrometry Instrumentation[END_REF]. In order to mitigate those limitations, the subsequent versions of Orbitrap™ expanded the analytical capabilities to tackle more complex applications. The transmission power of the C-trap was improved and new fragmentation methods implemented. To do so, different modules have been added to complement the commercial version, with for example a higher energy collision-induced dissociation (HCD) or an electron transfer dissociation [START_REF] Mcalister | A Proteomics Grade Electron Transfer Dissociation-Enabled Hybrid Linear Ion Trap-Orbitrap Mass Spectrometer[END_REF].

To improve the overall performances of the Orbitrap™ and compete with the state-of-the-art ultra-high mass resolution of ICR mass spectrometers, Thermo Fisher went back to the initial equation of the ion oscillations (Equation II.8), which can be rewritten as follows : With this new version of the commercial Orbitrap™, the Orbitrap Elite, Thermo Fisher was able to exceed a mass resolution of 1 000 000 for m/z below 300-400 within 3 seconds acquisition time (Denisov et al., 2012) and to diversify their science applications through different molecule fragmentation modes [START_REF] Michalski | Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes[END_REF].

ω = e (m/z) . 2 .Ur R 2 m ln R 2 R 1 -1 2 (R 2 2 -R 2

TOWARDS A SPACEBORNE ORBITRAP CELL CHAPTER II. A NEW ORBITRAP-BASED MS 2 Towards a Spaceborne Orbitrap Cell

As the space environment presents serious constraints of energy consumption, size or mass, many high resolution MS techniques could hardly been considered. But thanks to a very compact size and small mass of the cell (~250 g for a D30), the Orbitrap cell is ideal for space mission development. In that regard, a consortium of five French laboratories has been created in 2009 with the objective of adapting the Thermo Fisher Orbitrap cell for space applications, and spatialise a new mass analyser (Briois et al., 2016). The original consortium was composed of five French laboratories : the LPC2E (Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace) in Orléans, the LATMOS (Laboratoire Atmosphères Milieux et Observations Spatiales) in Guyancourt, the LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques) in Créteil, the IPAG (Institut de Planétologie et d'Astrophysique de Grenoble) in Grenoble, the IJCLAb (Laboratoire de physique des 2 infinis -Irène Joliot-Curie) in Orsay. The consortium is cooperating with Thermo Fisher under non-disclosure-agreements and A. Makarov as a consultant. In 2018, Ján Žabka from the J.Heyrovský Institute of Physical Chemistry in Prague joined the team, and built the laboratory setup on which this work was performed, OLYMPIA. The project is mainly funded by the CNES (Centre National des Études Spatiales).

The CosmOrbitrap is not only the space compatible mechanical version of an Orbitrap cell, it also includes the electronic components required for its functioning (e.g. ultrastable HV) and the acquisition and data treatments unit, as seen on Figure II.12. Because of the additional challenge that would represent adapting the C-trap module featured in the commercial instruments for space applications, the CosmOrbitrap does not include one. It would require embedding a Nitrogen gas tank to sufficiently rise the pressure in the C-trap chamber, but also a pumping subsystem to recreate a high vacuum in the Orbitrap cell. To qualify the CosmOrbitrap flight model, the LPC2E built a custom-made laboratory laser ionisation mass spectrometer, the LAb-CosmOrbitrap (Briois et al., 2016). As the CosmOrbitrap is not a stand-alone mass spectrometer, the ion source subsystem is developed in the frame of collaborations. Currently, developments are ongoing and aim for the Moon and Jupiter's moon Europa, with the projects CRATER (Characterization of Rock And Trace Economic Resources) and CORALS (Characterization of Ocean Residues And Life Signature), respectively (Arevalo et al., 2018). Both are part of responses to NASA's ROSES (Research Opportunies in Space and Earth Science) call for proposals and are in collaboration with the Goddard Space Flight Center/University of Maryland with Dr. Arevalo as Principle Investigator. For both instruments, the CosmOrbitrap is to be coupled with a laser ablation ionisation system. The integration of the CosmOrbitrap in more complex instruments adapted to several planetary targets is also considered with the AROMA (Advanced Resolution Organic Molecule Analyser). AROMA is a multi ionisation multi mass analyser instrument that could study a wide range of bodies, such as Enceladus, Europa or Ceres (Southard et al., 2022).

The potential targets for the CosmOrbitrap are numerous, and the ionisation method can be chosen accordingly. The instruments presented above are all carried by a lander, but could also be proposed on an orbiter, as part of a Rosetta-like mission, with a device capable of collecting dust grains with a velocity of less than 1 km/s on a target. This has been recently proposed in the framework of the Castalia+ mission (ESA M7 call for proposals), by coupling a near infrared hyperspectral microscope and the CosmOrbitrap with a laser ionisation [START_REF] Briois | A Space Instrument Combining NIR Hyperspectral Microscopy and Laser-CosmOrbitrap Mass Spectrometry for the in Situ Analysis of Extraterrestrial Dust[END_REF].

The coupling of the CosmOrbitrap with an impact ionisation ion source can therefore also be investigated, and this is the idea behind the birth of the OLYMPIA project.

OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

OLYMPIA

Overall Presentation

OLYMPIA (Orbitrap anaLYser MultiPle IonisAtion) is not to be developed as a space instrument, but rather as a testbench to assess the different possible designs for a future flight instrument, in support of the LAb-CosmOrbitrap (more dedicated to space development of the CosmOrbitrap, its performance evaluation and as calibration set up of CORALS and CRATER developments). For that reason, OLYMPIA is similar in design to the CosmOrbitrap and does not feature a C-trap module to handle the ions kinetic energy as in commercial instruments. This greatly simplifies the overall design of the instrument, and as it was intended to couple OLYMPIA with different ion sources, in different laboratories in Europe, this allows the setup to be compact and easily transportable.

The different laboratories involved in the project are the LPC2E in Orléans, the J.Heyrovský Institute of Physical Chemistry in Prague, the Freie Universität in Berlin and the IOM in Leipzig. The teams in Germany took care of the adaptation of the LILBID ionisation setup, the LPC2E and the Heyrovský Institute of the analytical part, which includes the Orbitrap cell, the ion optics and acquisition. Even if the final objective of OLYMPIA was to be coupled with LILBID, a first configuration with an electron impact (EI) ionisation source was developed to optimise the settings of the ion optics developed for this project and allowing the analysis of gases. This configuration is ideal for optimising the transmission of ions to the mass analyser and for verifying its correct operation.

Concerning the coupling with the LILBID setup, the first campaign took place in August 2018 in Leipzig, in order to do the first mechanical integration and characterise the ion cloud created by a laser shot. A second campaign was then organised in May 2019. This was very successful with first mass spectra from laser shots onto metal recorded by the LILBID-OLYMPIA combination. To go forward, the team attempted to analyse water ice doped with salts, which was successful as well. This proved the feasibility of the LILBID-OLYMPIA mechanical coupling, but also of the laser-surface interaction regime. This brings us to the third LILBID-OLYMPIA campaign that took place in October 2019, when I started my PhD. The purpose of this campaign was to measure for the first time ions from a liquid created by laser pulses, or in other words, actual LILBID desorbed ions The results of this campaign are presented in Chapter V, dedicated to LILBID-OLYMPIA. After this third Leipzig campaign, OLYMPIA was back in Orléans in the EI configuration, where I could work on the setup and get familiar with it, in preparation of the move to Berlin for a long-term coupling with the LILBID setup that was originally planned in summer 2020 but then was realised only in early 2021 (due to covid-19 pandemic travel restrictions).

OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

OLYMPIA Subsystems

OLYMPIA has been built with commercial components for the vacuum chamber, custom-made designs for the different interfaces, and some subsystems such as the ion optics. The Orbitrap cell is a standard D30 that is also used in commercial instruments. The functioning is therefore the same as the one described in Section 1. This section will focus on the description of the other subsystems of OLYMPIA, as they were at the beginning of my PhD in October 2019. The LILBID-OLYMPIA specificities, like the description of the liquid ion source, will be described in the LILBID-OLYMPIA chapter.

EI Ion Source

The Electron Ionisation technique uses high energy electrons to ionise samples. The electrons are produced by applying a high current (~5 A) through a filament. This high current heats up the filament, and through thermoionic emission electrons are produced. The electrons will then go through a small aperture and collide with the gas in the source, which is mainly the gas sample, but residual air can also be present. The collisions will remove at least one electron from an atom or a molecule and creates radical ions. Radical molecular ions are highly energetic and can dissipate this energy by breaking bonds between atoms of the molecule and therefore create further ionic molecular fragments. The resulting fragmentation patterns, and hence the appearance of the mass spectrum, are unique to this technique. Because of the highly energetic electron bombardment, the ionisation can be very efficient and the sample extensively fragmented. The reproducibility of this technique is a major advantage, and is therefore used to build calibration databases, such as the well-known National Institute of Standards and Technology (NIST) database. An electron impact source is simple to operate and can be custom made, making it the ion source of choice for the precalibration of OLYMPIA.

Filament The current applied to the filament is a key parameter and is controlled by a custom-made power supply. We always used the same tungsten filament with 0.04 mm thickness from Goodfellow. The thickness of the filament is important as it will determine the current needed for an optimal ionisation. Indeed, a too low current will not heat the filament enough and the ionisation will not be possible. Also, a too high current will result in a less efficient ionisation and a premature filament wear. The filament is indeed damaged by the thermoionic emission The filaments can be seen on the left picture on their white ceramic holder. The aperture towards the ion optics can be seen in the circle in the middle, this is also where the gas sample is directly injected. Small apertures allow the passage of the electron from the filament to the middle circle. and will progressively become thinner over time, until it breaks. This means that the filament current needs regular adjustments to stay at an optimal value for an optimal and reproducible ionisation. If the filament breaks, it has to be replaced by a new one. This implies to switch off all the turbopumps and break the vacuum, remove the whole ion source from its support, remove the filament holder (the white ceramic parts in the left picture of Figure II.15) and place a new filament on it with a spot welder. Because this operation is long and tedious, there are two filaments on the source for redundancy. Only one is usable at the same time, but this extends the measurements time before having to open again the setup.

Source Position Once the filaments have been replaced, the source can be reinstalled on the setup. The source is placed directly in front of the ion optics first electrode, thanks to four rods and the four bolts that can be seen in the outer circle of Figure II.15 (right). As explained in Section 1, the geometry of the ion packet must be well defined when reaching the Orbitrap cell. It is therefore important to place the source correctly, by making sure that its aperture is aligned with the hole of the first ion optics electrode, which should be visible through the aperture.

HV Settings The kinetic energy of the ion bulk is also a critical parameter. The whole source potential is controlled by a custom-made power supply. To ensure a proper definition of the kinetic energy, the voltage in the source is directly set to the desired energy at the time of injection into the Orbitrap cell, around 1030 V. The whole ion source is covered by a pusher electrode (right picture of Figure II.15) on which a higher potential (up to +30 V relative to the source) than the source is set to repel the ions inside the aperture, towards the ion optics.

Gas Inlet

The gas samples are injected directly in the ion source through a needle valve that allows to control the gas flow. Using a gauge in the ion source chamber, the input pressure can be set to a precise level. From the inlet flange, a plastic tube drives directly the gas in the middle circle of the ion source, just where the aperture towards the ion optics is situated.

Ion Optics

Principle The ion optics is an essential subsystem interfacing the ion source and the Orbitrap cell. It has been specifically designed for OLYMPIA, with the objective of being able to focus LILBID desorbed ions, but also EI ions. The ion optics is used to focus the ions in the Orbitrap cell. Depending on the polarity applied on each electrode, the ions will be either focused or defocused, by repulsion or attraction from or towards the electrode. A circular-shaped electrode will act evenly on the ion packet. On cations, a positive potential will repel the ions. Therefore, by going through a circular electrode the ion packet will be focused at a certain distance, like a ray of light through an optical lens that is focused at a certain focal length. The difference to an optical lens is that the "focal length" can be controlled by the voltage applied. The higher the voltage, the shorter the focal length. Along the ion optics, the voltages are set to keep as many ions as possible in the ion packet and prevent them from colliding in electrodes, with the objective of properly focussing the ion packet inside the Orbitrap cell and allow an optimal capture by the central electrode. Before Makarov invented the C-trap to inject the ion packet with the 3. OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS optimal definition, he used an ion optical system (ion optics) to focus the ion packet towards the Orbitrap cell, the so-called Electrostatic Acceleration Lenses technique. (Makarov, 1999;Makarov, 2000). Tuning The optimisation of the ion optics potentials is a tedious work. If one of the seven electrodes is not properly set, the ion packet can be lost. The difficulty of the task is due to the fact that it is not possible to know which voltage is wrong. It is basically an equation with seven unknowns, and even if it is possible to simulate the ion path via SIMION to get an idea of the values, geometric imperfections will make the simulation inaccurate. The way to go is first to always keep the same voltage in the source. Indeed, if the electrostatic conditions at the ionisation are different, all the optimal voltages in the ion optics will change. In addition, because the optimal KE for ions is around 1030 eV, it is important to ionise at this potential.

One way to monitor the ion packet along the ion optics is to remove the HV power supply connection, and to plug a Picoamperemeter. As every ion is charged, it is possible to measure the current if they collide on a conductive surface. This approach is of great help to optimise the ionisation settings, such as the filaments current or the inlet gas flow.

Regarding the ion optics, it allows to monitor three parameters, (i) the position of the packet along the optic, (ii) the width of the packet (which determines if ions can go through the electrodes apertures), and (iii) its final position. Measuring a current on electrode 10 gives the information that at least some ions are going through the whole optic (i). The width can be adjusted with the voltages on the circular electrodes to focus or defocus the bunch (ii) . Finally, the aim can be modified with the half circular electrodes (iii). As seen in Figure II.17, the highest current would mean that the ion packet is fully colliding with the electrode, and if an ion packet is properly focused, the current should show a local minimum.

Kinetic Energy As previously mentioned, there is no C-trap module in OLYMPIA. Therefore, the ion optics, along with the ion source, are the only subsystems that allow to control the Kinetic Energy of the ions. As presented above, the ion source electrode voltage is set at 1030 V to start with a proper KE. In the ion optics, the potentials should help to sustain this KE as it was defined. But the ion optics can also be used to assess the KE of the ion packet. Indeed, rising the potential of a circular electrode with the same polarity as the ions will act as a focus. By rising the potential of an electrode while measuring with the Picoamperemeter, it is possible to see when most of the ions are affected by the voltage, and therefore the average kinetic energy of a bunch.

Electron Multiplier

The Picoamperemeter is a useful tool to monitor the ion packet, but still presents some limitations. For example, it averages the measured current over approximately half a second, which is considerably longer than the ion transit time. This does not allow to assess the time distribution on the ion packet. In addition, once the ion packet has been focused after the ion optics, there needs to be a way to characterize the bunch after the ion optics and the Orbitrap cell.

For that reason, OLYMPIA's design features an Electron-Multiplier (or detector, DeTech 2300), placed after the Orbitrap cell, aligned with the ion optics and the source. An Electron-multiplier is a device, as the name suggests, that increases the intensity of a signal, here our ion packet. It is composed of successive electrodes chained by resistors. If a negative potential (~-2 kV) is applied on the front electrode, the positive ion of the bunch will be strongly attracted and will collide with it, creating electrons. Those electrons are then attracted by following successive electrodes. Because of the voltage difference induced by the resistors, each time they collide with an electrode they produce more and more electrons. The current can then be measured on the grounded-dynode at the end of the multiplier. The typical gain for the Electron-Multiplier that we use is in the order of 1.10 7 .

The output signal of the detector can be displayed on an oscilloscope. This greatly helps to visualise the ion packet, its intensity, timing and size. A screenshot of the oscilloscope is shown in Figure II. 19. The ion packet is clearly visible, at around 3 μs after the ionisation (here a laser shot), and is quite well defined as it lasts less than 1 μs. Thanks to the display on the oscilloscope, a precise optimisation of the Orbitrap cell electrodes timing can be done. Also, ions that reach the detector are evidence that the packet went through the Orbitrap cell. The KE can be poorly defined, if the size of the packet is too large, but they are detected after the Orbitrap cell, which means that the gross settings for the ion optics voltages are in the right order of magnitude. A second round of optimisation of the voltages can be done, with a better visualisation of the effects.

OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

An optimisation bias on the detector signal is that if the ion packet is perfectly focused on it and the signal maximised, it would mean that the 'focal' point of the ion packet is at the detector and not at the entrance of the Orbitrap cell. What can be done is rising the potential on EL9 to focus the bunch before the detector. However, this cannot be visualised, and is a blind optimisation.

Electronic Hardware

The power supplies must be selected according to the needs of the sub-system they supply to ensure an optimal functioning of the instrument.

Ion Optics HV Power Supply Each electrode must be powered by a separate power supply to be able to correctly tune the optic. Because the KE of ions is around 1 keV the maximum potential required in the ion optic is in the same range. There can also be a need for changing the polarity. The precision over time for the voltage value is not as much constrained as for the Orbitrap cell electrodes, a variation of one or two volts is usually negligible. Considering the empirical method used to optimise the ion optics, it must be possible to change the voltages easily. The choice was made to use ISEG Spezialelektronik modules (NHR 2260r & NHR 4260r). They offer several channels on the same module to power the different electrodes and can be set up to 2 kV in both polarities with a 10 mV step. They also fit in a NIM rack, a compact standard for electronic hardware, which is useful considering that OLYMPIA is intended to travel to different laboratories in Europe. The ion optics voltages value will be refered to as HV optics .

Orbitrap Cell HV Power Supply The Orbitrap cell HV power supply is obviously extremely important as it is used to capture and maintain on stable orbit the ions inside the trap. Unlike the HV optics power supply, there is no need for a precise tuning of the voltage. However, the requirements for stability are strong, a drift or a variation of a few mV during the measurement time can result in a variation of the trapped ion frequency and a widening of the peaks in the mass spectra. We also used ISEG modules for the Orbitrap cell electrodes. The most adapted choice would of course have been a Thermo Fisher power supply, which is designed to work with an Orbitrap cell, but such modules are expensive and could not be purchased during the beginning of OLYMPIA's build, but were available at the end of 2020. The behaviour and optimisation of the Orbitrap cell HV power supply was tackled during my PhD and will be presented in Chapter III. The Orbitrap cell voltages will be refered to as HV Orbitrap .

HV Switch As presented in Section 1.2, the potential of the central electrode must be switched from an injection value (VCE in jection ) to a measure value (VCE measure ). The HV switch module of OLYMPIA is from CGC company (Quadruple Switch AMXTE500-2+1500H-2). A key parameter of such a module is the time profile of the commutation. Different subsystems can require different time profiles. For example, in case of a HV switch in the ion optics, a fast commutation (< 100 ns) is needed because of the speed of the ions. On the contrary, the Orbitrap cell central electrode needs a smoother slope with a ramp between 20 to 100 μs. Our CGC switch commutes in less than 100 ns, which is too fast for the Orbitrap cell electrodes. To be able to fulfil both needs with the same module, some capacitance in the system must be added. The self-capacitance of a system represents the amount of charge needed to raise its electric potential. It is an important factor and is usually kept as low as possible. Every hardware, from cables to connectors adds some capacitance to its system. The longer a cable is from the power supply to the electrodes, the longer it will take to commute its potential. This is how the ramp of the Orbitrap cell central electrodes has been smoothed, by adding capacitor with the proper (30 nF) capacitance between the switch and the Orbitrap cell.

TTL Generator

As mentioned, the time accuracy of some elements, such as the ions focus or the commutation of the Orbitrap cell central electrode, are at the microsecond level. To be able to control such precise timings, we use a Transistor-Transistor Logic (TTL) delay generator, the CompactRIO (National Instruments cRIO-9023 CompactRIO Controller with embedded chassis NI 9113 and NI 9401 module). Monitored with a software developed by Bertrand Gaubicher, an engineer in Orléans, the CompactRIO module is able to deliver TTL signals and trigger the different hardware at a precise timing. Figure II.20 shows a scheme of the different modules controlled by the CompactRIO. It is possible to adjust the trigger time with a 0.1μs precision. Depending on OLYMPIA's configuration (i.e. the ionisation method used), one hardware is selected as "master TTL". All the other components are synchronised relatively to the master TTL.

Vacuum

The requirements of an ultra-high vacuum for an Orbitrap cell comes from its detection methods. Because better performances are linked with longer acquisition time, the ions must be stable as long as possible in their orbit around the central electrode. To avoid the ions colliding with the neutral background and being scattered from their orbit, there must be as few background molecules as possible in the cell. Multi-stage Vacuum For those reasons, the vacuum is a key element in the proper functioning of the setup. OLYMPIA is separated into three different vacuum chambers that are represented in the scheme of Figure II.14. Each stage is pumped by a different turbomolecular pump and has its own pressure gauge to allow a monitoring. The first chamber is pumping the ion source and ion optics area. The second one, the "cube" chamber, includes

Resolution versus

OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

the Orbitrap cell placed in its own chamber, pumped from above. Because OLYMPIA is to analyse gas or liquid, and therefore outgassing samples, it was particularly important to have an efficient differential pumping and this 3-stage vacuum chamber. Each chamber is interfaced by gaskets and the only connection is through the small apertures of the ion optics, which are 0.7 mm wide. The design works well, with a pressure that can be as high as 10 -3 mbar in the source, pressures of ~5.10 -8 mbar in the Orbitrap cell can still be reached.

Acquisition

The principle of the ion detection has previously been described in Section 1. Pre-amplifier Considering the faint signal produced by the ions on the outer electrodes, it is mandatory to amplify the signal. On commercial Orbitrap™ instruments, the pre-amplifier is placed outside the vacuum chamber, behind the Orbitrap cell. This is to reduce as much as possible the cable length and therefore the self-capacitance for the ion signal, and avoid any additional noise. A pre-amplifier is not able to determine and filter from where a signal is coming from, it records everything. For that reason, there can be on the data some noise produced by the environment around OLYMPIA, such as other instruments in the building or even other subsystems of the setup. A good way to get rid of this ambient noise is to place the pre-amplifier inside the vacuum chamber. This way, it will be protected by a thick layer of steel. However, the commercial pre-amplifier of Thermo Fisher is not designed to work under vacuum, and a custom-made pre-amplifier has later been built. A trade-off between both pre-amplifiers will be presented hereafter.

PicoScope In our setup, the pre-amplifier output is connected to a PicoScope (Pico Technology) unit. The PicoScope is an Analog-to-Digital Converter (ADC) which digitises the measured signal and allows to save it on the computer for further data processing. The maximum measurable frequency of the PicoScope is 62.5 MHz, which is higher than the frequency of Hydrogen ions (~7 MHz), ensuring a complete scan of low mass ions. The PicoScope is a user-friendly hardware that comes with its own software to ease the data processing.

Data Processing

Once the measured signal has been digitised and saved on the laptop, the data processing can be done. The raw data are in a time-domain and are under the form of a transient. An example is shown in the top panel of Figure II. 23. By applying an FFT on this transient, the time domain is decomposed in frequencies (right panel). Those are the actual frequencies of the axial motion of the ions inside the trap. The mass corresponding to each frequency can then be calculated through Equation II.8.

PicoScope Software

The computation time for FFT depends on the acquisition time of a spectrum. Additional improvements (e.g. apodisation or zero-padding) can also be applied to the signal, the resulting computation time for a spectrum can then be up to several seconds. This is hardly compatible with a real-time work and optimisation of the setup in the laboratory, as many parameters must be controlled and the impact of their modifications directly assessed. The PicoScope software is therefore very handy for a real-time display of the data and has been used in the laboratory during my whole PhD. It basically downgrades the data in order to be able to apply the FFT and to display them in real-time. There is also a possibility to average several frequency spectra, which helps to significantly reduce the noise level, and sometime allows to extract peaks with a very low SNR. The acquisition time can easily be modified, which is useful as it is not necessary to record a long signal if the setup is not yet optimised.

However, the PicoScope software presents some limitations and needs to be complemented by self-developed Matlab programs. Indeed, because the data are downgraded, it is necessary to reapply the FFT to access the real quality of the data. I wrote numerous Matlab scripts to enhance the data processing of OLYMPIA, that will be presented hereafter.

Apodisation A widespread technique in FFT data processing is the application of an apodisation window (Harris, 1978) to the raw signal. It consists in selecting specific portions of the raw signal and giving them more weight in the FFT than the rest, to improve the shape of the mass spectrum, as seen in Figure II.24. The spectral leakage, that causes "waves" around chemical species peaks is effectively removed by the window application, cleaning the peak foot, and thus improving the detection limit around it. In the case of a low abundant species close to an abundant one, this can allow to see the minor species. However, if we compare both peaks of Figure II.24, the unapodised peak is thinner than the apodised one. This is the price of apodisation, the mass resolution is usually divided by a factor of two (Scigelova et al., 2011).

OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

Zero-padding Another technique to enhance FFT is the zero-padding (Marshall and Verdun, 2016). It consists in multiplying the signal length by a selected factor, and adding zeros at the end of it. This is to increase the number of points in the frequency/mass spectrum after the FFT. The longer a signal, even filled by zeros, the more points there will be in the mass spectrum. This helps to get a better definition of the shape of a peak. Figure II.26 shows a comparison between a mass spectrum processed with and without zero-padding. On the blue spectrum, the peak is only defined by 5 points, which lead to angular shapes. The orange peak on the other hand is defined by 32 times more points, leading to a greater definition of the peak maximum. This is relevant for mass resolution, but more importantly for the mass accuracy. Indeed, the peak maximum of the mass spectrum without zero-padding is shifted from the one with zero-padding, decreasing, in this case, the mass accuracy by a factor of two.

The zero-padding is a simple way to increase the discrete resolution of peaks, and thus to have access to their real values of mass accuracy, SNR and mass resolution. However, this also comes with a price, the computation time for each spectrum depends of its length, therefore to keep the data processing in reasonable time, the zeropadding multiplier is usually in the range of 4 times. Mass Calibration As previously mentioned, the spectra obtained after an FFT are in a frequency domain. With a simple manipulation of Equation II.8, the mass corresponding to each frequency can be obtained, as well as entire mass spectra. Equation II.8 is also composed of the k factor, which is defined by the geometry of the electrodes and their potential. The geometry is obviously constant and we tend to select an optimised, and thus fixed value, for the central electrode voltages. The k factor should therefore be a constant. Nevertheless, to ensure a proper calibration of each mass spectrum and access the real mass accuracy values, a recalculation of the k factor is done after each FFT. To do so, one chemical species of the spectrum must be identified. As mentioned, the k factor does not vary much from one mass spectrum to another, so a peak will always be around its expected mass even with a k factor slightly different, facilitating the identification. The k factor is then recalculated and used with Equation II.8 on each point of the mass spectrum. The calibration will be more precise for masses close to the calibration peak. The masses distant from the calibration peak (>100 u) will start to show some shift in the mass accuracy. To prevent this, a double calibration can be done by selecting a second calibration peak.

Slicing the Signal A strong advantage of an Orbitrap™ signal acquisition and its subsequent FFT is that it is possible to apply the FFT on a specific part of the time domain signal. As the ions behaviour in the trap evolve over the acquisition, it is interesting to change the length of the studied signal. Indeed, as the electrostatic field in the Orbitrap cell is not perfect and the vacuum not good enough, the ions have a limited lifetime. For that reason, applying the FFT on a shorter part of the recorded data can improve the performances, as it is irrelevant to apply an FFT on 500 ms if the lifetime of ions is only 100 ms. In addition, the signal can be cut into slices, as shown in Figure II.27 where a raw signal of 500 ms is cut into 10 slices of 50 ms each. Each colour of the signal represents a 50 ms slice, and can be processed separately. This allows to follow, for example, the amplitude of the ions through time, and give access to the actual lifetime of ions. The drawback with this method is that a short duration FFT considerably reduces the mass resolution. Resampling & Averaging A way to reduce the variability between measurements is to average several spectra into one. There are several methods to properly average spectra, which can be applied on raw time domain signals, or after the FFT, both in frequency and mass domain spectra. Averaging significantly reduces the noise level and increases the quality of quantitative estimations, especially for the calculation of isotope ratios. However, it is not possible to average the spectra abruptly, either in the frequency or mass domain. One spectra is usually composed of 4 million points, between measurements, the X-axis values of the points and the peaks can vary along axis (mainly due to variability of the k calibration factor from one acquisition to the other). The method I use in this work is to resample the data (using the msresample Matlab function) into the same controlled X-axis. With this, it is certain that all the mass spectra are properly aligned with the same X-axis and then the average can performed.

Figure II.28 shows three single mass spectra in colour. The black mass spectrum is the resampled and averaged spectrum of the same data set. The noise level is significantly reduced, resulting in an increase of the SNR of around 5 times. The averaging also greatly improves the detection limit, the 78 Kr + that is not detected on single spectra stands out on the averaged one. The effect of averaging and resampling. The coloured mass spectra are unaveraged mass spectra and the black mass spectrum is the average of 32 mass spectra. On the averaged spectrum, the noise level is significantly reduced and lower abundant species can be detected.

Calculation of Relative Isotopic Abundances

A standard method for the isotope comparison is to average a significant number of spectra and look at the difference from theoretical abundances. This is helpful to give an approximation of the measurement accuracy for isotopes. However, because all the Relative Isotopic Abundances (RIA) errors are averaged after the resampling, it is not possible to assess the real variability of the data. If the quality of single mass spectrum is high enough, and that the main isotopes are detected, the error for each isotope can then be stored and plot as a diagram, as shown in LILBID setup and will be presented in Chapter V). This allow to see the full range of the RIA errors. A Gaussian fit can then be applied to the diagrams to get the maximum of the errors normal distribution. The 1-sigma interval is calculated on the fitted normal distribution. By definition, the probability that the a measured error is between the 1-sigma interval is 68.2%.

The total ion count of one isotopes must be precise, as it is the value compared to theoretical abundances. To enhance the precision of the ion count, the value compared is the area under the curve of each isotope. The area from the maximum to 10% of the peak height is considered. This method takes into account the variation in the width of the peaks, and is therefore more accurate.

The sensitivity of the acquisition should be high enough to detect the low abundant isotopes, as no averaging is made to reduce the noise level. However, as they are not always detected it is possible to measure only a noise peak. To avoid including error values calculated on noise peak, a filter is applied. It is based on the mass accuracy of the detected peak, and excludes peaks with more than 15 ppm deviation. This chapter will focus on the work performed on the hardware parts and some crucial parameters of OLYMPIA. I started my PhD in October 2019, the same month the third OLYMPIA-LILBID campaign was happening in Leipzig (the chronology and objectives of the different campaigns has been described in Chapter II Section 3). The objectives of this campaign was to measure desorbed water ions with a high mass resolution. To ease the reading, the scientific results and specifics of the LILBID mass spectra measured during this campaign will be described in Chapter V, dedicated to LILBID.

During the October 2019 campaign mass spectra could be successfully measured, but a strong lack of performance was observed. The mass resolution of the peaks was capped at a few thousands (FWHM) where tens of thousands were expected. At that time, the long-term coupling with the LILBID installation in Berlin was planned for summer 2020. The time available before the move was therefore used to improve different sub-systems of OLYMPIA, to increase its reliability and performances. We identified several subsystems that needed improvements, such as the ion optics, the vacuum efficiency or the Orbitrap cell HV stability. The latter was most likely responsible for the low mass resolution results. As these modifications took place at the LPC2E in Orléans, they were performed with the EI configuration. For that reason, some results obtained with the EI configuration will be shown in this chapter. However, they are only a support for the work that have been carried out and will be specifically presented in the following chapter, dedicated to this configuration. Therefore, to assess the performances of the setup, we will only focus on mass resolution, SNR or mass accuracy, without taking into account the Relative Isotopic Abudance (RIA).

There have been two different phases of optimisation. The first one was directly after the campaign. We decided to dismount the whole setup to do a deep cleaning and improve some technical aspects. This was a great opportunity for me, as it is usually rare to entirely disassemble a setup and actually see what is inside. Once this was finally done, the measurements with the Electron Ionisation could start again at the beginning of 2020. I was first alone in the laboratory, but then received the help of Illia Zymak, a researcher from the J.Heyrovský Institute who came to do a one-year postdoctoral fellowship at the LPC2E in Christelle Briois' group (LE STUDIUM Loire Valley grant). We were hampered by the pandemic and lockdowns, which made us lose months and we really struggled to obtain again a mass spectrum with OLYMPIA. We dedicated a lot of time to find what was preventing the ions from being measured, and to improve each subsystem as much as possible. Because no signal was measurable during this period, not all the modifications effects could be quantified. We finally succeeded in recording some mass spectra again in July 2020. These results are presented and discussed in the Subsection 2.1.

Once the setup was operational again, the second optimisation phase could begin. This was dedicated to measure high mass resolution mass spectra. We performed trade-offs on the different power supplies of the Orbitrap cell (i.e. the central and the deflection electrodes). Those experiments are shown in the Section 2.2.

Thanks to those improvements, some larger scale enhancements could be achieved. A trade-off between two different Pre-amplifier has been performed, as well as the determination of the optimal deflection electrode value. Those are described in Section 3 and 4, respectively.

Figure III.1 sums up the modifications undertaken during this period. The white boxes are the technical modifications of phase 1 and were performed before measuring the signal again. The yellow boxes represent the work done on the power supplies during phase 2 and allowed the measurement of high mass resolution mass spectra. Finally, the blue boxes depict the subsequent work, once OLYMPIA was operational and performing as expected. Ion Optics The whole ion optics have been dismounted, deeply cleaned and placed back on the setup. Due to the strength of the EI ionisation, a thin layer, most likely from the filament materials, can deposit on the electrodes. This layer is not homogeneous and can disturb the ion focusing.

Ion Source

The ion source is a crucial subsystem and as previously mentioned, the alignment with the ion optics must be done manually after each dismounting. But the distance between the ion source and the ion optics was also variable. So, to ensure a more reliable position of the whole source we placed some spacers. With those, the distance to the ion optics was constant. We also replaced the connectors from the power supply to the filament, ensuring a better contact and less parasitic capacitance.

Vacuum The background pressure inside the Orbitrap cell can disturb the trapped ions and reduces their total lifetime. As a longer lifetime leads to a larger mass resolution, we dedicated some time to improve this subsystem.

The measurement of liquid and gaseous samples is a challenge with direct injection, as the pressure inside the Orbitrap cell must remain below 1.10 -8 mbar for optimum performance. We therefore improved the pumping efficiency in the three vacuum stages, described in Chapter II.

To improve the vacuum, we replaced the old primary pump with a cleaner and more efficient oil free scroll pump (Anest Iwata, ISP-90). We also replaced the turbopump that is pumping the main cube by a bigger one (Pfeiffer Vacuum, HiPace 300). To reduce the pumped volume, we also shortened the length of the flange connecting the turbopump to the Orbitrap cell.

With all those improvements, the ultimate vacuum of the setup went from ~5.10 -8 mbar to ten times lower, ~5.10 -9 mbar. This value is low enough to avoid a significant effect on the mass resolution from the neutral background (Selliez, 2018). Noteworthy, this pressure is achieved without outgassing samples, during measurements in the EI configuration, the pressure in the cell is usually around 1.10 -8 mbar.

Detector Electron multipliers have a limited lifetime and can only amplify a finite number of ions. We reached the end of its lifetime during our experiments and had to replace it. With the new detector, the signal was much more manageable, both in terms of timing and spatial resolution but also in terms of intensity. We were able to detect the signal of a single ion and define the ion bulk in a proper way.

Orbitrap Cell Cleaning The cleaning of an Orbitrap cell however is a tedious work and is rarely done. In principle an Orbitrap cell is a very simply device (see the picture in Figure II.4), once it is out of the vacuum chamber it rests on a custom support, held by few screws. The Orbitrap cell itself is held at both extremities by a screw with a specified torque. Even if the design is simple, the conception of the electrodes is accurate to the micrometer, thus, millimetre misalignment during the reassembly can result in large disturbances in the electrostatic field, as explained in [START_REF] Grinfeld | Control of Aberration and Space-Charge Effects in the Orbitrap Mass Analyzer[END_REF].

As it is a risky operation, the cleaning of the Orbitrap cell was planned to be done last, only if necessary. We had decided to disassemble the cell, due to the remaining difficulty to obtain a signal after the cleaning operations. Basically, if one conductive particle enters the Orbitrap cell, it can disturb the whole electrostatic field inside and could in theory prevent the trapping of ions. However, the opening and cleaning of the cell must be carried out in a controlled environment, as no additional particles should contaminate it.

We opened the cell under the laminar fume hood of the LAb-CosmOrbitrap at the LPC2E and controlled the interior. There were indeed some particles on the receiving electrodes, with sizes ranging from 0.1 to 0.5 mm, and a 0.2 mm dusty particle on the central electrode.

Krypton Gas Preliminary Study : Results and Diagnostic

After all the troubleshooting, the mechanical improvements and the cleaning we finally managed to measure mass spectra with OLYMPIA. We used a Krypton gas bottle (Sigma-Aldrich, 99.998% purity) as a sample and could detect the four main isotopes, 82 Kr, 83 Kr, 84 Kr and 86 83 Kr + and 84 Kr + is noise. Lower panels : zoom on isotope 84 Kr + and 86 Kr + .

REACHING HIGH MASS RESOLUTION CHAPTER III. -ENHANCING OLYMPIA

The performance after the measurements of the first phase of improvements is shown in the mass spectrum in Figure III.2 of Krypton and its major isotopes. With a maximal achievable mass resolution of only 5 000 and a mass accuracy above 10 ppm OLYMPIA still did not fulfil the expected performances. An Orbitrap-based mass spectrometer is supposed to reach a high mass resolution (usually in the range of 50 000 at 50 m/z) and a mass accuracy of a few ppm. In addition, two isotopes of Krypton are missing, 78 Kr + and 80 Kr + . Even if their natural abundance is relatively low (0.36% and 2.3%, respectively (Berglund and Wieser, 2011) they should be detectable if the dynamic range had been close to normal.

With mass analysers using an FFT, a longer signal duration leads to larger theoretical mass resolution. A long ion lifetime inside the Orbitrap cell therefore leads to a better data quality. As the maximum mass resolution we could obtain was only a few thousand, there was an issue with the ion lifetime in our measurements. To reach a mass resolution of 50 000 at the mass of Krypton (84 u for the major isotope), the minimum FFT duration should be in the range of 150 ms. With a value of only 5 000, it seems that the lifetime of the ions in the trap is only few tens of milliseconds. Ion signal intensity naturally decreases through time because of pressure effects and geometric imperfections, but with the achieved pressure (in the order of 10 The SNR significantly rises during the first 20 ms and reaches a maximum at around 30 ms. However, this maximum is not stable and the SNR decreases to the noise level at around 40 ms. No signal is detectable afterwards. Ion instabilities in the cell are most likely due to an instability in the electrostatic field. All the parameters affecting the field can therefore be the cause. The two main ones are either a variation of the central electrode potential (VCE measure ) or a poor optimisation of the deflection electrode potential (VDE measure ). As the potential applied on the deflection electrode is supposed to compensate the electrostatic field aberration caused by the injection aperture, a non-optimised value could strongly disturb the ion motion. The injection level of both electrodes is also important, however it is more relevant for the ion trapping, and as the disturbances seems to occur after a few tens of milliseconds it seem to point to a voltage instability during the measurement.

Another issue with the data is some recurring noise in the mass spectra.

Second Phase -Power Supply Trade-off

Through the improvements made during the first phase, we could finally measure mass spectra with OLYMPIA. However, as shown above, the quality of the data was below the expected performances. The flaws in the first data seemed to originate from an unstable electrostatic field, we therefore tested different power supplies to see if the ions behaviour would change. This subsection describes the yellow boxes in Figure III.1.

VCE measure Power Supply

Chapter II highlighted the key role of the Orbitrap cell central electrode Power Supply (PS). We naturally made a lot of tests on the power supply to ensure that it is operating correctly. As described previously, VCE was supplied by an ISEG power supply, both for the injection and measure level, and the commutation was handled by the switcher from the company CGC. This subsection presents the tests carried out in order to select the best power supply for the VCE measure level, the one that meets the stringent stability requirements.

The best way to figure out if a subsystem is not functional is to replace it by another one and see if it behaves differently. Fortunately, at that time we had another power supply at our disposal. In addition to the ISEG power supply, we had a commercial Orbitrap™ Thermo Fisher power supply. As the ion motion in the cell is directly linked to the voltage stability, we expected significantly better results with the Thermo Fisher power supply, as it has been designed for such stability requirements.

Test Protocol To assess the performances and select the best power supply we will focus on two linked indicators : the maximum signal duration and the best mass resolution. To assess the maximum signal duration, the SNR for each slice is calculated. To avoid variability between measurements, the results presented hereafter are the average value (of a minimum of 30 mass spectra) of the SNR in each slice. This means that the mass spectra are not averaged into a single one as has been presented with the resample method (Subsection 3.2.8 of Chapter II), but the values of SNR of each mass spectrum are. With the information on the lifetime of ion, the mass spectra can be recalculated with the appropriate FFT duration and show the best possible mass resolution.

