Experiencing the Sacred Béatrice Caseau

Experiencing Byzantium naturally included participating in religious rituals and, for the majority of the population, in Christian liturgical ceremonies. 1 On a regular basis, Christians entered churches, taking in the interior decor and division of space, smelling the odour inside, hearing clerics and singers, sometimes responding, lighting lamps and tapers, approaching and touching sacred objects or elements of the church. Whether in a small chapel in Cappadocia, in a monastery in Syria or in the Hagia Sophia cathedral in Constantinople, church going and ritual participation involved the senses: viewing and hearing, but also smelling, touching and tasting. While many scholars have commented on the importance of sight and the role of icons and other images in focusing the attention of the faithful present inside churches, few scholars have devoted their time to studying the other senses, especially touch. 2 Among the senses, touch was not the favourite of the philosophers, who tended to prefer the visual or the auditory sense. 3 Touch is an overlooked sense in many accounts of Byzantine culture, yet it was an extremely important one in most religious rituals. Let us try to recapture some of the sensory experiences of Byzantine Christians, focusing specifically on touch,

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ExPERIENCING BYzANTIUM 60 and taking examples from the fourth to the fifteenth centuries, mostly in the Eastern Mediterranean.

Naturally, recapturing the sensations the Byzantines could have felt when entering a church is difficult because this varied depending on the individual, the time of day and the type of church. However, it is possible to attempt a history of the sensory experiences by paying attention both to texts that have been previously studied from a different angle, and to interior architecture and images. 'When you enter the church', writes Choricius of Gaza, 'you will be staggered by the variety of the spectacle.' 4 In a similar vein, writing about the Hagia Sophia cathedral in Constantinople, Paul the Silentiary writes, 'everything fills the eye with wonder'. 5 Wealthy churches were awe-inspiring buildings, decorated to impress the visitor. However, experiencing the liturgical offices taking place inside these splendid churches was certainly different depending on whether one stood in the sanctuary, in the nave, in the galleries or in the narthex.

The Byzantines are known for their obsession with taxis. Everyone has a proper place in society and should also occupy his or her proper place in church. While we have the middle-Byzantine taktika to understand how the taxis worked for the aristocracy, invited to dine at the imperial palace, we need to go back in time to find texts pointing to the ideal proper place for each category of Christians inside a church. Early Christian normative literature spelled out rules to distribute each group depending on sex, age, sanctity of lifestyle or place in the ecclesiastical hierarchy. Each category of Christians was bound by a set of rules, which included restrictions of access, either temporally or spatially, to areas of the church building. As early as the third century, 6 and certainly up to the time of Symeon of Thessalonika in the fifteenth century, sources reveal the desire to allocate a particular space to the different social groups, taking into consideration whether they were clerics, consecrated persons, or laypeople, and distinguishing men and women, the young and the elderly. 7 It remains difficult to assert that these rules were enforced at all times in all churches, but they certainly indicate how the Byzantines imagined the hierarchical value of different spaces inside The Didascalia apostolorum is one of the first texts discussing the proper place for each group of Christians. Dating to the third century, it belongs to a time when Christians were a minority and most converts were adults. Naturally, the main distinction at that time was between catechumens and baptised Christians. While the latter were standing or sitting inside the nave and allowed to remain throughout the liturgy, the former, located either in the narthex or close to the doors of the church, had to leave after the sermon. They were not completely initiated and had no access to the Eucharistic table. Their location inside the church showed that they were members of the Christian community, but not yet full members. They were sometimes called hearers, because they were allowed to hear the readings and the sermon, but not to see, hear or taste what came after. A special prayer was said for the catechumens before they were invited to leave the church. It seems that deacons were responsible for supervising their departure.

This distinction between catechumens and baptised Christians remained throughout the Byzantine middle ages, but when most of the population was born Christian and baptised during childhood, often the only catechumens were babies, who could hardly leave the church on their own. They were nevertheless often placed with their mother (or care-giver) in the same area occupied by the adult catechumens: close to the doors, or in the narthex. Besides their status as catechumens, one practical reason for that location was also the possible noise coming from babies, or very young children. Keeping them far away from the sanctuary, where the liturgical action took place, was intentional. Being close to the narthex meant that little children, unable to stay still, could run in the courtyard. At the end of Late Antiquity and during the middle ages, unless they came from non-Christian backgrounds, older children were often baptised Christians and could stay after the sermon for the Eucharistic liturgy. Children were usually supervised by one parent: young boys with their father, and girls with their mother, which is an indication of the separation of sexes inside the churches. Older boys were isolated under the supervision of a deacon. Likewise consecrated virgins were grouped together.