Another possibility for the source of the problem was the HV switcher from CGC. Indeed, the power supply could behave properly and the switcher could be the reason for the instabilities post-switch. To verify this, we tested different combinations of PS and Switcher. The Thermo Fisher PS comes with a switcher that is also designed for the Orbitrap™. This means that there is no need to add any capacitance in the system, as it is already included in the switcher. If the CGC switch is responsible for the instabilities, a coupling between the Thermo Fisher Switch and the ISEG PS should show some better results.

We still use krypton gas as a calibrant, which is directly injected in the setup via the gas inlet valve. The gas flow is set at the same level and the pressure in the Orbitrap cell is in the range of 3.10 -8 mbar.

Results

ISEG -CGC

The ISEG-CGC results are the ones shown in the previous subsection and have already been presented.

Thermo Fisher -Thermo Fisher Switch The results obtained with the Thermo Fisher power supply coupled with the Thermo Fisher switcher are shown in Figure III.5. The left panel shows the evolution of the SNR through time, and the right panel is a zoom on the major isotope peak for a 250 ms FFT. The performances are significantly better and allow to apply an averaging on the whole dataset. The SNR through time shows a much stronger maximum with an SNR of more than 70 in just 10 ms slices. The maximum is also much longer (roughly between 50 and 120 ms), and some signal can still be detected after 200 ms. There is still a variability between the different acquisitions, however all mass spectra show the same trend.

The mass spectra and the mass resolution naturally increase proportionally, with a mass resolution of 35 000 and a total SNR of 200. This is the first high mass resolution mass spectra obtained with OLYMPIA. The theoretical mass resolution at the mass of Krypton for a 250 ms mass spectra (and apodisation) is 47 000. With the Thermo Fisher power supply, OLYMPIA is therefore able to reach 75% of the theoretical mass resolution, which demonstrates that there is no major flaw in the design of the instrument. ISEG -Thermo Fisher Switch The last configuration is the ISEG power supply coupled with the Thermo Fisher switcher. We could measure some mass spectra with this configuration. However the results are inconclusive. The different acquisitions performed with this configuration present a large variability, applying an averaging therefore hides the variations. To better understand the ions behaviour under this configuration, a single mass spectrum is shown. Figure III.6 shows the evolution of the SNR through time for 300 ms (left panel), and a zoom on the 84 Kr + peak (right panel) of a single mass spectrum. The ions last much longer than with the CGC switch, even though the SNR is much lower. It seems that a signal is still measurable at 240 ms. In addition, the SNR through time does not decrease regularly. There are some ups and downs, at 80 ms in particular. If we look at the shape of the peak, it is not symmetric like with the other configurations. Some small peaks can be seen on the side of the main one, especially towards higher masses. The mass resolution is slightly better than that of ISEG-CGC, however it is far lower than expected for such a long FFT duration. Discussions Table III.1 summarises the different configurations tested during this study, as well as the performances. There are strong indicators that the different power supplies, when applied on the Orbitrap cell central electrodes, do behave very differently. From one to another, but also depending on the switch they are coupled to. The initial configuration with the ISEG-CGC power supply and switch has been selected due to its low price. The fact that this configuration is less performing was expected. However the lifetime of ions is too limited and equipping the setup with the set of Thermo Fisher hardware was necessary to reach the desired high performances.

Thanks to the Thermo Fisher power supply and switch we could measure for the first time high mass resolution mass spectra with OLYMPIA. The setup is now reaching 75% of the theoretical resolution, which is an achievement and will allow to resolve close isobaric interference in the future. Nevertheless, 25% difference with the theoretical values is still important, and further optimisation is needed.

With the Thermo Fisher configuration, the SNR is also greatly improved by 10 to 20 times compared to the first results. This directly points to a more efficient capture of ions in the trap. Even though the power supplies can have small differences in the actual voltage applied, this cannot cause such big differences in the SNR. It must therefore come from the commutation of the central electrode. The Thermo Fisher PS is equipped with a Thermo Fisher switcher with built-in capacitance to have the proper slope for the commutation, whereas for the CGC switch additional capacitors had to be connected in the system to control the slope. With such a difference in the ion trapping the Thermo Fisher switch behaves in a much proper way than the CGC one.

VCE measure Potential Estimation Method To better understand where the issue is with the ISEG-CGC power supply we need to get back to Equation II.3. As presented, the k factor is dependent on the electrode geometry and the potential applied on them. k is calculated for each mass spectrum. If the signal is cut in slices (as in Figure III.3, III.5 and III.6), a k factor is calculated for each slice. Therefore, if there is a variation in the k factor, the only term in the equation that can vary is the potential applied on VCE measure . When looking at the evolution of k through the different slices of the signal, we can directly access the relative potential variation on VCE measure with the following equation :

V VCE = V * k measure k theoretical (III.1)
k theoretical being the mean value obtained during stable periods of acquisition. V is the potential value in volts applied on the electrode. In this study V = 3500, the usual optimum value for the Orbitrap cell. The absolute V value is not important anyway, as we want to assess the relative variation through time. One limitation of this method to recover the VCE measure value is that it is only possible if a proper k factor can be calculated, which means that a known mass peak must be found. Otherwise, the mass calibration will be done on a noisy peak signal and the calculated value will be inaccurate. This method is useful to follow the evolution of the VCE measure potential, however the translation into true volts must be done with caution (even when a calibration peak is found), as the values might be different from the real one. One could ask why use this indirect method and not directly measure the VCE measure potential with an HV probe. Firstly, an HV probe would add some capacitance in the system and degrade the data quality. And secondly, because of the rapid commutation of the potential a precise measurement of the potentials would require a high-end HV probe and acquisition system, which was not available in our laboratory. Figure III.7 shows the variation of the potential through time for each configuration. As a reminder, a variation of 10 mV already has an impact on the ions and can alter the data quality in the final mass spectra. The ISEG-CGC configuration shows a 5.5 V variation in just 40 ms. Such voltage variations make the ions drift away from their initial orbit which explains why no signal is detectable (e.g. at 40 ms on the ISEG-CGC subplot). However, even though this would widen the mass peaks and reduce the mass resolution, it should not necessarily mean that the ions are lost and we should normally see some secondary peaks at the new ion frequencies.

As seen in Chapter II, a fast ion trapping after the injection is crucial for a thin ion ring orbiting the Orbitrap cell central electrode. If the trapping of ions with the CGC switch and the capacitors circuit behind is not efficient, the ions will, from the very beginning of the measurement, be spread along the axial axis. Coupled with the variation of the potential and the effect of the pressure, the ion could spread so much along the axial axis that no signal is no longer detectable. This was modelled in Kharchenko The Thermo Fisher PS potential, on the other hand, is much more stable. Throughout the first 220 ms of the signal, variation of less than 0.2 V are detected before the potential goes back to its original value. This allows to analyse the data with a long signal duration (here 250 ms), and we can still obtain a perfectly shaped peak with high mass resolution. The decrease of the signal through time is most likely the effect of the pressure, which is still one or two orders of magnitude higher than the optimum for Orbitrap™ measurements.

The question that remains is : what is wrong with the ISEG-Thermo Fisher configuration ? The lifetime of ions is as long as for the Thermo Fisher configuration, if not longer, yet the mass resolution is 10 times lower than expected. The third panel of Figure III.7 helps to understand the issue. There are entire time slices where the VCE value becomes aberrant, which means that no peak is detectable in the mass range of the calibrant. During those periods, the 84 Kr + ions drift away from their original orbit and therefore change their oscillations frequency. This is why the general shape of the peak in Figure III.6 is asymmetric, with the frequency variation, the ions slowly build secondary peaks next to the main one.

The surprising part is that the ions actually come back, which would indicate that the VCE potential also gets back to its original value. This confirms that a variation of VCE measure potential does not necessarily lead to a loss of all the ions, and that for the ISEG-CGC configuration another parameter has to disturb them. The potential over time for ISEG-Thermo Fisher is far more stable (apart from the aberrant parts) than ISEG-CGC, with 1.9 V of 2. REACHING HIGH MASS RESOLUTION CHAPTER III. -ENHANCING OLYMPIA variation throughout 300 ms. The fact that the ISEG power supply becomes stable coupled with a proper switch highlights the importance of this subsystem, and the issue with the ISEG-CGC couple. This also confirms the inefficient ion trapping hypothesis for this configuration.

The conclusion of this study led us to the conclusion that it was mandatory to order a new Thermo Fisher Power supply specifically for OLYMPIA. The use of the ISEG power supply for the Orbitrap cell central electrode leads to excessive disturbances in the cell electrostatic field, preventing the measure of high mass resolution mass spectra.

VCE Injection & VDE Power Supplies

After this focus on the VCE measure power supply and the selection of the Thermo Fisher PS for this electrode, we had some high resolution data and proper mass spectra to work with. As the Orbitrap cell of the OLYMPIA setup will therefore now be performing with a TF PS module, the other power supplies defining the electrostatic field also have to be optimised (i.e. VCE in jection , VDE in jection and VDE measure ). In theory, it would be possible to use the Thermo Fisher power supply for all Orbitrap cell electrode channels. However, the potential values of our Thermo Fisher PS are not adjustable, which is necessary for OLYMPIA as the kinetic energy is less defined than on commercial instruments. As a result, the optimum values for injection and measurement level may differ from the standard provided by the commercial supply. A schematic of the different optimisation tests is presented in Figure III.8. We had four different power supplies at our disposal. The Thermo Fisher is always used for VCE measure , as we just saw that it is the best for this channel. There are two possibilities for VCE in jection , the ISEG NHR (which was the standard OLYMPIA HV module) and a FUG HCP. For VDE, we can either take the ISEG NHR again, or use a different ISEG power supply, the ISEG SHQ. In total this gives 4 possible configurations (summarised in Table III.2). Test protocol For each configuration, 32 acquisitions of 500 ms have been acquired, with the Krypton sample previously used. To select the best possible configuration, we will focus on one main criterion : the SNR and the sensitivity of the setup. As previously mentioned, Krypton has 6 stable isotopes. The SNR of 84 Kr + (major isotope with 57% abundance), 86 Kr + (second most abundant with 17%) will be compared for each configuration. In addition, we want to check if the 78 Kr + isotope (0.36% of abundance) is detectable, to assess the sensitivity. To do so, the mass spectra will be averaged, with the method presented in the Subsection 3.2.8 of Chapter II. In order to also assess the lifetime of ions, the signal is also cut into slices and the SNR of 84 Kr + is measured between 475 and 500 ms. This gives the information if ions are still measurable at the end of the signal. Results The results of the performance of each configuration are presented in Table III.2. For the first two configurations, the SNR is 3 to 4 times lower than with the FUG HCP. The 78 Kr + is barely detected for the configuration #1 and in the noise level for #2. By contrast, with the FUG HCP, the SNR of 78 Kr + is around 10. The best configuration seems to be #3, with ISEG NHR supplying the deflection electrode. In any case the FUG HCP seems to be a good choice as the power supply of VCE in jection . The SNR is greatly improved, even that of the 78 Kr + isotope with its very low abundance. The SNR values between 475 and 500 ms are also improved with configuration #3 and #4, on which a SNR of 6 or 7 can still be detected. Even if some ions are still detected for the configurations #1 and #2, those are only from the major isotope 84 Kr + , the second more abundant, 86 Kr + , is already not detected, whereas 86 Kr + SNR on configuration #3 and #4 is still around 2.5.

The common point between the two worst configurations, #1 and #2, is the ISEG NHR used for the VCE in jection level. Noteworthy, in the previous Subsection 2.2.1, the ISEG NHR power supply used for VCE measure was already very unstable. It seems there is an issue with the NHR ISEG modules. For each configuration, the potential set on the power supply was the same. However, there can be some differences between the set and the applied potential. This could explain the difference between the high and low SNR, if the absolute value of VCE is not the same, fewer ions could be captured. In general, they seem to perform well as static power supply, like for the ion optics electrodes, but degrade the performances of the setup when coupled with a switcher. This can come from the power supplies themselves as they are actually not designed to be switched.

VCE Cable Length

To better understand why the ISEG power supplies are not performing correctly, we made some tests with configuration #2 (i.e. ISEG NHR used for VCE in jection ). As capacitance can have a strong effect on commutation slopes, we tried to add some capacitance by extending the length of the cable, before the switcher. Adding cables after the switcher is not possible, as it would change the slope of the Orbitrap cell central electrodes and prevent an efficient ion trapping. Table III. 3 shows the SNR values for the configuration #2 with different cable length. The cable length significantly changes the performances with the same power supply. The SNR can be multiplied by a factor of 3 with 2 more meters of cable. With 1, 2 and 4 m the 78 Kr + is even detectable. The best signal amplitude is obtained with an additional length of 2 m. The results are quite puzzling as the amplitude is decreasing before rising again with longer cables. If the only issue was a lack of capacitance, the performances should increase toward the capacitance optimum and decrease after it. Here they show no logical pattern, so it is hard to conclude on the actual issue of the ISEG NHR power supplies. Adding cables is not only adding capacitance but also changing other parameters. To do a proper characterisation of the capacitance effect before the switcher, the proper way would be to add capacitors in the electrical circuit, which we could not undertake during this work.

We also unfortunately had no time to try to add cables to other configurations, as we had to move the setup to Berlin. However, the configuration #4 with the FUG HCP used for VCE in jection and the ISEG SHQ for both VDE channels, present satisfying results, with high mass resolution and a detection limit that allows to measure 78 Kr + isotope and its low abundance (0.36%).

Pre-amplifier

As presented in Chapter II, the pre-amplifier (PA) is the device used to amplify the signal measured by the outer electrodes of the Orbitrap cell. The PA is therefore playing a major role in the quality of the data. Should the radio frequency environment be polluted by external hardware or extra capacitance in the acquisition cables, noisy pattern or disturbance of the mass peak amplitude could appear. For that reason, extra care should be taken for the assembly of the PA on the setup.

This subsection presents the results obtained with two different PA, that we tested in order to characterise the noise present in the data. The first PA is the commercial one from Thermo Fisher, that equips the commercial Orbitrap™ and OLYMPIA in the standard configuration. It has been modified in the laboratory to fit the specific connectors of OLYMPIA. The modified Thermo Fisher PA is directly plugged on the electrical feedthrough behind the Orbitrap cell, to avoid adding cables and disturbing the signal. The amplification factor is estimated to be x5 000. The second PA is custom made, and has been assembled by the JanasCard company in Prague. We will therefore call it CZ PA. The CZ PA has the peculiarity of being composed of two different stages, each with an amplification factor, x100 in the first and x500 in the second one for a total of x50 000.

RF Noise Environment

The RF noise is very polluted, and the PA must be protected from it as much as possible. There are few solutions to effectively protect the PA from the ambient noise, the easiest being to wrap the device in aluminium foil, which will act as shield. The whole circuit must be protected, from the connectors to the PA itself. Inside the vacuum chamber, the circuit is protected by the thick layer of stainless steel that composed the flanges. Figure III.9 shows two mass spectra recorded with the modified Thermo Fisher PA. The upper mass spectrum shows very strong noise patterns coming from the surroundings. The mass spectrum is polluted from the mass 40 to higher masses, almost hiding the krypton peaks. This has been recorded without any shielding (i.e. aluminium foil) on the PA nor the electrical feedthrough. The bottom mass spectrum is recorded with the same PA but properly shielded. This perfectly highlights the needs for protection for the PA.

Test Protocol

The strong advantage of the CZ PA is the ability of the first stage to operate under vacuum. It can therefore be placed inside the vacuum chamber, closer to the Orbitrap cell, and protected by the stainless steel flanges from the RF environment. We made some tests with the first stage of the CZ PA both outside and inside the vacuum chamber. As the Thermo Fisher PA is not designed to go in vacuum, we could not only test it connected from outside. Figure III.10 presents a schematic of both configurations.

To characterise the behaviour of the two PA we will focus on two main factors, the noise level and the associated SNR, as well as the appearance of the whole mass spectrum to see if the recurrent noises are still present.

Results

Figure III.11 shows an example of mass spectra obtained for the tests performed with the CZ PA. Upper and bottom panels respectively show the results when its first stage is placed outside or inside the vacuum chamber. The upper panel with the PA placed outside shows some disturbances. The noise patterns are at the same place as for the Thermo PA without shielding (from mass 40 to 140). The lower panel shows a mass spectrum with the first stage placed inside the vacuum chamber, and is free of any form of noise. As for the aluminium shielding applied for the Thermo PA, putting the first stage into vacuum significantly protects the signal amplified by the PA, leading to a clean mass spectrum. The value of SNR and noise level for each configuration are presented in Table III.4. The gain factor of the CZ PA is 10 times higher, which explains why the noise level is an order of magnitude higher than that of the Thermo Fisher PA. However, the amplitude of the peak is of course also amplified, which gives a SNR in the same range. Quite surprisingly, the noise level of the CZ Out configuration is lower than with the CZ In, and the SNR of the resampled mass spectrum higher than the other two.

Overall, the performances of each PA are quite equivalent. That being said, there is still a notable difference in the average value of the SNR with the CZ PA. Indeed, when averaging the SNR of the 32 mass spectra, the mean value is 50% higher than that of Thermo Fisher PA. About the SNR difference between both CZ configuration, it is worth mentioning that the CZ In configuration has been measured a day after the CZ Out configuration. Because the setup must be opened and the vacuum broken to change the CZ PA position, it is not possible to do both measurements in a short period of time, and with the same ionisation condition. The CZ Out and Thermo Fisher PA configurations however, have been performed with only 10 minutes difference, these two are thus more comparable in terms of the measurement conditions.

Table III.4: SNR (of major isotope) and noise values of the mass spectra. The SNR of the "Averaged value" column is calculated by averaging the SNR of 32 mass spectra, whereas the "Value of the averaged" column value is obtained after the averaging of the same 32 mass spectra in a single mass spectrum.

Averaged value of 32 mass spectra Value of the averaged of 32 mass spectra SNR 84

PA Selection

When looking at pure SNR, both PA are in the same order of magnitude. There are still better amplitudes with the CZ PA, with 50% more SNR for averaged values. This number drops to 10% for averaged mass spectra. However, the biggest advantage of the CZ PA is the possibility to place it under vacuum and protect it from the RF environment in the laboratory, as no recurrent noise is seen with this configuration. It is possible to properly shield the Thermo Fisher PA with aluminium foil, but this is less reliable as the shielding can move over time. In addition, placing the first stage of the CZ PA inside the chamber reduces the cable length, which avoids additional noise. We therefore selected the CZ PA as the new standard configuration of OLYMPIA.

VDE Measure Optimisation

To increase the mass resolution of OLYMPIA, longer experimental acquisition signals have to be recorded. The set up is now equipped with efficient electronics, conditions are therefore sufficient to play with a crucial parameter of the Orbitrap cell : the VDE measure value. As the VDE in jection value is only playing a role in the ion trapping and not their behaviour inside the trap, it is out of the scope of the current study.

Purpose of VDE

The main objective of the deflection electrode is to electrostatically "seal" the inlet hole in the Orbitrap cell outer electrode. By applying the correct potential on this electrode, this compensates the disturbance induced by the hole. The ion motion around the central electrode will be stable, as well as their oscillations frequency, which will have a direct impact on the data performances as longer acquisition time will be possible. The ions have a strong sensitivity to the VDE measure value. Usually, some effects on the data can be seen with variations in the range of only 1 V. With a poorly optimised VDE measure several things can happen. When the ions are close to the aperture and with a non-optimised VDE measure value, they will be repelled out of their orbit and their frequency will be modified. At a low level, this can make the peak foot asymmetric, but can also lead to an asymmetric peak shape with even secondary peak close to the main one (as seen on the mass peak of Another known effect is that a poorly optimised VDE measure will differently impact isotopes. Because each ion has its own radial position and heavier ions will orbit closer to the outer electrode (Equation II. Protocol To determine the optimised value for VDE measure , we acquired a large set of data and looked for the poor optimisation evidence presented hereabove. VDE measure potential is usually in the range of 350 V, but can go up to 420 V [START_REF] Grinfeld | Control of Aberration and Space-Charge Effects in the Orbitrap Mass Analyzer[END_REF]. To characterise the behaviour on a large scale, we started already at 0 V, up to 380 V. Even though it was possible to record mass spectra with a potential below 150 V, the results are not very relevant given their variability and poor quality, they will therefore not be presented.

Data acquisition

We acquired two different sets of data in two different voltage regions. (i) The first one to have an overview on the effect of VDE measure on a large scale with acquisitions from 150 V to 380 V with a 1 V step and 32 files per step. (ii) Then, after a preliminary analysis of the results, we focused more on the higher voltages in the region between 340 and 380 V. In the framework of the development of the OLYMPIA software, Bertrand Gaubicher upgraded the acquisition software and added a feature to automatically change the VDE measure potential. In the 340 -380 V regions, three different batches have been acquired. Each on different days, and therefore with different ionisation conditions. For each of batch, 32 mass spectra have been recorded, this gives a total of 96 mass spectra for each volt step applied on VDE measure .

Data processing With the data going from 150 V to 380 V, we will look at the values and the evolution of mass resolution, SNR and mass calibration (more details in the results paragraph). For the data from 340 V to 380 V, I wrote dedicated Matlab scripts. Each mass spectrum has been analysed, always with the same script and same settings. No apodisation window but a zero filling of 4 was applied on each transient, which were 335 ms long.

To assess the performances (i.e. mass resolution, mass accuracy and SNR), the average value of each batch has been calculated. Figure III.12 shows an example of the average value of SNR for 84 Kr + and 86 Kr + . The SNR is calculated for each mass spectrum and each isotope, and is then averaged into a single value. The same is done for the mass resolution and the mass accuracy. The three averaged values of each batch are finally averaged into one. To characterise each isotope behaviour over time, I cut the signal into twenty slices with the same method presented hereabove, and calculated the SNR for each slice, with a 30 ms long FFT. With an optimised VDE measure value, each isotope should have the same decrease curve through time. To objectively compare the decrease patterns, the cross-correlation factor is calculated between lower abundant isotopes and the major one. With a cross-correlation factor close to one, the decrease patterns are similar. Figure III.13 displays an example of the data obtained with the method described, and the cross-correlation values. Because the two lowest abundant isotopes, 78 Kr + and 80 Kr + , are not always detected on a single mass spectrum, they are not taken into account in this calculation. This method is applied to each of the three batches from 340 to 380 V, giving 3 cross-correlation numbers per 1-volt step applied on VDE measure . Finally, the three values are averaged into one. The last parameter looked at is the isotopic quantification ratio. Indeed, with the proper value of VDE measure , no specific ions should be favoured over the others. For this, the measured amplitude will be compared with the theoretical one, for each value of VDE measure potential. Showing the 3 values for each volt step allows to compare each batch and have a look at the variability over the different measurements.

Results

150 -380 V region I will first focus on the global scale with potentials ranging from 150 V to 380 V for the VDE measure value. For this study, the signal has been analysed with a 20 ms long FFT. This is done in order to get an idea of the behaviour of the ions before they are disturbed by other processes, such as collisions with neutral background. Figure III.14 shows the evolution of the mass resolution over time. Each point represents one volt step and corresponds to the averaged value of the 32 files acquired. It is clear that with the increase of the VDE measure value, the mass resolution rises as well. The values goes from around 3 000 with 160 V up to ~6 000 above 320 V, where they seem to reach a plateau. The theoretical mass resolution for an FFT of 20 ms is 7 000. Here, on such a small time period the setup is able to reach 85% before getting disturbed. An increase of the mass resolution points to a better defined electrostatic field, which occurs at higher VDE measure values. The SNR shows a maximum between 220 and 300 V. Below and above those values, it is roughly the same. It is interesting to point out that even though the mass resolution was decreasing below 320 V, the SNR does not show the same trend. Although the same amount of ions are captured, they are less confined in a proper orbit. We find the same peak enlargement already seen hereabove when the electrostatic field is not properly defined. The SNR for each Krypton isotope as a function of VDE measure potential on slices processed with a 20 ms FFT duration. Red : 84 Kr + Black : 86 Kr + Purple : 82 Kr + Blue : 83 Kr + Green : 80 Kr + and Yellow : 78 Kr + .

Finally, we can have a look at the mass value given for a fixed k factor. By manipulating the ion motion equation (Equation II.8) it is possible to isolate the m (mass) factor, and compare its relative value for each VDE measure value. On Figure III.16, the m determined for each voltage is compared to the value obtained with 350 V. This allows to see that at high values of VDE, above 340 V, the points are clustered together whereas for lower values, and especially below 220 V, the calculated mass varies significantly. This highlight that for high VDE measure values the measurements are reproducible. Looking at the three figures above (III.14, III.15, III.16), it can be stated the best region for the VDE measure potential is above 340 V. In terms of pure SNR the area around 240 V is better, however the drop in mass resolution and scattering of the mass calibration value shows that higher values are more reliable.

Zoom on the 340 -380 V region For those reasons, we will now have a closer look at the region between 340 and 380 V, with the three batches measured and processed with the techniques presented hereabove. As we now want to have more representative mass spectra, the following results are calculated on 335 ms FFT mass spectra.

Performances -Resolution, Mass accuracy and SNR Figure III.17 shows the performances, mass resolution, mass accuracy and SNR for isotope 86 Kr + . The same plot for each isotope has been made and used but are not presented here, to avoid redundancy.

In the mass resolution panel, there is no strong tendency along the 40 V, nor any other specific value that stands out. The three data sets are roughly similar and the mean curve rather flat. The only noteworthy pattern is a greater variability between the data sets above ~370 V, and a minimal one around 347 V.

The same conclusion can be drawn for the mass accuracy in the middle panel. The average value is under ±1 ppm below 350 V, and varies more above this value even though it is still in a reasonable range.

The SNR shows a continuous decrease with the increase of VDE measure . The average SNR value starts at 13 for 340 V and is at 7 for 380 V. This, however, could have been biased by the automatic acquisition of the setup : taking the 32 files for one volt takes around 1min. For a whole data set, this brings the duration to around 45 min. In such a long time the thickness of the EI source filament can be reduced, and the current applied on it is no longer optimised. Even though I tried to maintain the current at the right value, this should be kept in mind. The performances of the setup are not significantly different along the 40 V scanned here. A tendency of greater variability can be observed for high values but generally the impact of variations in VDE measure potentials is much greater than this. If a specific value cannot always be selected, at least a small window (few volts) is, which is not the case with OLYMPIA. . The averaged amplitude of each batch for each isotope is displayed for all the VDE measure values. This allows to assess the variability between the batches. The theoretical amplitudes of the isotopes are represented by the horizontal lines. The normalisation for the theoretical values is quite unusual, as it is the addition of the amplitude of all the krypton peaks (minus the noise level), which is then compared to the natural abundance of the isotopes. This representation, as opposed to the normalisation on only the major isotope amplitude, allows to see if the amplitude of the major isotope is incorrect. On the first order, 86 Kr + , 82 Kr + and 83 Kr + seem to oscillate around their theoretical amplitude. 84 Kr + lacks amplitude of several percent, and shows a greater variability between the three batches. By contrast, both minor isotopes 78 Kr + and 80 Kr + are above their expected abundance.

Decrease of SNR through time

A detailed study of the RIA deviation will be presented in the EI chapter (Section 3) and will further discuss the results and the deviation from the theoretical amplitude. For the time being, the VDE measure value does not significantly impact the RIA deviation. The behaviour of each isotope seems identical all along the 40 V scanned. The variability between the data is also quite similar, although not particularly small.

Discussions & Conclusion

Despite all the data measured and processed with numerous methods, no clear value for OLYMPIA's VDE measure can be chosen. Apart from higher mass resolution and reliability above 340 V, the closer look taken on the data did not point out to other specific impact of the VDE measure value. However, VDE measure is supposed to be very sensitive [START_REF] Grinfeld | Control of Aberration and Space-Charge Effects in the Orbitrap Mass Analyzer[END_REF], and OLYMPIA should not be an exception. This means that the sensitivity of OLYMPIA is not good enough to measure the variations induced by the variation of the VDE measure values.

This can come from several factors. However, my hypothesis is that the problem lies in the ion injection method we use. VDE measure is supposed to correct the electrostatic field in the trap by applying a potential outside of the aperture. But we used a continuous ion injection with the EI source. Not just a continuous ionisation, but also a continuous injection, and this even during the measurements. Injecting additional ions once the central electrode has been switched and the ions are trapped in orbit, leads to injecting disturbances into the trap. Because of the high potential of VCE measure , the injected ions most likely fall directly onto the electrodes. However, before that, they can collide with the trapped ones, and disturb them. In addition, the collision between injected ions and the central electrode can also create electrons and with that disturb even more the orbiting ions.

Because of this continuous injection of disturbances in the trap, even a proper correction of the field aberration by VDE measure cannot avoid perturbations. To confirm this theory, and be able to actually find the proper value for VDE, we would need to go from a continuous injection to a pulsed one. This will be further developed in the EI chapter.

Even if the study of OLYMPIA VDE measure optimisation did not deliver the expected results and the selection of a single value, the protocol applied, as well as the scripts used for the processing can be used for the optimisation of other Orbitrap-based mass spectrometers such as the LAb-CosmOrbitrap.

Chapter IV

High Mass Resolution and Ions Behaviour in Electron Impact Configuration

Owing to all the optimisation work presented in the previous chapter, OLYMPIA is now able to record high mass resolution spectra of gaseous compounds using the Electronic Impact ionisation technique. Part of the results and the discussions, mostly for the gas mixture, presented in this chapter are the subject of a publication (Zymak et al.,

2023, Appendix II).

To demonstrate the new capabilities of OLYMPIA, we analysed a gas sample relevant to the atmospheres of planetary bodies. It is a mixture of three gases with a very close m/z ratio : carbon monoxide CO (27.9949 u), ethylene C 2 H 4 (28.0313 u) and dinitrogen N 2 (28.0061 u). The quantification of the N 2 abundance in celestial bodies gives information on the conditions in which they formed (e.g. where in the protosolar nebula [START_REF] Mousis | The Dual Origin of the Nitrogen Deficiency in Comets: Selective Volatile Trapping in the Nebula and Postaccretion Radiogenic Heating[END_REF]. However, due to its m/z proximity with the CO molecule, the ratio is rarely quantified, because of the low mass resolution of the spaceborne mass spectrometers [START_REF] Eberhardt | To CO and N 2 Abundance in Comet P/Halley[END_REF][START_REF] Barnun | Trapping of N 2 , CO and Ar in Amorphous Ice-Application to Comets[END_REF]. A mass resolution of at least ~5000 FWHM is required, and only ROSINA DFMS was able during the ESA Rosetta mission to directly determine the ratio in the comet 67/P thanks to its high mass resolution [START_REF] Rubin | Molecular Nitrogen in Comet 67P/Churyumov-Gerasimenko Indicates a Low Formation Temperature[END_REF]. To go further, we also added ethylene, which has been detected in the atmosphere of gas giants [START_REF] Romani | Temporally Varying Ethylene Emission on Jupiter[END_REF]. Those measurements have been carried out during the optimisation work presented in the previous chapter, and therefore do not benefit from all these improvements.

It is also important to assess OLYMPIA's ability to determine true quantities by measuring the ion counts for each species. Quantifying the ions resulting from the ionisation of the mixture is very difficult, as the ionisation rate of each species must be taken into account, as well as the production of fragments. We therefore assessed the quantification accuracy of OLYMPIA by measuring the deviation to the relative isotopes abundances of Krypton. By contrast to the gas mixture study, the Krypton measurements were performed just before the move to Berlin, with all the modifications described in the previous chapter.

Technical Aspects

OLYMPIA and its subsystems in EI mode were described in Chapter II. This section focuses on specific operational features relevant for the subsequent experiments.

Operating Pressure

The requirement of low pressure during measurements has been addressed in Subsection 3.2.6 of Chapter II. However, the EI brings additional constraints to the goal of achieving the lowest possible vacuum. The gas sample of interest will inevitably increase the pressure in the setup, impacting the behaviour of ions in the cell. It may be tempting to open the inlet valve as little as possible, but this results in a less efficient ionisation. Consequently, there is a trade-off between effective ionisation and a sufficiently low pressure to allow a long measurement time.

After some tests at pressure in the ionisation chamber ranging from 6.10 -6 to 1.10 -3 mbar, we found that the best operating pressures were around 5.10 -4 mbar in the ion source, corresponding to around 1.10 -8 mbar in the Orbitrap cell. Lower pressures improve the conditions in the trap, but produce fewer ions, so the performances are not improved.

TECHNICAL ASPECTS CHAPTER IV. ELECTRON IMPACT

Continuous Injection

The standard ion injection with commercial Orbitrap™ is pulsed, and the ion bulk is created and well defined by the C-trap module before the injection. OLYMPIA features a direct injection (i.e. without a C-trap module) which is also continuous, as nothing prevents the ions from getting into the trap during measurements. In theory, it is possible to perform a pulsed injection even with our current configuration. The ion optics are used to focus the ions toward the Orbitrap cell, and rising the potential on a circular electrode to a value above the kinetic energy of the ions can prevent them from going through the optics (Figure II.18). This "ion chopping" effect can be used to block the subsequent ions once a packet has been trapped inside the cell. During the optimisation and troubleshooting period, this method was tried and we could let ions go through the ion optics during short time periods (> 100 μs). It was however not easy to create a precisely defined ion bulk, and therefore the SNR of the peaks was lower than with continuous injection. This method increases the complexity of the settings, as the right timing between the Orbitrap cell electrodes and ion optics switch must be found, as well as the proper values for the electrode potential. In the end, we could obtain better results with the direct injection and this became the standard configuration for the ion optics. An example of the potential applied on each electrode can be seen in

Gas Mixer

To prepare the gas mixture with the selected gases, we built a gas mixing station (Figure IV.2). Assembled with commercial components from Swagelok, the mixer allows the preparation of the samples needed for the experiments. The setup is connected to a primary pump to evacuate the sample tank before mixing, and the pressure can be controlled by a pressure gauge connected to the system. The minimum background pressure of the system is around 0.8 mbar. This limits the purity of the gas mixture, typically prepared at 1 000 mbar. Due to the properties of the gauge, the error in the partial pressures of the gases is expected to be around 0.2%.

Gas Mixture Study

Using the gas mixer, we prepared a 1:1:1 partial pressure ratio of CO/N 2 /C 2 H 4 . The Krypton and CO gas bottles were purchased at Sigma-Aldrich, with a purity of 99.998% for Krypton and ≥ 99.0% for CO. The N 2 is from Air Liquide, with ≥ 99.9999 % purity.

Results

The measured mass spectra are presented in Figure IV.3. The left panel displays the mass spectra from 25 to 29 u for two different FFT duration, 20 and 50 ms, respectively. The three species of the mixture are detected at mass 28 u. Fragments of C 2 H 4 , C 2 H + 2 and C 2 H + 3 as well as the protonated ions C 2 H + 5 are detected. On the 50 ms mass spectra, C 2 H + is also detected. The right panel, shows a zoom at mass 28 u, overlaying three different FFT durations for the same acquisition. We successfully resolved the three peaks, even with a short FFT duration of 20 ms. The increase of the mass resolution with longer FFT can be seen with the superposition of the mass spectra obtained with three different FFT length. The performances of the mass spectra are gathered in Table IV.1. The theoretical mass resolution for each FFT duration is 6 500, 16 300 and 81 000, respectively. For 20 and 50 ms spectra, all three chemicals are at the maximum achievable value. Noteworthy, because of the post processing enhancement (i.e. zero-filling, apodisation, resampling and averaging), the measured mass resolution can slightly exceed the theoretical value. With the increase of the FFT duration to 250 ms, the mass resolution deviates from the theoretical. The maximum mass resolution achieved is 51 000 for C 2 H + 4 , reaching around 60% of the theoretical maximum. The raw acquisitions last 500 ms, however the ions are not stable for such a long time and longer FFT duration do not improve the performance. This is well highlighted by the strong decrease over time of the peak amplitude. In terms of SNR, the decrease is less pronounced as the noise level also decreases through time. Even though the initial concentration of the mixture was equal for all three molecules, the recorded amplitudes are much different. C 2 H + 4 has the highest SNR, whereas CO + and N + 2 are less intense. The mass accuracy is very precise, with just a few ppm deviation.

Discussion

Even if the concentration in the gas mixture for each species was identical, there are some significant differences between the three peak amplitudes. The intensity of the peaks does not only depend on the initial concentration of a sample, but also on additional factors that can impact the ionisation or the ions behaviour. With the EI technique, the electrons produced in the source ionise the sample by bombardment. This means that larger molecules will interact more with electrons, and are more likely to be ionised (this effect is described by the Binary-Encounter-Bethe model, Hwang et al., 1996). This ionisation probability is represented by the ionisation cross-section of molecules. The electron ionisation cross-section of the three molecules is quite different, with C 2 H 4 (4.0 Å 2 ) being almost twice that of CO and N 2 (2.3 Å 2 ). This results in a higher ionisation efficiency of ethylene molecules and ultimately a higher peak intensity. In addition, after the ionisation, charge transfer reactions can occur. This will produce more cations of the species with lower ionisation energy. C 2 H + 4 (1014 kJ/mol, Ohno et al., 1995) will therefore be more produced than CO + (1352 kJ/mol, Erman et al., 1993)

Krypton Isotopes Study

The gas mixture data presented hereabove were measured over the same period as the technical improvements listed in Chapter III, and therefore could not benefit from all the optimisation work (in particular the power supply tradeoff for the HV Orbitrap of the second phase, presented in Section 2.2). However, the following krypton measurements were recorded at the very end of the stay in Orléans, and thus benefit from all the improvements compared to the results shown in Zymak et al. (2023).

Results

Ion lifetime The extended lifetime of ions after the power supply improvements was briefly addressed in Table III.2. Figure IV.4 shows the SNR decrease through time for three Krypton isotopes. For the major isotope 84 Kr + , the SNR reaches a maximum at around 20 at 100 ms. It then progressively decreases throughout the rest of the signal. 84 Kr + ions can clearly be detected at 500 ms with a SNR of ~8, which is almost twice as long as what was measured with OLYMPIA for the gas mixture measurements. The isotopes 86 Kr and 82 Kr roughly show the same behaviour with a maximum for 82 Kr + also around 100 ms. The decrease is also steady throughout the rest of the signal. The variability of the data, highlighted by the error bars derived from the standard deviation is significant. The figure shows the evolution of the mass resolution for all isotopes with different FFT length, as well as the theoretical maximum at m/z 84. The measured mass resolution increases linearly with time throughout the 500 ms, remaining close to the theoretical resolution. For a 500 ms FFT, the mass resolution of 84 Kr + reaches 80 000, which is around 85% of the maximum achievable value for 500 ms at 84 u. However, the other isotopes do not show the same pattern. The mass resolution shows a similar increase up to about 250 ms and then has a less upward slope, to finally reach values around 40 000 at 500 ms (42% of the theoretical value).

Amplitude study The differences in the peak amplitude for the species in the gas mixture can be attributed to the different physical properties of the molecules. To minimise those effects, and make sure we have the same behaviour for the ions, we performed a quantification of the Krypton isotopes, a polyisotopic monoatomic gas that has a well-documented isotopic ratio (Table IV.2, Berglund and Wieser, 2011).

As seen in Chapter III, the six Krypton isotopes are detectable with OLYMPIA. Before the optimisation work, the lowest abundant isotope, 78 Kr + , required an averaging in order to be detectable. Owing to the better experimental conditions, 78 Kr + is now detected in one mass spectrum out of two, and 80 Kr + almost every time.

The measured mass spectrum, along with the theoretical abundances normalised to the major isotope ( 84 Kr + ) amplitude is shown in Figure IV.6. The peak amplitudes are in average well above the theoretical values : 78 Kr + is six times as high as the theoretical value, and 80 Kr + almost twice times higher (an error of 503% and 95%, respectively). Those values are however biased, because as seen in Figure IV.5, the mass resolution is not the same for each isotope. By only taking the amplitude for the ion count, the peaks with a lower mass resolution than the major on which the normalisation is done will be underestimated.

To correct this, the area under curve must be calculated, with the method explained in Subsection 3.2.8 of Chapter II. The results are shown in Table IV.2, and the histograms in Figure IV.7. To assess the evolution of the errors over time, the method has been applied on 50 ms and 250 ms spectra.

Overall, the ions count for the isotopes in each mass spectrum are very variable, and can be several times lower or higher than the theoretical values. Because of the low abundance of 78 Kr + , these variations are particularly prominent, reaching in some cases over 1000%. The three isotopes 82 Kr + , 83 Kr + and 86 Kr + which have an abundance of more than 10% all show errors between 30 to 60%. Looking at the centre of the Gaussian for all the data at different FFT durations, it is obvious that there is a systematic overestimation of all ions other than the main isotope 84 Kr + that was used as calibrant.

Interestingly, the errors values at 50 ms are higher than at 250 ms. This could come from and instability at the beginning of the signal, originating for example from the Orbitrap cell electrodes, which would require some time to stabilise after the commutation.

Conclusions on the RIA Accuracy

The long FFT duration achieved for the Krypton measurements (Figure IV.4) proves that the setup is able to reach about 85% of the theoretical mass resolution (Figure IV.5). The pressure was in the same range as usual, around 1.10 -8 mbar. Because the background pressure effects are similar, the longer ion lifetime highlights a more stable electrostatic field in the trap. This is the results of the optimisation and selection of the power supply trade-off described in Chapter III. However, the mass resolution is lower for less abundant isotopes (Figure IV.5). After 250 ms, the increase is less pronounced and the values are more and more distant from the theoretical ones. This means that there are too few ions in the late part of the acquisition to measure a correct signal.

An oversensitivity effect is observed on the Krypton isotopic quantification for low abundant ions. This overthan-expected amplitude can be up to ten times higher than the natural abundances for 78 Kr + . The peaks of the other isotopes can be tens of percent higher. As the ions are all normalised to the major isotope 84 Kr + , this could actually come from an underestimation of the 84 Kr + amplitude. If we look at Figure III.19, where the normalisation has been made based on the sum of all krypton isotope intensity, it becomes obvious that 84 Kr + amplitude is indeed lower than expected.

This could come from several factors. For Orbitrap measurements, if different m/z behave differently, this usually comes from a non-optimised value for the deflection electrode VDE. Unfortunately, no significant changes in the isotopes behaviour could be found during the VDE optimisation study. The insensitivity of the results to VDE variation could come from the continuous ion injection during the acquisition. The injected ions could disturb the ones trapped in the cell, which form a ring around the central electrode, and oscillate from one side of the cell to the other. With the continuous injection of disturbances during measurements, the ion ring could become less and less well defined, spreading along the X-axis of the cell. This would first result in a decrease of the intensity, and lead to a loss of the signal, as modelled by Kharchenko et al. (2012, Figure II.8) or stated in Hu et al. (2005). This would result in an underestimation of the major isotope intensity. For the less abundant ions, the disturbances would also impact their ring definition, but this could be less visible due to their relatively low number inside the trap. This effect, coupled with the disturbances induced by space charge effects from the major isotope ion ring (Hofmann et al., 2020) could result in a loss of those low abundant isotopes, rather than a spread of their ring. The space charge effects are even more active than usual, as the major isotope ring is widely spread in the cell. The loss of the low abundant ion through time is consistent with their lower mass resolution at the end of the acquisitions.

This hypothesis is based on the fact that the initial ion rings are well defined. However, also due to the continuous injection, no ion packets are created prior to the injection. The ion trapping could therefore be quite inefficient, and the ion ring already not well defined at the beginning of the measurements. The fact that the errors become lower over time could support this hypothesis. However, if there is indeed an HV Orbitrap instability on the central electrode at the beginning of the signal, it is difficult to conclude because the first part of the signal is already not trustworthy. These two hypotheses are not exclusive, as an already ill-defined ion ring could still deteriorate over time.

Whatever physical process is occurring in the cell, if it is induced by the continuous injection, the oversensitivity effect should be removed by a pulsed injection, and this is the method used for LILBID ionisation, the subject of the following chapter.

Outlook

The optimisation work for the EI configuration is not over, and we have planned some design improvements for OLYMPIA. For the moment, we have not really been limited by the pressure with the sample used in our studies, a pressure of 1.10 -8 mbar might be sufficient for most inorganic materials. However, should the EI measurements go on with various types of gaseous samples, the pressure could become a limiting factor for long acquisition times (> 500 ms). The pressure is limited by the fact that gaseous compounds must be injected into the setup, the ionisation requiring a pressure of 5.10 -4 mbar to be optimised.

To improve the pressure in the cell without decreasing the inlet flow, several things can be done. The first one would be to improve the vacuum in the source, by improving the design and allow a better pumping. That way, less gas would go from the ion source chamber to the Orbitrap cell. To achieve this, a new flange has been designed for the ionisation chamber, thus reducing its overall volume. Secondly, improving the efficiency of ionisation could reduce the amount of gas required for an optimised ionisation, ultimately reducing the pressure. To do so, a new design for the ion source has been built (Ján Žabka, pers. commun.). In the current design, the filaments are as close as possible to the incoming gases. On the new design, the filaments are more distant from the gas inlet, but electrodes focus the electron beam precisely onto the gas sample, resulting in a more efficient bombardment. The new ion source and flange were ready just before the move to Berlin, and unfortunately could not be tested until now as the time there was fully dedicated to the LILBID measurements.

Another issue with the setup is the continuous injection. As mentioned hereabove, it is theoretically possible to use the ion optics as an ion chopper to create an ion bulk (this technique would however still allow the neutral to go through). This could remove the disturbance in the trap caused by the ion injection. Our tests on the creation of an ion bulk led to a significant loss of amplitude. However, this has been tried before the power supplies study, and a suboptimal ISEG power supply was used with a switcher. As it seems that ISEG power supplies are not behaving properly when switched, it would be interesting to try this method with another power supply. Another idea to remove the continuous injection would be to pulse the gas injection. There are some commercial gas injectors that are able to inject the sample during ~40 ms pulse. This is still enough to disturb the first part of the signal, however it could help to have suitable conditions for longer measurements, and this solution would also stop the flow of neutral gases.

Chapter V Simulating Hypervelocity Icy Grains Impact Ionisation with OLYMPIA

The Laser Induced Liquid Beam Desorption and Ionisation (LILBID) setup at the Freie Universität of Berlin reproduces the icy grains mass spectra obtained by spaceborne impact ionisation mass spectrometers such as CDA during the NASA/ESA Cassini-Huygens mission and SUDA onboard the upcoming NASA Europa Clipper mission. The main objective of the project I integrated during my PhD is to extend the existing set of LILBID calibration mass spectra with ultra high-resolution ones for interpreting impact ionisation mass spectra of icy materials that SUDA will obtain during the Europa Clipper mission as well as potential future dust hypervelocity impact detectors. This chapter will present the different efforts made to fulfil this objective. I will start with some information about the LILBID setup, its specificities and how different experimental parameters can mimic different kinds of CDA's measurement. Then, I will present the particularities of this new ion source and mass analyser combination. To be able to couple OLYMPIA and LILBID, some mandatory modifications had to be done, on OLYMPIA, but also on the LILBID technique. We will then have a look at the results obtained with the setup. To first give some context, I will present the results measured during the campaign in Leipzig at the very beginning of my PhD, in October 2019. Then, the preliminary work with a Tin wire sample performed to control that the mechanical integration was successful, and finally the desorbed water ions.

Because of the Covid-19 pandemic, the move of OLYMPIA and myself to Berlin that was originally planned in summer 2020 was postponed to February 2021. With the travel restrictions at that time, it was not possible to organise some verification or measurement campaigns with the team before the end of 2021. Global supply delays also made the mechanical improvements of the setup more challenging. Thanks to the help and experience with the LILBID technique of the team at the FU Berlin, the ionisation part was quickly operational. We will however see hereafter that the focus and measurements of desorbed ions to the Orbitrap is a tedious task and can still be improved.

The LILBID Technique 1.The Standard LILBID-TOF Configuration

The LILBID-TOF setup at the Freie Universität in Berlin has been duplicated from the one in Leipzig and was first described in [START_REF] Charvat | New Design for a Time-of-Flight Mass Spectrometer with a Liquid Beam Laser Desorption Ion Source for the Analysis of Biomolecules[END_REF]. A pulsed IR laser ionises a micrometre-sized water beam in which samples of interest are diluted. After a free flight through a skimmer, the ions are subsequently accelerated with ion optics, which uses the principle of delayed extraction. The ions are focused toward a Time-of-Flight (TOF) mass analyser, which is a reflectron type MS from the company Kaesdorf. The mass resolution of the RTOF is reaching a m/Δm of 800. Even if the mass resolution is low compared to Orbitrap mass analysers, the advantage of TOFMS is a very low detection limit. The setup in Berlin is able, with the LILBID ionisation, to detect amino or fatty acids with concentrations below μM level (Klenner et al., 2020b).

Vacuum The instrument is divided into two different vacuum stages, the first one is the ionisation chamber with the liquid water beam, and the second the chamber of the TOF mass analyser (Figure V.1). The two stages are interfaced with a skimmer, a conic shaped electrode that allows an efficient differential pumping. Injecting liquid water into vacuum greatly raises the pressure. To avoid the water vapour filling the chambers, a first cryotrap is placed below the water beam and collects the liquid water. The cryotrap is placed inside a liquid nitrogen reservoir to keep the liquid frozen inside the setup. To capture water vapour molecules, a second cryotrap filled with liquid nitrogen is placed in the ionisation chamber and further lowers the remaining pressure. On top of this, a dedicated turbopump evacuates the whole chamber. At best, the pressure in the ionisation chamber is in the range of 10 -5 mbar. Two turbopumps ensure that the pressure in the TOF below 10 -7 mbar. The needs for high vacuum with TOFMS are lower than for ion traps, therefore 10 -7 mbar is enough to operate in proper conditions. Water Beam The water system is composed of an HPLC pump (model 300c, Gynkotek) on which a sample injector is connected. Capillaries bring the liquid towards the nozzle holder, which is finally injected in the setup through a quartz nozzle that has a micrometer aperture. The aperture size can be changed depending on the nozzle used, the standard used during experiments being 15 µm in diameter. The nozzle holder is mounted on a 3-axis manipulator that allows to precisely adjust the position of the water beam. The positioning of the water beam needs to be extremely precise, misalignment of a fraction of a millimetre can lead to the loss of the signal. For that reason, a camera is placed outside the vacuum chamber with a 45°angle and can help to properly align the water beam with the skimmer that leads to the TOFMS chamber (Figure V.2). The flow rate of the water beam can be adjusted with the HPLC pump, usually in the range of 0.15 -0.3 mL/min. The stability of the water beam can be quite erratic, a small particle can clog the nozzle, resulting in the instant freezing of the beam. Most of the time if the beam is frozen, the vacuum must be broken, the nozzle cleaned (sometimes by sonication) before placed back on the setup. A higher flow rate is usually more stable. However since some samples can be hard to produce or expensive, the flow rate should therefore stay as low as possible. In addition, 1. THE LILBID TECHNIQUE CHAPTER V. LILBID-OLYMPIA the pressure in the ionisation chamber would quickly rise if the flow rate was too high.

Laser The laser used for ionisation is an Opolette HE 2731 (OPOTEK) with a 7 ns pulse width. The standard wavelength of 2840 nm has been chosen to match the absorption frequency of the OH-stretch vibration of water molecules, the ionisation is therefore optimal. To focus the laser beam at the water beam, two lenses are used. In order to avoid energy losses during focusing, gold coated CaF 2 lenses (highest transmission at the chosen wavelength) have been chosen. Noteworthy, the laser in Leipzig features a second output, that allows to ionise samples with a 1064 nm wavelength.

Simulating Different Impact Speeds

Delayed Extraction

The principle of delayed extraction is known for a long time to enhance the mass resolution of TOFMS [START_REF] Wiley | Time-of-Flight Mass Spectrometer with Improved Resolution[END_REF]. It is also used here as a selector for ions with a specific velocity. Figure V.4 shows the design of the TOF ion optics. After ionisation, a portion of the ion cloud goes through the grounded skimmer. Directly after it, there is the acceleration region, between the repeller and extractor electrodes. The delay time represents the time after ionisation at which the potentials of both repeller and extractor are switched, resulting in an ion acceleration towards the flight zone region. The acceleration region is only few centimetres away from the water beam but this is already enough to see some masses separate. Therefore, a short delay time (< 4 µs) will only accelerate the fastest ions which typically have low masses. By contrast, high delay times will prefer slow ions and heavy masses. The delayed extraction method narrows the mass range of a single acquisition, it is therefore needed to co-add several mass spectra to get a full range mass spectrum. Noteworthy, no ions are usually detected with a delay time shorter than 3 µs.

Laser Energy In addition to the delay time before acceleration, the energy of the laser also plays a role in setting the analogue impact speed. The laser energy is a function of the laser flashlamp energy, and the time difference between the flashlamp and the Qswitch, as well as the spot diameter (see Subsection 2.3 for more details). The effect of the laser energy is quite intuitive, more energy will induce more destructive conditions, fragmentation, and the measure of lower masses.

The final objective of this work and the new LILBID-OLYMPIA setup is to create a high resolution mass spectra database for impact ionisation mass spectrometer. One major milestone towards this objective is to be able to reproduce Figure V.3 with the new high resolution setup. The ability to mimic all the analogue impact speeds is an asset, but the most important would be the lower ones. Europa Clipper with SUDA will perform

Mechanical & Hardware Adaptation for OLYMPIA Integration

Although the ionisation and the mass analyser are two separate subsystems of a mass spectrometer, the adaptation and coupling can require some modifications of the design at the interface. OLYMPIA was developed with the goal of being coupled with LILBID, therefore the main ion optics was already designed for this application. LILBID, on the other hand, is a technique that has been around for a more than twenty years and had to be modified.

OLYMPIA Integration

After the move of OLYMPIA from Orléans to Berlin the setup had to be coupled with the LILBID experiment. During the previous campaigns in Leipzig and Berlin, OLYMPIA was mounted in place of the TOF, to benefit from the space and the TOF mechanical interfaces. This was therefore the initial plan when arriving for the extended campaign in Berlin.

The LILBID-TOF in Berlin is dedicated to sustain the database of spaceborne icy grain impact ionisation mass spectrometer. To avoid regular tedious work of dismounting and reassembly of the two different mass analysers, we decided to keep both mass analysers mounted at the same time. OLYMPIA was then placed on the other side of the vacuum chamber, as presented in the picture of Owing to the parallel integration, it is possible to leave both MS connected to the main vacuum chamber at the same time. It is particularly important to have the turbopumps running at all times and keep the vacuum at an operable level. The two MS are not totally independent, the cryotrap that collects the liquid from the water beam needs to be placed under the running setup. The laser also needs to be moved and put close to the operating MS (see Subsection 2.3 for more details). Despite these repositionings, it is possible to perform measurements with both mass spectrometers on the same day, with approximately half an hour for the modifications to switch from one mode to the other (assuming the laser realignment and the water beam ignition go smoothly).

LILBID Water beam & Ion Optics Adjustments

The interfacing of OLYMPIA with a LILBID setup is not only about the surrounding vacuum flanges. The ions have to be focussed from the ionisation source at the water beam, towards the Orbitrap cell. As described in Chapter II Section 1.2, the Orbitrap cell can only measure ions with a defined kinetic energy (KE). For the EI source, the KE was set at the ion creation with a potential of 1 kV applied directly in the source. To set the KE of the LILBID ions, the ion source for the LILBID-OLYMPIA configuration has been modified compared to the standard LILBID-TOF source. To focus the ions toward the Orbitrap cell, four electrodes have been added, and with the new design, it is possible to apply a potential on the water beam.

Water Beam Adaptation

To set the ions KE at their creation, the nozzle has been modified compared to the TOF quartz nozzle. A comparison of both nozzles can be seen on Figure V.7. The tip of OLYMPIA's nozzle is made of stainless steel, just behind it lies the actual nozzle with a diameter of 20 µm. To apply a potential, an electrical connector has been added. The water is coming from an isolated capillary inside the nozzle holder. Should the water touch any part of the stainless steel nozzle holder, it would freeze immediately. The HV Jet potential applied on the nozzle holder tip is therefore creating an electrostatic field around the water beam.

Additional Ion Optics

To focus the ions towards OLYMPIA's ion optics, some additional electrodes around the water beam are needed. To complete the HV Jet "electrode", a repeller is placed behind the water beam to push the ions inside the Skimmer. The skimmer here has two functions, it allows an efficient differential vacuum pumping, but is also used as an electrode. There is a fourth electrode after the skimmer, named focus. A schematic of OLYMPIA source optics is shown in This alternative LILBID design is quite different from the standard LILBID-TOF one (Figure V.4), which has a fully grounded source. OLYMPIA source brings much more ions in the Orbitrap cell, as the electrostatic field will focus them toward it, where the TOF ion source configuration only measure the small portion of the ion cloud that geometrically goes through the skimmer. OLYMPIA's source design also allows to define the KE of the ion bunch. Hereafter, the four electrodes presented in this Subsection will be referred to as source optics, and the potentials applied on those four electrodes as HV source , whereas the original OLYMPIA electrodes numbered from 4 to 10 as described in the Chapter II will be referred to as ion optics and HV optics .

Laser Adjustments for the LILBID-OLYMPIA Configuration

With the coupling of OLYMPIA to the LILBID setup, the EI source has been removed from OLYMPIA and we had to adapt the laser at the FU Berlin for LILBID. We first tried to leave the laser at its original position, close to the TOF (as seen in Figure V.5). However, the energy losses to reach OLYMPIA were too significant, so I assembled an extension to the table to place the laser next to OLYMPIA.

Triggers Control

A laser is handled with two subsystems, the flashlamp and the Qswitch. The flashlamp is creating the laser energy, and when the Qswitch is activated, the beam is fired. The flashlamp is a sensitive device, and should be handled with caution. One strong recommendation is to always activate the flashlamp with a 20 Hz frequency, for a better stability. The energy of the flashlamp should also be constant (5.44 J with our laser). On the contrary, the use of the Qswitch can be adapted to the needs of the experiments.

The TOF uses the laser with a 20 Hz frequency both for flashlamp and Qswitch. The parameters are handled with the software from the laser manufacturer. For OLYMPIA, it is not possible to use the laser with the same settings as the LILBID-TOF. Indeed, for the LILBID-OLYMPIA configuration the laser shot is not necessarily the "master TTL" (Transistor-Transistor Logic), i.e. the one trigger that gives the clock for the other subsystems. This means that the laser triggers must be handled in "External mode", with custom TTL. To handle the flashlamp in External mode some adaptation to the trigger scheme had to be done. First of all, the output intensity of the CompactRIO is around 3 V, when the laser threshold is above 5 V. To increase the output level, we use an analogical pulse generator (TGP 110 from the company Aim-TTi). The TTL is then handled by a delay generator. The TTL scheme can be seen in Figure V.9. In theory, the flashlamp could have been handled in External mode and the Qswitch in Internal. However, with this configuration there can be a small jitter in the range of 1 µs. As a reminder, the time precision needed for the Orbitrap cell central electrode switch is also in the range of a microsecond, handling the Qswitch in External mode is therefore mandatory. However, this optic path was very unreliable. The last lens had to be realigned by hand every time we switched the laser position, and the spacers were adapted for the TOF skimmer but were not exactly at the proper position for OLYMPIA's. During a campaign in June 2022, Ales Charvat (researcher from Institute of Chemical Technology at the Leipzig University), modified the optics and made a second version. The new optic path uses a periscope with two coated mirrors to modify the height of the laser beam, removing the need for the non-adapted spacers. The first 100 mm lens has been removed. The 50 mm lens is now fixed, but mounted on a mirror holder, that includes three screws for millimetre adjustments. This new configuration is much more reliable, is quickly readjustable after a laser repositioning and uses all available energy.

Laser Optic Path

Laser Energy Estimation

The energy of the laser that ionises the water beam is an important parameter as it also affects the analogue impact speed of the experiment. For that reason, the energy available at the water beam must be characterised and the energy variation controlled.

Principle The power density is expressed in MW/cm². The power value depends on the laser parameters (see below for details). To get the energy density, the laser beam spot diameter must be known. There are different techniques for the estimation of the laser spot diameter, the most precise is the knife-edge method (Skinner and Whitcher, 1972). To apply this technique, we first need to rebuild the laser path outside the vacuum chamber. This is to include in the calculations the energy lost through the different lenses and mirrors, and to characterise the laser spot diameter of the actual optic path. The laser energy estimation was performed on the first version of the optic path, used before June 2022. A razor blade is placed at the position of the focus, and a Watt-meter behind it, which measures the energy. The experiment first starts without the razor blade and thus with all the energy available. Little by little, the razor blade is moved inside the laser beam. The height of the razor blade is noted when the energy measured dropped of 10% and 90%, corresponding to the points A and B in Figure V.11, respectively. This gives the diameter that includes 80% of the total energy. From this, the size of the laser spot that includes 100% of the energy can be retrieved. Because it is not possible to be sure that the razor blade is exactly at the focus position, the experiment must be repeated several times, before and after the focus point. The razor blade is therefore placed in a two-axis holder (z for height and x to travel around the focus point) as seen in the picture of Protocol During the second campaign in Leipzig in May 2019, mass spectra from surface-interaction (i.e. on a metal wire and water ice) have been recorded. To go further, the objective of the third campaign was to measure ions from the laser-liquid interaction. We ionised the water beam with the laser at 2840 nm wavelength, producing actual LILBID ions (i.e. desorbed ions from a liquid beam). Even though the ion creation was successful, we could not efficiently focus the ion packet towards the Orbitrap cell, and thereby record a mass spectrum with the OLYMPIA set up connected to the Leipzig LILBID facility. We concluded that kinetic energy of the ions was too low to be properly captured by the Orbitrap cell. To compensate for this energy deficit, we used the second output of the Leipzig laser and lowered the wavelength to 1064 nm. By decreasing the laser wavelength, the laser energy strongly increases, going away from the desorption regime and toward harder ionisation and plasma creation. The pulse energy at 2840 nm is around 2 mJ, where the 1064 nm is expected to be around 25 mJ. This extra energy creates a much larger number of ions, with a higher kinetic energy. Most of the laser shots created a plasma when hitting the water beam. Thanks to this configuration, we could measure mass spectra with the setup. The sample used for those measurements was deionised water doped with 10 -3 M of NaCl and 10 -3 M of CsI.

Results

The results are presented in Figure V.14. We acquired 100 mass spectra of 50 ms each, and the mass spectrum presented here is an averaged (with averaging method, see Chapter II. Section 3.2.8) of 74 mass spectra, selected with a minimum amplitude threshold (0.3 mV) to avoid including blank mass spectra in the averaging. As seen in Figure V.14, water species, O + , OH + , H 2 O + and H 3 O + , are detected. Even though the concentration of Na + , Cs + and I + is quite low relatively to OLYMPIA limit of detection, those species are also detected. At m/z 37, the (H 2 O)H 3 O + water cluster ion can be seen. The laser wavelength modification changed the energy available for ionisation, but also the final spectral appearance of the measurements. For this reason, even if water molecules and clusters are detected, the creation of plasma during ionisation makes the results not applicable for our science application, as only the desorption regime is analogous to impact ionisation in the desired velocity range.

FU Berlin Tin Experiments

The thesis will now turn to the FU Berlin and to the newly assembled LILBID-OLYMPIA setup. The first steps towards the laser-liquid interaction in Berlin were dedicated to the control of the alignment between the electrodes in the source and the Orbitrap cell. As mentioned, the laser-surface interaction produces many more ions and is more stable than the laser-liquid configuration. Ionising a metal as a starting point allows to have an idea of the required potential values in the ion optics, and to control the global alignment of the setup by measuring the ions at the detector (i.e. behind the Orbitrap cell). The first preliminary experiments were made by ionising a Tin wire (a standard soldering wire with 99.98% purity). Tin has 10 stable isotopes with abundances going from 0.34% to 32.58% (see Table V.2). Using Tin as a calibration sample has the advantage to quantify the RIA (Relative Isotopic Abundance) deviation. Thanks to the use of the laser, the ionisation is no longer continuous like with the EI configuration but pulsed. The determination of the RIA deviation in pulsed ionisation configuration will allow to test the hypothesis that the oversensitivity of the EI configuration was due to the continuous ionisation and injection.

As the experiments are now realised at the FU Berlin, the only available laser wavelength is 2840 nm. The power supply trade-off for the best HV Orbitrap shown in Section 2.2 of Chapter III, leads to the conclusion that the ISEG power supply is not suitable for the Orbitrap cell specification. We therefore purchased a Thermo Fisher power supply, but because of delays in the delivery of this new module, the first measurements on the Tin wire had to be performed with the ISEG power supply. For that reason, we will not go through the performances (i.e. mass resolution, mass accuracy or RIA accuracy) of this preliminary mass spectra of the Tin sample. The pressure in the Orbitrap cell for the following measurement was the lowest ever achieved with OLYMPIA. This is due to a long pumping time as no measurements were made before those first experiments with the Tin wire. In addition, unlike the EI configuration and later the water beam measurements, no outgassing samples were used. The pressure during measurements was down to 3.10 -9 mbar.

The peak of the major isotope 120 Sn + , is shown in Figure V.15. The shape of the peak is extremely disturbed by the voltage drift of the VCE measure potential. The peak moves away from its initial value and a wide hump forms towards the heavier masses. The acquisition lasts 1 full second but the VCE potential was switched back to the injection level at 850 ms, ending the ion trapping. The signal is still present, and intense, at 850 ms. This is way longer than the results presented with the EI configuration (see Section 2.1 of Chapter III), that only lasted 50 ms with the same ISEG power supply for VCE measure . This is most likely due to the better vacuum in the Orbitrap cell for the Tin measurements.

Results with the Thermo Fisher Power Supply (HV Orbitrap )

During autumn 2021, the Thermo Fisher power supply ordered for OLYMPIA was delivered. Supplying the VCE measure level, the high stability of this HV power supply allowed for long, but also high performances measurements. I could perform a second set of Tin metallic sample, this time with the expected performances. Figure V.17 shows a zoom on the major isotope 120 Sn + and 112 Sn + (0.97% abundance) for an averaged mass spectrum with 500 ms FFT duration. Ions can be detected throughout the whole acquisition, and the mass resolution of 120 Sn + reaches 76 000 m/ ∆m. The SNR can reach values about 10 times higher than for the EI configuration for ions with the same abundance. The mass accuracy of all isotopes is better than 3 ppm. Noteworthy, the peak foot of 120 Sn + is abnormally large. This is due to a peak duplication that can occur with long FFT duration. This effect is mitigated by the averaging, but is visible on single mass spectrum. The peak duplication will be further discussed hereafter. With the laser surface interaction on the Tin sample, the setup is able to reach really high performances. The achieved mass resolution is at 97% of the theoretical mass resolution (~79 000 m/ ∆m at mass 120 with apodisation, and 500 ms FFT duration). This configuration is not relevant to simulate impact ionisation of CDA and SUDA mass spectra, but with the high-quality data recorded due to optimal hardware, it demonstrates a successful mechanical coupling of OLYMPIA to LILBID.

Relative Isotopic Abundance With the setup recording high quality data, the deviation from the Relative Isotopic Abundance (RIA) could be performed. The method used for the ion count calculation and comparison has been presented in the Section 3.2.8 of Chapter II. Because pressure effects and imperfections inside the cell can affect the ions over time, the accuracy of the RIA is theoretically better on short acquisition time. The study has therefore been applied on 50 ms FFT, but is also shown for 250 ms. The ppm exclusion filter is extended to 30 ppm for 250 ms FFT duration because secondary peaks at around 25 ppm can built through time. This specific pattern will be discussed in the following section. The deviation from the theoretical values for each isotope are displayed in Table V.3. For the 50 ms FFT mass spectra, excluding the isotopes with less than 1% abundance, the error is usually below -5%, with a 1-sigma error around ± 2%. The error for low abundant ions is higher, around -20%. The errors for the mass spectra with 250 ms are also quite low, staying roughly below +7%. The increase in the 1-sigma interval compared to the 50 ms FFT mass spectra highlights the degradation of the data over time.

Noteworthy, the mass resolution of each isotope shows only little variations, the amplitudes are therefore a good ion count indicator. This is noticeable in the mass spectrum shown in Figure V.18, on which the normalisation is made on the raw amplitude of 120 Sn + . All isotope amplitudes are close to the theoretical and the errors are in the same range as with the area under the curve method.

Discussions & Conclusions of the Tin Experiments

Ion lifetime under an Unstable Electrostatic Field Acquisitions with the ISEG power supply for VCE measure have been performed with the Tin sample. The lifetime of ions is much larger than with the EI configuration. As seen on Figure V.16, some ions can be detected up to 850 ms where for the EI configuration ions could only last 50 ms (Figure III.3). It was difficult to determine the cause of the short ion lifetime for the EI measurements, as they were performed at high pressure and with an unstable electrostatic field. Thanks to the Tin measurements carried out at low pressure, it is now possible to conclude that variable electrostatic field does not necessarily lead to a short ion lifetime, and that this is rather related to the high pressure.

Mass Resolution When comparing the mass resolution achieved with the Thermo Fisher power supply for VCE measure and that of the EI configuration for the same lifetime, the Tin results are much closer to the maximum achievable. As a reminder, the EI measurements could reach 85% of the theoretical mass resolution (Figure IV.5) where the Tin mass spectra reached 97% (Figure V.17). In addition, only the major isotope of Krypton could reach the 85%, the others dropping at 70%. The Tin isotopes for comparison are all measured with similar mass resolution, above 95%. The performances of the setup are much higher with the low pressure and pulsed injection configuration.

Accuracy of the RIA The estimation of OLYMPIA's accuracy RIA with Krypton isotopes have been undertaken with the EI configuration and showed errors in the range of tens of percent (Table IV.2). In addition, an over- sensitivity effect of low abundant ions with an important overestimation was observed and has been attributed to poor ion bulk definition and trapping conditions. The Tin isotopic measurements presented hereabove are much more precise and are in the range of 2 to 3% for averaged mass spectra. This particularly highlights the better quantification power of the OLYMPIA new configuration. Regarding the low abundant ions overestimation, the Tin mass spectra do not show this effect, but rather the opposite. The three Tin low abundant isotopes show an underestimation of about -20%. This is however expected, as the minor isotopes are less stable in the trap than the major ones. Indeed, the faster transient decay of minor ions is a known effect in Orbitrap cells and has been explained by Hofmann et al. (2020). Basically, ions are oscillating in a space in which other ions are oscillating at other frequencies. The space charge effects induced by major isotopes on minor is stronger than the reciprocal, leading to a destabilisation and premature loss of low abundant ions.

Both mass resolution and RIA accuracy strongly improved compared to EI measurements. The two major changes between the set of experiments are the pressure, roughly ten times lower for the Tin measurements, and the injection, which is pulsed and not continuous as it was for the EI study. As two variables have changed, it is not possible to discriminate which had the larger impact on the results. The next section will present the water beam measurement, performed at high pressure but with a pulsed ionisation. This configuration will allow to isolate the parameters responsible for the poor RIA accuracy or the relative deficit of mass resolution.

LILBID-OLYMPIA

With the Tin study, it is now certain that the mechanical integration and alignment of OLYMPIA has been successful. Not only do the ions reach the detector behind the Orbitrap cell, but the signals detected in it are of far better quality than with the EI configuration. The ion injection is now pulsed, which increases the stability of the ions during measurements. The Tin study has also been useful to make a first calibration of the ion optics potentials as well as the Orbitrap power supplies stability, and finally the TTL timings and controls.

That being done, the study on the water beam could begin. The starting points are the data obtained in Leipzig in 2019 (see Section 3), even though no ions from a desorption regime could be measured, as the experiments were performed with a laser wavelength of 1064 nm.

Ions Behaviour

Because the laser in Berlin is only equipped with the 2700 -3100 nm wavelength output, I directly went for the desorption regime, and 2840 nm laser wavelength to ionise the water beam. Compared to the Tin wire, the water beam is much thinner, which makes the alignment procedure more challenging. The alignment is done by optimising the ion signal, either on ion optics electrodes, or on the detector placed behind the Orbitrap cell, when the ions are going through the whole optics.

Once the water beam is roughly aligned, the tuning of the HV optics can begin. With the experiences of the Leipzig campaign, a potential higher than the regular ~1 kV in the source seems to be useful for water ions. I therefore explored higher potentials (~1.8 kV), while measuring on EL4, the first electrode of the ion optics. With high potentials, the ion signal was quite intense and I could easily focus the ion bulk on the detector. From there, the alignment can be reoptimised with the detector signal, as well as the HV optics .

The next step is to define the kinetic energy of the ion bulk, which is challenging. With the source at 1.8 kV, the KE must be lowered along the way. Quickly, I noticed that there are two kinds of ions that reach the detector. The first one is easy to obtain, quite intense and seems to be stronger with higher potentials. This bulk is actually not sensitive to the ion optics voltages and can still go through when a few hundred volts are applied on the deflective electrodes, or 2 kV on circular electrodes. Because the KE is too high, those ions cannot be measured by the Orbitrap cell, and they go through its apertures even when the -3.5 kV are applied on it. The second bulk, on the other hand, is sensitive to the variations in the HV optics . Because the first bulk is more intense, it is actually not always possible to discriminate sensitive ions from high-energetic ions, making their optimisation difficult. As explained in Chapter II, if one electrode is wrongly tuned, the whole bunch is lost. With the LILBID ions, the insensitive ions also prevent from assessing the behaviour of the sensitive ions. However, with the proper settings, it is sometimes possible to see this bulk and to reoptimise the optics accordingly. Figure V. 19 shows the signal measured on the detector and the different HV optics applied on the electrodes. Among the gap that is created by the ion signal, both ion bulks are mixed.

Results

Finally, after a long period of optimising the instruments parameters, I succeeded in measuring ions desorbed from the liquid water beam with OLYMPIA's Orbitrap cell. The results in this section are the first mass spectra of a LILBID-Orbitrap combination, and therefore the first high mass resolution mass spectra of LILBID ions. The results have been recorded with the HV optics values shown in Figure V.19, when both sensitive and insensitive ions bulks were measurable. The Thermo Fisher power supply is used for VCE measure . Noteworthy, the pressure in the Orbitrap cell during water measurements is usually settling in the range of 4.10 -8 mbar. Along the day, the vacuum is deteriorating due to the outgassing of more and more water samples. Should the start-up be done quickly (i.e. the laser and water beam alignment) and the ionisation efficient, the best achievable pressure would be around 9.10 -9 mbar. + ions can still be detected at around 300 ms, whereas H 2 O + fades into the noise shortly after 150 ms. The SNR is however for short time slices (20 ms), if the data are processed for 500 ms, the performance can still slightly increase, pointing at the presence of some ions. The signal is however too faint and too disturbed to be usable. As usual with a Fourier Transform mass analyser, the mass resolution is much higher with long acquisition time, reaching 126 000 m/Δm for H 3 O + . However, with the increasing FFT duration, a secondary peak can be observed in both plots. The secondary peak of H 2 O + actually becomes more intense than the real peak, after around 100 ms. The H 3 O + secondary peak is at around the main peak half maximum. Both peaks grow at the same distance from the original peak, corresponding to a frequency difference of about 23 Hz. Additional experiments have been made with a lower laser energy, as it is the main parameter influencing the ionisation. So I tried to decrease it and to detect water clusters, but this only resulted in a decrease of the H 3 O + and H 2 O + amplitudes.

Conclusion of the Water Beam Experiments

Analogue Velocities If we now compare the results obtained with the 1064 nm wavelength in Leipzig (Subsection 3) and the results in Berlin at 2840 nm, the major species in Leipzig was not H 3 O + but H 2 O + , and peaks of O + , OH + or O 2 + were detected. The mass spectra at 2840 nm are clearly from a different ionisation regime, with a major abundance of H 3 O + and a smaller H 2 O + one. Rarely, and probably with a perfectly optimised laser path, some peaks of OH + could be measured. This highlights the fact that the mass spectra recorded and presented in this section are originating from a desorption regime.

As shown in Klenner et al. (2019) the LILBID measurements can be translated to impact velocities of spaceborne icy grains onto metal targets. By comparing the recorded LILBID-OLYMPIA mass spectra with the LILBID-TOF mass spectra, the spectral appearances match those of ice grains at impact speeds of 15 -18 km/s, in a regime where neither water clusters nor plasma species (i.e. O + or OH + ) are detected. This is consistent with the laser energy measured for OLYMPIA, slightly lower than the maximum of the LILBID-TOF measurements.

The coupling of OLYMPIA to Berlin's LILBID setup has been successful, and for the first time, desorbed water ions could be measured with high mass resolution. The new LILBID-OLYMPIA combination is a unique setup, and with the detection of H 3 O + and H 2 O + , proved its ability to reproduce a specific range of impact ionisation mass spectra with a mass resolution a hundred times greater than what was previously achieved. These results have been published in Analytical Chemistry [START_REF] Sanderink | OLYMPIA-LILBID: A New Laboratory Setup to Calibrate Spaceborne Hypervelocity Ice Grain Detectors Using High-Resolution Mass Spectrometry[END_REF]. They were presented at the 2021 AGU Fall meeting in New Orleans [START_REF] Sanderink | A New Approach for Calibrating Spaceborne Hypervelocity Ice Grain Detectors Using High-Resolution Mass Spectrometry[END_REF] and at the EPSC in 2022 [START_REF] Sanderink | High Resolution Mass Spectrometry for the Calibration of Spaceborne Hypervelocity Ice Grain Detector[END_REF]. The work achieved until now is an important first step towards the calibration of a wide range of analogue impact velocities. The objective is now to be able to control this analogous impact velocity, and to decrease it to values closer to the 4 -5 km/s expected with the upcoming Europa Clipper mission and the SUDA measurements.

6. THE QUEST FOR WATER CLUSTERS CHAPTER V. LILBID-OLYMPIA 6 The Quest for Water Clusters Lower impact velocities are especially interesting because they allow the detection of unfragmented heavier species, like organic materials (Klenner et al., 2020a;[START_REF] Cable | Plume Grain Sampling at Hypervelocity: Implications for Astrobiology Investigations[END_REF][START_REF] Jaramillo-Botero | Understanding Hypervelocity Sampling of Biosignatures in Space Missions[END_REF]. The emphasis here is put on water clusters because they are markers of these low impact velocities. However, the real features of interest are the chemicals contained in the liquid or ice water sample. With the achievement of the detection of small water ions (i.e. H 3 O + and H 2 O + ), the next step was focused on the detection of heavier water cluster ions detection (37 u, 55 u, 73 u and more) and to be able to control the spectral appearance of the measurements. Paving then the way to measuring more complex samples, such as organics.

Two parameters play a role in the spectral appearances, the laser energy and the delayed extraction (see Section 1 of this chapter). The laser energy is easy to vary, but apart from a decrease in the peaks SNR, no change in the spectral appearance was observed. OLYMPIA's LILBID ion source is different from the standard LILBID source used with a TOF mass analyser, as an electrostatic field is constantly applied in it. With such settings, a delayed extraction is by definition not possible.

The lack of detection of the heaviest clusters raised many questions, that could be separated into two categories, (1) are the water clusters forming at all in the source, and (2) are they formed but not measured by the Orbitrap cell. First, we investigated the water clusters formation.

Investigating the Effects of an Electrostatic Field in LILBID-TOF Source

The LILBID-TOF source features a region where the ions drift freely before being accelerated. The ions fly freely over around three centimetres before reaching the extracting region. With the continuous field applied in OLYMPIA source, and the resulting constant acceleration of ions, the process is quite different. The acceleration at the time of the ionisation in the LILBID-OLYMPIA configuration could prevent the water cluster formation. In addition, even if the water clusters are formed in the source with an HV source potential, they might not be able to reach the cell. Because the water beam is constantly outgassing, the vacuum in its close vicinity is poor. Where the LILBID-TOF ion cloud expands in a field free region, OLYMPIA's cloud is directly pushed into the Skimmer, creating a denser volume. The denser ion cloud, combined with the relatively high pressure due to the outgassing water, could result in a volume where collisions are more frequent. The bond created between H 3 O + and H 2 O may not be able to withstand this higher intermolecular collision rate, and clusters would therefore not be detectable.

To test those hypotheses, we needed to learn more about the water clusters physical behaviour, and how they are impacted by the electrostatic field in the LILBID-TOF source. We mounted OLYMPIA's metal nozzle (Right picture of Figure V.7) in front on the TOF Skimmer. By adding an electrical feedthrough to the setup, a potential can be applied in the LILBID-TOF source, and the effect of the HV source on the clusters can be assessed.

Noteworthy, in contrast to OLYMPIA, there is no HV potential on the TOF Skimmer and no electrode that pushes the ions into the TOF, (i.e. OLYMPIA's Repeller).

Protocol

To mimic OLYMPIA's configuration, we also used deionised pure water and full laser energy. To characterise the water clusters behaviour, we first set a standard extraction delay time (6.5 μs) and gradually increase the HV source applied on the nozzle, from 0 to 1 800 V. To assess the effect of the delayed extraction, we then changed the delay from 0.5 μs to 10.5 μs. We also measured mass spectra at different laser energies for a fixed HV source and delay time value.

Results

HV source Effects Figure V.24 presents the different results with an increasing voltage on the water beam, for a constant delay time of 6.5 μs. The mass spectrum at 0 V shows numerous water clusters with a Gaussian distribution, centred on the third cluster at 73 u. When applying a potential, the behaviour of the ions is strongly influenced by the HV source . At 100 V, the mass range is nearly twice that of the grounded source. Heavier water clusters are measured, and the Gaussian centre is also shifted, peaking around the seventh water cluster at 127 u. This effect is already observable with only 20 V on the Jet. By further increasing the potential of the Jet, the amplitude distribution is changed. Starting at ~250 V, lighter ions such as H 3 O + and later H 2 O + become dominant. Above 500 V, the water clusters are still measurable, but their respective amplitudes are flattened, and the Gaussian distribution no longer observable. The SNR is also reduced for the clusters. Above 1500 V, H 2 O + is exceeding H 3 O + amplitude, which is never observed with a grounded source. Intermediate steps in the HV source potentials (at 20, 50, 250 and 1500 V) have also been measured. Delay at High HV source To better characterise the role of the delayed extraction and the ions behaviour at a high HV source value (in the range of the one applied in OLYMPIA's source), we then fixed the potential to 1 000 V and varied the delay time to lower values. Noteworthy, with the standard grounded LILBID-TOF ion source, no ions can be measured with a delay time lower than 3 μs. Figure V.25 shows different delay times with a fixed potential of 1 000 V. Shortening the delay time led to the loss of heavier masses by simply lowering the mass range, without significantly changing the relative peaks amplitude. At a very low delay time (i.e. 0.5 μs) water clusters are no longer detectable. The mass spectrum is very similar to the measured OLYMPIA's mass spectra obtained when operating with LILBID, with mainly H 3 O + and H 2 O + . The amplitude of both peaks is in the same range, with H 3 O + from two to three times higher than H 2 O + . At high delay time (10.5 μs), the amplitude of all peaks decreased, and masses above 150 m/z are no longer measurable.

Laser Energy at High HV source Measurements have also been performed at 1 000 V and 6.5 μs delay time for different laser energies. The decrease of the energy does not change the flattened distribution for the cluster. From 100 to 90% energy, the only noticeable feature is the reduction of the SNR. At even lower values (88 and 85%, see Figure V.26), the mass range starts to be reduced and heavier water clusters are no longer detected, because all amplitudes have decreased significantly and the weaker ones fall into the noise level.

Discussions

Water Clusters Formation At least one question is quickly answered : a high HV source value does not prevent the water clusters formation, neither do they need a field free drift region. Their amplitudes distribution is strongly affected, but even with 1.8 kV on the nozzle, heavy water clusters can be detected with the TOF mass analyser. We however observe two different regimes depending on the potential applied. At low HV source (< 250 V), the ions species show a distribution as expected with a desorption ionisation, as characterised in Klenner et al. (2019). No H 2 O + peaks are detected, and the peaks with the highest amplitudes are water clusters. By rising the potential at the source, the kinetic energy of the ions is larger than with a grounded source. The ion cloud is therefore denser, and with a single acceleration a wider range of masses can be accelerated. As seen at 100 V, the amplitudes are generally higher, indicating that more ions are measured, and thus focused from the water beam into the acceleration region.

At higher HV source values (above 500 V), the ions behave differently. As all the water clusters have the same amplitude here, it seems that the m/z distribution in the ion cloud is more homogeneous, as the mass of its ions becomes less relevant in the acceleration process. The clusters velocity might be so high, that for any sufficient For classical LILBID-TOF measurements with a grounded source, a high delay time (> 5 μs) shifts the maximum amplitudes to higher masses. With even longer delays (> 8 μs), light ions are no longer detected, as they already went through the acceleration region when the HV of the two acceleration electrodes is switched. However, with 1 000 V applied at the source, no shift is observable when increasing the delay time to high values, just an overall decrease of the amplitudes without favouring a specific mass range (Figure V.25 upper left panel). This also indicates that the m/z distribution in the ion cloud is more homogeneous, and that most of it already went through the acceleration region at the time of the switch (noteworthy ; in Figure V.25 a tiny peak of heavy water clusters (up to n = 12) can still be detected at 10.5 μs).

However, the early part of the ion cloud is not homogeneous. With shorter delay time, the mass range decreases and heavier water clusters are no longer detected. This indicates that the cloud becomes homogeneous after a certain delay time (> 4.5 μs). Other experiments have been performed with high delay time (7 -9 μs) for lower HV source (250 V). This shifts the moment where the m/z distribution in the ion cloud becomes more homogeneous towards longer delay times, to about 8 μs.

Water Cluster Detection If we now focus on OLYMPIA's settings : the standard potential in the source is around 1 000 V (even though mass spectra have been measured with a potential of up to 1 800 V). At such high voltage, the late part of the ion cloud should have a flat cluster distribution. The strong resemblance of LILBID-OLYMPIA's results with LILBID-TOF mass spectra recorded at 0.5 μs delay, seems to indicate that a delay time is mandatory to accelerate heavy ions. However, it is more likely that there is an issue with the kinetic energy, the delay time just being a consequence of the clusters low KE. They are not detected on the TOF at 0.5 μs because they could not reach the acceleration region yet. OLYMPIA features a continuous acceleration in its source, therefore the water clusters ions, that, as just shown, are indeed created, should be accelerated at the same time as H 3 O + and H 2 O + . My hypothesis is that the reason why they are not detected is their intrinsic lower KE. Because the clusters are secondary produced (they first need H 3 O + molecules coming from the laser shot) their KE is lower than the direct ionisation products (i.e. H 3 O + and H 2 O + ). The Orbitrap cell is only able to capture ions with a specific KE. If the energy is too high, the ions would go through the cell unaffected by its field, or collide in the outer electrodes. With a too low KE and the ion trajectory too much bended by the cell electrostatic field, they directly collide in the central electrode. This probably explains the current lack of detection of water clusters, if they reach the cell at all.

But why was there a successful water cluster detection with the 1064 nm wavelength during the campaign in Leipzig (Figure V.14) ? Due to the lower wavelength, the laser energy was much higher than the current one (~5 times), and the potential in the source was 1 500 V. Such high values could have given the first water cluster enough KE to be measured by the Orbitrap cell. This hypothesis could be tested with the LILBID-TOF. By using an increased energy given by both a potential of > 1 000 V in the source, and a wavelength of 1064 nm, the energy available would be much higher. This could allow a detection of the first cluster with a very short delay time (~0.5 μs).

One last factor that could prevent the water cluster detection is the low sensitivity of OLYMPIA. The clusters could be trapped in the cell but with an insufficient SNR. On the HV source TOF measurement at 1 000 V, the amplitude of (H 2 O)H 3 O + is less than 10 times lower than H 3 O + . On the LILBID-OLYMPIA results presented in the previous section, the H 3 O + SNR on averaged mass spectra is in the range of 100, the first water cluster is therefore expected to be detectable. Thus, we can discard low sensitivity as a reason for the non-detection of clusters.

LILBID-TOF Improvements from the HV source Study

The described measurements with the HV applied on the source were made to better understand the reason why clusters were so difficult to measure with LILBID-OLYMPIA. However, the results also turned out to be interesting for the LILBID-TOF configuration. To simulate low velocities mass spectra and to obtain the plots in Figure V.3 (and central panel of Figure V.27), an addition of mass spectra with different parameters must be done. However, changing parameters during measurements can induce biases. In addition, some samples can be available in very few quantities, and the capability of faster acquisitions times can be an asset. As presented, applying a potential in the TOF source significantly changes the appearance of the mass spectra. With the proper HV source and delay settings, the appearance of a mass spectrum can be very similar to the grounded source co-added mass spectra (right panel of Figure V.27), and by extension CDA/SUDA mass spectra. By contrast to previous approaches (Klenner et al., 2019) this can now be achieved with a single set of parameters. The mass range of a single acquisition with the TOF is also limited (up to n = 7, as shown in the top panel of Figure V.24). The mass range with HV on the nozzle is much higher (at least up to n > 20 in Figure V.27), allowing a study of both light and heavy species with a single acquisition.

The metal nozzle and the HV in the LILBID source could be used to improve the setup and ease the measurements for the SUDA calibration. But as mentioned in Chapter 1, the LILBID technique is also used in a wide range of application including biochemistry and medical diagnoses. All applications could benefit from such an improvement. Only a short amount of times has been dedicated to HV measurements with the TOF, and this would require further work to better characterise the various effects on the mass spectra. We intend to present those results in a publication. Only one set of parameters was used to record this mass spectrum, 500 V was applied in the source.

Adaptation for Clusters

With the certitude that an electrostatic field in the source does not prevent the water cluster formation, and the knowledge of how it affects their distribution, we can now think of further improvements of the LILBID-OLYMPIA configuration to measure the water clusters.

Source Electrostatic Field

The most probable explanation for the absence of water cluster is their insufficient KE. A simple approach would be to raise the potential in the source to higher values, and better accelerate the water clusters. However, although the water clusters detection would be a significant step forward, their relevance to impact ionisation lies in their characteristic distribution. Measuring water cluster with a flat distribution would not be applicable for our science objective. For that reason, it seems that the HV source should be suppressed, or at least reduced to a point where the water clusters still have the typical distribution (Figure V.27).

Delayed Extraction

Increasing the source potential to higher values is not an option, but a way must still be found to accelerate the clusters to the right KE. One solution would be to use the same principle as the TOF, with a delayed extraction. By adding this feature, it would theoretically be possible to accelerate the water clusters after their formation and spatial separation, thus ensuring their relevance for impact ionisation. With a successful handle of the delayed extraction, if HV is still applied in the source, then by increasing the delay time we should still be able to see a time-of-flight effect before acceleration, like in the right panel of Figure V.27 where 500 V was applied.

To perform a delayed extraction, the potential must be switched after the ionisation. To be as close as possible to the operational source of the LILBID-TOF, the idea is to use OLYMPIA's skimmer and/or focus electrodes (Figure V.8) as accelerator. In a grounded source, the ions created at the water beam would fly freely through the skimmer, and if the HV of the electrodes is switched on at the right time, then the ion cloud should be properly accelerated.

Hardware The performance requirements for OLYMPIA HV and switch are mainly constrained by the Orbitrap cell. The rise time of the Thermo Fisher switch is set at around 100 μs, it is therefore not possible to use this switch for the source because the ion bulk time range is only a few microseconds in total. I was also limited by the CGC switch, which only has a maximum commutation amplitude of 1.5 kV. To use a switch that fits our short time window, I dismounted the switch of the laboratory old TOFMS (HTS 121-03, Behlke) and connected it with LILBID-OLYMPIA's skimmer and focus. Coupled with the old TOFMS power supply, the rise time is only 100 ns, which is low enough to accelerate a defined ion bulk.

A common way to perform a delayed extraction is to place a tube-shaped electrode and to switch its potential. At the time of the switch, all the ions inside the tube will be impacted by the electrostatic field and be accelerated at its output. We 3D-printed a tube electrode that we coated with a conductive layer and placed inside the Focus electrode (Figure V.28).

Ions Behaviour with the New Source Settings

Once the adaption just presented was made, I could once again try to detect the water clusters, but this time with 0 V applied around the water beam (that is the repeller, jet and skimmer electrodes). The HV on the focus electrode is now switched after a few μs.

Laser-surface The first tests were carried out with laser-surface interaction by shooting directly on the stainless steel nozzle. The ion focus on the detector, even without HV source was relatively simple to obtain. The ions could also be measured with the Orbitrap cell. This was a positive outcome. In theory, fewer ions go through the aperture and reach the cell without the repeller (used to push ions inside the skimmer) or a negative potential on the skimmer to attract ions. The signal could have been too low to be measured. This configuration works fine for the LILBID-TOF configuration, however the Orbitrap cell needs more ions for proper measurements.

The new settings allowed a much better definition of the KE. The insensitive ion bulk that was created before was no longer observable and each electrodes could affect the ion bulk. This better definition actually compensates for the decrease in total ion count, one single mass spectrum could be measured with a SNR of 6 000, which is the highest ever recorded with OLYMPIA, all ion sources considered. This of course also increases the sensitivity of OLYMPIA for trace compounds.

This represents a significant achievement. However, it seems that the ions are not really impacted by the HV commutation of the focus electrode, but more by a continuous potential applied on it. Indeed, the same results were obtained with a switch on the focus before the laser shot.

Laser-liquid When shooting on the water beam, the ions behave quite differently compared to the Laser-surface behaviour just presented. First of all, the total number of ions created is, as usual, much lower, which makes the first detection on the ion optics tedious. Secondly, the ions are no longer reactive to the focus electrode. This could be because too few ions go naturally through the skimmer aperture.

Because the ions were not visible with a commutation on the focus electrode, I tried to switch the skimmer. The skimmer strongly affects the water ions, but again it seems that a continuous applied voltage is more efficient than a commutation after a certain delay time.

I tried many different HV source configurations ; switching the skimmer, switching the focus or switching both electrodes like on the TOF. This with numerous voltages values and associated delay times, but nothing could be detected, even on the first electrode of OLYMPIA's ion optic (EL4).

Because of this, I tried to raise the potential on the Jet to low values (< 500 V) while keeping the Repeller at 0 V, as its effect on the bulk could not be assessed on the TOF. The idea with those settings is to be able to measure water clusters, even if they do not have the proper distribution. A sensitive ion bulk could be created, however only measured by the detector and not the Orbitrap cell. In that case, the best explanation would be a poorly defined kinetic energy for the ions. Further work is needed to better constrain the ion bulk KE.

LILBID-OLYMPIA Conclusion & Perspectives

The ultimate objective of this work is to be able to record impact ionisation analogue mass spectra mimicking low to moderate impact velocities (3 -15 km/s). At the moment, only high velocities (15 -18 km/s) analogue mass spectra could be recorded. The next step now is the ability to detect water clusters, markers of such lower impact velocities. The detection of the first water cluster could be performed in Leipzig with a 1064 nm wavelength (Figure V.14). However, based on the experiences realised with high voltage applied on the LILBID-TOF jet, we now know that with the parameters at that time, the mass spectra do not feature an ion distribution analogous to that of impact ionisation. The effect of the electrostatic field on the clusters before their acceleration is now understood, and it is not inconsistent with an analogous distribution. Nevertheless, the parameters must be effectively controlled to be in the right regime. Thus, delayed extraction seems to be a mandatory step to obtain the proper distribution. Some design modifications have been implemented to comply with this new information, with for example the addition of the tube-shaped electrode and the switching of its potential after ionisation. This was however not successful. Nevertheless, before placing the new tube-shaped electrodes inside the focus electrode, I did not have the possibility to switch both electrodes due to limitations of the switch and power supplies. For the time being, with the tube in place, the acceleration method is still different from the TOF. In addition, the skimmer is actually not designed to be used as an electrode with a high voltage applied to it. Its primary function is to create a differential vacuum, and because of its shape it cannot create the homogeneous electrostatic field that the ions would need for proper acceleration. This leads to a new test that requires another design modification. The idea is to fully mimic the TOF ion optics, with a skimmer for pressure issues, and then two different flat electrodes switched at the same time. With a higher potential on the first electrode than on the second, the ions will be accelerated towards the Orbitrap cell. Therefore, the KE can be controlled by the voltage applied on those two electrodes, and then on the way to the Orbitrap cell by the ion optics. Figure V.29 presents a 3D model of this new design. The spacing between the two electrodes is the same as for the TOF source, 20mm. This is an arbitrary value : on the TOF the kinetic energy of ions is much higher than what the Orbitrap cell can measure, with two acceleration electrodes switched to ~5 kV. With lower potential values, the proper spacing for the two electrodes could be different. This new ion optics have not been yet tested, and the following step is to make a new plastic holder for those two electrodes, and to try again to measure water clusters. This new design is based on a trial-and-error strategy. To be able to better understand the ions behaviour with our current design, or to better constrain a future one, the ion source could also be simulated using SIMION software.

There is another possibility to detect water cluster with LILBID ionisation coupled to an Orbitrap-based mass analyser. The main identified problem for the absence of cluster detection is an insufficient kinetic energy of the ions, which could for now only be circumvented by increasing the laser energy, but with that leaving the desorption regime for the ablation regime (during the Leipzig campaign, see Section 3). The kinetic energy definition issue was first faced by Alexander Makarov when he developed the Orbitrap™ prototype. The solution was to create the C-trap module (Hu et al., 2005) to precisely define the ion bulk shape and kinetic energy. The absence of the C-trap module on OLYMPIA is due to the requirements of future space development. However the current science objective of creating a high-resolution database for SUDA does not require such a constraint. Adding a C-trap module might be a way to solve the kinetic energy issues and allow to match the spectral appearance of impact ionisation.

Aside from the water cluster handling, the LILBID-OLYMPIA apparatus is a new worldwide unique prototype, and even though functional to the first order, its start-up can be tedious and some design improvement should be performed to make the setup even more reliable and easy to operate. To perfectly align the water beam with the skimmer, the LILBID-TOF is equipped with a camera. By contrast, with LILBID-OLYMPIA, the alignment has to be done by eye and only small windows allow to see the nozzle inside the vacuum chamber. The main issue is that only a view from 45°above the source is possible, and therefore if the water beam is close to the skimmer, as it should be for a optimal focus of the ions, it is no longer possible to see it. A new flange that allows to observe with a better angle would greatly ease the alignment and make it more reproducible. Still in the ionisation chamber, the whole ion source optics is mounted on a PEEK support that is fixed to the valve used to separate the ionisation chamber to OLYMPIA. Because of this, the whole source optics is moving with the valve. The LILBID-TOF skimmer is in a fixed position, and the valve is moving independently behind it. An identical design on LILBID-OLYMPIA would help to leave the water beam in front of the skimmer at all time. This would ensure that the alignment remains in place, and avoid possible errors during start-up.

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Multi-Ionisation Results Comparison

The greatest asset of OLYMPIA lies in its capability to be easily adaptable to different ionisation techniques. During this work, mass spectra from gaseous, solid and liquid compounds have been measured, with the high mass resolution expected from an Orbitrap-based mass spectrometer. The first mass spectra with OLYMPIA were obtained in 2019. As is often the case, the specifics of a newly built custom instrument can be difficult to assess and manage. Having the opportunity to characterise OLYMPIA's performances with three different ionisations techniques greatly helped the understanding of the setup, and opened several perspectives.

The results of each ionisation method can help to address the questions that were left unanswered, as they could not be concluded during the optimisation phases of each single configuration.

Discrimination Between Pressure Effects and Continuous Injection

Thanks to the measurements acquired with both continuous and pulsed injection at different pressure it is possible to differentiate between the effects of high pressure and continuous ion injection. The EI study was performed in continuous injection mode with a relatively high pressure in the Orbitrap cell (1.10 -8 mbar) and a continuous injection. For the pulsed injection, the Tin study was performed at low pressure (3.10 -9 mbar), and the LILBID study was a bit higher than for the EI (4.10 -8 mbar for the D 2 O measurements). The maximum ion lifetime, the differences from the theoretical mass resolution and the RIA deviation have been determined for each configuration. The results are shown in Table VI

Ion Lifetime

The Tin ions could be measured up to 850 ms, even with the unstable ISEG power supply (Figure V.16). No measurements with longer duration were carried out. However, given the high intensity still present at the end of the measurement the ions could have survived even longer. The LILBID ions, and more especially H 3 O + , can last up to 300 ms in the trap (Figure V.21). The last ion detection for Krypton with the EI was around 500 ms (Figure IV.4). Those three lifetime values show that the pressure has a major impact on the lifetime of ions. This is of course expected, as the ions are disturbed by the neutral background. The lifetime of ions seems to be linearly decreasing with increasing pressure. An interesting fact is that the continuous injection does not seem to significantly impact the lifetime of ions in the cell.

The mass resolution linked to the ion lifetime is an interesting parameter that gives information about the stability of the remaining ions. Figure VI.1 shows the mass resolution through time for the three samples. From the figure, it is clear that the Tin ions are the most stable ones, and this for all the isotopes. For Krypton, only the major isotope is reaching the 85% of the theoretical value, the others dropping to 60% at 500 ms. The water ions are even more disturbed, only reaching 55% of the theoretical maximum. As expected, the mass resolution decreases with increasing pressure, but no noticeable impact of the continuous injection is observed when compared to the pulsed injection. However, the pressure is not the only parameter that plays a role for the mass resolution. The peak duplication observed on the Tin and water mass spectra (Figure V.22) was not observed with Krypton. Due to the use of different power supplies for VDE, the electrostatic field might be more disturbed for the Tin and Water measurements, and this could hide the benefits of the pulsed injection. Further work is needed to better define the electrostatic field for water measurements. If the mass resolution was then larger than for Krypton measurements but with a higher pressure, the continuous injection effects might become visible. Another test would be to degrade the pressure of Tin measurements, and to analyse the ions behaviour under such conditions. That way, at the same pressure, the continuous injection effects could also be assessed.

Higher pressure also intensifies the effects of the VCE measure HV drift. The Tin mass spectra with a 850 ms FFT duration were recorded with the ISEG power supply for both Orbitrap cell electrodes (VCE and VDE) and the drift of the ion frequency could be followed throughout the entire acquisition (creating the wide hump in the peak of

Relative Isotope Abundances

Isotopic abundances measurements were also performed with each ionisation technique. The EI study showed an oversensitivity for low abundant species, and RIA errors are in the range of several tens of percent, indicating an underestimation of the major Krypton isotope. For the Tin and the D 2 O measurements, the RIA errors were significantly lower. The Tin low abundant isotopes were even underestimated (by about -20%). The detection and quantification of DH 2 O + was made at a pressure higher than for the EI measurements. Despite this, the peak amplitude were in the range of what was expected from the concentrations, with a mere 1% of difference. This points out that the oversensitivity/lack of amplitude for the calibrant is indeed due to the continuous injection. That would confirm the idea that ions injected throughout the measurement are destabilising the Krypton major isotope ion ring, leading to its amplitude underestimation.

To better confirm the greater RIA capacity with pulsed injection at high pressure, a reliable quantification with concentration from the detection limit to at least 50% can be done with D 2 O mixed with H 2 O.

Peak Duplication

The origin for the peak duplication observed during Tin and water measurement is still puzzling. Such patterns have not been observed with the EI configuration, supposedly less optimal due to the continuous injection. For that reason, we needed to verify the stability over time of the new Thermo Fisher HV power supply acquired during the stay in Berlin. An extensive characterisation of the potential over time has been made. However, we faced some technical limitations to accurately record the HV delivered by the PS. Indeed, the values recorded by the HV probe were strongly fluctuating (±100 V) and had to be smoothed to access the real potential. But because of this smoothing, the information on small variations is lost and inaccessible. As in the PS trade-off made in Section 2.2 of Chapter III, we also needed to verify the performances of the Thermo Fisher switch. To confirm that both the Thermo Fisher switch and PS were behaving correctly, we made measurements with another Thermo Fisher PS and switcher. This did not change anything and the secondary peaks were still present, indicating that the VCE power supply was most likely behaving properly.

Because such patterns are the markers of disturbances in the electrostatic field inside the trap, this could also originate from the deflection electrode potential VDE. When coupled with LILBID, the deflection electrode is connected to a TOF power supply that could be not adapted to the requirements of VDE stability and commutation, which could have led to the observed peak duplication.

The conclusion of the VDE measure optimisation in Chapter III (Section 4) was that the setup was not sensitive to the variations of VDE measure potential, probably because of the continuous injection. By switching to pulsed injection, the disturbance caused by a non-optimised VDE measure could now become visible, leading to the observed peak duplication. A complete study such as the one in Chapter III but in pulsed injection could help to identify if VDE is indeed responsible for these secondary peaks, and which VDE value gives the best results.

General Conclusions & Perspectives Thesis Summary

Habitability and search for extra-terrestrial life have become cornerstones of planetary exploration. Organic molecules, composing the building blocks of life, are widespread in the Solar System and beyond. In situ instruments onboard space missions should more and more allow the detection and unequivocal identification of organic compounds in complex environments such as the icy moons of the outer Solar System. Liquid water being a prerequisite for life as we know it, ocean worlds of our Solar System are appealing bodies from an astrobiological point of view. Among these moons, Enceladus and Europa, respectively orbiting Saturn and Jupiter, are believed to harbour hydrothermal activity on their seafloors, thereby enriching their oceans with the elements essential for life. In the case of Enceladus and potentially Europa, gas, dust, and ice grains from the liquid ocean are emitted from the surface through plumes, allowing a direct access to the ocean materials from space. The characterisation of their subsurface oceans is part of the major goals of planetary exploration and therefore ocean worlds are targets of future space missions.

Laboratory experiments provide valuable support to reproduce the data with better performances than spaceborne instruments. The work described in this manuscript is supporting the development of a mass spectra database to prepare the data interpretation of the SUrface Dust Analyser, which will study the icy moon Europa onboard NASA's Europa Clipper spacecraft. This database is already fed by numerous mass spectra, which have been measured using the LILBID (Laser Induced Liquid Bead Ion Desorption) ionisation technique coupled with a TOF (Time-of-Flight) mass analyser. The acceleration of µm-sized icy grains to hypervelocity is a challenge, and therefore the LILBID technique is of great help for the composition analysis of icy grains. Even though LILBID-TOF setups reproduce in situ measurements of hypervelocity icy grains, the mass resolution is also limited and does not allow for unambiguous species identification.

To complement the spectral database with high resolution mass spectra, the aim is to couple a LILBID setup with OLYMPIA (Orbitrap anaLYser MultiPle IonisAtion), a brand new instrument composed of an Orbitrap™ mass analyser, capable of ultra high mass resolution. Several laboratories across Europe are involved in this development : the LPC2E in Orléans, the J.Heyrovský Institute of Physical Chemistry in Prague, the Freie Universität in Berlin and the IOM in Leipzig. The LPC2E and the Heyrovský Institute collaborated to build OLYMPIA, while the teams at the FU Berlin and IOM adapted the LILBID setup. The major goal of this team effort is to improve the performances of the laboratory calibration of spaceborne hypervelocity impact dust detectors, and therefore our understanding of the icy moons and their subsurface oceans.

In addition, this international collaboration also aims to pave the way for a future spaceborne mass spectrometry instrument based on the Orbitrap™, for the in situ compositional analysis of hypervelocity dust particles.

Chapter II of this thesis presented the Orbitrap™ development history and functioning, and the instrument used during the course of this work, OLYMPIA. At the beginning of my PhD in October 2019, OLYMPIA was only 1year old and the first mass spectrum was obtained only a few months before. Prior to the coupling with the LILBID setup, OLYMPIA has been coupled with an Electron Impact (EI) ion source to optimise the ion transmission to the Orbitrap cell. The EI technique was chosen for the precalibration as it is a relatively simple, highly reproducible and cost-effective ionisation method. However, it also brings some challenges in the setup operation (e.g. high pressure, continuous ion injection) that needed to be tackled. This chapter also presents the tuning method for OLYMPIA, and the processing tools I have developed and used throughout the PhD.

Chapter III is dedicated to the improvement and optimisation phases of OLYMPIA performed at LPC2E in Orléans with the EI ionisation source. Several phases of technical improvements have been performed to handle the challenge induced by the ionisation, and reach the expected performances. A first phase aimed to make OLYMPIA more reliable and operable. The data obtained thanks to this first phase allowed to do a characterisation of the setup. The performance were below expectations for an Orbitrap-based mass spectrometer : with an ion lifetime of only about 50 ms, the maximum mass resolution achievable was 5 000 at the mass of Krypton, and the mass spectra featured strong noise patterns.

Follow up studies and trade-offs have therefore been carried out to reach the expected performances with the setup. After a characterisation of the poor definition of the electrostatic field in the Orbitrap cell, the power supplies used for each of the Orbitrap electrode have been changed. Owing to this more stable electrostatic field obtained with the proper power supplies, the lifetime of ions was extended from 200 ms to about 500 ms, and the mass resolution reached 80 000 for the main Krypton isotope, which is 85% of the maximum theoretical value for this FFT duration. By replacing the preamplifier with a custom-built vacuum-compatible one, the mass spectra are also free of significant noise pattern.

OLYMPIA being able to record mass spectra with the expected mass resolution performances, some specific optimisations of crucial parameters could be performed, such as the search for the optimal VDE measure value. Unfortunately, and most likely due to the continuous injection, this study could not conclude on a unique value.

The high performances also led to the first scientific studies with the setup. Chapter IV presents the results obtained with OLYMPIA coupled with the EI source. A study of a gas mixture with a very close m/z value around 28 u (CO/N 2 /C 2 H 4 ) and a pure Krypton gas sample have been analysed. The analysis of the gas mixture and the successful detection of the three species demonstrated the resolving power of OLYMPIA. With the Krypton analysis and the determination of the RIA error, the physical behaviour of ions inside the Orbitrap cell could be characterised. An intensity several times higher than expected has been measured for low abundant (< 2%) isotopes, and of about 50% for isotopes with a higher concentration, this pointing out to an underestimation of the major Krypton isotope measured intensity. The EI study with OLYMPIA provided interesting results and allowed a better understanding of the injection specificities. Before further analysis on gaseous samples with this ionisation method, some improvements have been identified and should be made. However, this is not the prime objective of this thesis.

The move in Berlin finally took place in February 2021, and since then, my work has been fully dedicated to the coupling of OLYMPIA to the LILBID setup (see Chapter V). The chapter begins with an overview of previous technical campaigns in Leipzig and Berlin in which measurements of ions resulting from a laser-liquid interaction have been performed. However, even though water clusters, markers of low impact velocities, could be measured with laser ablation, the ionisation regime was not relevant for our science objective which requires ions from desorption ionisation. By contrast to previous mechanical coupling, OLYMPIA has been mounted in parallel of the LILBID-TOF setup, providing a unique LILBID dual mass analyser facility.

After a study performed with a metallic sample (Tin), which allowed a verification of the alignment between the ion source and the Orbitrap cell, as well as the characterisation of the ion behaviour under a pulsed injection regime, the LILBID ion measurements were carried out. This has been a success, and for the first time, water ions desorbed from a liquid beam could be measured with an Orbitrap cell, with an unprecedented high mass resolution. The recorded mass spectra match the spectral appearances of LILBID-TOF and CDA's data with velocities between 15 and 18 km/s. As lower velocities preserve the integrity of heavier molecules, the goal was then to control and lower this analogous impact speed. This proved to be the biggest challenge of this work, and a thorough characterisation of the water clusters was carried out to better understand how to be able to measure the clusters in the Orbitrap cell. This led to several experiments on the LILBID-TOF facility, and to the understanding of the effects induced by an electrostatic field at the ionisation site for heavier ions. Based on these results, further experiments were carried out on the LILBID-OLYMPIA setup but with new experimental parameters. This work is still ongoing, as the latest findings have led to modifications in the design of the source ion optics.

Finally, with measurements performed on gas, metal and liquid water, the physical behaviour of ions under each configuration could be assessed and compared. Gas sample measurements have been carried out with a continuous injection, and high pressure. By contrast, the Tin and the water ions were measured with a pulsed injection, but with a respectively low and high pressure. These three different configurations allow for direct comparison and to determine the effects of each parameter. The large errors in the Krypton RIA observed with the continuous injection are no longer observable with a pulsed injection, regardless of the pressure in the cell.

Towards a Spaceborne Orbitrap-based Hypervelocity Dust Detector

As described in Chapter I, the orbit of planetary bodies is populated by icy and rocky dust grains. The LILBID-OLYMPIA setup is intended to be able to only mimic impact ionisation mass spectra of icy grains but not rocky ones. However, as the ionisation source of OLYMPIA is interchangeable, the setup could in the future be coupled with a dust accelerator (Mocker et al., 2011;[START_REF] Shu | 3 MV Hypervelocity Dust Accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies[END_REF] for the calibration of refractory dust compounds with high mass resolution. This will enlarge the possible samples that can be measured with the setup, and thus further complement the high mass resolution database. Further in the future, and depending on advances in the development of an ice-grain accelerator at speeds relevant to impact ionisation (Belousov et al., 2021;[START_REF] Miller | Production and Impact Characterization of Enceladus Ice Grain Analogues[END_REF], OLYMPIA could also be coupled with such a device, and directly measure ions from hypervelocity icy grains.

Measuring hypervelocity impact ionisation analogue mass spectra in the laboratory would already greatly improve our understanding of the icy moons. However, the building of a spaceborne high-resolution mass spectrometer, and more particularly those equipped with an Orbitrap cell, would represent a milestone in space exploration. The unambiguous identification of organics coming from the subsurface ocean of the icy moons could discriminate between pre-biotic and biotic compounds, with the exciting possibility of discovering life form under the ice crusts. A ruggedised spacefligth version of the Orbitrap™ analyser, the CosmOrbitrap (Briois et al., 2016) with a Technical Readiness Level of 5 and a dual ion polarity is nowadays available (CosmOrbitrap's TRL5 was awarded by CNES experts during an end of R&D review on 16 May 2019). Although the current framework for the CosmOrbitrap is to be integrated into landers targeting airless bodies (Arevalo et al., 2018;[START_REF] Arevalo | Laser Desorption Mass Spectrometry with an Orbitrap Analyser for in Situ Astrobiology[END_REF], it could also be coupled with a dust ion source and constitute the analytical subsystem of an hypervelocity dust detector. The work described in this manuscript therefore critically supports the development of an Orbitrap-based spaceborne hypervelocity dust detector, such as the Dust OrbiTrap Sensor (DOTS). DOTS has been proposed by [START_REF] Briois | DOTS: A High Resolution Orbitrap Mass Spectrometer for In Situ Analysis of the Surface Samples of Airless Planetary Bodies[END_REF] for ESA's JUICE mission, and is composed of the CosmOrbitrap and a CDA-like target.

The design of OLYMPIA has been thought through to be compatible with a space environment (see Section 3 of Chapter II). This allows the setup to be a calibration testbench for the development of future spaceborne hypervelocity dust mass spectrometers including an Orbitrap cell mass analyser. The coupling of OLYMPIA and an hypervelocity dust impact ion source would bring the setup even closer to the space configuration of an Orbitrapbased hypervelocity dust detector, LILBID-OLYMPIA being an analogue to this technique. The major challenge of such an instrument would be the focus of ions from a large source to the small Orbitrap cell aperture. Being able to efficiently handle this focus would demonstrate the feasibility of such a spaceborne instrument.

In this framework, and as part of a national mission selection in the Czech Republic, HANKA (Hmotnostný ANalyzér pre Kozmické Aplikace, Principle Investigator : Ján Žabka) is being developed. HANKA is one of the three instruments that compose the payload of the SLAVIA (Space Laboratory for Advanced Variable Instruments and Applications) mission, which consists of two twin 16U cubesats aiming for a sun-synchronous Earth orbit at ~600 km altitude to study micrometeoroids [START_REF] Zabka | HANKA -Cubesat Space High Resolution Mass Analyser[END_REF]. A 3D model of the HANKA prototype and a preliminary design of its ion source are shown in Figure VII.1. I have been involved in HANKA development since the beginning of the mission study, in autumn 2021. Depending on the selection of the SLAVIA mission, HANKA could be the first hypervelocity dust detector including an Orbitrap cell in space.

After a bit more than 3 years of work on OLYMPIA, the ultimate goal of being able to reproduce impact ionisation mass spectra with high resolution has not been fully achieved. But as all lab workers learn after some time : 'That's lab work'. Things rarely go as planned, and the simplest tasks can take weeks to achieve. This work leaves more perspectives than results, but one thing I have also learned from the search of mass peaks is that as long as there are ideas to work on, it is worth continuing. If it was not (yet) possible to measure the water clusters, this work has at least given optimism for the future of the project, which I hope will be long and successful.

Introduction

Impact ionization mass spectrometers on spacecraft perform in situ analysis of dust grains made of refractory material as well as ice grains, thereby providing important information about the grains' compositions and their sources (e.g., Hillier et al., 2007;Hsu et al., 2015;[START_REF] Kempf | The E ring in the vicinity of Enceladus: I. Spatial distribution and properties of the ring particles[END_REF]Khawaja et al., 2019;[START_REF] Kissel | Composition of comet Halley dust particles from Vega observations[END_REF]Postberg et al., 2008Postberg et al., , 2009Postberg et al., , 2011Postberg et al., , 2018)). In such a mass spectrometer, grains impinge onto the detector's target plate at hypervelocities (>1 km/s) and form impact clouds of cations, anions, electrons and neutral fragments. The cations or anions, depending on the instrument's polarity, are accelerated through an electric field toward a multiplier, which measures the flux of ions as a function of arrival time and subsequently result in time-of-flight (ToF) mass spectra.

Measurements by one such mass spectrometer, the Cosmic Dust Analyzer (CDA; Srama et al., 2004) on board the past Cassini spacecraft, showed that a large number of the ice grains, ejected into space in the Saturnian Abstract Spaceborne impact ionization mass spectrometers, such as the Cosmic Dust Analyzer on board the past Cassini spacecraft or the SUrface Dust Analyzer being built for NASA's upcoming Europa Clipper mission, are of crucial importance for the exploration of icy moons in the Solar System, such as Saturn's moon Enceladus or Jupiter's moon Europa. For the interpretation of data produced by these instruments, analogue experiments on Earth are essential. To date, thousands of laboratory mass spectra have been recorded with an analogue experiment for impact ionization mass spectrometers. Simulation of mass spectra of ice grains in space is achieved by a Laser Induced Liquid Beam Ion Desorption (LILBID) approach. The desorbed cations or anions are analyzed in a time-of-flight mass spectrometer. The amount of unstructured raw data is increasingly challenging to sort, process, interpret and compare with data from space. Thus far this has been achieved manually for individual mass spectra because no database containing the recorded reference spectra was available. Here we describe the development of a comprehensive, extendable database containing cation and anion mass spectra from the laboratory LILBID facility. The database is based on a Relational Database Management System with a web server interface and enables filtering of the laboratory data using a wide range of parameters. The mass spectra can be compared not only with data from past and future space missions but also mass spectral data generated by other, terrestrial, techniques. The validated and approved subset of the database is available for general public (https://lilbid-db.planet.fu-berlin.de).

Plain Language Summary Thousands of laboratory mass spectra, each with an individual set of experimental parameters, have been recorded so far using a facility situated at Freie Universität Berlin, Germany. The mass spectra help analyze and interpret data returned from spacecraft in the vicinity of icy moons in the Solar System. The unstructured laboratory data is increasingly challenging to sort and compare to the data from space. We developed an extendable database containing the laboratory data. The database is available for general public and allows filtering the stored data for a wide range of experimental parameters and, in turn, significantly improves analysis of data not only from past space missions but also future missions in particular. KLENNER ET AL.

Earth and Space Science

KLENNER ET AL. 10.1029/2022EA002313 2 of 11 system from Enceladus, were formed from liquid subsurface ocean water from within the icy moon (Postberg et al., 2009(Postberg et al., , 2011)). Analysis of the ice grain spectra provides insights into the chemical and physical properties of the subsurface ocean and the interactions between the ocean and the moon's rocky core (Hsu et al., 2015;Khawaja et al., 2019;Postberg et al., 2009Postberg et al., , 2011Postberg et al., , 2018;;[START_REF] Sekine | High-temperature water-rock interactions and hydrothermal environments in the chondrite-like core of Enceladus[END_REF]. Other impact ionization mass spectrometers are currently being built, such as the SUrface Dust Analyzer (SUDA; Kempf et al., 2014) or proposed, for example, the ENceladus Ice Analyzer (ENIA; Srama et al., 2015) for future space missions to icy moons in the outer Solar System (e.g., Howell & Pappalardo, 2020;Reh et al., 2016). Another impact ionization mass spectrometer, selected for JAXA's future Destiny + mission [START_REF] Ozaki | Mission Design of DESTINY + : Toward active asteroid (3200) phaeton and multiple small bodies[END_REF] to the asteroid 3200 Phaethon, is the Destiny Dust Analyzer (DDA; [START_REF] Srama | Dust astronomy with DESTINY PLUS at 1 AU. 21st European geosciences union general assembly[END_REF]. For instrument calibration and data interpretation, laboratory analogue experiments are crucial (e.g., Klenner et al., 2019;[START_REF] Taubner | Experimental and simulation efforts in the astrobiological exploration of exooceans[END_REF]. Accelerating nm-or μm-sized ice grains to relevant speeds in the laboratory is technically challenging (e.g., Belousov et al., 2021;[START_REF] Miller | Production and Impact Characterization of Enceladus Ice Grain Analogues[END_REF], and the Laser Induced Liquid Beam Ion Desorption (LILBID) approach (Kleinekofort, Avdiev, & Brutschy, 1996; [START_REF] Kleinekofort | Observation of noncovalent complexes using laser-induced liquid beam ionization/desorption[END_REF] has therefore been adapted to simulate mass spectra analogous to those generated by impacts of ice grains onto metal targets in space (e.g., Klenner et al., 2019). By using LILBID analogue experiments for instrument calibration, compositional and non-compositional variations in mass spectra from space can be reproduced, and the compounds mixed with the water matrix and their concentrations are known. This makes the LILBID simulation facility an essential tool for the interpretation of past and future space mission data (e.g., Klenner, Postberg, Hillier, Khawaja, Cable, et al., 2020; Klenner, Postberg, Hillier, Khawaja, Reviol, et al., 2020). In addition to applications in space, LILBID mass spectrometry is commonly used for the analyses of organic molecules [START_REF] Charvat | Analytical laser induced liquid beam desorption mass spectrometry of protonated amino acids and their non-covalently bound aggregates[END_REF][START_REF] Mager | LILBID-mass spectrometry of the mitochondrial preprotein translocase TOM[END_REF][START_REF] Morgner | A new way to detect noncovalently bonded complexes of biomolecules from liquid microdroplets by laser mass spectrometry[END_REF][START_REF] Morgner | A novel approach to analyze membrane proteins by laser mass spectrometry: From protein subunits to the integral complex[END_REF][START_REF] Morgner | LILBID-mass spectrometry applied to the mass analysis of RNA polymerase II and an F1Fo-ATP synthase[END_REF][START_REF] Peetz | LILBID and nESI: Different native mass spectrometry techniques as tools in structural biology[END_REF]. Further applications also include the medical field, such as the diagnoses of diseases (Patel, 2015;Sim et al., 2015) and pancreatic cancer research [START_REF] Grüner | MALDI imaging mass spectrometry for in situ proteomic analysis of preneoplastic lesions in pancreatic cancer[END_REF][START_REF] Padoan | Usefulness of MALDI-TOF/MS identification of low-MW fragments in sera for the differential diagnosis of pancreatic cancer[END_REF][START_REF] Zhong | Identification of prohibitin 1 as a potential prognostic biomarker in human pancreatic carcinoma using modified aqueous two-phase partition system combined with 2D-MALDI-TOF-TOF-MS/MS[END_REF].

In LILBID, a pulsed and focused infrared laser irradiates a μm-sized liquid water beam with substances at known concentrations dissolved therein. The transferred laser energy mechanically disrupts the liquid beam, producing charged and uncharged fragments (Charvat & Abel, 2007;[START_REF] Wiederschein | Charge separation and isolation in strong water droplet impacts[END_REF]. The created cations or anions are analyzed in a commercial ToF mass spectrometer. Collisional impacts onto space detectors and LILBID create almost exclusively singly charged species (e.g., Karas et al., 2000) and the ions' flight times therefore only dependent on their masses.

Much of the data collected by mass spectrometers on board spacecraft (e.g., CDA on board Cassini) remains uninvestigated because manual evaluation of the large datasets is required. Laboratory LILBID datasets have also been manually investigated thus far. A complete comparison of for example, CDA spectra with laboratory LILBID spectra is extremely time consuming, and still in progress. Only about 15% of all CDA mass spectra obtained from July 2004 to September 2017 have so far (2022) been investigated and compared with laboratory analogue data. It is therefore evident that an easily accessible and well organized database containing all laboratory LILBID mass spectra will facilitate the more rapid evaluation of flight data not only from CDA but particularly future spaceborne instruments, such as SUDA (Kempf et al., 2014) or ENIA (Srama et al., 2015). In contrast to CDA data, the prospective data can then be investigated without any further delay.

Existing databases containing mass spectrometric data created through diverse ionization methods include the NIST Chemistry WebBook (https://webbook.nist.gov/), the mzCloud Advanced Mass Spectral Database (https:// www.mzcloud.org/), the MassBank of North America (MoNA; https://mona.fiehnlab.ucdavis.edu/) and a database for oligosaccharides in human milk [START_REF] Remoroza | Creating a mass spectral reference library for oligosaccharides in human milk[END_REF]. However, to the best of our knowledge, no such openly accessible spectral database for LILBID data exists.

We here describe the development and functionality of our new extendable database containing LILBID mass spectra based on a Relational Database Management System (RDBMS) and SQL (Structured Query Language). The frontend of the RDBMS enables the sorting and filtering of laboratory LILBID data via a range of adjustable parameters specific to the used experimental setup (e.g., laser energy) as well as parameters that depend on the measured substances (e.g., compositions). These parameters are important for the analysis and subsequent interpretation of data from space as, for example, the combination of delay time and laser energy in the LILBID system can be correlated to the impact speeds of the ice grains onto the spaceborne mass spectrometer (Klenner et al., 2019). A Python-based peak detection routine applied to all stored data enables queries for certain spectral signals, that is, single mass lines as well as combinations of mass lines.

Earth and Space Science

KLENNER ET AL. The ease and rapidity of interrogating this large library of spectral calibration data significantly improves and accelerates analyses of mass spectra from space and thereby aids planning for future space missions. The LILBID data can also be compared rapidly and reliably with other kinds of available mass spectrometric data. The developed database system is available for community use and will continuously be extended and improved in the future.

Methods

The experimental LILBID setup, the data pre-processing, the development of the database, and the manual data post-processing are described below.

The LILBID Facility

The experimental setup used to generate the LILBID mass spectra is described in detail in Klenner et al. (2019). We therefore only provide a brief overview here.

A liquid water beam (radius of 7-12 μm) containing dissolved, or suspended, substances is injected into a high vacuum (5 × 10 -5 mbar) at an adjustable flow rate of typically 0.15-0.30 mL/min. The liquid beam is irradiated by a pulsed and focused infrared laser (20 Hz, 7 ns pulse length, wavelength = 2840 nm) with adjustable pulse energies of up to 4 mJ, heats up due to the energy transferred from the laser, and explosively disperses into atomic, molecular and macroscopic fragments. The created cations or anions, depending on the instrument's polarity, are analyzed in a commercial reflectron-type [START_REF] Mamyrin | Production and impact characterization of Enceladus ice grain analogues[END_REF] ToF mass spectrometer at ∼10 -7 mbar. In addition to pure water, mixtures of water with organic solvents can be used as matrix solutions and therefore all water soluble and many water insoluble substances can be measured and investigated with the LILBID setup. The mass spectrometer uses the principle of delayed extraction, in which the created ions are extracted as a function of their initial velocities (Klenner et al., 2019). The generated mass spectral signals (sampling interval: 1 ns) are amplified, digitized using an 12-bit Analogue to Digital Converter (ADC; Acqiris) and recorded with a LabVIEW®-controlled computer that calibrates the ions' flight times onto a mass scale by using a second order equation [START_REF] Christian | Improved calibration of time-of-flight mass spectra by simplex optimization of electrostatic ion calculations[END_REF]. Typically 300-500 mass spectra are averaged to improve the signal-to-noise ratio. The recorded mass spectra have a mass resolution of between 600 and 800 m/Δm (Full Width at Half Maximum, FWHM).

Data Pre-Processing

At the time of implementing the data acquisition process using LabVIEW, use of a database to store the spectra was not foreseen. Instead, a major focus was on the quick and easy manual location of different measurements stored on the hard drive of the analyzing scientist's computer. Therefore it was originally decided to have one line (the "solution" line; Figure S1 in Supporting Information S1) in the header of the recorded raw data files (level-0), which includes numerous significant parameters, such as the names of the used analyte substances and their concentrations, separated by the "underscore" special character. This line, combined with other significant experimental parameters that are provided in other header lines, is then used as the filename for the raw data files. This enabled easy manual location of the measurements relevant to certain substances, their concentrations and significant experimental parameters. However, combining different parameters in the same header line of the data files (Figure S1 in Supporting Information S1) turned out to be a major challenge with regards to automatic processing of the data files and this information could not simply be ingested into a RDBMS. Additionally, there were inconsistencies in the naming of the files depending on the respective person performing the measurement. For these reasons, we apply a validation script which checks for the correct number of seven underscores in the solution name. If the data file does not pass this first validation script, it has to be manually examined and edited to conform to the right format. The other values from the headers of the mass spectra text files are extracted and re-arranged (data cleaning). The data files are automatically reformatted such that each header line contains information about a single experimental parameter. An example header from such a level-1 data file can be found in Figure S2 of Supporting Information S1.

The level-1 mass spectra files are reorganized text files (Figure S2 in Supporting Information S1) with a header that contains a unique spectral identifier (date and time) and information about experimental parameters (examined substances, solution, delay time, number of averaged spectra etc.). Below the header, the text files contain two columns with the x-and y-values (floats) of the mass spectra, with x representing mass (in u) and y representing intensity (in V). The time interval between two consecutive lines of the columns corresponds to the sampling interval (1 ns) of the measurement computer (see Section 2.1).

After the file format check and any required manual editing, a peak detection routine is applied to the spectra. The peak detection routine is implemented in Python using the find_peaks_cwt algorithm within the SciPy scientific library. Its general approach is to smooth the data by convolving it using a wavelet transformation and then find relative maxima which appear over sufficient length scales and with suitably high signal-to-noise ratios (https:// docs.scipy.org/doc/scipy/reference/signal.html). The peak detection routine calculates a local baseline for a variable number of data points and uses a local percentile rank for the peak detection threshold. The resulting peak tables are stored in separate text files on the internal server.

The complete data pre-processing, including data validation and peak detection is implemented via a combination of several Python scripts called from a Bash shell script. After copying the raw data from the laboratory computer this script is manually executed on the database server and creates new text files which are then ready for ingestion into the internally accessible version of the database.

The Database System

We use a client-server infrastructure as the general system design, with the web browser representing the frontend and an RDBMS together with a web server acting as the backend. The spectrum parameters and extracted peaks are stored in relational tables in a MariaDB (https://mariadb.org/) database instance. The frontend's web pages are composed using HTML (Hypertext Markup Language), PHP (Hypertext Preprocessor), CSS (Cascading Style Sheets), and JavaScript. An Apache™ (https://apache.org/) web server serves a query form with entry fields for several possible parameter filters as the start page. After the user enters none, one or several filter parameters and submits the query, the server connects to the database (via the PHP module) and retrieves the relevant entries. When no values for filtering are entered and submitted, the server lists all available entries. As the peak identities are stored in the database, the data can be filtered not only for the experimental parameters used during the measurements but also for the peaks present in the mass spectra. The layout of the user interface allows for adjustable block-wise (10,25,50, or all entries per block) browsing of the results.

The automatic workflow of the steps from data acquisition in the laboratory, data pre-processing, data ingestion and finally the data query is shown in Figure 1. As new laboratory data is acquired, the database is regularly updated using the combined Bash/Python script (see Section 2.2).

Data Post-Processing

Software on the measurement computer converts the ions' flight times into their masses by use of a second order calibration equation. The applied delayed extraction method (Klenner et al., 2019) and variable initial ion velocities result in unavoidable mass shifts (deviances up to >1 u) of the converted masses compared to the real ion masses in level-1 spectra during conversion of the ions' flight times into their masses [START_REF] Christian | Improved calibration of time-of-flight mass spectra by simplex optimization of electrostatic ion calculations[END_REF], with increasing mass shifts for increasing ion masses.

For a reliable analysis of the mass spectra, it is critical to recalibrate the mass spectra to minimize the mass shifts. Recalibrated level-2 mass spectra are produced by applying a Python script developed in-house. The script calculates a polynomial function based on real peak masses (x-values) for previously detected (shifted) peaks and fits the corresponding data file with this function.

The resulting level-2 spectra often possess an uneven baseline due to instrumental, chemical and random background noise during the measurements [START_REF] Urban | Noise and baseline filtration in mass spectrometry[END_REF]. The noise can either produce false positive signals or hide small peaks in the mass spectra. To fully interpret the mass spectra and further improve the spectral analysis, the background noise needs to be smoothed. Several methods and programs that are capable of subtracting the baselines from mass spectra exist (e.g., [START_REF] Urban | Noise and baseline filtration in mass spectrometry[END_REF][START_REF] Xu | Baseline correction method using an orthogonal basis for gas chromatography/mass spectrometry data[END_REF]. We here apply an in-house developed Python script based on the Penalized Least Squares Method [START_REF] Zhang | An automatic baseline correction method based on the penalized least squares method[END_REF] to create baseline subtracted data (level-3). The peaks in the level-3 mass spectra are then labeled with their corresponding masses (x-values). The peak labeling can be done either manually, or automatically using a software. Automatic peak detection routines can reliably detect peaks with significantly high amplitudes (y-values) but might overlook smaller peaks and detect false positives. For the reliable detection of small peaks, manual peak identification is indispensable. After peak detection, graphical plots of level-3 mass spectra are created using Python Matplotlib and stored on the server (Figure 1).

Earth and Space Science

The validated subset of the data (exclusively level-3) is accessible via the public database web server interface (see Section 3.1).

Results and Discussion

The LILBID Spectral Database

The in-house version of the spectral database currently contains more than 12,000 LILBID mass spectra recorded using a wide range of experimental parameters. The publicly available version contains a selection of validated and published reference spectra (level-3) and is accessible via the following link: https://lilbid-db.planet.fu-berlin.de.

Figure 2 shows the search interface of the publicly available database. The spectra in the database can be searched using numerous experimental parameters, as described below, in order from upper left to lower right in the search interface. Moving the cursor over one of the parameters in the search interface shows a popup window (hover) with more descriptive information about this parameter.

Substance: The name of the analyte.

Matrix: The name of the solvent.

Peaks: The peaks in the mass spectra (x-values with significantly high y-values) created by the analyte, the solvent and physico-chemical interactions between both. The peaks are detected by a peak detection routine (see Ion Mode: Ion mode of the mass spectrometer, that is, positive (cations) or negative (anions).

Numerical abundances of the most common elements in the used analytes' molecular structures. The most common elements are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), sodium (Na), potassium (K), chlorine (Cl), phosphorus (P), and sulfur (S).

Laser intensity: The intensity of the laser (typically varying from 85% to 100%).

Delay Time: The time between laser shot and ion acceleration (typically between 4 and 8 µs). A combination of delay time and laser energy can be correlated to impact speeds of ice grains onto mass spectrometers in space (Klenner et al., 2019).

The data can be filtered using either a single experimental parameter or a combination of multiple experimental parameters. When applying the filter, all matches will be shown in the results interface (Figure 3) and can be sorted by individual parameters. Clicking on the name of the substance redirects to the corresponding Wikipedia article to provide additional information about the measured substances (solubility in water, toxicity, etc.) without adding new columns to the Database Management System to maintain the database as small and efficient as possible. Graphical plots of the mass spectra can be retrieved via the "Images" column. The "Files" column allows to download the spectral text files. A search function on the top right of the results interface lets one search for individual spectra within the results interface (Figure 3).

Other available databases (see Section 1) can provide structural information or thermodynamic data about an analyzed single substance. In contrast, the LILBID spectral database contains mass spectra of single substances and mixtures of substances in variable background matrices recorded with individual sets of experimental The data in the LILBID spectral database can be searched for particular peaks in the mass spectra after processing with the peak detection routine (see Section 2.2 and Section 2.4). In rare cases, if the baseline is extremely uneven and varies by at least half an order of magnitude (caused by e.g., very salty measuring solutions or high detector voltages) or if the dynamic range (ratio of the largest to smallest detected signal) of the recorded mass spectrum is clearly below 10 1 , tiny peaks are potentially not detected and the routine detects a sparse number of false positives instead. This algorithm will be further improved in the future.

Science Case: Data Post-Processing of a LILBID Mass Spectrum and Comparison With a CDA Mass Spectrum

Graphical plots of an example LILBID mass spectrum at different data processing levels are shown in Figure 4. The mass spectrum was recorded in the positive ion mode using water containing about 10 -7 M NaCl. The applied experimental parameters correspond to intermediate impact speeds (8-10 km/s) of ice grains onto spaceborne mass spectrometers (Klenner et al., 2019). Peaks in the mass spectrum represent cationic water species of the form [H 2 O] 0-3 H 3 O + and cationic sodium-water species of the form [H 2 O] 0-2 Na + .

The level-1 mass spectrum has a slightly uneven baseline and peak shifts of about 0.1 u from the correct isotopic masses. Uneven baselines and peak shifts can hinder analysis, especially of more complex mass spectra (e.g., spectra of organic mixtures or high salinity solutions). In level-2 mass spectra, peak shifts are reduced and level-3 mass spectra are additionally baseline corrected, which aids peak detection and subsequent spectral analyses (Figure 4). After processing to level-3, and with the current mass resolution of the laboratory ToF-MS (600-800 m/Δm), it is often possible to resolve interfering species at the same integer mass with a mass difference of about 0.15-0.25 u (Klenner, Postberg, Hillier, Khawaja, Cable, et al., 2020). So-called Type-1 mass spectra of ice grains recorded by the CDA in the Saturnian system show peaks that are almost exclusively related to cationic water species of the form [H 2 O] n H 3 O + with n ranging from 0 to >10 (Postberg et al., 2008(Postberg et al., , 2009)). In addition to cationic water species, occasional traces of sodium can be observed in Type-1 spectra. One such spectrum is shown in Figure 5. The much lower mass resolution of the CDA instrument (20-50 m/Δm; Srama et al., 2004) compared to the LILBID setup (600-800 m/Δm) is apparent. The spectrum shows the same water and sodium-water species as the laboratory LILBID spectrum at similar relative abundances (Figure 4), with [H 3 O] + at m/z 19 being slightly more abundant in the CDA spectrum and [H 2 O] 3 H 3 O + at m/z 73 being slightly more abundant in the LILBID spectrum. For an even better quantitative match with flight mass spectra, laboratory spectra generated using different experimental parameters can be co-added (Klenner et al., 2019).

As well as water dominated LILBID mass spectra, more complex spectra, such as those from organic mixtures, salty solutions or even both together, can be compared to impact ionization mass spectra from space (e.g.,

Conclusions and Outlook

The laboratory LILBID facility has been proven to simulate mass spectra produced by ice grain impacts onto spaceborne mass spectrometers. Variations in spectra due to the ice grains' compositions and impact speeds can be accurately reproduced by adjusting appropriate experimental parameters (Khawaja et Postberg et al., 2009Postberg et al., , 2018)). Over 12,000 LILBID mass spectra of more than 200 substances, each with their associated experimental parameters, have been uploaded to the internal version of the LILBID mass spectral database and are available to group members at Freie Universität Berlin and cooperation partners only. A subset of validated and approved data is available for the general public (https://lilbid-db.planet.fu-berlin.de). The database, containing cation and anion mass spectra, can filter the stored spectra for the used experimental parameters that can be correlated with different properties of the encountered ice grains in space. Processing by a peak detection routine allows the mass spectra to be selected based on the appearance of particular peaks. Besides the spectral data, the database contains all compositional and experimental setup information, as well as

Introduction

Mass spectrometry is one of the most efficient techniques for in situ experimental studies of the chemical composition of samples of astrochemical relevance. In situ measurements carried out during recent space missions to Saturn and its moons (Cassini-Huygens [1][2][3][4]) and the 67P/Churyumov-Gerasimenko comet (Rosetta [5][6][7]) have provided unique data on the composition of the environment and surface of the Solar System's bodies. These missions unveiled the complexity of the chemical composition of both the atmosphere of Saturn's moon Titan [3,4,[8][9][10] and of comets, which are considered to be relatively primitive small space bodies.

One of the most advanced space mass spectrometers flown onboard space missions, the Rosetta Double Focusing Mass Spectrometer (DFMS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) module, provided a mass resolution of m/∆m ≈ 3000 at 1% of the peak height (corresponding to ≈9000 at full width at half maximum (FWHM)) with a 1-150 u mass range [11][12][13], which was sufficient to resolve N 2 from CO [14]. Detection of prebiotic organic molecules, such as glycine, was also performed, but deconvolution tools and careful examination of the fragmentation pattern were necessary as the resolution was not sufficient for direct and unambiguous identification of complex organic molecules (Altwegg et al., 2016). For this purpose, when the mass resolution of the measured mass spectra is not sufficient, supplementary analytical deconvolution algorithms [15] and complex chemical models [16,17] are required for a comprehensive description of the chemical composition of extraterrestrial environments.

The chemical diversity of the extraterrestrial medium and the limited mass resolution of current state-of-the-art space instruments call for a new generation of spaceborne mass spectrometers and the development of ground-based analytical instruments for additional comparative laboratory studies of space-relevant samples. High-resolution mass spectrometry allows the identification of complex organic compounds without a need for complementary separation techniques, e.g., chromatography [18], spectroscopy [19], or collision-induced dissociation [20]. In recent years, significant technological and scientific advances have been made in the field of high-resolution space mass spectrometry. Several flight instruments and prototypes of high-resolution mass spectrometers are currently under development and are at different space technology readiness levels (TRL). The MAss SPectrometer for Planetary EXploration (MASPEX) (Brockwell et al., 2016) on board NASA's future Europa Clipper mission is characterized by sufficient mass resolution to identify simple hydrocarbons, i.e., m/∆m ≈ 7000 at m/z 2-32 and around 24,000 at m/z 16-114, using the time-of-flight (ToF) technique. Two high-resolution laser ablation space mass spectrometers, the Characterization of Ocean Residues and Life Signatures (CORALS) instrument and the Characterization of Regolith and Trace Economic Resources (CRATER), are being developed as part of an international collaboration between NASA and CNRS laboratories with the support of CNES [21]. They both include the CosmOrbitrap, a space-flight prototype of a high-resolution mass analyzer developed by a consortium of six laboratories [22], based on the commercial Orbitrap TM cell (Thermo Fisher Scientific, Bremen, Germany). The CosmOrbitrap has a mass resolution that varies from 474,000 to 90,000 for a 9 to 208 m/z range and an acquisition time of 832 ms [22].

In this work, a novel compact high-resolution mass spectrometry (HRMS) laboratory instrument based on the Orbitrap technology, named OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion) is presented. The instrument is compatible with different types of ion sources that have recently been built in our laboratory. This setup is being used as a proof of concept for laboratory analytical applications and as a workbench platform. In this work, a configuration that uses a continuous electron ionization (EI) ion source for the high-resolution gas analysis of compounds relevant to planetary environments has been tested. Certain decreases in the mass resolution compared to the ultimate values of the best commercially available Orbitrap mass analyzers are expected due to the higher kinetic energy distribution spread of ions and probable diffusion of the gas from the source inside the trap volume for the proposed configuration of the device. Experimental characterization of the mass analyzer is required to facilitate future use of the proposed configuration for laboratory and space applications.

Materials and Methods

OLYMPIA (Figure 1) is a HRMS instrument based on the Orbitrap technology for mass analysis proposed and developed by A. Makarov [23]. Its configuration is intended to support the development of future compact and low-resource space instruments without C-traps. The C-trap is a proprietary device used in commercial Orbitrap mass spectrometers for the concentration and increasing monochromaticity of the kinetic energy of ions by collision with the neutral buffer gas prior to injection into an electrostatic trap. It allows achieving ultra-high mass resolution (m/∆m > 10 6 [24]), but it increases the complexity, mass, and power consumption of the instrument and requires an additional gas reservoir. In contrast, the low-resource design without a C-trap makes OLYMPIA lighter, more transportable, and easier to maintain and operate. It is designed to provide mass resolution adequate for the next generation of space mass spectrometers (m/∆m around 50,000) and is equipped with a modular structure ionization source.

ions by collision with the neutral buffer gas prior to injection into an electrostatic trap. It allows achieving ultra-high mass resolution (m/∆m > 10 6 [24]), but it increases the complexity, mass, and power consumption of the instrument and requires an additional gas reservoir. In contrast, the low-resource design without a C-trap makes OLYMPIA lighter, more transportable, and easier to maintain and operate. It is designed to provide mass resolution adequate for the next generation of space mass spectrometers (m/∆m around 50,000) and is equipped with a modular structure ionization source.

Ion Source and Ion Optics

In this work, a continuous EI ion source, built in our laboratory, has been used to produce ions from neutral gas samples. It consists of an ionization chamber with a gas inlet capillary, tungsten filaments, and a pusher electrode that deflects ions towards the ion optics. The variable ionization potential values used for the experiment are within the range of 100-150 V. A gas mixing station was used to prepare samples with a defined mixture ratio. The station is connected to a dry-scroll backing pump and a ceramic technology membrane capacitance pressure gauge (Pfeiffer Vacuum CMR 361, Asslar, Germany). The background pressure of the system, 0.8 mbar, limits the purity of the gas mixture, typically prepared at 1000 mbar. The used gauge ensures equal sensitivity to various gases, and the tolerance of the partial pressure of component gases is rated at 0.2% over the selected pressure measurement range. The gas mixture vessel is first filled with the less abundant gas to improve accuracy. The connecting piping is evacuated to a vacuum level better than is measurable with the gauge after each mixture vessel filling. The commercially available pure gas containers used to prepare the mixture have a purity grade several orders of magnitude higher than the resulting mixture.

Similar to the LAb-CosmOrbitrap (Briois et al., 2016, Selliez et al., 2019), ions are directly injected into the trap from the ion source. For this work, a custom electrostatic ion optics module controlled with high voltage (HV) power supplies (iseg Spezialelektronik GmbH, Germany) was used. The ion optics module is composed of in-line electrodes, as shown in Figure 2. The ion optics is used to transport ions extracted from the ion source, to form the focused bunch of ions, and to correct its pointing if it is needed for the optimal injection conditions. The set of ion lenses is directly connected to the Orbitrap mounting

Ion Source and Ion Optics

In this work, a continuous EI ion source, built in our laboratory, has been used to produce ions from neutral gas samples. It consists of an ionization chamber with a gas inlet capillary, tungsten filaments, and a pusher electrode that deflects ions towards the ion optics. The variable ionization potential values used for the experiment are within the range of 100-150 V. A gas mixing station was used to prepare samples with a defined mixture ratio. The station is connected to a dry-scroll backing pump and a ceramic technology membrane capacitance pressure gauge (Pfeiffer Vacuum CMR 361, Asslar, Germany). The background pressure of the system, 0.8 mbar, limits the purity of the gas mixture, typically prepared at 1000 mbar. The used gauge ensures equal sensitivity to various gases, and the tolerance of the partial pressure of component gases is rated at 0.2% over the selected pressure measurement range. The gas mixture vessel is first filled with the less abundant gas to improve accuracy. The connecting piping is evacuated to a vacuum level better than is measurable with the gauge after each mixture vessel filling. The commercially available pure gas containers used to prepare the mixture have a purity grade several orders of magnitude higher than the resulting mixture.

Similar to the LAb-CosmOrbitrap (Briois et al., 2016, Selliez et al., 2019), ions are directly injected into the trap from the ion source. For this work, a custom electrostatic ion optics module controlled with high voltage (HV) power supplies (iseg Spezialelektronik GmbH, Germany) was used. The ion optics module is composed of in-line electrodes, as shown in Figure 2. The ion optics is used to transport ions extracted from the ion source, to form the focused bunch of ions, and to correct its pointing if it is needed for the optimal injection conditions. The set of ion lenses is directly connected to the Orbitrap mounting plate. The ion beam is focused into the Orbitrap input orifice and can be detected after passing through the Orbitrap cell using an electron multiplier (DeTech 2700, Detector Technologies, Inc., Palmer, AK, United States) placed behind the Orbitrap, opposite the ion optics. The timing parameters of the injection of an ion packet can be optimized using a pulsed ion optics system controlled by an HV switch module (CGC Instruments, Chemnitz, Germany). In the current experiment, this option has been used as a transition mode between pulsed and continuous ion source modes.

plate. The ion beam is focused into the Orbitrap input orifice and can be detected after passing through the Orbitrap cell using an electron multiplier (DeTech 2700, Detector Technologies, Inc., Palmer, AK, United States) placed behind the Orbitrap, opposite the ion optics. The timing parameters of the injection of an ion packet can be optimized using a pulsed ion optics system controlled by an HV switch module (CGC Instruments, Chemnitz, Germany). In the current experiment, this option has been used as a transition mode between pulsed and continuous ion source modes.

Mass Analyzer, Data Acquisition and Processing

The core part of the instrument is the D30-type commercial Orbitrap TM cell (Figure 2). Similarly to commercial devices based on the Orbitrap cell, in OLYMPIA, after injection into the trap and electrodynamic squeezing [25], ions are dynamically confined inside the trap by the electrostatic field, spinning around the axis with an oscillating movement along the central electrode axis. The frequency of the cyclic motion of ions is defined by the parameters of the trap and the m/z values of the ions [23].

The axial oscillations of the trapped ions induce the current between the receiving electrodes of the Orbitrap cell. This current is detected by the preamplifier. The signal is then converted by an analog-to-digital converter (ADC) and further processed using Fourier transformation algorithms. Finally, the mass-to-charge ratio of ions is evaluated by the frequency of their oscillation [23].

A new customized high-gain differential preamplifier has been developed and constructed by JanasCard Company (Prague, Czech Republic) for the OLYMPIA setup. This preamplifier has been tested to be functional under vacuum conditions. The preamplifier output voltage is digitized by a 16-bit, 20 MHz, Picoscope ® ADC unit (Pico Technology, Cambridge, UK).

The time domain data are pre-processed with doubling signal duration by zero-padding to increase the discrete resolution and, thus, the frequency accuracy. Then, a Hann function-shaped window apodization to minimize spectral leakage [26] is applied. The main data processing includes the application of fast Fourier transformation (FFT) using an FFTW implementation of the Cooley-Turkey algorithm [27] to convert the measured

Mass Analyzer, Data Acquisition and Processing

The core part of the instrument is the D30-type commercial Orbitrap TM cell (Figure 2). Similarly to commercial devices based on the Orbitrap cell, in OLYMPIA, after injection into the trap and electrodynamic squeezing [25], ions are dynamically confined inside the trap by the electrostatic field, spinning around the axis with an oscillating movement along the central electrode axis. The frequency of the cyclic motion of ions is defined by the parameters of the trap and the m/z values of the ions [23].

The axial oscillations of the trapped ions induce the current between the receiving electrodes of the Orbitrap cell. This current is detected by the preamplifier. The signal is then converted by an analog-to-digital converter (ADC) and further processed using Fourier transformation algorithms. Finally, the mass-to-charge ratio of ions is evaluated by the frequency of their oscillation [23].

A new customized high-gain differential preamplifier has been developed and constructed by JanasCard Company (Prague, Czech Republic) for the OLYMPIA setup. This preamplifier has been tested to be functional under vacuum conditions. The preamplifier output voltage is digitized by a 16-bit, 20 MHz, Picoscope ® ADC unit (Pico Technology, Cambridge, UK).

The time domain data are pre-processed with doubling signal duration by zeropadding to increase the discrete resolution and, thus, the frequency accuracy. Then, a Hann function-shaped window apodization to minimize spectral leakage [26] is applied. The main data processing includes the application of fast Fourier transformation (FFT) using an FFTW implementation of the Cooley-Turkey algorithm [27] to convert the measured time domain signal into a frequency spectrum. The frequency spectrum is then converted to a mass spectrum using the theoretical model of Orbitrap-based mass analyzers [25,28]:

f = 1 2π k m/q (1)
where f is the frequency of ion axial motion, m is the mass of the ion, k is a calibration factor that characterizes the curvature of the electrostatic field, and q is the electrical charge of the ion. The calibration factor k is calculated for each dataset using the measured frequency and the known exact mass of the calibration ion.

Experimental Results

Laboratory measurements have been performed to benchmark the instrument's capabilities to resolve isobaric ions in several gas mixtures. Samples composed of molecular nitrogen (N 2 ), carbon monoxide (CO), and ethylene (C 2 H 4 ) have been used to determine the resolving power of the mass analyzer at m/z 28. Quantitative measurement capability has been examined with CO and N 2 samples at different mixing ratios. Finally, a pure krypton sample was used to assess the quantification of isotopic abundances. The relative abundance of ions, which can be determined from the measured spectrum as peak amplitudes, does not only depend on the initial partial concentration of gases in the mixture. The ionization cross-section (1) and further chemical processes inside the ion source, such as charge transfer (2) and fragmentation (3), have a strong impact on the quantitative composition of the ion bunch injected into the trap.

(1) According to the binary encounter Bethe (BEB) model [29], the electron ionization cross-section, and thus the ionization probability of the C2H4 molecules (4.0 Å The different sampling times from 20 to 500 ms have been used to measure mass spectra for the estimation of the optimal value for the current configuration of OLYMPIA. The maximal reasonable signal duration is about 250 ms due to the relatively high pressure inside the ion trap chamber, approximately 10 -8 mbar. Longer acquisition reduces the total amplitude of the effective signal and, thus, the signal-to-noise ratio and dynamic range.

The partial mass spectra of the CO/N 2 /C 2 H 4 mixture, are presented in Figure 3. The mass accuracy of the measured peaks varies from 5 to 20 ppm compared to NIST atomic weights and isotopic composition data. A zoom of the region around m/z 28 is shown in Figure 4. Three different peaks corresponding to CO + , N 2 + , and C 2 H 4 + have been successfully resolved. A mass resolution of about 40,000 at m/z 28 has been achieved with a sampling time of less than 250 ms (Figure 4). In Figure 4, a combination of increasing resolution and variation in abundance accuracy is observed for a longer acquisition time.

CO/N2 Gas Mixture

CO and N2 gases of similar ionization cross-sections mixed in different ratios have been used to examine the quantitative measurement capability of OLYMPIA. These molecules have the same ionization cross-section and so does the probability of the produc- The relative abundance of ions, which can be determined from the measured spectrum as peak amplitudes, does not only depend on the initial partial concentration of gases in the mixture. The ionization cross-section (1) and further chemical processes inside the ion source, such as charge transfer (2) and fragmentation (3), have a strong impact on the quantitative composition of the ion bunch injected into the trap.

(1) According to the binary encounter Bethe (BEB) model [29], the electron ionization cross-section, and thus the ionization probability of the C 2 H 4 molecules (4.0 Å The combination of these three factors results in a higher abundance of C 2 H 4 + and a lower abundance of CO + and N 2 + ions at equal concentrations of neutrals (Figure 5). The exact current of ions extracted from the source and its ratio is not constant and depend on the parameters of the setup, such as the pressure in the source and the accelerating potential of ionizing electrons. Therefore, calibration measurements at relevant conditions are required for quantitative in situ characterization of the sampled gas mixtures.

CO/N2 Gas Mixture

CO and N2 gases of similar ionization cross-sections mixed in different ratios have been used to examine the quantitative measurement capability of OLYMPIA. These molecules have the same ionization cross-section and so does the probability of the production of ions by electron-neutral interactions, according to the BEB model. Nevertheless, they have different ionization energies, which affect further chemical reactions and the ratio of ions extracted from the source. + ions as a function of nitrogen gas ratio in the known mixture. The fit function is calculated for the linear scale data using the least squares method.

CO/N 2 Gas Mixture

CO and N 2 gases of similar ionization cross-sections mixed in different ratios have been used to examine the quantitative measurement capability of OLYMPIA. These molecules have the same ionization cross-section and so does the probability of the production of ions by electron-neutral interactions, according to the BEB model. Nevertheless, they have different ionization energies, which affect further chemical reactions and the ratio of ions extracted from the source.

Several mixtures with CO fractions ranging from 2% up to 98% in the N 2 gas have been used (Figure 5). The relative intensity of CO + in N 2 + ions was measured with a mass resolution sufficient to identify ions of the same molecular mass (m/∆m ≈ 5000). A trace amount of carbon monoxide gas was found to be detectable in mixtures with a relative abundance of less than 2%.

Measurement of the CO/N 2 mixture showed an estimation of species abundance over two orders of magnitude of the CO concentration. At low N 2 concentrations, the measured N 2 + to CO + ion ratio is slightly higher (but within the range of the statistical error) than the neutral gas ratio in the prepared mixture. The higher number of detected CO + ions can also be explained by the higher resulting efficiency of ion production due to the charge transfer processes, compared to Figure 4. The measurable amounts of C + , O + , and N + fragment ions were not observed.

Krypton Gas

The sensitivity of the instrument has been verified using a polyisotopic monoatomic gas to improve the amplitude measurement accuracy. The use of one monoatomic gas eliminates the effects of further chemical reactions of formed ions and fragmentation of neutrals. Meanwhile, the isotopic composition of krypton allows to estimate the accuracy of the quantitative characterization of the sample over a broad range of ratios. Krypton gas with 99.998% purity and natural isotopic abundance was selected as a calibrant as it has a well-documented isotopic ratio. It has also been detected in the coma of the 67P/Churyumov-Gerasimenko comet [14], so the study of the possibility of accurate measurement of its isotopic composition is of planetary science interest. A krypton gas container could also be proposed to be used as an onboard calibrant for future space missions that would use an Orbitrap-based spectrometer.

Spectra were measured with a 40 ms acquisition time (Figure 6). All six main isotopes of Krypton, even 78 Kr + , which is only 0.355% abundant, were successfully detected. The statistical error of the 82 Kr, 83 Kr, 84 Kr, and 86 Kr peak amplitude measurements was 9-11%.

eliminates the effects of further chemical reactions of formed ions and fragmentation of neutrals. Meanwhile, the isotopic composition of krypton allows to estimate the accuracy of the quantitative characterization of the sample over a broad range of ratios. Krypton gas with 99.998% purity and natural isotopic abundance was selected as a calibrant as it has a well-documented isotopic ratio. It has also been detected in the coma of the 67P/Churyumov-Gerasimenko comet [14], so the study of the possibility of accurate measurement of its isotopic composition is of planetary science interest. A krypton gas container could also be proposed to be used as an onboard calibrant for future space missions that would use an Orbitrap-based spectrometer.

Spectra were measured with a 40 ms acquisition time (Figure 6). All six main isotopes of Krypton, even 78 Kr + , which is only 0.355% abundant, were successfully detected. The statistical error of the 82 Kr, 83 Kr, 84 Kr, and 86 Kr peak amplitude measurements was 9-11%. A higher-than-expected amplitude has been observed in the OLYMPIA data for the least abundant ions of the krypton gas 78 Kr + and 80 Kr + (Figure 5) and for the CO/N2 mixture Figure 6. Mass spectra of the krypton gas calibrated and normalized to 84 Kr + ion compared to the NIST isotopic composition database (red marks). Experimental m/z values are indicated near labels of isotopes by green numbers (better than 20 ppm mass accuracy).

A higher-than-expected amplitude has been observed in the OLYMPIA data for the least abundant ions of the krypton gas 78 Kr + and 80 Kr + (Figure 5) and for the CO/N 2 mixture (Figure 6). The measured difference from the normal isotopic distribution for less abundant ions is statistically significant. It indicates an accuracy limit for the measurement of trace amounts of components in the studied samples for the current configuration of the mass analyzer.

Outlook for Limited-Resources Space Missions

OLYMPIA is one of the laboratory concepts for future compact Orbitrap-based HRMS instruments for space missions. It specifically targets low-resource missions, including CubeSat-class ones, e.g., the currently developed Space Laboratory for Advanced Variable Instruments and Applications (SLAVIA) space mission dimensioned to 12U size and less than 20 kg mass format. The constraints imposed by the space environment (miniaturization, pressure, low power consumption, limited data transfer, especially for outer solar system bodies) have been considered during the development of this prototype.

For the OLYMPIA setup, the choice was made to not include a C-trap module present in commercial Orbitrap in order to reduce the overall complexity of the space instrument. The feasibility of this configuration had already been proven for pulsed ion sources using the LAb-CosmOrbitrap [22]. In this work, it has been demonstrated that the proposed configuration is compatible with a continuous EI source while ensuring the sufficient performance expected for HRMS.

A mass resolution of 50,000 is desirable to obtain a new level of scientific output and state-of-the-art knowledge for the extraterrestrial medium composition. Selection of the optimal sampling duration for specific tasks of the mission, and target mass resolution, is an important phase of the instrument design. Effective sampling duration is defined by (a) the time stability of power supply designed for space applications (e.g., compact HV source for CubeSats), (b) the pressure in the vicinity of the spacecraft (e.g., in low Earth orbit), and (c) the computing resources required to apply the FFT on board.

Finally, for most space missions, and in particular for low-resource CubeSats, data transfer is highly limited by the transmission capability of the spacecraft. In order to meet the challenges resulting from the proposed space mission application, a trade-off on the optimal signal duration is required to ensure sufficient mass resolution, ion abundance accuracy, and data handling. While the short signal duration decreases the mass resolution, it improves the signal-to-noise ratio and limits computations and data transfer requirements (Figure 4).

Conclusions

A new Orbitrap-based HRMS laboratory instrument has been built and characterized. The first operation of the Orbitrap-cell mass analyzer without a C-trap module with the continuous EI ion source has been demonstrated. Its performance has been evaluated by the analysis of gas mixtures composed of chemical species of the same nominal molecular mass (CO, N 2 , and C 2 H 4 ). The achieved mass resolution for 14 N 2 + is more than 40,000 for a 250 ms FFT duration. The experimental resolution value, limited by the pressure inside the Orbitrap cell, is close to the value of about 50,000 (for at least 2-3 points per peak) defined by the FFT theory for this acquisition time and allows to resolve all three chemical species without any additional analytical techniques. With a mixture of CO and N 2 at different mixing ratios and a pure krypton gas sample, the ability of OLYMPIA to measure ion abundances over two orders of magnitude has been assessed with an accuracy of 5-50% from the most abundant to the least abundant fractions. Despite a higher-than-expected measured intensity for less abundant ions (oversensitivity), the error range is less than 10% for the most abundant ions. The dynamic range of the instrument allows the detection of chemical species with a volume ratio of less than 1%. Indeed, the krypton isotope ( 78 Kr) with an abundance of less than 0.4% is clearly detectable in the spectrum with a signal-to-noise ratio of better than 250 for the major isotope.

The performed experiment demonstrates the technical feasibility of space applications of the OLYMPIA setup using a configuration of Orbitrap-based mass spectrometers without a C-trap module (see Outlook for limited-resource space missions). It can be used with continuous or pulsed ion sources, even for applications with high mass resolution requirements. This instrument configuration will reduce mechanical, high-voltage control, and timing module complexity while providing reasonable performances and a mass resolution exceeding that of previous space missions by at least one order of magnitude. The experiment also facilitates the analysis of ions abundant in atmospheres; however, the sensitivity and signal-to-noise ratio of the system should be improved.

With the current mass analyzer configuration, OLYMPIA proves to be an efficient tool, with certain trade-offs related to simplified system design, to study complex gas mixtures relevant to the atmospheres of the Solar System bodies (e.g., Titan), including the Earth, and can be used as a research and development workbench for future space missions. T he search for extra-terrestrial life has always been a major endeavor in science, and has driven planetary exploration efforts since its debut. Planetary bodies with strong habitability potentials (i.e., whether life could originate or be sustained on such bodies) are the target of many space missions. 1-4 In the search for life as we know it, liquid water is a mandatory prerequisite. This is why icy moons with subsurface oceans 5,6 in the outer solar system are such interesting bodies for astrobiology investigations. Among these moons, Europa and Enceladus, respectively, orbiting Jupiter and Saturn, are of particular interest because hydrothermal activity is believed to occur on their rocky sea floors. 7,8 Those liquid water oceans do show favorable conditions for the creation of a variety of organic molecules. 9-11 In the case of Enceladus 12 and potentially Europa, 13 gas, dust, and ice grains from the liquid ocean are emitted from the surface through plumes, allowing a study of the oceans composition from space by in situ instruments. 14-18 Mass spectrometers are amongst the most prevalent in situ instruments in space exploration. They enable the measurement of the samples' compositions, give access to their exact chemical formula, and reveal the complexity of their environments. They are specifically suitable to agnostically investigate the composition of organic materials. For this reason, they have flown onboard numerous probes toward a wide variety of solar system bodies, such as Venus, 19 Mars, 20 or smaller bodies like Saturn icy moon Titan 21 or the comet 67P/ Churyumov-Gerasimenko. 22,23 On the latter mission, the instrument ROSINA was able to detect prebiotics chemicals, such as amino acids, in the coma of the comet. 24 Although mass spectrometry is an in situ technique, it does not necessarily require to land on the body or even to stay in its close vicinity. Hypervelocity impacts' detectors are able to sample emitted grains during spacecraft flybys, using the impact ionization technique, which generally starts to produce useful amounts of ions at impact velocities above 1-2 km/s. 25 As an example, the impact ionization mass spectrometer Cosmic Dust Analyzer 26 (CDA) on board the Cassini spacecraft was studied for 13 years around Saturn dust and ice grains emitted by Enceladus. By measuring the composition of μm-sized E-ring ice grains, it allowed characterizing Enceladus' ocean, 7,14,16 revealing a complex organic chemistry. 15,27,28 CDA could measure cationic mass spectra up to a mass to charge ratio (m/z) of ∼230 with a mass resolution of 20-50 m/Δm, 26 where m is the mass of the ion and Δm is the full width at half maximum of the peak. The next generation of TOF hypervelocity detectors with a wider mass range and better resolving power is the SUrface Dust Analyzer (SUDA) 29 on board the Europa Clipper spacecraft, which aims to study Jupiter's icy moon Europa. 2 The mass resolution of SUDA is 150-300 m/Δm in the range of m/z 1-500 and will be able to measure both cationic and anionic mass spectra. Further in the future, TOF detectors with even higher performance are proposed, like ENIJA 30 (ENceladus Icy Jet Analyzer), which is planned to have a mass range of up to 2000 m/z, with a 1000-2000 m/Δm mass resolution. 31,32 To simulate hypervelocity dust impacts, mass analyzers can be coupled with dust accelerators and reach spacelike impact velocities that are typically of the order of 10 km/s for μm-sized dust grains. 33 However, the acceleration of μm-sized ice grains to such an impact speed is not yet feasible. 34 Instead, to mimic in the laboratory icy grains mass spectra, the laser-induced liquid beam ion desorption (LILBID) technique is used. 35 Indeed, the LILBID technique is able to reproduce the ionization process of hypervelocity ice grain impacts. The ability to simulate the ice grains from a plume or ejected from the surface of an icy moon is a great asset, which has been extensively and successfully used to characterize the habitability of Enceladus with CDA data. 15,16,27,28 Using a pulsed infrared laser, a μm-sized water beam is subjected to a fast laser-induced dispersion, resulting in gas-phase ions. Relevant materials, such as minerals or organics, can be dissolved or finely dispersed in the water beam and studied at different experimental parameters (e.g., laser energy densities) that can be correlated to different ice grain impact speeds. 36 Initially, LILBID setups were coupled with a TOF mass spectrometer. At the FU Berlin laboratory, the setup can reach a mass resolution m/Δm of around 600-800. The SUDA team is building a database 37 containing calibration mass spectra for impact ionization MS that will help for future data interpretation. Even with this laboratory setup, the mass resolution is not sufficient to resolve isobaric interferences and to allow an unambiguous determination of chemical species. To resolve such interferences, a high-resolution mass spectrometer is needed. Laboratory mass spectrometers with such a resolving power have already been developed; however, the constraints of the space environment do not allow a simple spatialization of all techniques. The size, weight, and energy consumption of the instrument present serious limitations. Among the high-resolution mass analyzers, the commercial Orbitrap by Thermo Fisher Scientific 38 could fulfill those criteria after adaptations. Using a quadro-logarithmic electrostatic ion trap (QLEIT), based on a so-called Kingdon trap, 39 this mass analyzer uses a Fourier transform detection method, which means the mass resolution increases with the acquisition time. Orbitrap is able to reach a mass resolution of up to 1 000 000 at m/z below 300-400 within a 3 s detection time, 40 in an ultrahigh vacuum (10 -10 mbar). A consortium of six laboratories 41 is currently developing the CosmOrbitrap, a space-ruggedized version of the Orbitrap mass analyzer plus its power supply electronics and data processing Fourier transform system for space applications. Coupled with a laser ablation ionization system, the CosmOrbitrap achieved mass resolution performances varying from 474 000 at m/z 9 to 90 000 at m/z 208 for a 830 ms signal duration. 42 The CosmOrbitrap is intended to be the mass analyzer of various laser ionization instruments currently under development for future planetary body missions. 43-45 In this work, we coupled the LILBID technique with a newly built laboratory Orbitrapbased mass spectrometer not intended for space applications, the Orbitrap anaLYzer MultiPle IonizAtion (OLYMPIA). 46 OLYMPIA was designed to be easily coupled with different ionization techniques, either continuous or pulsed. The coupling with the LILBID setup will allow a study of ice grain analogue samples with high mass resolution. The recorded mass spectra are intended to be included in the LILBID database built for SUDA's calibration in the Europa Clipper mission and future icy moons missions. With the current LILBID-TOF setup, isobaric interferences prevent an unambiguous peak assignment and an agnostic interpretation of the results. For this reason, hypervelocity detectors like ■ EXPERIMENTAL SECTION OLYMPIA Mass Spectrometer. OLYMPIA uses a commercial quadro-logarithmic electrostatic ion trap (QLEIT), an Orbitrap cell from Thermo Fisher Scientific. Thanks to a modular design, the ionization technique of OLYMPIA is easily interchangeable. Although it is a great challenge to use direct injection, to compact its design, our current setup does not feature a C-trap module, usually included in commercial instruments. 47 A C-trap is used as an intermediate storage device from which the ions are injected into the Orbitrap, in a spatially and energetically well-defined ion packet. As a first stage of development, OLYMPIA has been used with an electron ionization (EI) ion source to test each subsystem and to study gas samples relevant for planetary atmospheres. 46 OLYMPIA is composed of a commercial D30 cell from Thermo Fisher, which is around 60 mm long for 40 mm diameter. A detailed description of the Orbitrap functioning can be found in the literature. 38,40,47,48 Briefly, after focus, the ions are injected into the trap through a millimetric aperture and are squeezed electrodynamically around the central electrode. 48 The timing for the squeezing is relative to the laser pulse and is triggered a few microseconds after the ionization. The trapped ions oscillate in the cell with a frequency defined by the trap parameters and their m/z value. A large window of frequency can be measured during a single acquisition. As the frequency difference between heavy ions is lower than light ions, the mass range of an Orbitrap is not linear and increases with the m/z ratio. The maximum mass range is defined by a minimum to maximum mass ratio of 30. The mass range in this work is around 10 to 300 u. The detected signal is amplified by a preamplifier and converted by an analogue-to-digital convertor (ADC). Finally, using a discrete or fast Fourier transformation (DFT and FFT, respectively), the oscillation frequency of the ions is obtained. 47 For this work, we coupled OLYMPIA with a LILBID setup at the FU Berlin to simulate hypervelocity ice grain impacts and measure their composition with high mass resolution. We adapted the LILBID setup presented in Charvat et al. (2007). 35 Coupling in Parallel of the TOF-MS. OLYMPIA has been implemented in the LILBID-TOF setup on the opposite side of the main vacuum chamber (Figure 1). This configuration offers the possibility to use both methods to measure the same samples, allowing a direct data comparison. Switching from one mass spectrometer to the other can be done simply by changing the laser position.

OLYMPIA-LILBID: A New Laboratory Setup to Calibrate Spaceborne Hypervelocity Ice Grain Detectors Using High-Resolution Mass Spectrometry

Laser and Optics. We use a pulsed IR laser (Opolette HE 2731, OPOTEK) at 2840 nm with a 7 ns pulse width at a 20 Hz repetition rate. The laser energy is around 2 mJ per pulse. The measurement time for the Orbitrap usually spans a few hundred milliseconds. To minimize in the Orbitrap charge effects and radio frequency (RF) noise, the Q-Switch of the laser is fired only once per second. The triggering and synchronization with the Orbitrap cell are ensured by a CompactRIO controller (cRIO-9023, National Instruments). The laser radiation is steered by gold-coated mirrors and focused on the liquid beam with two CaF 2 AR-coated lenses through a CaF 2 window. We measured the spatial distribution of the laser energy on the OLYMPIA side using the knife-edge method 49 and estimated the laser power density at the water beam to be about 950 MW/cm 2 , a value close to that used in the LILBID-TOF setup (∼1150 MW/cm 2 ). 36 Liquid Beam. Using an HPLC pump (model 300c, Gynkotek) and a nozzle mounted on a 3-axis manipulator, a water beam with a diameter of 20 μm and a flow rate of typically 0.2-0.3 mL/min is created. The quartz nozzle of the standard LILBID-TOF setup has been replaced by a metallic nozzle, which can easily be set to a defined electric potential (see below).

Ion Optics. The electrodynamic squeezing by the Orbitrap requires defined kinetic energy 48 (KE) distribution of the ions. If so, both the number of trapped ions and their lifetime inside the cell increase, and thus the data quality improves (e.g., mass resolution or reproducible conditions for quantitative measurements). As already mentioned, in commercial Orbitrap instruments, the size and KE distribution of ion packets injected into the Orbitrap are guaranteed by the C-Trap module. Because of the absence of C-Trap in our design, the control of the KE must be accomplished with the ion optics only. In our setup, the measuring potential of the Orbitrap central electrode is -3500 V; for this value, the optimal KE for the ions to be captured is around 1100 eV. At the location of ion generation, the ion optics creates an electrostatic field that accelerates the ions to this desired KE. The surroundings of the water beam have been modified compared to the LILBID-TOF source, which does not require an electrostatic field at the ionization site. In addition to the metallic nozzle, a repeller electrode has been added to push the ions toward the Orbitrap and a potential can be applied on the skimmer close to the water beam (Figure 1). A fourth electrode is placed after the skimmer. A high voltage of up to 2000 V relative to the electrical ground can be applied on each of these electrodes with HV power supplies (iseg Spezialelektronik). It is worth noting that using the LILBID-TOF source, the ions fly from the water beam toward the extraction region of the TOF in a field-free environment and are then accelerated by applying a short HV pulse to the TOF electrodes. By changing the delay time between ion generation (i.e., laser pulse) and this commutation, different ions can be selected. While at short delay times fast ions with smaller masses are selected, at longer delays, heavier ions can be detected. The main difference with the LILBID-OLYMPIA source with the current settings is that the ions are not allowed to fly freely but are immediately accelerated to a rather high KE. However, if required, the timing for the Orbitrap central electrode can be adjusted to analyze, e.g., the trailing part of the ion distribution. A postacceleration is also possible by switching the potentials after the ion's creation. After the first four electrodes, the ion beam is focused into a seven-element manifold/stack. It consists of four circular lenses that allow focusing or defocusing according to the voltage polarity applied and three half-circular elements for deflection of the ion beam (Figure 1).

Electron Multiplier for Alignment. To adjust and optimize the ion optics settings, an electron multiplier (DeTech 2300) has been placed behind the Orbitrap and measures the ions going through the cell. The output signal of this detector allows visualization of the ion packet duration, intensity, and velocity.

Multistage Vacuum Design. As mentioned above, the lifetime of the ions is one of the key parameters for highresolution measurements.

C

commercial Orbitrap is usually several seconds 50 and the vacuum of the order of 10 -10 mbar. To minimize collisions with the neutral background molecules in our experiments, a four-stage vacuum system has been designed. First, in the main vacuum chamber, a turbomolecular pump (STP-iS2207, Edwards Vacuum) evacuates the water beam chamber. Two liquid nitrogen-cooled cryotraps are used to efficiently pump out the water vapor. Another cryotrap is used as a liquid beam dump. The resulting pressure in the main chamber is around 5 × 10 -5 mbar. Downstream the main chamber, ion optics, OLYMPIA chamber, and the Orbitrap cell are interfaced through differential pumping walls with apertures of less than 1 mm in diameter. Each of these three stages is pumped with a turbomolecular pump (HiPace 80 & HiPace 300, Pfeiffer Vacuum). The resulting pressure in the cell during measurements is typically ∼10 -8 mbar, which is a rather high value for Orbitrap measurements. Previous studies have shown 41,51 that the mass resolution starts to deteriorate by the neutral background gas at pressures above 1 × 10 -8 mbar. We thus expect a difference between the measure, and theoretical mass resolution of the measurements.

■ RESULTS AND DISCUSSION

Tin Study Results and Performances. After a successful parallel mechanical integration of the OLYMPIA setup on the LILBID-TOF at the FU Berlin laboratory, the first steps were to control the correct alignment of the ion source with the ion optics and the Orbitrap. To ease this step and those of ion optics precalibration and timings, we first ionized a metal wire, as higher production of ions under laser-surface interaction is obtained than under the laser-liquid performed by LILBID. We analyzed a tin wire with 99.98% purity (Figure 2). The 10 stable isotopes of tin, which present an abundance variation of up to 3 orders of magnitude, allow to estimate the relative isotopic abundance (RIA) accuracy of the setup. The tin measurements also give a first idea of the setup's overall performances, such as mass resolution, mass accuracy, or detection limit.

The lifetime of ions in the Orbitrap cell is limited by several factors such as geometry imperfections, collision with a neutral background, or HV instabilities during the measurement time. 48 Moreover, the free induction decay transient of each isotope through time can be different, as less abundant ions are more affected by space charge effects than isotopes in higher The horizontal lines represent the theoretical abundance value of each isotope (see Table 1) normalized to the major isotope ( 120 Sn + ) intensity. Intensity deviation shows the center of the normal distribution fit and the 1-σ uncertainties (see Figure S2 for the histograms and fit plots). Unless indicated otherwise, values are for 250 ms mass spectra.

D

proportions. 53 The less abundant ions are therefore more likely to be repelled from a stable orbit, inducing an underestimation of these species. For the same reason, minor species will also be more impacted by the field imperfections. Overall, the deviation of quantitative measurements is affected over time, even for major ions, resulting in increasing errors over time. However, to improve the RIA accuracy, we can choose to analyze a short fraction (∼50 ms) of the measured signal and calculate the deviation before it is too much disturbed by space charge effects or imperfections in the electrostatic field. The same data can then be analyzed with a longer signal duration (a few hundreds milliseconds) to greatly improve the mass resolution. For this study, we show the mass resolution and mass accuracy for a 250 ms signal. The method for ion count quantification and isotopic comparison is explained in the Supporting Materials. Briefly, the total ion count for one isotope is the area under the curve of its peak, starting at 10% peak height (Figure S1). Each isotope ion count is normalized to the major 120 Sn + . The deviation errors are gathered in histograms on which a normal distribution fit is applied. The maximum of the fit is the mean error, and the 1-σ value is the confidence interval for 68.2% of the data (Figure S2). The deviation between the measured and theoretical abundances is shown for both a 50 ms signal and a 250 ms signal (Table 1). The different tin isotope abundances are shown in Table 1. The recorded mass spectrum is shown in Figure 2. To improve statistics and reduce the noise, we coadded and averaged 28 single mass spectra, selecting mass spectra only with high signal intensity. On each raw data recorded with the Orbitrap, we apply a Hann function-shaped window 54 to minimize spectral leakage and a 32 times zero-padding 55 to increase the discrete resolution. We managed to detect all 10 major isotopes of Tin, even the lowest abundant one 115 Sn + (0.34%), which brings the dynamic range of the setup with the current settings to about 10 3 . The intensity deviation of the more abundant isotopes (>4%) is on average -4% (± 2.2%). For the lowest abundant isotopes (<1%), the deviation is higher, around -20%. With a 250 ms signal, the intensity deviations become more variable. The peaks are all around 40 000 mass resolution (FWHM) with a highly precise mass accuracy of a few ppm (Table 1). The theoretical mass resolution at the mass of tin for a 250 ms mass spectra is around 80 000 without a function-shaped window and about half this value 56 when using a Hann window as we do in this work. As we do not use an outgassing sample, the pressure in the cell is around 2 × 10 -9 mbar. The results in Table 1 reach this theoretical mass resolution, demonstrating that the setup is highly efficient. It is worth noting that the mass resolution values of Table 1 correspond to mass spectra that have been averaged and resampled. The measured mass resolution may therefore be slightly above the theoretical one. The mass resolution for unaveraged mass spectra is at 95% of the theoretical.

On a short signal duration (50 ms), the intensity quantification has only a few percent deviation. We observe a greater deviation for low abundant ions due to space charge effects, which have a larger effect on low abundant ion packets compared to major isotopes. 53 Over time, the decrease of each ion intensity can be different due to neutral background or imperfections in the electrostatic field, resulting in an increasing deviation error between 50 and 250 ms.

Water Beam Results and Performances. The study of the tin wire has confirmed the success of the mechanical integration and allowed us to do a precalibration of the ion optics potentials and commutation timings. We then analyzed purified water ionized with the LILBID technique. We successfully measured water ions (H 2-3 O + ) with OLYMPIA. A mass spectrum is shown in Figure 3. The current results are presented with a signal duration of 80 ms. Both H 3 O + and H 2 O + ions stand out from the noise level with an SNR of around 20 and 10, respectively. By coadding and averaging only a few mass spectra, we can significantly reduce the noise level and reach SNR ratios of about 100 (Figure S3).

The lifetime of ions in the cell was sufficient to reach the high mass resolution expected with an Orbitrap. As shown in Figure 4, the recorded mass resolution is above 25 000 m/Δm for both peaks, for an 80 ms mass spectrum. The theoretical mass resolution at the mass of water and for this FFT duration and the use of a Hann window is around 31 000 m/Δm. As for the tin mass spectra, the measured mass resolution is much close to the theoretical value. In addition, the mass accuracy is also in the same range as with the tin wire data, with 11 ppm on the single mass spectrum presented, but which is usually below 3 ppm for an averaged mass spectrum.

Discussions of the Water Beam Experiments. To characterize the lifetime of ions and the maximum acquisition time, the signal can be divided into different slices through time and analyzed separately. This helps to follow the decrease of the signal through time. Figure 5 presents the averaged SNR during the measurements. The major species, H 3 O + , starts with an SNR of around 30. The amplitude shows a dip of around 75 ms. This could be attributed to variations or an improper optimization of the Orbitrap electrode (i.e., central or deflection) potential during the acquisition time, although this point is the subject of further work. With such variations, the ions would drift away from their original oscillation frequency, hence the amplitude diminution. After a potential stabilization, the H 3 O + ions return to their initial frequency and the SNR increases again. The SNR then steadily decreases, and an SNR of around 5 can still be observed at 250 ms. The H 2 O + ions are less abundant with the current setting; at the beginning of the signal, the SNR is around 10 and decreases faster than H 3 O + ions. After 150 ms, the signal is too low to be measurable.

On single mass spectra, H 3 O + ions can be detected up to 500 ms in the cell, reaching a mass resolution of around 150 000 FWHM (Figure S3). H 2 O + ions are, for now, destabilized after 80 ms, and a longer signal duration would not increase the data quality for this chemical species.

Laser Energy to Analogue Velocity. As shown by Klenner et al. (2019), the laser energies used during the experiments can be translated to impact speeds of spaceborne icy grains onto metal targets. By comparing the recorded OLYMPIA spectra with the LILBID-TOF spectra, we find that the spectral appearances match those of ice grains at impact speeds of 15-18 km/s.36 This demonstrates the proof-ofconcept objective of this work. Future experiments will aim to simulate lower impact speeds, which will require a modification of the current experimental setup.

■ CONCLUSIONS AND OUTLOOK

We successfully coupled OLYMPIA, a newly built Orbitrapbased mass spectrometer device to an LILBID setup, the reference technique for the simulation of hypervelocity ice grain mass spectra. This unique device is now able to record high-resolution mass spectra of liquid water. The focusing of water ions from the adapted LILBID source to the OLYMPIA mass analyzer has been achieved, and the first recorded mass spectra show H 3 O + and H 2 O + peaks, which look analogues to mass spectra of ice grains with the impact speed between 15 and 18 km/s measured with a CDA-type instrument. With sufficient SNR, the mass resolution of the mass spectra is usually between 80 and 95% of the theoretical mass resolution of an Orbitrap cell. This demonstrates the overall great performance of the setup. The lifetime of H 3 O + ions in the trap can be up to 500 ms, allowing us to measure peaks with a mass resolution of around 150 000 m/Δm. H 2 O + ions are destabilized earlier and survive for a shorter time period. Work is currently in progress on the setup to increase its performance and better stabilize the ion packet.

The tin isotopic study showed that the RIA deviation of OLYMPIA was deviated by less than a few percent from the theoretical value for isotopes with at least a few percent of abundance.

The LILBID-OLYMPIA setup has shown its ability to measure high laser energy mass spectra. Further work will now focus on producing and measuring water clusters, which appear at lower impact speeds in impact ionization data. To do so, we will first decrease the laser energy but also explore the effect of pulsing the electrodes of the ion optics and varying this delay time parameter, which we for now left aside. We will then dissolve inorganic and organic samples of interest in the liquid water and will be able to contribute to the SUDA database with high-resolution mass spectra. 37 In parallel, we are also exploring the impact of the electrostatic field in the ion source. By performing measurements on the LILBID-TOF setup with

III. 1

 1 Summary of the different configuration performances. . . . . . . . . . . . . . . . . . . . . . . . III.2 Summary of the different configurations performances. The SNR at 500 ms represents the value calculated only on 25 ms, from 475 to 500 ms. . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3 SNR values with additional cable length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.4 SNR (of major isotope) and noise values of the mass spectra. The SNR of the "Averaged value" column is calculated by averaging the SNR of 32 mass spectra, whereas the "Value of the averaged" column value is obtained after the averaging of the same 32 mass spectra in a single mass spectrum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1 Performances of the measurements shown in Figure IV.3, for the three species of the mixture and three different FFT durations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.2 RIA errors for mass spectra with 50 ms and 250 ms FFT duration, respectively. The N spectra columns represents the number of spectra that passed the ppm filter (± 15 ppm). Isotope abundances from Berglund and Wieser (2011). . . . . . . . . . . . . . . . . . . . . . . . . . . V.1 Energy density vs flashlamp Qswitch delay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.2 Mass and abundances of the ten natural stable isotopes of Tin (values from Berglund and Wieser, 2011). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.3 Deviation of the RIA for 50 ms and 250 ms FFT duration. The N spectra columns represent the number of mass spectra that passed the ppm filter (50 ms : 15 ppm -250 ms : 30 ppm). . . . . . VI.1 Results of each ionisation configuration. The lifetime value is taken when a significant signal is still detected on the 25 ms time slices (Krypton : Figure IV.4, Tin : Figure V.16, Water : Figure V.21). The differences with the theoretical resolution are taken at 300 ms (Figure VI.1). . . . .

  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.10 The evolution of spaceborne mass spectrometry and the major milestones. The figure show the variety of mass analyser used and the associated performances (mass resolution and mass range). (From Arevalo et al. 2020). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.11 Left : Picture of the flight model of CDA. Right : Technical drawing of CDA. HRD : High Rate Detector; EG : Entrance Grid; EMB : Electronics Main Box; MP : Multiplier; IG : Ion Grid; IIT : Impact Ionisation Target; CAT : Chemical Analyser Target (from Srama et al., 2004). . . . . . . I.12 Zoom of CDA mass spectra revealing the three types of grains measured around Enceladus during the E5 flyby at impact speeds of ~18 km/s. (a) Type I -Pure water with traces of sodium (b) Type II -organic rich (c) Type III -salt rich. The rhodium peaks are ejecta ions coming from CDA's Chemical Analyser Target (from the supplementary materials of Postberg et al., 2011a). . . . . I.13 Zoom of CDA mass spectra with different impact speed. The n number of H 2 O molecule is labelled next to the peak. The blue diamonds represent water clusters, the green triangles water molecules clustered with sodium and orange circle with Rhodium (baseline corrected, adapted from Klenner et al., 2019). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.14 SUDA and its different subsystems. The signal produced by incoming particles measured by each subsystem is displayed on the right side of the figure (adapted from Kempf et al. 2014). . . I.15 SUDA detection events for two different flyby altitudes. The dark blue points represent the detection of the targeted chaos region (here Thera Macula). The light blue points represent detection of other surface points. C/A : Closest Approach (from Goode et al. 2021). . . . . . . . I.16 ENceladus Icy Jet Analyser (from Srama et al. 2015). . . . . . . . . . . . . . . . . . . . . . . . I.17 Left : Impact Ionisation schematic coupled with a TOF mass analyser. Right : The LILBID technique coupled with a TOF mass analyser (adapted from Klenner et al. 2019). . . . . . . . . I.18 Baseline corrected laboratory analogue mass spectra of CDA Type 1 mass spectra measured with FU Berlin LILBID-TOF MS. 10 -7 M NaCl were diluted in the water sample to match Type I grains concentration. Those two mass spectra are the laboratory reproduction of the two CDA mass spectra shown in Figure I.13. Left panel : Analogous impact speed for CDA between 18 and 21 km/s. Right panel : Analogous impact speed for CDA between 4 and 6 km/s. To produce this mass spectrum, mass spectra with different experimental parameters have been co-added (different laser energy and HV commutation, see Chapter V for details). The blue diamonds represent water clusters peak in the form of (H 2 O) n H 3 O + , the green triangle water and NaCl clusters (H 2 O) n Na + . The value of n is labelled besides the respective symbols (adapted from Klenner et al., 2019). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.1 Schematic of the Kingdon Trap and the motion of one ion inside it. The black curves represent the simulated ions trajectories (Credit : MASS SPEC PRO). . . . . . . . . . . . . . . . . . . . II.2 Knight trap schematic and the motion of ions inside it (Credit : MASS SPEC PRO). . . . . . . II.3 SIMION representation of equipotential lines. Left : Original Kingdon trap with -10 V applied on the wire and a grounded cylinder. Right : Knight trap representation with end plates at 14 V and the central wire at -1 V (from Gillig et al., 1996). . . . . . . . . . . . . . . . . . . . . . . II.4 Left : A commercial D30 Orbitrap cell open along the axial axis, allowing to see the shape of the central electrode. The inner diameter of the cell is 30 mm and 40 mm long (from Makarov, 2000). Right : SIMION simulation of the electrostatic field inside the cell (Credit : Roland Thissen). . II.5 Cross-section of an Orbitrap cell with a representation of ions trajectory. Left : Ion path in red, the ions injection direction is represented by the red arrow. Right : Representation of ions radial position with different m/z, the orbital cross-section is exaggerated for illustration purpose. The green horizontal arrows represent the axial motion of the ions from one side of the Orbitrap cell to the other (from Hu et al., 2005). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.6 Theoretical mass resolution as a function of the m/z ratio of ions, for different FFT duration. With mass spectrometers using a Fourier Transform, a longer acquisition time results in a higher mass resolution. With increasing m/z ratio, the mass resolution decreases. . . . . . . . . . . . . . . . II.7 Simulation of the ions path with a static field or after an electrodynamic squeezing. The squeezing results in a decrease of both r and z radius (Credit : MASS SPEC PRO). . . . . . . . . . . . . . II.8 Simulation of the ion cloud in the Orbitrap cell through time and the measured signal shape. The simulation has been made by Kharchenko et al. (2012), more information can be found in their publication. Briefly : the authors added from Equation II.3 non-harmonic factors (here A 30 and A 40 ) that degrade the electrostatic field and provoke a broadening of the ion ring. The three simulations (a,b and c) are for different values for the non harmonic-factors. . . . . . . . . . . . II.9 Schematic of the C-trap module and the ion injection method. Ion path in yellow. The ions are stored in the C-trap module, before a fast injection in the Orbitrap cell (Credit : MASS SPEC PRO). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.10 Schematic of the LTQ Orbitrap™ commercialised in 2005 (from Eliuk and Makarov, 2015). . . II.11 Comparison of the two size of Orbitrap cells. (A) D30 cell. (B) D20 cell (from Denisov et al., 2012). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.12 The CosmOrbitrap subsystems. The CosmOrbitrap is composed of an Orbitrap cell, its electronics, the acquisition and data treatment subsystems. . . . . . . . . . . . . . . . . . . . . . . . . II.13 The vacuum chamber of OLYMPIA in Orléans in the EI configuration (without cable). The height of the setup is approximately 1 meter. It directly stands on its electronics cart containing all the HV and turbopumps controllers. The whole is about 2.2 m. . . . . . . . . . . . . . . . . II.14 OLYMPIA functional scheme of the EI configuration in 2019. The ions are created by applying a high current on the filament. The ion optics focus the created ions towards the Orbitrap cell, where they are captured and analysed. The ion signal is then measured by the pre-amplifier and the signal digitised by the PicoScope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.15 Left : OLYMPIA EI ion source without the Pusher electrode. Right : EI Ion source mounted on OLYMPIA, with the Pusher electrode. The filaments can be seen on the left picture on their white ceramic holder. The aperture towards the ion optics can be seen in the circle in the middle, this is also where the gas sample is directly injected. Small apertures allow the passage of the electron from the filament to the middle circle. . . . . . . . . . . . . . . . . . . . . . . . . . . II.16 OLYMPIA ion optics. Electrode 4 on the left and electrode 10 on the right, circled by the mounting interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.17 Scheme of the ion packet (in red) colliding with an electrode (seen in blue with a front view) and the current measured by a Picoamperemeter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.18 OLYMPIA ion optics simulation with SIMION. Left : 1 000 V on EL9, just below the KE of ion. Note the focus effect that allows the ions to go through EL10. Right : 1 350 V on EL9, the ions are almost all repelled backwards because of the strong electrostatic field and their KE lower than EL9. (Credit : Illia Zymak

  SNR through time. The signal is cut into 20 slices of 5 ms and the SNR is calculated for each of those slices. The signal shows a maximum around 25 ms, then rapidly decrease and is lost after 40 ms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.4 A broader view of the Krypton mass spectrum presented in Figure III.2. The mass spectral features show some strong noisy patterns at high masses. . . . . . . . . . . . . . . . . . . . . . III.5 Evolution of the SNR through time for the Thermo Fisher power supply (left) and a zoom on the 84 Kr + peak of a single mass spectrum with a 250 ms FFT (right). The calculated SNR represents the averaged SNR value on each time slice for 32 mass spectra. The error bars are the standard deviation for the 32 values of each slice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.6 SNR through time for the ISEG-Thermo Fisher configuration (left) and a zoom on the 84 Kr + peak of a mass spectrum recorded with the ISEG PS coupled with the Thermo Fisher Switcher (250 ms FFT duration). The calculated SNR represents the averaged SNR value on each slice for 32 mass spectra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.7 VCE variation for each PS configuration The signal is cut in 5 ms slice for ISEG-CGC and in 10 ms for the two others. The data used in this plot are the same data as for the zooms on the peak in the previous subsection, therefore it is the values of a single mass spectrum. At the end of each signal the values become aberrant because no signal is detectable anymore (calibration on noise). The special case of the ISEG-Thermo Fisher configuration is discussed at the end of this subsection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.8 Schematic of the different possible configurations for each HV Orbitrap channel. . . . . . . . . . III.9 Two mass spectra recorded with the Thermo Fisher PA (500 ms FFT duration). The upper mass spectrum is polluted with strong noise patterns from mass 40 to mass 140 and was recorded without any shielding. The bottom mass spectrum is with the same PA, but a proper shielding has been put in place. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.10 The possible configuration for both Pre-amplifiers. Left : Thermo Fisher and CZ PA outside the vacuum chamber. Right : The first stage of the CZ PA has been placed under vacuum. The other subsystems of OLYMPIA have been removed for clarity. . . . . . . . . . . . . . . . . . . . . .

  value. The amplitude measured for the three batches (respectively represented by a circle, a star and a plus symbols) are shown for each 1-volt step. The dotted lines represent the theoretical abundance of each isotope, normalised to the sum of the amplitude of the six isotopes (minus the noise level). . . . . . . . . . . . . . . . . . . . . IV.1 Example of the voltage applied on OLYMPIA ion optics in the EI configuration. From left to right : Source electrode, EL4 to EL10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.2 Picture of the gas mixer station. The gas sample bottles are connected from the lower tubes. Closing valves allow to entirely open or close each tube. The needle valves allows to inject a controlled amount of gas from a bottle (minimum flow rate ~0.3 stdL/min). Due to the primary pump, the minimum background pressure is around 0.8 mbar. The sample tank can be disconnected from the mixer and directly placed on the OLYMPIA inlet valve. . . . . . . . . . . . . . IV.3 Gas mixture mass spectra of CO/N 2 /C 2 H 4 with a 1:1:1 partial pressure ratio. Left : Zoom of mass spectra from 25 u to 29 u, with 20 and 50 ms FFT duration. Right : Zoom at m/z 28 with three different FFT durations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.4 SNR through time of three Krypton isotopes. The solid line represents the averaged SNR value of 32 files. Each file has been divided in 20 slices of 25 ms. The errors bars represent the standard deviation between 32 different acquisitions for each slice. . . . . . . . . . . . . . . . . . . . . IV.5 Comparison between the measured and the theoretical mass resolution. The black dotted line shows the theoretical mass resolution at 84 u. The measured mass resolution of each isotope is given with a 50 ms time step. The mass resolution is drawn from an averaged mass spectra (32 acquisitions). The same batch of acquisitions is processed multiple times with a different FFT duration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.6 Averaged krypton mass spectra with a 250 ms FFT. The horizontal blue lines are the theoretical abundances normalised to the intensity of major isotope 84 Kr + . . . . . . . . . . . . . . . . . . IV.7 Errors diagrams of the Krypton isotopes. The error is calculated relatively to major isotope 84 Kr + . The Gaussian fit is applied only on data that actually detected a peak, around ± 15 ppm from the isotopes m/z. The legend of each subplot shows on which value the Gaussian is centred, and the 1-sigma error associated (250 ms spectra with apodisation and 32 times zero-filling). The abundances of each isotope are indicated below the subplots. The bottom right subplot is the comparison of each isotope vs the theoretical value. On this subplot, the intensities represent the area under the curve starting at 10% peak height. . . . . . . . . . . . . . . . . . . . . . . . . .

  ). For readability, only one in two clusters is labelled. . . . . . V.25 LILBID-TOF configuration mass spectra with 1 000 V on the jet and various delay time (different Y-axis range for 0.5 μs). Lower right panel : LILBID-OLYMPIA mass spectrum of Figure V.20. V.26 LILBID-TOF configuration mass spectra with 1 000 V on the jet and different laser energy (different Y-axis range from Figure V.24 and Figure V.25). . . . . . . . . . . . . . . . . . . . . . . V.27 Left : CDA mass spectrum for impact velocities between 4 -6 km/s. Centre : LILBID-TOF mass spectrum. This mass spectrum is the result of the addition of mass spectra recorded with three different settings for the laser energy and delay times that are displayed in the panel. Both from Klenner et al., 2019. Right : LILBID-TOF mass spectrum from this work. Only one set of parameters was used to record this mass spectrum, 500 V was applied in the source. . . . . . . V.28 Top : 3D model of the source optics with the new tube electrode placed after the Skimmer (circled in red). Bottom : 3D printed tube-shaped electrode. . . . . . . . . . . . . . . . . . . . . . . . . V.29 Cross-section of a new design for OLYMPIA source optic. The two electrodes are in beige, the Orbitrap cell is towards the left of the figure. . . . . . . . . . . . . . . . . . . . . . . . . . . . VI.1 Measured mass resolution vs theoretical value. Left : Krypton isotopes, 1.10 -8 mbar. Centre : Tin isotopes, 3.10 -9 mbar. Right : H 3 O + and H 2 O + , 4.10 -8 mbar. Values are taken from an averaged mass spectrum (~30 mass spectra), with Hann window apodisation and no zero-filling. One value was measured every 50 ms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII.1 Left : 3D model of HANKA prototype. Each cube measures 10 cm 3 , and represents 1 unit of a Cubesat. Two units are dedicated to the electronics, and two to the Dust Ion Source, the Ion Optics and the Orbitrap cell. Noteworthy, HANKA ion optics is the same as OLYMPIA's. Right : A preliminary design of the dust ion source. The dust grains collide with the grids and the ions created are focused by an electrostatic field towards the right side of the figure, to the Orbitrap cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 .

 1 Figure I.1: Artist view of the Habitable Zone (Credit : NASA).

Figure I. 2 :

 2 Figure I.2: (Mostly) Icy worlds of the Solar System (to scale). Satellites labelled in blue are confirmed ocean worlds (Credit : Emily Lakdawalla/Planetary Society).

Figure I. 3 :

 3 Figure I.3: Europa (Credit : NASA).

Figure I. 4 :

 4 Figure I.4: Enceladus (Credit : NASA/ESA).

  Figure I.5 shows a representation of the icy moons interiors.

Figure I. 5 :

 5 Figure I.5: The interiors of ocean worlds and thickness of the hydrosphere (adapted from Vance et al., 2018).

Figure I. 6 ,

 6 [START_REF] Kelley | An Off-Axis Hydrothermal Vent Field near the Mid-Atlantic Ridge at 30[END_REF]). Earth hydrothermal vents host an extremely rich ecosystem at the seafloor of our oceans, which thrives even without photosynthesis. Hydrothermal vents are extensively studied as they could potentially be at the origin of life on Earth[START_REF] Martin | Hydrothermal Vents and the Origin of Life[END_REF], and by extension at the seafloor of the icy moons (Deamer and Georgiou, 2015; Sojo et al., 2016; Barge and White, 2017).

Figure I. 6 :

 6 Figure I.6: Lost City carbonate chimneys (Credit : D. Kelley/ M. Elend/UW/URI-IAO/NOAA/The Lost City Science Team).

Figure I. 7 :

 7 Figure I.7: Multiple jets located along the tiger stripes of Enceladus south pole forming the plume (Credit : NASA/JPL/Space Science Institute).

Figure I. 8 :

 8 Figure I.8: The different subsystems of a Mass Spectrometer (from Arevalo et al., 2020).

Figure I. 9 :

 9 Figure I.9: The same mass spectrum with different mass resolution. A : 5 000, B : 8 000, C : 15 000, D : 24 000 m/ ∆m (Credit : ScienceDirect).

1 A

 1 Powerful Tool for Space Exploration

Figure I. 10 :

 10 Figure I.10: The evolution of spaceborne mass spectrometry and the major milestones. The figure show the variety of mass analyser used and the associated performances (mass resolution and mass range). (From Arevalo et al. 2020).

Figure I. 11 :

 11 Figure I.11: Left : Picture of the flight model of CDA. Right : Technical drawing of CDA. HRD : High Rate Detector; EG : Entrance Grid; EMB : Electronics Main Box; MP : Multiplier; IG : Ion Grid; IIT : Impact Ionisation Target; CAT : Chemical Analyser Target (from Srama et al., 2004).

Figure I. 12 :

 12 Figure I.12: Zoom of CDA mass spectra revealing the three types of grains measured around Enceladus during the E5 flyby at impact speeds of ~18 km/s. (a) Type I -Pure water with traces of sodium (b) Type II -organic rich (c) Type III -salt rich. The rhodium peaks are ejecta ions coming from CDA's Chemical Analyser Target (from the supplementary materials of Postberg et al., 2011a).

Figure I. 13 :

 13 Figure I.13: Zoom of CDA mass spectra with different impact speed. The n number of H 2 O molecule is labelled next to the peak. The blue diamonds represent water clusters, the green triangles water molecules clustered with sodium and orange circle with Rhodium (baseline corrected, adapted from Klenner et al., 2019).

Figure I. 14 :

 14 Figure I.14: SUDA and its different subsystems. The signal produced by incoming particles measured by each subsystem is displayed on the right side of the figure (adapted from Kempf et al. 2014).

Figure I. 15 :

 15 Figure I.15: SUDA detection events for two different flyby altitudes. The dark blue points represent the detection of the targeted chaos region (here Thera Macula). The light blue points represent detection of other surface points. C/A : Closest Approach (from Goode et al. 2021).

Figure I. 16 :

 16 Figure I.16: ENceladus Icy Jet Analyser (from Srama et al. 2015).

Figure I. 17 :

 17 Figure I.17: Left : Impact Ionisation schematic coupled with a TOF mass analyser. Right : The LILBID technique coupled with a TOF mass analyser (adapted from Klenner et al. 2019).

Figure I. 18 :

 18 Figure I.18: Baseline corrected laboratory analogue mass spectra of CDA Type 1 mass spectra measured with FU Berlin LILBID-TOF MS. 10 -7 M NaCl were diluted in the water sample to match Type I grains concentration. Those two mass spectra are the laboratory reproduction of the two CDA mass spectra shown in Figure I.13. Left panel : Analogous impact speed for CDA between 18 and 21 km/s. Right panel : Analogous impact speed for CDA between 4 and 6 km/s. To produce this mass spectrum, mass spectra with different experimental parameters have been co-added (different laser energy and HV commutation, see Chapter V for details). The blue diamonds represent water clusters peak in the form of (H 2 O) n H 3 O + , the green triangle water and NaCl clusters (H 2 O) n Na + . The value of n is labelled besides the respective symbols (adapted from Klenner et al., 2019).

1. 1

 1 History of Development 1.1.

Figure II. 1 :

 1 Figure II.1: Schematic of the Kingdon Trap and the motion of one ion inside it. The black curves represent the simulated ions trajectories (Credit : MASS SPEC PRO).

  Figure II.1 the trajectory of the ions 1. THE ORBITRAP™ MASS ANALYSER CHAPTER II. A NEW ORBITRAP-BASED MS

Figure II. 2 :

 2 Figure II.2: Knight trap schematic and the motion of ions inside it (Credit : MASS SPEC PRO).

  , Gillig, Bluhm and Russel were able to simulate the electrostatic field lines inside the Kingdon and Knight trap (Figure II.3) showing the importance of the shape of the central electrode and the quadrologarithmic shape of the field associated.

Figure II. 3 :

 3 Figure II.3: SIMION representation of equipotential lines. Left : Original Kingdon trap with -10 V applied on the wire and a grounded cylinder. Right : Knight trap representation with end plates at 14 V and the central wire at -1 V (from Gillig et al., 1996).

4 )

 4 With z=0 the axial plane of symmetry, the subscript 1 and 2 the central and outer electrode and R 1 and R 2 the radii of the central and outer electrodes, respectively, as labelled in the right panel of Figure II.4.

Figure II. 4 :

 4 Figure II.4: Left : A commercial D30 Orbitrap cell open along the axial axis, allowing to see the shape of the central electrode. The inner diameter of the cell is 30 mm and 40 mm long (from Makarov, 2000). Right : SIMION simulation of the electrostatic field inside the cell (Credit : Roland Thissen).

Figure II. 5 :

 5 Figure II.5: Cross-section of an Orbitrap cell with a representation of ions trajectory. Left : Ion path in red, the ions injection direction is represented by the red arrow. Right : Representation of ions radial position with different m/z, the orbital crosssection is exaggerated for illustration purpose. The green horizontal arrows represent the axial motion of the ions from one side of the Orbitrap cell to the other (from Hu et al., 2005).

Figure II. 6 :

 6 Figure II.6: Theoretical mass resolution as a function of the m/z ratio of ions, for different FFT duration. With mass spectrometers using a Fourier Transform, a longer acquisition time results in a higher mass resolution. With increasing m/z ratio, the mass resolution decreases.

Figure II. 7 :

 7 Figure II.7: Simulation of the ions path with a static field or after an electrodynamic squeezing. The squeezing results in a decrease of both r and z radius (Credit : MASS SPEC PRO).

Figure II. 8 :

 8 Figure II.8: Simulation of the ion cloud in the Orbitrap cell through time and the measured signal shape. The simulation has been made by Kharchenko et al. (2012), more information can be found in their publication. Briefly : the authors added from Equation II.3 non-harmonic factors (here A 30 and A 40 ) that degrade the electrostatic field and provoke a broadening of the ion ring. The three simulations (a,b and c) are for different values for the non harmonic-factors.

Figure II. 9 :

 9 Figure II.9: Schematic of the C-trap module and the ion injection method. Ion path in yellow. The ions are stored in the C-trap module, before a fast injection in the Orbitrap cell (Credit : MASS SPEC PRO).

  to protect the geometry of the Orbitrap cell with the company HD Technologies Ltd that got later transferred to the firm Thermo Fisher Scientific in 2003. Since then, Makarov has still been working at Thermo Fisher and has developed several versions of commercial Orbitrap™ instruments. The first Orbitrap-based commercial instrument was available in 2005, the LTQ Orbitrap™ mass spectrometer (Figure II.10). The first version of the Orbitrap™ demonstrated very high mass resolution (120 000 FWHM at m/z 400) and mass accuracy of a few ppm. Coupled with a linear ion trap mass analyser (the "low-pressure cell" on Figure II.10

Figure II. 10 :

 10 Figure II.10: Schematic of the LTQ Orbitrap™ commercialised in 2005 (from Eliuk and Makarov, 2015).

1 )(

 1 II.10)With R 1 and R 2 the size of the central electrode, R m the ion distance from the centre, e the charge of an ion and Ur the applied voltage. From this equation, it is straightforward that by increasing the voltage Ur of the central electrode the oscillation frequency will increase proportionally to the square root of Ur, and therefore as the frequency is directly connected to the mass, also increase the mass resolution. In addition, the size parameter (R m , R 1 , R 2 ) can also directly change the oscillations frequency, in an inversely proportional way. After numerous prototypes with different sizes of cells and higher applied voltage[START_REF] Makarov | Performance Evaluation of a High-Field Orbitrap Mass Analyzer[END_REF], Thermo Fisher finally settled on a new design of an Orbitrap cell, 1.5 times smaller than the original one (with a diameter of 20 mm compared to the previous 30 mm cell, respectively called D20 and D30), and using 5 kV on the central electrode[START_REF] Michalski | Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes[END_REF]. A comparison of both sizes is showed in FigureII.11.

Figure II. 11 :

 11 Figure II.11: Comparison of the two size of Orbitrap cells. (A) D30 cell. (B) D20 cell (from Denisov et al., 2012).

Figure II. 12 :

 12 Figure II.12: The CosmOrbitrap subsystems. The CosmOrbitrap is composed of an Orbitrap cell, its electronics, the acquisition and data treatment subsystems.

Figure II. 13 :

 13 Figure II.13: The vacuum chamber of OLYMPIA in Orléans in the EI configuration (without cable). The height of the setup is approximately 1 meter. It directly stands on its electronics cart containing all the HV and turbopumps controllers. The whole is about 2.2 m.

  Figure II.13 displays a picture of OLYMPIA in its EI configuration. Figure II.14 shows its functional scheme, with the different subsystems and cables connections for the EI configuration.

Figure II. 14 :

 14 Figure II.14: OLYMPIA functional scheme of the EI configuration in 2019. The ions are created by applying a high current on the filament. The ion optics focus the created ions towards the Orbitrap cell, where they are captured and analysed. The ion signal is then measured by the pre-amplifier and the signal digitised by the PicoScope.

Figure II. 15 :

 15 Figure II.15: Left : OLYMPIA EI ion source without the Pusher electrode. Right : EI Ion source mounted on OLYMPIA, with the Pusher electrode.The filaments can be seen on the left picture on their white ceramic holder. The aperture towards the ion optics can be seen in the circle in the middle, this is also where the gas sample is directly injected. Small apertures allow the passage of the electron from the filament to the middle circle.

Figure II. 16 :

 16 Figure II.16: OLYMPIA ion optics. Electrode 4 on the left and electrode 10 on the right, circled by the mounting interface.

Figure II. 17 :

 17 Figure II.17: Scheme of the ion packet (in red) colliding with an electrode (seen in blue with a front view) and the current measured by a Picoamperemeter.

  3. OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS But if rising even more, i.e. above the kinetic energy of the ions, they will be repelled backwards. A SIMION simulation by I. Zymak is shown in Figure II.18 to illustrate this effect.

Figure II. 18 :

 18 Figure II.18: OLYMPIA ion optics simulation with SIMION. Left : 1 000 V on EL9, just below the KE of ion. Note the focus effect that allows the ions to go through EL10. Right : 1 350 V on EL9, the ions are almost all repelled backwards because of the strong electrostatic field and their KE lower than EL9. (Credit : Illia Zymak)

Figure II. 19 :

 19 Figure II.19: Oscilloscope screenshot of the detector signal (darker blue) after a laser shot (TTL signal in lighter blue). X-axis scale : 2 μs per division. Y-axis scale : 2 mV per division.

  Figure II.20: Subsystems controlled by the CompactRIO.

  Pressure Some studies at the LPC2E have already been carried out to assess the effect of the pressure on the CosmOrbitrap performances. The results are presented in Selliez (2018), from which Figure II.21 is drawn. The graph shows a diminution of the mass resolution of an order of magnitude, when rising the pressure from 2.10 -8 to 3.10 -7 mbar. Because of the experimental setup (i.e. gas injection in the source and not directly in the Orbitrap cell), it was not possible to clearly point out why the mass resolution of Indium was less impacted. Several hypotheses are plausible, the size of an adenine molecule is much bigger than an Indium atom (1.5 Å versus ~125 Ų[START_REF] Zhou | Large-Scale Prediction of Collision Cross-Section Values for Metabolites in Ion Mobility -Mass Spectrometry[END_REF]), and therefore their relative Collision-cross section is different. In any case, the pressure clearly strongly impacts the mass resolution and the overall performances of the Orbitrap™.

Figure II. 21 :

 21 Figure II.21: Impact of pressure on the mass resolution at a constant acquisition time (from Selliez, 2018).

  2.4. The image current induced by the axial oscillations of the ions must be measured differentially on both outer electrodes to estimate the signal difference between them. To that end, two screw pitches are drilled on each of the outer electrodes to insert conductive rods. The screw pitches are shown in Figure II.22.

Figure II. 22 :

 22 Figure II.22: OLYMPIA Orbitrap cell in its vacuum chamber. The two screw pitches that allow an image current measurement can be seen on both outer electrodes.

Figure II. 23 :

 23 Figure II.23: Top panel : A time domain spectrum recorded with the PicoScope and its associated software. Here, the acquisition time (X-axis) is 500 ms. Lower panel : Frequency spectrum obtained after applying the FFT.

Figure II. 24 :

 24 Figure II.24: Effect of apodisation window on a mass spectrum. The apodisation reduces the spectral leakage next to the mass peak but also widen the main mass peak (from Scigelova et al., 2011).

Figure

  Figure II.25: A raw signal (in blue) with the corresponding Hann shaped window (orange). The apodisation gives more weight in the Fourier Transform to the orange points.

Figure II. 26 :

 26 Figure II.26: The same mass spectrum processed twice, without zero-filling (in blue) and with 32 times more discrete resolution (orange). The orange mass peak is better defined.

Figure II. 27 :

 27 Figure II.27: A raw time domain signal cut into 50 ms slices. Each slice can be processed separately to monitor the shape of the signal through time, albeit at the expense of some performances (mass resolution in particular).

Figure II. 28

 28 Figure II.28: The effect of averaging and resampling. The coloured mass spectra are unaveraged mass spectra and the black mass spectrum is the average of 32 mass spectra. On the averaged spectrum, the noise level is significantly reduced and lower abundant species can be detected.

  Figure II.29 (the data in the diagrams were recorded with the 3. OLYMPIA CHAPTER II. A NEW ORBITRAP-BASED MS

Figure II. 29 :

 29 Figure II.29: Errors diagrams of 3 Tin isotopes. The error is calculated relatively to major isotope 120 Sn + . The Gaussian fit is applied only on data that actually detected a peak. The title of each subplot shows on which value the Gaussian is centred, and the 1-sigma error associated (50 ms spectra with apodisation and 8 times zero-filling).

Figure III. 1 :

 1 Figure III.1: Product Breakdown Structure of OLYMPIA and the improvement performed on each sub-system. The white boxes are modifications realised during the first phase of improvements and are detailed in Subsection 2.1. The yellow boxes were performed to increase the mass resolution and are presented in Subsection 2.2. The blue boxes were carried out later on, with high mass resolution mass spectra and are detailed in Subsection 2.2. The orange boxes represent plans for future work.

  Kr, as shown in Figure III.2 top panel. Zooms of the mass spectrum are presented in the lower panels. The exact ion mass, the mass accuracy, the SNR and the mass resolution are displayed next to the peak. A red cross is drawn inside the peak, which helps to better visualise what the performances values are referring to. The horizontal line is the full width at half maximum, and the vertical line is from the amplitude maximum to the noise level. The SNR is calculated by dividing the top of the vertical line by its base. Concerning the noise level, it is calculated by averaging only the positive values of the whole mass spectra because if both negative and positive values are taken, the noise level is close to 0 and is not representative of the actual SNR.

Figure III. 2 :

 2 Figure III.2: Top panel : Krypton mass spectrum averaged by the PicoScope software (32 mass spectra) with an FFT duration of 50 ms. The peak between83 Kr + and 84 Kr + is noise. Lower panels : zoom on isotope84 Kr + and 86 Kr + .

  -8 mbar in the cell) they should last few hundred milliseconds. To determine the actual ion lifetime value, the raw signal was cut into different time slices. The SNR of a peak is then calculated into each time slices, as shown in Figure III.3.

Figure III. 3 :

 3 Figure III.3: 84 Kr + SNR through time. The signal is cut into 20 slices of 5 ms and the SNR is calculated for each of those slices. The signal shows a maximum around 25 ms, then rapidly decrease and is lost after 40 ms.

  Figure III.4 displays a broader view of the mass spectrum shown in Figure III.2. Some artefacts are clearly visible, some at low masses, and some above 100 u.

Figure III. 4 :

 4 Figure III.4: A broader view of the Krypton mass spectrum presented in Figure III.2. The mass spectral features show some strong noisy patterns at high masses.

Figure III. 5 :

 5 Figure III.5: Evolution of the SNR through time for the Thermo Fisher power supply (left) and a zoom on the 84 Kr + peak of a single mass spectrum with a 250 ms FFT (right). The calculated SNR represents the averaged SNR value on each time slice for 32 mass spectra. The error bars are the standard deviation for the 32 values of each slice.

Figure III. 6 :

 6 Figure III.6: SNR through time for the ISEG-Thermo Fisher configuration (left) and a zoom on the 84 Kr + peak of a mass spectrum recorded with the ISEG PS coupled with the Thermo Fisher Switcher (250 ms FFT duration). The calculated SNR represents the averaged SNR value on each slice for 32 mass spectra.

Figure III. 7 :

 7 Figure III.7: VCE variation for each PS configurationThe signal is cut in 5 ms slice for ISEG-CGC and in 10 ms for the two others. The data used in this plot are the same data as for the zooms on the peak in the previous subsection, therefore it is the values of a single mass spectrum. At the end of each signal the values become aberrant because no signal is detectable anymore (calibration on noise). The special case of the ISEG-Thermo Fisher configuration is discussed at the end of this subsection.

  FigureIII.7 shows the variation of the potential through time for each configuration. As a reminder, a variation of 10 mV already has an impact on the ions and can alter the data quality in the final mass spectra. The ISEG-CGC configuration shows a 5.5 V variation in just 40 ms. Such voltage variations make the ions drift away from their initial orbit which explains why no signal is detectable (e.g. at 40 ms on the ISEG-CGC subplot). However, even though this would widen the mass peaks and reduce the mass resolution, it should not necessarily mean that the ions are lost and we should normally see some secondary peaks at the new ion frequencies.As seen in Chapter II, a fast ion trapping after the injection is crucial for a thin ion ring orbiting the Orbitrap cell central electrode. If the trapping of ions with the CGC switch and the capacitors circuit behind is not efficient, the ions will, from the very beginning of the measurement, be spread along the axial axis. Coupled with the variation of the potential and the effect of the pressure, the ion could spread so much along the axial axis that no signal is no longer detectable. This was modelled inKharchenko et al. (2012) and showed in Figure II.8.The Thermo Fisher PS potential, on the other hand, is much more stable. Throughout the first 220 ms of the signal, variation of less than 0.2 V are detected before the potential goes back to its original value. This allows to analyse the data with a long signal duration (here 250 ms), and we can still obtain a perfectly shaped peak with high mass resolution. The decrease of the signal through time is most likely the effect of the pressure, which is still one or two orders of magnitude higher than the optimum for Orbitrap™ measurements.The question that remains is : what is wrong with the ISEG-Thermo Fisher configuration ? The lifetime of ions is as long as for the Thermo Fisher configuration, if not longer, yet the mass resolution is 10 times lower than expected. The third panel of Figure III.7 helps to understand the issue. There are entire time slices where the VCE value becomes aberrant, which means that no peak is detectable in the mass range of the calibrant. During those periods, the84 Kr + ions drift away from their original orbit and therefore change their oscillations frequency. This is why the general shape of the peak in Figure III.6 is asymmetric, with the frequency variation, the ions slowly build secondary peaks next to the main one.The surprising part is that the ions actually come back, which would indicate that the VCE potential also gets back to its original value. This confirms that a variation of VCE measure potential does not necessarily lead to a loss of all the ions, and that for the ISEG-CGC configuration another parameter has to disturb them. The potential over time for ISEG-Thermo Fisher is far more stable (apart from the aberrant parts) than ISEG-CGC, with 1.9 V of

Figure III. 8 :

 8 Figure III.8: Schematic of the different possible configurations for each HV Orbitrap channel.

2 .

 2 REACHING HIGH MASS RESOLUTION CHAPTER III. -ENHANCING OLYMPIA

Figure III. 9 :

 9 Figure III.9: Two mass spectra recorded with the Thermo Fisher PA (500 ms FFT duration). The upper mass spectrum is polluted with strong noise patterns from mass 40 to mass 140 and was recorded without any shielding. The bottom mass spectrum is with the same PA, but a proper shielding has been put in place.

Figure III. 10 :

 10 Figure III.10: The possible configuration for both Pre-amplifiers. Left : Thermo Fisher and CZ PA outside the vacuum chamber. Right : The first stage of the CZ PA has been placed under vacuum. The other subsystems of OLYMPIA have been removed for clarity.

Figure III. 11 :

 11 Figure III.11: Two mass spectra recorded with the CZ PA (500 ms FFT duration) with the first stage outside (upper panel) and inside the vacuum chamber (lower panel). The upper mass spectrum features the same noisy patterns as for the Thermo Fisher PA without shielding.

  Figure III.6 recorded with the ISEG-Thermo Fisher power supply configuration). Ultimately, as seen on Figure II.8 and the simulation from Kharchenko et al. (2012), strong electrostatic disturbances can broaden the ion ring and lead to a premature loss of the signal.

5 ,

 5 Figure II.5, Hu et al. 2005), each of them will see a different electrostatic field. Different behaviour for isotopes, like differences in the natural decrease of amplitude through time or even false quantitative estimation, also point out to a nonoptimised VDE measure value.

Figure III. 12 :

 12 Figure III.12: The SNR of 32 single mass spectra and the averaged value.

Figure III. 13 :

 13 Figure III.13: Example of the SNR through time for the four main isotopes of Krypton (for VDE measure = 350 V). The signal is cut into 20 slices of 30 ms, and the SNR is calculated on each file. The averaged SNR value (over the 32 mass spectra composing each batch) is then plotted. The cross-correlation value between the major, 84 Kr + , and the others is calculated and indicated above each subplot.

Figure III. 14 :

 14 Figure III.14: The mass resolution as a function of VDE measure potential on 20 ms long FFT mass spectra. The maximum theoretical mass resolution for such short FFT duration is 7 000 (without apodisation window).

Figure III. 15

 15 Figure III.15:The SNR for each Krypton isotope as a function of VDE measure potential on slices processed with a 20 ms FFT duration. Red :84 Kr + Black :86 Kr + Purple :82 Kr + Blue :83 Kr + Green :80 Kr + and Yellow :78 Kr + .

Figure III. 16 :

 16 Figure III.16: The evolution of the calibration peak, 84 Kr + , measured mass. The red line is the value obtained with VDE measure = 350 V.

Figure III. 17 :

 17 Figure III.17: Averaged performances for the second most abundant isotope 86 Kr + for the 3 data sets recorded from 340 to 380 V. The thick red lines are the average value of the three blue, yellow and orange thinner lines which are the value for one data set. Top panel : Mass resolution vs VDE measure value. Middle panel : Mass accuracy vs VDE measure value. Lower panel : SNR vs VDE measure value.

  The next investigation is the decay of the ion transient through time. Figure III.18 displays the evolution of the cross-correlation factor vs VDE measure value. A proper VDE measure value should mean an equal decay of each isotope transient through time, and thus, a cross-correlation value close to 1. Again, no specific value stands out. The cross-correlation factor is rather high (~0.85) but is quite variable from one data set to the other, and no pattern can be taken out.

Figure III. 18 :

 18 Figure III.18: Cross-correlation value of the SNR through time (10 slices of 33.5 ms FFT) vs VDE measure potential. The crosscorrelation factor of 86 Kr + , 82 Kr + and 83 Kr + vs 84 Kr + are averaged in a single value. As 80 Kr + and 78 Kr + are not always detected on single mass spectrum, they are left out of this averaging.

4 .

 4 VDE MEASURE OPTIMISATION CHAPTER III. -ENHANCING OLYMPIA Isotopic ratios Having established the SNR values for the isotopes, I then checked one of the most important parameters, the ability of the setup to measure proper isotopic ratios. For Figure III.19, the SNR of each isotope in the first FFT slice of 33.5 ms has been plotted

Figure III. 19 :

 19 Figure III.19: Amplitude of each krypton isotope vs VDE measure value. The amplitude measured for the three batches (respectively represented by a circle, a star and a plus symbols) are shown for each 1-volt step. The dotted lines represent the theoretical abundance of each isotope, normalised to the sum of the amplitude of the six isotopes (minus the noise level).

  Figure IV.1.

Figure IV. 1 :

 1 Figure IV.1: Example of the voltage applied on OLYMPIA ion optics in the EI configuration. From left to right : Source electrode, EL4 to EL10.

Figure IV. 2 :

 2 Figure IV.2: Picture of the gas mixer station. The gas sample bottles are connected from the lower tubes. Closing valves allow to entirely open or close each tube. The needle valves allows to inject a controlled amount of gas from a bottle (minimum flow rate ~0.3 stdL/min). Due to the primary pump, the minimum background pressure is around 0.8 mbar. The sample tank can be disconnected from the mixer and directly placed on the OLYMPIA inlet valve.

Figure IV. 3 :

 3 Figure IV.3: Gas mixture mass spectra of CO/N 2 /C 2 H 4 with a 1:1:1 partial pressure ratio. Left : Zoom of mass spectra from 25 u to 29 u, with 20 and 50 ms FFT duration. Right : Zoom at m/z 28 with three different FFT durations.

Figure IV. 4 :

 4 Figure IV.4: SNR through time of three Krypton isotopes. The solid line represents the averaged SNR value of 32 files. Each file has been divided in 20 slices of 25 ms. The errors bars represent the standard deviation between 32 different acquisitions for each slice. The increase of the maximum ion lifetime has a direct effect on the mass resolution, as seen on Figure IV.5.The figure shows the evolution of the mass resolution for all isotopes with different FFT length, as well as the theoretical maximum at m/z 84. The measured mass resolution increases linearly with time throughout the 500 ms, remaining close to the theoretical resolution. For a 500 ms FFT, the mass resolution of84 Kr + reaches 80 000, which is around 85% of the maximum achievable value for 500 ms at 84 u. However, the other isotopes do not show the same pattern. The mass resolution shows a similar increase up to about 250 ms and then has a less upward slope, to finally reach values around 40 000 at 500 ms (42% of the theoretical value).

Figure IV. 5 :

 5 Figure IV.5: Comparison between the measured and the theoretical mass resolution. The black dotted line shows the theoretical mass resolution at 84 u. The measured mass resolution of each isotope is given with a 50 ms time step. The mass resolution is drawn from an averaged mass spectra (32 acquisitions). The same batch of acquisitions is processed multiple times with a different FFT duration.

Figure IV. 6 :

 6 Figure IV.6: Averaged krypton mass spectra with a 250 ms FFT. The horizontal blue lines are the theoretical abundances normalised to the intensity of major isotope 84 Kr + .

Figure IV. 7 : 93 3.

 793 Figure IV.7: Errors diagrams of the Krypton isotopes. The error is calculated relatively to major isotope84 Kr + . The Gaussian fit is applied only on data that actually detected a peak, around ± 15 ppm from the isotopes m/z. The legend of each subplot shows on which value the Gaussian is centred, and the 1-sigma error associated (250 ms spectra with apodisation and 32 times zero-filling). The abundances of each isotope are indicated below the subplots. The bottom right subplot is the comparison of each isotope vs the theoretical value. On this subplot, the intensities represent the area under the curve starting at 10% peak height.

Figure V. 1 :

 1 Figure V.1: Schematic of the LILBID-TOF setup.For illustration reason, the laser has been placed on top, but the laser beam hits the water beam perpendicularly to the direction of the ion flight. After ionisation, the ions fly in field free environment through a skimmer that allows a differential pumping. The electrodes in the ion optics are then switched to accelerate the ions at a specific delay time. A strong potential (~6 kV) is applied on the Reflector to deflect the ions toward the detector.

Figure V. 2 :

 2 Figure V.2: Picture of the water beam ionised in front of the skimmer.

  As presented in Section 4 of Chapter I, the velocity of impact ionisation can vary from soft ionisation (~5 km/s) to very destructive ionisation (> 20 km/s). With high velocities, molecular fragmentation is frequent and species like O + , OH + or H 2 O + are dominant, whereas soft ionisation produces numerous water clusters of the form (H 2 O) n H + . Klenner et al. (2019) demonstrated that it is possible to mimic the different regime of impact speed with the LILBID setup. Figure V.3 drawn from that paper shows a comparison between CDA's measurements of Type 1 grains (i.e. icy grains composed of almost pure water with traces of sodium, Postberg et al., 2008) at different impact speed ranges, and laboratory analogue mass spectra measured with the LILBID-TOF setup with the same spectral appearances. The increase of concentrations of heavy water clusters with lower velocities is well visible on the figure.For LILBID-TOF analogue mass spectra, a single set of settings does not allow to mimic the full mass range of CDA's measurements. For that reason, acquisitions with two or three different experimental parameters (i.e delay time and laser energy) are co-added. The laser energy and delay time for each subplot are displayed next to each mass spectra. By co-adding mass spectra with the proper combination of both parameters, it is possible to mimic CDA's data and to attribute analogue impact speed to LILBID-TOF mass spectra. The two regimes (i.e. soft and hard ionisation) are easily recognisable with the increase of the water cluster concentration for low impact speed, and the apparition of species like O + , OH + or H 2 O + at high speeds.

Figure V. 4 :

 4 Figure V.4: Zoom on the TOF ion optics. After a specific delay time, the potential of the Repeller and Extractor is switched and the ion between the two electrodes accelerated.

Figure V. 3 :

 3 Figure V.3: Comparison of CDA's measurement at different impact speed with LILBID-TOF measured with different experimental parameters. Left column : baseline corrected CDA mass spectra of ice grains with different range of impact velocities. The velocity of impact changes the appearance of the mass spectra, with an increase of the concentration of heavy water clusters. Right column : Baseline corrected laboratory analogue mass spectra of CDA type 1 mass spectra (see main text) measured with FU Berlin LILBID-TOF MS. 10 -7 M NaCl were diluted in the water sample to match Type I grains concentration. For velocities below 13 -15 km/s, mass spectra with different experimental parameters are co-added (see main text for details). The blue diamonds represent water clusters peak in the form of (H 2 O) n H 3 O + , the green triangle water and NaCl clusters (H 2 O) n Na + , and orange circles water and Rhodium clusters (H 2 O) n Rh + . The value of n is labelled besides the respective symbols (adapted from Klenner et al., 2019).

2 .

 2 ADAPTATION FOR OLYMPIA INTEGRATION CHAPTER V. LILBID-OLYMPIA flybys of Europa at velocities between 4 and 5 km/s, where even heavy organic molecules are preserved mostly unfragmented (Klenner et al., 2020a; Jaramillo-Botero et al., 2021; Cable et al., 2021).

  Figure V.5, and in the schematic in Figure V.6.

Figure V. 5 :

 5 Figure V.5: Picture of the double-headed setup with the two mass analysers at FU Berlin. LILBID-OLYMPIA on the left, LILBID-TOF on the right. The laser is placed for TOF measurements in this picture.

Figure V. 6 :

 6 Figure V.6: Schematic of the LILBID-OLYMPIA and LILBID-TOF double setup. For illustration reasons, the laser has been placed on top, but the laser beam strikes the water beam perpendicular to the direction of the ion flight. The ions paths are in dark red. The LILBID additional electrodes (see Subsection 2.2.2) are labelled. Jet : Water beam HV; SK : Skimmer; R : Repeller; F : Focus. (from Sanderink et al., 2023)

  Figure V.8, and the repeller jet and skimmer are visible in the right picture of Figure V.7.

Figure V. 7 :

 7 Figure V.7: Left : Standard quartz nozzle used for the LILBID-TOF configuration. Right : Stainless steel nozzle used for the LILBID-OLYMPIA configuration. The little green dot below the nozzle is the laser hitting the water beam.

Figure V. 8 :

 8 Figure V.8: LILBID-OLYMPIA ion source. A potential of up to ±2 kV can be applied on Jet, Repeller, Skimmer and Focus.

Figure V. 9 :

 9 Figure V.9: Laser TTL scheme. The CompactRIO is controlled by a custom-made software and send the TTL signals to the delay generator (via the TGP 110 for the flashlamp signal).

Figure V. 10 :

 10 Figure V.10: Reflectance of the lenses antireflection coating. The reflectance is minimal at the wavelength of the laser, at 2840 nm. (Credits : Thorlabs) During my PhD, two different optic paths have been used. The first version was mimicking the TOF path, as the geometries are quite similar. To have the proper height, the laser is placed on custom spacers. An AntiReflection (AR) coated CaF 2 lens with 100 mm of focal distance is placed just after the laser output. The AR coating has been chosen to minimise the energy losses through the lens, as the reflectance is minimum at our 2840 nm (Figure V.10). As a comparison, an uncoated CaF 2 lens only reaches ~95% of transmission in near-IR wavelength. A gold-coated mirror (Thorlabs' MIR Enhanced Gold with >98% reflectance) redirects the laser beam inside OLYMPIA chamber and a final 50 mm coated lens focuses the laser beam at the water beam. The final lens is mounted on a 1-axis adjustable holder, to precisely set the focus point.However, this optic path was very unreliable. The last lens had to be realigned by hand every time we switched the laser position, and the spacers were adapted for the TOF skimmer but were not exactly at the proper position for OLYMPIA's. During a campaign in June 2022, Ales Charvat (researcher from Institute of Chemical Technology at the Leipzig University), modified the optics and made a second version. The new optic path uses a periscope with two coated mirrors to modify the height of the laser beam, removing the need for the non-adapted spacers. The first 100 mm lens has been removed. The 50 mm lens is now fixed, but mounted on a mirror holder, that includes three screws for millimetre adjustments. This new configuration is much more reliable, is quickly readjustable after a laser repositioning and uses all available energy.

  Figure V.11.

Figure V. 11 :

 11 Figure V.11: Knife-edge method for the laser power density estimation. The razor blade is progressively moved in front of the laser spot. The power measured with the Watt-meter is noted when the razor blade occults 10% (A) and 90% (B) of the total power. A picture of the experimental setup is shown on the right.

Figure V. 12 :

 12 Figure V.12: Spot diameter as a function of the X displacement.

Figure V. 13 :

 13 Figure V.13: Laser timing scheme. The Qswitch delay can navigate around the maximum of the rod fluorescence to adjust the laser energy.

Figure V. 14 :

 14 Figure V.14: Laboratory mass spectrum obtained with the LILBID-OLYMPIA setup in Leipzig with a 1064 nm laser wavelength (as opposed to the usual wavelength of 2840 nm). A solution of deionised water doped with 10 -3 M of NaCl and 10 -3 M of CsI was used. This mass spectrum is an averaged one from 74 mass spectra, a Hann function shaped window has been applied. Enlargements of the mass range 14 to 40 and 125 to 135 are displayed to better visualise the peaks with low intensities. On standard LILBID-TOF mass spectra, O + , OH + and H 2 O + are the characteristic water species for high energy mass spectra, with analogue impact speed above 18 km/s (see Figure V.3 & Klenner et al. 2019). On the contrary, the first water cluster (H 2 O)H 3 O + , is a marker of lower energy and analogue velocities, appearing only below 15 km/s. Although the speeds may seem close, the joint occurrence of these two markers is barely observed in individual LILBID-TOF mass spectra.The laser wavelength modification changed the energy available for ionisation, but also the final spectral appearance of the measurements. For this reason, even if water molecules and clusters are detected, the creation of plasma during ionisation makes the results not applicable for our science application, as only the desorption regime is analogous to impact ionisation in the desired velocity range.

Figure V. 15 :

 15 Figure V.15: Zoom on the Tin major isotope 120 Sn + , measured with the ISEG power supply for both level of VCE. (850 ms FFT duration). Because of the drift of the HV Orbitrap during the acquisition, the peak significantly drifts towards higher masses. Plot of a single mass spectrum.

Figure V. 16 :

 16 Figure V.16: SNR through time of three Tin isotopes. The signal has been cut into 50 slices of 20 ms. The VCE potentials was set back to injection level at 850 ms.

Figure V. 16

 16 Figure V.16 shows the SNR through time of three Tin isotopes. The acquisition lasts 1 full second but the VCE potential was switched back to the injection level at 850 ms, ending the ion trapping. The signal is still present, and intense, at 850 ms. This is way longer than the results presented with the EI configuration (see Section 2.1 of Chapter III), that only lasted 50 ms with the same ISEG power supply for VCE measure . This is most likely due to the better vacuum in the Orbitrap cell for the Tin measurements.

Figure V. 17 :

 17 Figure V.17: Two Tin isotopes in an averaged mass spectrum obtained with the Thermo Fisher power supply for VCE measure . The FFT duration is 500 ms (with apodisation and 16 times zero filling).

Figure V. 18 :

 18 Figure V.18: Averaged 50 ms Tin mass spectra. The horizontal blue lines are the theoretical abundance normalised to the intensity of major isotope 120 Sn + (from Sanderink et al., 2023).

Figure V. 19 :

 19 Figure V.19: Top panel : Screenshot of the signal measured by the detector (yellow) displayed on an oscilloscope. The oscilloscope was in average mode (5 samples, representing 5 laser shots), the orange signal is the Qswitch TTL output (i.e. the actual laser shot). Scale : Horizontal : 5 µs / division -Vertical 1 mV / division. Bottom panel : the different HV optics values applied on each electrode. From left to right : Repeller, Jet, Skimmer, Focus, electrode 4 to electrode 10.

Figure V. 20

 20 shows an averaged (6 files) mass spectrum, in which H 3 O + and H 2 O + are detected, two enlargements of the peaks are shown in the lower panels. The mass spectrum processed with a 50 ms FFT duration. Overall, the mass spectrum is very clean, and no structured noise can be seen, apart from a tiny peak at 12.2 u (1.97 MHz). The mass spectrum shown here and the associated SNR is quite representative of what is usually measured with the setup, with a H 2 O + peak roughly one third the intensity of H 3 O + . The achieved mass resolution is at 97% of the theoretical (20 000 m/Δm for 50 ms FFT duration), and the mass accuracy of H 2 O + is + 6 ppm. 5. LILBID-OLYMPIA CHAPTER V. LILBID-OLYMPIA The mass spectrum shown in Figure V.20 is obtained from the first portion of a 500 ms signal. If we look at the SNR through time in the rest of the mass spectrum, H 3 O + and H 2 O + behave quite differently. Figure V.21 shows the transient decay for both ions. H 3 O

Figure V. 20 :

 20 Figure V.20: Top panel : LILBID-OLYMPIA averaged mass spectrum from 1 to 150 u. 50 ms FFT duration, average of 6 different acquisitions, 8 times zero filling and apodisation Hann window. Lower panels : zooms on H 3 O + and H 2 O + peaks.

Figure V. 21 :

 21 Figure V.21: SNR through time of H 3 O + and H 2 O + . The SNR values of about 20 files are averaged into the ones displayed on the figure (25 slices of 20 ms). The error bars are calculated with the standard deviation between the SNR values of all files for each slice. The files in this mass spectra are the same as used for Figure V.20.

Figure V. 22

 22 Figure V.22 shows both ions peaks for a long acquisition time (500 ms for H 3 O + and 200 ms for H 2 O + ).As usual with a Fourier Transform mass analyser, the mass resolution is much higher with long acquisition time, reaching 126 000 m/Δm for H 3 O + . However, with the increasing FFT duration, a secondary peak can be observed in both plots. The secondary peak of H 2 O + actually becomes more intense than the real peak, after around 100 ms. The H 3 O + secondary peak is at around the main peak half maximum. Both peaks grow at the same distance from the original peak, corresponding to a frequency difference of about 23 Hz.

Figure V. 22 :

 22 Figure V.22: Left : H 3 O + peak with 500 ms FFT duration, 16 mass spectra averaged. Right : H 2 O + with 200 ms FFT duration, 6 mass spectra averaged. A secondary peak can be observed for both species, at 23 Hz from the main peak.

5 .

 5 LILBID-OLYMPIA CHAPTER V. LILBID-OLYMPIA Measurements of a Deuterium-doped Solution To explore the detection limit of the setup, I made some measurements with deuterium-rich water. 2% of D 2 O have been diluted in the water sample. To directly compare two species, they must have the same physical behaviour, which is why isotopes are suitable for RIA deviation determination. The detection of DH 2 O + was successful, as shown in Figure V.23. A zoom on the DH 2 O + peak is displayed on the right panel. The mass spectrum shown is the average of 77 mass spectra selected with an intensity filter on H 3 O + (at least 1 mV of amplitude). H 3 O + , H 2 O + and DH 2 O + are detected, all with a mass resolution close to 20 000 m/Δm (for 50 ms FFT duration). The mass accuracy is below 10 ppm for both peaks. In the averaged mass spectrum, the amplitude of the DH 2 O + peak is 3% of the H 3 O + . Due to the high mass resolution of the Orbitrap cell, it is possible to attribute the peak to DH 2 O + (20.0241 u) and not to D 2 O + (20.0226 u) which is not detected. It is expected to measure a higher concentration of DH 2 O + than D 2 O + , as it is consistent with the higher amplitude of H 3 O + than H 2 O + observed with pure water. A sample with 0.2% of D 2 O has been tested, but no signal DH 2 O + was detected.

Figure V. 23 :

 23 Figure V.23: Mass spectrum of deionised water doped with 2% of D 2 O. 50 ms FFT duration, 77 mass spectra, 4 times zerofilling, Hann apodisation

Figure V. 24 :

 24 Figure V.24: LILBID-TOF mass spectra with HV applied on the Jet. The labelled peaks are water molecules (H 2 O + , H 3 O + and (H 2 O) n H 3 O + ). For readability, only one in two clusters is labelled.

Figure V. 25 :

 25 Figure V.25: LILBID-TOF configuration mass spectra with 1 000 V on the jet and various delay time (different Y-axis range for 0.5 μs). Lower right panel : LILBID-OLYMPIA mass spectrum of Figure V.20.

Figure V. 26 :

 26 Figure V.26: LILBID-TOF configuration mass spectra with 1 000 V on the jet and different laser energy (different Y-axis range from Figure V.24 and Figure V.25).

Figure V. 27 :

 27 Figure V.27: Left : CDA mass spectrum for impact velocities between 4 -6 km/s. Centre : LILBID-TOF mass spectrum. This mass spectrum is the result of the addition of mass spectra recorded with three different settings for the laser energy and delay times that are displayed in the panel. Both from Klenner et al., 2019. Right : LILBID-TOF mass spectrum from this work.Only one set of parameters was used to record this mass spectrum, 500 V was applied in the source.

Figure V. 28 :

 28 Figure V.28: Top : 3D model of the source optics with the new tube electrode placed after the Skimmer (circled in red). Bottom : 3D printed tube-shaped electrode.

Figure V. 29 :

 29 Figure V.29: Cross-section of a new design for OLYMPIA source optic. The two electrodes are in beige, the Orbitrap cell is towards the left of the figure.

. 1 .

 1 Table VI.1: Results of each ionisation configuration. The lifetime value is taken when a significant signal is still detected on the 25 ms time slices (Krypton : Figure IV.4, Tin : Figure V.16, Water : Figure V.21). The differences with the theoretical resolution are taken at 300 ms (Figure VI.1).

  Figure V.15). By contrast, Krypton ions only survived about 50 ms with the same power supply (Figure III.3).

Figure VI. 1 :

 1 Figure VI.1: Measured mass resolution vs theoretical value. Left : Krypton isotopes, 1.10 -8 mbar. Centre : Tin isotopes, 3.10 -9 mbar. Right : H 3 O + and H 2 O + , 4.10 -8 mbar. Values are taken from an averaged mass spectrum (~30 mass spectra), with Hann window apodisation and no zero-filling. One value was measured every 50 ms.

Figure VII. 1 :

 1 Figure VII.1: Left : 3D model of HANKA prototype. Each cube measures 10 cm 3 , and represents 1 unit of a Cubesat. Two units are dedicated to the electronics, and two to the Dust Ion Source, the Ion Optics and the Orbitrap cell. Noteworthy, HANKA ion optics is the same as OLYMPIA's. Right : A preliminary design of the dust ion source. The dust grains collide with the grids and the ions created are focused by an electrostatic field towards the right side of the figure, to the Orbitrap cell.

Figure 1 .

 1 Figure 1. Flowchart of the extendable, publicly accessible database system including (from right to left) data acquisition, data pre-processing, data ingestion and post-processing. Processes shown to the right, with exception of the laser induced Liquid Beam Ion Desorption (LILBID) technique itself, are performed on the laboratory computer (sampling). Processes shown to the left are performed on the server (pre-processing, ingestion and data retrieval) and on the user computer (information selection and output).

  Section 2.4). An error (+/-) can be applied because of the potential peak shifts in level-1 mass spectra (see Section 2.4).

Figure 2 .

 2 Figure 2. Search interface of the Laser Induced Liquid Beam Ion Desorption (LILBID) mass spectral database. It is possible to filter the database output via parameters that depend on the measuring solution (e.g., substance name and apparent peaks in the mass spectra) as well as adjustable setup parameters (e.g., laser intensity and delay time). Here, as an example, given input parameters are I. Substance = sodium chloride, II. Ion Mode = positive, III. Delay Time = 4.8-6.0 µs. Filtering for these input parameters results in the interface shown in Figure 3.

  parameters that are important for the comparison with and interpretation of impact ionization mass spectra recorded in space.

Figure 3 .

 3 Figure 3. Results interface of the Laser Induced Liquid Beam Ion Desorption (LILBID) mass spectral database after filtering for example, input parameters (see Figure2). Formula: Chemical formula of the analyte. Concentration: Concentration of the analyte. Images: Graphical plot of the level-3 file. Files: Download of the spectral text file.

  et al., 2019; Postberg et al., 2009, 2018). The LILBID mass spectra can also be used to forecast the potential mass spectral appearance of all water soluble and many water insoluble substances that might appear in ice grains emitted by extraterrestrial active ocean worlds (e.g., as demonstrated in Klenner, Postberg, Hillier, Khawaja, Cable, et al., 2020; Klenner, Postberg, Hillier, Khawaja, Reviol, et al., 2020).

Figure 4 .

 4 Figure 4. Graphical plots (created using the commercial software OriginPro) of the same Laser Induced Liquid Beam Ion Desorption mass spectrum at different data processing levels. The plots show a cation mass spectrum of water with a NaCl concentration of approximately 10-7 M generated using a delay time of 5.5 µs and a laser intensity of 98.5%. The peaks are labeled with corresponding masses (x-values). Top left: The pre-processed data (level-1) shows a slightly bumpy baseline and peaks shifted from their real isotopic masses. The text file's header can be found in Figure S2 of Supporting Information S1. Top right: The recalibrated data (level-2) shows corrected isotopic masses but still a slightly bumpy baseline. Bottom left:The recalibrated and baseline corrected data (level-3) exhibits an even baseline and corrected isotopic masses.

Figure 1 .

 1 Figure 1. Schematic of the OLYMPIA instrument: principal components of the vacuum system (left panel); CAD model of the arrangement of the vacuum system (right panel) made of Pfeiffer Vacuum, Edwards Vacuum, and Hositrad Vacuum Technologies commercial off-the-shelf components (publicly available models of turbo pumps, vacuum chambers, ion gauges, flanges, and feedthroughs have been used).

Figure 1 .

 1 Figure 1. Schematic of the OLYMPIA instrument: principal components of the vacuum system (left panel); CAD model of the arrangement of the vacuum system (right panel) made of Pfeiffer Vacuum, Edwards Vacuum, and Hositrad Vacuum Technologies commercial off-the-shelf components (publicly available models of turbo pumps, vacuum chambers, ion gauges, flanges, and feedthroughs have been used).

Figure 2 .

 2 Figure 2. Functional illustration of OLYMPIA. Components inside (resp. outside) the vacuum chamber are indicated in grey (resp. in blue).

Figure 2 .

 2 Figure 2. Functional illustration of OLYMPIA. Components inside (resp. outside) the vacuum chamber are indicated in grey (resp. in blue).

3. 1 . 12 Figure 3 .

 1123 Figure 3. The EI mass spectrum of N2/CO/C2H4 gas mixture with a 1:1:1 ratio. Ionization chamber pressure is estimated at 1 mbar. Accuracy of the measured peak mass values is 5-20 ppm compared to NIST atomic weights and isotopic composition data. Spectra are evaluated from the same time domain data measurement by adjusting its duration at the processing phase to remain fixed conditions of the experiment.

Figure 3 .

 3 Figure 3. The EI mass spectrum of N 2 /CO/C 2 H 4 gas mixture with a 1:1:1 ratio. Ionization chamber pressure is estimated at 1 mbar. Accuracy of the measured peak mass values is 5-20 ppm compared to NIST atomic weights and isotopic composition data. Spectra are evaluated from the same time domain data measurement by adjusting its duration at the processing phase to remain fixed conditions of the experiment.

Aerospace 2023 , 12 Figure 4 .

 2023124 Figure 4. Mass spectra of the N2/CO/C2H4 mixture measured with different FFT duration times of the same time domain measurement (m/∆m ≈ 6000 at 20 ms, m/∆m ≈ 16,000 at 50 ms, m/∆m ≈ 47,000 at 250 ms). The ionization cross-section of neutrals and the ionization energy are given for the three species. Direction of the charge transfer reaction is indicated using the arrows.

Figure 5 .

 5 Figure 5. Measured fraction of N2 + ions as a function of nitrogen gas ratio in the known mixture. The fit function is calculated for the linear scale data using the least squares method.

Figure 4 .

 4 Figure 4. Mass spectra of the N 2 /CO/C 2 H 4 mixture measured with different FFT duration times of the same time domain measurement (m/∆m ≈ 6000 at 20 ms, m/∆m ≈ 16,000 at 50 ms, m/∆m ≈ 47,000 at 250 ms). The ionization cross-section of neutrals and the ionization energy are given for the three species. Direction of the charge transfer reaction is indicated using the arrows.

Figure 4 .

 4 Figure 4. Mass spectra of the N2/CO/C2H4 mixture measured with different FFT duration times of the same time domain measurement (m/∆m ≈ 6000 at 20 ms, m/∆m ≈ 16,000 at 50 ms, m/∆m ≈ 47,000 at 250 ms). The ionization cross-section of neutrals and the ionization energy are given for the three species. Direction of the charge transfer reaction is indicated using the arrows.

Figure 5 .

 5 Figure 5. Measured fraction of N2 + ions as a function of nitrogen gas ratio in the known mixture. The fit function is calculated for the linear scale data using the least squares method.

Figure 5 .

 5 Figure 5. Measured fraction of N 2 + ions as a function of nitrogen gas ratio in the known mixture. The

Figure 6 .

 6 Figure 6. Mass spectra of the krypton gas calibrated and normalized to 84 Kr + ion compared to the NIST isotopic composition database (red marks). Experimental m/z values are indicated near labels of isotopes by green numbers (better than 20 ppm mass accuracy).

  Arnaud Sanderink,* Fabian Klenner, Illia Zymak, Jan Z ̌abka, Frank Postberg, Jean-Pierre Lebreton, Bertrand Gaubicher, Ales Charvat, Bernd Abel, Miroslav Polásěk, Barnabé Cherville, Laurent Thirkell, and Christelle Briois Cite This: https://doi.org/10.1021/acs.analchem.2c04429 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: The coupling of an Orbitrap-based mass analyzer to the laserinduced liquid beam ion desorption (LILBID) technique has been investigated, with the aim to reproduce the mass spectra recorded by Cassini's Cosmic Dust Analyzer (CDA) in the vicinity of Saturn's icy moon Enceladus. LILBID setups are usually coupled with time-of-flight (TOF) mass analyzers, with a limited mass resolution (∼800 m/Δm). Thanks to the Orbitrap technology, we developed a unique analytical setup that is able to simulate hypervelocity ice grains' impact in the laboratory (at speeds in the range of 15-18 km/s) with an unprecedented high mass resolution of up to 150 000 m/Δm (at m/z 19 for a 500 ms signal duration).The results will be implemented in the LILBID database and will be useful for the calibration and future data interpretation of the Europa Clipper's SUrface Dust Analyzer (SUDA), which will characterize the habitability of Jupiter's icy moon Europa.

Figure 1 .

 1 Figure 1. Schematic of the current setup at the FU Berlin laboratory. OLYMPIA has been connected in parallel to the TOF mass spectrometer. R: repeller, SK: skimmer, and jet: water beam high voltage (HV). The laser has been placed above the setup for illustration reasons; in reality the laser shot hits the water beam perpendicularly to both ion optics.

Figure 2 .

 2 Figure 2. Tin mass spectrum recorded with the setup. The acquisition time for this plot is 50 ms. Then, 28 mass spectra are coadded and averaged.The horizontal lines represent the theoretical abundance value of each isotope (see Table1) normalized to the major isotope ( 120 Sn + ) intensity.

Figure 3 .

 3 Figure 3. H 2 O + and H 3 O + single mass spectrum recorded with the LILBID-OLYMPIA setup. The acquisition time for this spectrum is 80 ms.

Figure 4 .

 4 Figure 4. Zoom on the H 2 O + and H 3 O + peaks shown in Figure 3. The mass resolution, the mass accuracy, and the SNR are shown on the plot. The mass resolution is calculated using the full width at half maximum (FWHM). The base of the vertical line represents the noise level calculated by averaging the positive values of the mass spectra; the features around the peaks are therefore noise artifacts. The horizontal line represents the width at half maximum. To increase the peak shape quality, we applied a zero-filling (4 times) and a Hann function-shaped window.

Figure 5 .

 5 Figure 5. Signal to noise ratio for H 3 O + and H 2 O + through time. Each slice represents the average SNR value of about 40 spectra. The total signal duration is 500 ms and is cut into 20 slices of 25 ms.

CONTENTS 3

 3 .2.3 Electron Multiplier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Electronic Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 TTL Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.7 Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.8 Data Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III Enhancing OLYMPIA : Technical Modifications and Trade-offs 1 Overview of Improvements and Optimisations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Reaching High Mass Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 First Phase -Technical Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Second Phase -Power Supply Trade-off . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 VCE measure Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 VCE Injection & VDE Power Supplies . . . . . . . . . . . . . . . . . . . . . . 2.2.3 VCE Cable Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pre-amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Test Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OLYMPIA Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 LILBID Water beam & Ion Optics Adjustments . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Water Beam Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Additional Ion Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Laser Adjustments for the LILBID-OLYMPIA Configuration . . . . . . . . . . . . . . . 2.3.1 Triggers Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Laser Optic Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Laser Energy Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Results of the October 2019 Leipzig Campaign . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 FU Berlin Tin Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Preliminary Experiments with ISEG Power Supply (HV Orbitrap ) . . . . . . . . . . . . . . 4.2 Results with the Thermo Fisher Power Supply (HV Orbitrap ) . . . . . . . . . . . . . . . . . The Quest for Water Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Investigating the Effects of an Electrostatic Field in LILBID-TOF Source . . . . . . . . . 6.1.1 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.3 Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.4 LILBID-TOF Improvements from the HV source Study . . . . . . . . . . . . . . 6.2 Adaptation for Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Source Electrostatic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Delayed Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Ions Behaviour with the New Source Settings . . . . . . . . . . . . . . . . . . 7 LILBID-OLYMPIA Conclusion & Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . .

	CONTENTS	CONTENTS
	6
	Multi-Ionisation Results Comparison
	General Conclusions and Perspectives

3.3 PA Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 VDE Measure Optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Purpose of VDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Discussions & Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV High Mass Resolution and Ions Behaviour in Electron Impact Configuration 1 Technical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Operating Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Continuous Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Gas Mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Gas Mixture Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Krypton Isotopes Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Conclusions on the RIA Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V Simulating Hypervelocity Icy Grains Impact Ionisation with OLYMPIA 1 The LILBID Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 The Standard LILBID-TOF Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Simulating Different Impact Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Mechanical & Hardware Adaptation for OLYMPIA Integration . . . . . . . . . . . . . . . . . . . 2.1 4.3 Discussions & Conclusions of the Tin Experiments . . . . . . . . . . . . . . . . . . . . . 5 LILBID-OLYMPIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Ions Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Conclusion of the Water Beam Experiments . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography Appendices LILBID Database Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electron Impact OLYMPIA Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LILBID-OLYMPIA Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

  Artist view of the Habitable Zone (Credit : NASA). . . . . . . . . . . . . . . . . . . . . . . . . I.2 (Mostly) Icy worlds of the Solar System (to scale). Satellites labelled in blue are confirmed ocean worlds (Credit : Emily Lakdawalla/Planetary Society). . . . . . . . . . . . . . . . . . . . . . . I.3 Europa (Credit : NASA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.4 Enceladus (Credit : NASA/ESA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.5 The interiors of ocean worlds and thickness of the hydrosphere (adapted from Vance et al., 2018). I.6 Lost City carbonate chimneys (Credit : D. Kelley/ M. Elend/UW/URI-IAO/NOAA/The Lost City Science Team). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.7 Multiple jets located along the tiger stripes of Enceladus south pole forming the plume (Credit : NASA/JPL/Space Science Institute). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.8

	I.1

  ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.19 Oscilloscope screenshot of the detector signal (darker blue) after a laser shot (TTL signal in lighter blue). X-axis scale : 2 μs per division. Y-axis scale : 2 mV per division. . . . . . . . . . II.20 Subsystems controlled by the CompactRIO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.21 Impact of pressure on the mass resolution at a constant acquisition time (from Selliez, 2018). . . .23 Top panel : A time domain spectrum recorded with the PicoScope and its associated software. Here, the acquisition time (X-axis) is 500 ms. Lower panel : Frequency spectrum obtained after applying the FFT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.24 Effect of apodisation window on a mass spectrum. The apodisation reduces the spectral leakage next to the mass peak but also widen the main mass peak (from Scigelova et al., 2011). . . . . . II.25 A raw signal (in blue) with the corresponding Hann shaped window (orange). The apodisation gives more weight in the Fourier Transform to the orange points. . . . . . . . . . . . . . . . . . II.26 The same mass spectrum processed twice, without zero-filling (in blue) and with 32 times more discrete resolution (orange). The orange mass peak is better defined. . . . . . . . . . . . . . . . II.27 A raw time domain signal cut into 50 ms slices. Each slice can be processed separately to monitor the shape of the signal through time, albeit at the expense of some performances (mass resolution in particular). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II.28 The effect of averaging and resampling. The coloured mass spectra are unaveraged mass spectra and the black mass spectrum is the average of 32 mass spectra. On the averaged spectrum, the noise level is significantly reduced and lower abundant species can be detected. . . . . . . . . . II.29 Errors diagrams of 3 Tin isotopes. The error is calculated relatively to major isotope 120 Sn + . The Gaussian fit is applied only on data that actually detected a peak. The title of each subplot shows on which value the Gaussian is centred, and the 1-sigma error associated (50 ms spectra with

II.22 OLYMPIA Orbitrap cell in its vacuum chamber. The two screw pitches that allow an image current measurement can be seen on both outer electrodes. . . . . . . . . . . . . . . . . . . . . IIapodisation and 8 times zero-filling). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.1 Product Breakdown Structure of OLYMPIA and the improvement performed on each sub-system. The white boxes are modifications realised during the first phase of improvements and are detailed in Subsection 2.1. The yellow boxes were performed to increase the mass resolution and are presented in Subsection 2.2. The blue boxes were carried out later on, with high mass resolution mass spectra and are detailed in Subsection 2.2. The orange boxes represent plans for future work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2 Top panel : Krypton mass spectrum averaged by the PicoScope software (32 mass spectra) with an FFT duration of 50 ms. The peak between 83 Kr + and 84 Kr + is noise. Lower panels : zoom on isotope 84 Kr + and 86 Kr + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3 84 Kr +

  III.11 Two mass spectra recorded with the CZ PA (500 ms FFT duration) with the first stage outside (upper panel) and inside the vacuum chamber (lower panel). The upper mass spectrum features the same noisy patterns as for the Thermo Fisher PA without shielding. . . . . . . . . . . . . . . III.12 The SNR of 32 single mass spectra and the averaged value. . . . . . . . . . . . . . . . . . . . . III.13 Example of the SNR through time for the four main isotopes of Krypton (for VDE measure = 350 V). The signal is cut into 20 slices of 30 ms, and the SNR is calculated on each file. The averaged SNR value (over the 32 mass spectra composing each batch) is then plotted. The cross-correlation value between the major,84 Kr + , and the others is calculated and indicated above each subplot. . III.14 The mass resolution as a function of VDE measure potential on 20 ms long FFT mass spectra. The maximum theoretical mass resolution for such short FFT duration is 7 000 (without apodisation window). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.15 The SNR for each Krypton isotope as a function of VDE measure potential on slices processed with a 20 ms FFT duration. Red : 84 Kr + Black : 86 Kr + Purple : 82 Kr + Blue : 83 Kr + Green : 80 Kr + and Yellow : 78 Kr + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.16 The evolution of the calibration peak, 84 Kr + , measured mass. The red line is the value obtained with VDE measure = 350 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.17 Averaged performances for the second most abundant isotope 86 Kr + for the 3 data sets recorded from 340 to 380 V. The thick red lines are the average value of the three blue, yellow and orange thinner lines which are the value for one data set. Top panel : Mass resolution vs VDE III.18 Cross-correlation value of the SNR through time (10 slices of 33.5 ms FFT) vs VDE measure potential. The cross-correlation factor of 86 Kr + , 82 Kr + and 83 Kr + vs 84 Kr + are averaged in a single value. As 80 Kr + and 78 Kr

	LIST OF FIGURES	LIST OF FIGURES

measure value. Middle panel : Mass accuracy vs VDE measure value. Lower panel : SNR vs VDE measure value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + are not always detected on single mass spectrum, they are left out of this averaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.19 Amplitude of each krypton isotope vs VDE measure

  The electrodes in the ion optics are then switched to accelerate the ions at a specific delay time. A strong potential (~6 kV) is applied on the Reflector to deflect the ions toward the detector. . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.2 Picture of the water beam ionised in front of the skimmer. . . . . . . . . . . . . . . . . . . . . V.4 Zoom on the TOF ion optics. After a specific delay time, the potential of the Repeller and Extractor is switched and the ion between the two electrodes accelerated. . . . . . . . . . . . . V.3 Comparison of CDA's measurement at different impact speed with LILBID-TOF measured with different experimental parameters. Left column : baseline corrected CDA mass spectra of ice grains with different range of impact velocities. The velocity of impact changes the appearance of the mass spectra, with an increase of the concentration of heavy water clusters. Right column : Baseline corrected laboratory analogue mass spectra of CDA type 1 mass spectra (see main text) measured with FU Berlin LILBID-TOF MS. 10 -7 M NaCl were diluted in the water sample to match Type I grains concentration. For velocities below 13 -15 km/s, mass spectra with different experimental parameters are co-added (see main text for details). The blue diamonds represent water clusters peak in the form of (H 2 O) n H 3 O + , the green triangle water and NaCl clusters (H 2 O) n Na + , and orange circles water and Rhodium clusters (H 2 O) .12 Spot diameter as a function of the X displacement. . . . . . . . . . . . . . . . . . . . . . . . . V.13 Laser timing scheme. The Qswitch delay can navigate around the maximum of the rod fluorescence to adjust the laser energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.14 Laboratory mass spectrum obtained with the LILBID-OLYMPIA setup in Leipzig with a 1064 nm laser wavelength (as opposed to the usual wavelength of 2840 nm). A solution of deionised water doped with 10 -3 M of NaCl and 10 -3 M of CsI was used. This mass spectrum is an averaged one from 74 mass spectra, a Hann function shaped window has been applied. Enlargements of the mass range 14 to 40 and 125 to 135 are displayed to better visualise the peaks with low intensities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.15 Zoom on the Tin major isotope 120 Sn + , measured with the ISEG power supply for both level of VCE. (850 ms FFT duration). Because of the drift of the HV Orbitrap during the acquisition, the peak significantly drifts towards higher masses. Plot of a single mass spectrum. . . . . . . . . . V.16 SNR through time of three Tin isotopes. The signal has been cut into 50 slices of 20 ms. Screenshot of the signal measured by the detector (yellow) displayed on an oscilloscope. The oscilloscope was in average mode (5 samples, representing 5 laser shots), the orange signal is the Qswitch TTL output (i.e. the actual laser shot). Scale : Horizontal : 5 µs / division -Vertical 1 mV / division. Bottom panel : the different HV optics values applied on each electrode. From left to right : Repeller, Jet, Skimmer, Focus, electrode 4 to electrode 10. . . . . . . . . . . V.20 Top panel : LILBID-OLYMPIA averaged mass spectrum from 1 to 150 u. 50 ms FFT duration, average of 6 different acquisitions, 8 times zero filling and apodisation Hann window. Lower panels : zooms on H 3 O + and H 2 O + peaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.21 SNR through time of H 3 O + and H 2 O + . The SNR values of about 20 files are averaged into the ones displayed on the figure (25 slices of 20 ms). The error bars are calculated with the standard deviation between the SNR values of all files for each slice. The files in this mass spectra are the same as used for Figure V.20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.22 Left : H 3 O + peak with 500 ms FFT duration, 16 mass spectra averaged. Right : H 2 O + with 200 ms FFT duration, 6 mass spectra averaged. A secondary peak can be observed for both species, at 23 Hz from the main peak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.23 Mass spectrum of deionised water doped with 2% of D 2 O. 50 ms FFT duration, 77 mass spectra, 4 times zero-filling, Hann apodisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.24 LILBID-TOF mass spectra with HV applied on the Jet. The labelled peaks are water molecules (H 2 O + , H 3 O + and (H 2 O) n H 3 O +

	LIST OF FIGURES	LIST OF FIGURES
	V.19 Top panel :

n Rh + . The value of n is labelled besides the respective symbols (adapted from

Klenner et al., 2019)

. . . . . . . . . . . V.

5

Picture of the double-headed setup with the two mass analysers at FU Berlin. LILBID-OLYMPIA on the left, LILBID-TOF on the right. The laser is placed for TOF measurements in this picture. V.

6

Schematic of the LILBID-OLYMPIA and LILBID-TOF double setup. For illustration reasons, the laser has been placed on top, but the laser beam strikes the water beam perpendicular to the direction of the ion flight. The ions paths are in dark red. The LILBID additional electrodes (see Subsection 2.2.2) are labelled. Jet : Water beam HV; SK : Skimmer; R : Repeller; F : Focus. (from Sanderink et al., 2023) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.7 Left : Standard quartz nozzle used for the LILBID-TOF configuration. Right : Stainless steel nozzle used for the LILBID-OLYMPIA configuration. The little green dot below the nozzle is the laser hitting the water beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.8 LILBID-OLYMPIA ion source. A potential of up to ±2 kV can be applied on Jet, Repeller, Skimmer and Focus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.9 Laser TTL scheme. The CompactRIO is controlled by a custom-made software and send the TTL signals to the delay generator (via the TGP 110 for the flashlamp signal). . . . . . . . . . V.10 Reflectance of the lenses antireflection coating. The reflectance is minimal at the wavelength of the laser, at 2840 nm. (Credits : Thorlabs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V.11 Knife-edge method for the laser power density estimation. The razor blade is progressively moved in front of the laser spot. The power measured with the Watt-meter is noted when the razor blade occults 10% (A) and 90% (B) of the total power. A picture of the experimental setup is shown on the right. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VThe VCE potentials was set back to injection level at 850 ms. . . . . . . . . . . . . . . . . . . . . . V.17 Two Tin isotopes in an averaged mass spectrum obtained with the Thermo Fisher power supply for VCE measure . The FFT duration is 500 ms (with apodisation and 16 times zero filling). . . . . V.18 Averaged 50 ms Tin mass spectra. The horizontal blue lines are the theoretical abundance normalised to the intensity of major isotope 120 Sn + (from Sanderink et al., 2023). . . . . . . . . . .

Table III . 1 :

 III1 Summary of the different configuration performances.

	Configuration	Maximum Mass resolution Last detectable ions
	ISEG -CGC	5 000	50 ms
	ISEG -Thermo Fisher Switch	7 000	200 ms
	Thermo Fisher Power supply & Switch	35 000	200 ms

Table III . 2 :

 III2 Summary of the different configurations performances. The SNR at 500 ms represents the value calculated only on 25 ms, from 475 to 500 ms.

	Configuration		VCE	VDE	SNR (over 500 ms)	SNR (475-500 ms)
		Measure	Injection	Measure Injection 84 Kr + 86 Kr + 78 Kr +	84 Kr +
	#1	Thermo ISEG NHR	ISEG NHR	112	28	2	2.5
	#2	Thermo ISEG NHR	ISEG SHQ	103	36	N/A	3.1
	#3	Thermo	FUG HCP	ISEG NHR	498	126	12	7.3
	#4	Thermo	FUG HCP	ISEG SHQ	381	134	8	6.4

Table III .

 III 3: SNR values with additional cable length.

	Additional cable length		SNR
		84 Kr + 86 Kr + 78 Kr +
	0 m	103	36	N/A
	1 m	156	57	2
	2 m	350	120	6
	3 m	150	51	N/A
	4 m	250	96	8

Table IV .

 IV 2: RIA errors for mass spectra with 50 ms and 250 ms FFT duration, respectively. The N spectra columns represents the number of spectra that passed the ppm filter (± 15 ppm). Isotope abundances from[START_REF] Berglund | Isotopic Compositions of the Elements 2009 (IUPAC Technical Report)[END_REF].

	Isotope	Theoretical Abund-ance (%)	Ion count error (%) 50 ms	1-sigma interval 50 ms	N spectra 50 ms	Error on Averaged spectra (%)	Ion count error (%) 250 ms	1-sigma interval 250 ms	N spectra 250 ms	Error on Averaged spectra (%)
						50 ms				250 ms
	78 Kr + 80 Kr + 82 Kr + 83 Kr + 84 Kr +	0.36 2.29 11.60 11.50 56.99	+ 1312 + 264 + 67 + 85 Calibrant Calibrant ± 440 ± 74 ± 35 ± 30	5 16 16 16 32	+ 364 + 118 + 12 + 78 Calibrant Calibrant Calibrant + 430 ± 140 + 139 ± 40 + 66 ± 19 + 41 ± 14	19 28 31 30 32	+ 423 + 116 + 52 + 36 Calibrant
	86 Kr +	17.3	+ 59	± 27	18	+ 26	+ 29	± 13	29	+ 23

Table V .

 V 1: Energy density vs flashlamp Qswitch delay.

	FL-Qs Delay	Resulting Power	Energy density
	[µs]	[%]	[MW/cm^2]
	140	100	947
	145	96	913
	150	89	849
	155	80	758
	160	71	670
	165	60	565
	170	48	460
	175	38	359
	180	28	266

Table V .

 V 2: Mass and abundances of the ten natural stable isotopes of Tin (values from[START_REF] Berglund | Isotopic Compositions of the Elements 2009 (IUPAC Technical Report)[END_REF].

	Tin isotope	Mass (Theoretical)	Abundance (Theoretical)
	112 Sn	111.9048	0.971 %
	114 Sn	113.9028	0.661 %
	115 Sn	114.9033	0.341 %
	116 Sn	115.9017	14.549 %
	117 Sn	116.9030	7.687 %
	118 Sn	117.9016	24.229 %
	119 Sn	118.9033	8.594 %
	120 Sn	119.9022	32.589 %
	122 Sn	121.9034	4.633 %
	124 Sn	123.9053	5.795 %

4.1 Preliminary Experiments with ISEG Power Supply (HV Orbitrap )

Table V .

 V 3: Deviation of the RIA for 50 ms and 250 ms FFT duration. The N spectra columns represent the number of mass spectra that passed the ppm filter (50 ms : 15 ppm -250 ms : 30 ppm).

	Tin iso-tope	Theoretical Abund-ance (%)	Intensity error (%) 50 ms	1-sigma interval 50 ms	N spec-tra 50 ms	Error on Averaged spectra (%) 50 ms	Intensity error (%) 250 ms	1-sigma interval 250 ms	N spec-tra 250 ms	Error on Averaged spectra (%) 250 ms
	112 Sn + 114 Sn + 115 Sn + 116 Sn + 117 Sn + 118 Sn + 119 Sn + 120 Sn +	0.971 0.661 0.341 14.549 7.687 24.229 8.594 32.589	-21.07 -16.72 -19.46 -5.53 -2.43 -2.61 -4.99 Calibrant Calibrant ± 5.84 ± 6.84 ± 11.11 ± 2.44 ± 2.58 ± 1.87 ± 1.16	24 21 8 31 31 31 31 31	-4 -18 -21 -2 + 1 -1 -2 Calibrant Calibrant Calibrant -14.18 ± 9.63 -24.92 ± 11.44 -39.69 ± 18.27 + 6.18 ± 10.21 + 3.89 ± 10.08 + 7.04 ± 6.29 + 2.08 ± 6.21	27 19 11 31 30 31 29 31	+ 12 -12 -22 + 10 + 10 + 11 + 3 Calibrant
	122 Sn + 124 Sn +	4.633 5.795	-3.37 -1.67	± 2.09 ± 2.43	31 31	-3 -6	-14.22 + 0.96	± 4.62 ± 7.54	30 28	-16 -17

  al., 2019; Klenner et al., 2019; Klenner, Postberg, Hillier, Khawaja, Cable, et al., 2020; Klenner, Postberg, Hillier, Khawaja, Reviol, et al., 2020;

  The lifetime of ions trapped inside a

	Analytical Chemistry	pubs.acs.org/ac	Article

https://doi.org/10.1021/acs.analchem.2c04429

Anal. Chem. XXXX, XXX, XXX-XXX

Table 1 .

 1 Theoretical Properties of Tin from the NIST Standard 52 and the Measured Values from This Work a

		mass	abundance	mass accuracy	mass resolution		intensity deviation (50	intensity
	isotope 112 Sn 114 Sn 115 Sn 116 Sn 117 Sn 118 Sn 119 Sn	(theoretical) 111.9048 u 113.9028 u 114.9033 u 115.9017 u 116.9030 u 117.9016 u 118.9033 u	(theoretical) 0.97% 0.66% 0.34% 14.54% 7.68% 24.22% 8.59%	(ppm) 0.4 1.3 -2.1 1 -0.9 0.0 3.3	(FWHM) 42 339 44 908 41 017 40 348 40 593 40 653 40 644	SNR 41 22 9 599 315 1014 338	ms) -19.4 ± 5.5% -25.2 ± 6.2% -17.5 ± 9.4% -5.8 ± 2.4% -3.2 ± 2.5% -2.6 ± 1.8% -6.4 ± 1.8%	deviation -6.8 ± 10.5% -17.9 ± 12.8% -15.8 ± 21.3% + 3.1 ± 6.8% + 1.4 ± 7.1% + 5.0 ± 6.2% + 3.3 ± 4.9%
	120 Sn 122 Sn 124 Sn	119.9022 u 121.9034 u 123.9053 u	32.58% 4.63% 5.79%	calibrant -0.7 0.6	41 145 41 157 41 136	1257 153 189	calibrant -3.0 ± 2.2% -3.5 ± 2.5%	calibrant -11.4 ± 5.6% -9.3 ± 4.9%
	a

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https://doi.org/10.1021/acs.analchem.2c04429Anal. Chem. XXXX, XXX, XXX-XXX E

Acknowledgments

This PhD thesis is the result of a personal adventure that started long before the beginning of the PhD. However as all personal adventures, many people were involved in the process and allowed its completion.

Acknowledgments

The authors thank Bertrand Gaubicher (LPC2E/CNRS, Orléans) for helpful Acknowledgments: Authors of the paper gratefully acknowledge Alexander Makarov for his kind support, starting from helping with the conceptual design of a new instrument to the final data analysis. This support motivated the research team to try new methods and approaches.

■ ACKNOWLEDGMENTS

The authors thank Dr. Alexander Makarov for valuable discussions about this work. A.S. thanks the French Space National Agency, the Centre National des Etudes Spatiales (CNES), as well as ERC Consolidator Grant 724908-Habitat OASIS for the funding of his Ph.D. The authors also gratefully acknowledge CNES for funding the instrumental development of OLYMPIA. This work was also supported by the Czech Science Foundation (grant no. 21-11931J). The authors are also grateful to M. Nezvedová for her help during the coupling campaign.

Data Availability Statement

Data-The LILBID mass spectrum raw data used in this paper (see Figure 4) can be retrieved from https://doi. org/10.5281/zenodo.6863855 [START_REF] Klenner | LILBID mass spectrum of water[END_REF]. Data-The CDA mass spectrum raw data used in this paper (see Figure 5) can be retrieved from NASA's Planetary Data System (PDS) Small Bodies Node via https://sbnarchive. psi.edu/pds3/cassini/cda/COCDA_0007.tar.gz (Planetary Science Institute, 2022).

Data Availability Statement:

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to use of sensitive information provided by Thermo Fisher Scientific, Bremen, Germany.

• We describe the development of a comprehensive spectral database containing laboratory analogue data for spaceborne mass spectrometers • The database is based on a Relational Database Management System with a web interface and accessible for community use • Filtering the laboratory data using a wide range of experimental parameters allows a straightforward analysis of returned flight data

Supporting Information:

Supporting Information may be found in the online version of this article. 10.1029/2022EA002313

9 of 11 the location of the peaks detected by a peak detection routine. By filtering for experimental parameters and peaks, characteristic mass spectra can be selected for further analysis.

LILBID data processing, mass spectral analysis and comparison of LILBID data with data from space follow a predictable, repetitive pattern. This pattern can be executed more rapidly and efficiently, with reducing risk of user error, by use of the automated processing steps and database storage described above. The database therefore improves the analysis of mass spectra of ice grains recorded in space, from not only past missions (e.g., Cassini) but also future missions with higher resolution mass spectrometers, such as in particular NASA's Europa Clipper (Howell & Pappalardo, 2020). Future data from space can straightforwardly be investigated without any delay.

The database can also be used to compare LILBID data with many other types of mass spectrometric data, for example, with electron ionization mass spectra from the NIST Chemistry WebBook (https://webbook.nist.gov/).

Newly recorded spectra will be regularly uploaded to the database, and the database system will be continuously improved. The peak detection algorithm will be modified to detect very small peaks and exclude false positive signals even more reliably. We will add a function to filter the measured substances for chemical families (alcohols, ketones, salts, etc.). The LabView component will be adapted to improve the header definition, so that manual data cleaning is no longer necessary.

LILBID data recorded with an Orbitrap™-based mass spectrometer, having significantly improved mass resolution, will complement the Time-of-Flight spectrometer data in the near future. We plan to enhance the capabilities of the LILBID setup to also analyze neutral atoms created by the infrared laser hitting the water beam, which are suspected to be more abundant than ions in the impact cloud of ice grains. The database will then also contain LILBID analogue mass spectra applicable to neutral gas mass spectrometers, such as the Particle Environment Package-Neutral Ion Mass Spectrometer (PEP-NIM; [START_REF] Barabash | Particle environment package (PEP). 8th European planetary science congress[END_REF] (Howell & Pappalardo, 2020) missions to the Jovian System, respectively. The neutral atom data will be stored separately from the cationic and anionic desorption data within the database.

Conflict of Interest

The authors declare no conflicts of interest relevant to this study.

Conflicts of Interest:

We have no conflict of interest to disclose.

F the HV-compatible metal nozzle, we will be able to characterize the effects of the HV on the ionization and water clusters.

■ ASSOCIATED CONTENT

* sı Supporting Information

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.analchem.2c04429.

Ion count quantification example. The area under the curve is calculated above the horizontal red lines, placed at 10% of the peak height (Figure S1); intensity deviation of tin isotopes (50 ms mass spectra) (Figure S2); and zoom on the H 3 O + peak with a 500 ms acquisition time (Figure S3) (PDF)

■ Depuis les débuts de l'exploration spatiale planétaire, l'un des principaux efforts scientifiques a toujours été la recherche de la vie extra-terrestre. Pour la vie telle que nous la connaissons, l'eau liquide est un prérequis obligatoire. C'est pourquoi, les lunes glacées avec des océans souterrains dans le système Solaire externe sont des corps particulièrement intéressants pour les recherches en exobiologie. Parmi ces lunes, Europe et Encelade, en orbite respectivement autour de Jupiter et de Saturne, présentent un intérêt particulier pour de futures missions spatiales.

Les spectromètres de masse sont parmi les instruments in situ les plus répandus dans l'exploration spatiale. Selon leurs performances, ils permettent de mesurer la composition des échantillons, donnent accès à leur formule chimique exacte et révèlent la complexité de leur environnement. Ils sont particulièrement adaptés à l'étude agnostique de la composition de la matière organique. Le Cosmic Dust Analyser embarqué à bord de la sonde de la mission NASA-ESA/Cassini Huygens est un spectromètre de masse à ionisation par impact qui a étudié les matériaux des panaches d'Encelade, caractérisant ainsi son océan. Dans les prochaines années, lors de la mission NASA/Europa Clipper, une version améliorée de CDA, le SUrface Dust Analyser, étudiera la lune jovienne Europa. En laboratoire, des expériences reproduisant des spectres de masse d'ionisation par impact peuvent aider à l'interprétation des mesures de CDA et préparer celles de SUDA. L'accélération de grains glacés micrométriques à des vitesses hypervéloces est un challenge, et à la place, la technique LILBID (Laser Induced Liquid Bead Ion Desorption) est utilisée avec succès pour reproduire les spectres de masses de ces grains. À l'aide d'un laser infrarouge pulsé, un faisceau d'eau micrométrique est ionisé par désorption. Classiquement les instruments LILBID sont couplés à un analyseur de masse par temps de vol. Cependant, même si elle est environ 20 fois supérieure à celle de CDA, la résolution en masse empêche toujours une identification non ambiguë des pics de masse.

L'analyseur en masse à transformée de Fourier Orbitrap™ offre des résolutions en masse ultra-élevée (>100 000 m/Δm pour des temps d'acquisition de 800 ms à m/z 100 avec une cellule D30). Cette thèse présente les travaux d'optimisation d'OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion), un nouvel instrument de laboratoire équipé d'une cellule Orbitrap™, pour son couplage à l'instrument LILBID. Cet instrument unique au monde permettra d'étudier des échantillons analogues de grains glacés provenant d'océans de subsurface avec une résolution massique inégalée, et représente une première étape importante pour la spatialisation d'un analyseur de poussières hypervéloces incluant une cellule Orbitrap™. Mots clefs : Environnements Planétaires, Spectrométrie de masse à haute résolution, Ionisation par impact, Orbitrap™, LILBID, OLYMPIA

Optimisation of OLYMPIA, a new Orbitrap Mass Spectrometer for the Characterisation of Subsurface Oceans in the Outer Solar System and Hypervelocity Dust

Since the beginnings of planetary space exploration, one of the major scientific endeavours has always been the search for extra-terrestrial life. For life as we know it, liquid water is a mandatory prerequisite. This is why icy moons with subsurface oceans in the outer Solar system are such interesting bodies for astrobiology investigations. Among these moons, Europa and Enceladus, respectively orbiting Jupiter and Saturn, are of particular interest for future space missions.

Mass spectrometers are amongst the most prevalent in situ instruments in space exploration. Depending on their performances, they enable the measurement of the samples' compositions, give access to their exact chemical formula and reveal the complexity of their environments. They are specifically suitable to agnostically investigate the composition of organic material. The Cosmic Dust Analyser on-board the NASA-ESA/Cassini Huygens spacecraft is an impact ionisation mass spectrometer that studied materials in Enceladus' plumes, characterising its ocean. In the next few years, during the NASA/Europa Clipper mission, an upgraded version of CDA, the SUrface Dust Analyser will study the Jovian moon Europa. Laboratory experiments which reproduce impact ionisation mass spectra can help the interpretation of the CDA measurements and prepare for SUDA's. The acceleration of µm-sized icy grains to hypervelocity is a challenge, and instead the LILBID (Laser Induced Liquid Bead Ion Desorption) technique is used with great success to reproduce mass spectra of such icy dust. A pulsed infrared laser ionises a µm-sized water beam by desorption. Classically, LILBID setups are coupled to a TOF mass analyser. However, even though about 20 times higher than CDA's, the mass resolution is still preventing an unambiguous mass peak identification.

The Fourier transform Orbitrap™ mass analyser offers ultra-high mass resolutions (>100 000 m/Δm for acquisition times of 800 ms at m/z 100 with a D30 cell). This thesis presents optimisation work of OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion), a new laboratory instrument equipped with an Orbitrap™ cell, for its coupling to the LILBID instrument. This worldwide unique device will allow the study of analog samples of icy grains from subsurface oceans with an unsurpassed mass resolution and is an important first step to develop Orbitrap-based impact ionisation dust analysers in space. Keywords : Planetary Environments, High Resolution Mass Spectrometry, Impact ionisation, Orbitrap™, LILBID, OLYMPIA