The separation of men and women inside church buildings seems to have been a common feature. 8 In some churches, men and women used different entrance doors. 9 In large churches, where deacons were numerous enough to stand at the entrance, they could direct people where to stand or sit. Three models coexisted in the early Byzantine world for this separation of the sexes: the first model had women standing on the left side of the church and men standing on the right (the 'better side'); in a second model, women would stand closer to the doors, behind the men, who stood closer to the sanctuary; and in a third possibility, where upper galleries existed, women could stand in the galleries. The first two models established a hierarchical distinction between men and women. The third model was meant to protect women from the gaze of men. In the Hagia Sophia church, this gallery was at the disposal of high-ranked women, the empress and the aristocrats. 10 This use of the galleries for upper-class women reveals another division inside the church, that between rich and poor, aristocrats and ordinary laywomen, who probably stood on the lower floor of the Hagia Sophia, on the left side of the church. In spite of a discourse of equality in front of God, the social divisions were reproduced in the spatial allocation of the different social groups, at least in that special church where the court was welcomed for important religious festivals.

Finally, there was a special area for a category of women, whose lifestyle was praised and close to members of the clergy: the deaconesses. In the fourth century, they played an important role during baptismal ceremonies: they anointed the body of women with oil during the period when it was common to anoint the whole body. They also had a mission of conversion and religious education for women. However, their liturgical role vanished when it became common to baptise young children. Some deaconesses remained on the clerical roll and they could stand in a special area in the left part of the nave. This particular area, quite close to the sanctuary, reflected their respected status in the community, as celibate women living for God. Being on the payroll of the church, they were given some privileges; however, as women, they were not allowed to enter the sanctuary, except for their own ordination. They did not touch the sacred vessel, nor distribute communion, but supervised the women standing in the left part of the nave. They also had door-keeping duties. 11 The area of the sanctuary and the ambo were reserved for the clergy and access to the sanctuary came to be forbidden to the laity. There were some exceptions to this rule: male children were carried around the altar when presented at church. 12 Also, when he attended church, at the start of the liturgy, the emperor entered into the sanctuary. The sanctuary was once accessible to the imperial family for the communion, but during the fifth century, that ceased to be the case. 13 Imperial women had to take communion outside the chancel barrier. Finally, a canon of the Council in Trullo (691-692) stated that no layperson should be allowed inside the sanctuary. 14 An exception was granted to the emperor, who could enter to deposit gifts and cense the altar, but he too had to remain outside to take communion. Altogether, the location of each group followed the gradient of sacredness of the church, progressing from the narthex to the sanctuary, and reflected the hierarchical difference between clerics and laypersons, and between men and women. Age was also a factor: when sitting is mentioned, young people must stand while older people sit. 15 Sitting was not frequently possible and during festivals the laity had to stand. The visual experience of the liturgical ceremonies was certainly quite different for those at the back of the church to that of those standing in front or in the galleries. Women placed at the back of the church, or even in the narthex, in the case of menstruating women, could hardly see anything taking place in or around the sanctuary. In a church as big as the Hagia Sophia, one wonders if they could even see and hear what was said on the ambo, when a crowd was standing in front of them. 16 In smaller churches, and less crowded ones, their experience might have been different. For men and women at the back of the church, processions, such as the great entrance, were moments of particular importance, where liturgical activity joined them where they stood.

Clergymen were aware of the fact that it was more difficult to follow the liturgy when one could not see what was going on, or hear very clearly prayers and sermons. In canonical-liturgical sources, older boys were placed in the nave ideally, very close to the sanctuary, in the hope that some of them would become familiar with the liturgy and enter the clergy. Miracle stories mention (Rome, 1978) boys learning the prayers said by the priest during the consecration of the host (something said in a low voice) and being able to repeat them, word for word. 17 They were placed in such a manner as to be able to follow the rituals, while their sisters were with their mother, either on the left side of the nave or at the back of the church. As a group, these young boys, no longer with their fathers, were under the supervision of a deacon, who had the sometimes arduous task of making them pay attention and keep silent.

M. Arranz, EÉvolution des rites d'incorporation et de réadmission dans l'EÉglise selon l'Euchologe byzantin, Gestes et paroles dans les diverses familles liturgiques

Sight and hearing may not have been the most important of the senses involved in participating in the liturgy. They certainly played a role, but not to the same extent for everybody present in a very large church such as the Hagia Sophia. For most laypeople, an active participation in church rituals and liturgy involved touching.

Pushing a door or a door curtain was probably the first active gesture, besides walking (Fig. 4.1a and Fig. 4.1b). Mosaics, such as those in the apse of the Eufrasiana church in Poreč, or of the Saint Vitale church in Ravenna, depict this gesture. Entrance doors were adorned with curtains, even in village churches, as the fifth-to sixth-century papyrus P. Grenf. II.111 proves: it lists six door curtains (plus an old one) in the inventory made by the archdeacon for the priest of a church in the village of Ibion. The number of curtains indicates that the church had three doors. 18 Curtains were especially important to mark the threshold, when the doors were opened. They created a visible boundary between outside and inside, or between two spaces inside a building. Curtain hooks are still visible in some churches, such as the Hagia Sophia church in Constantinople, the Eufrasiana in Poreč or the basilica of Sant'Apollinare in Classe. In these churches of the Justinianic period, cast bronze hooks in the shapes of fingers were set between the cornices and lintels above the doors. 19 Original finger hooks are still in place, for example, at Parentium (Poreč) and above the south and central doors leading to the inner narthex at the Hagia Sophia church (Fig. 4.2). Because churches adopted many features of domestic architecture, curtains must have been used very early on in entrance doors. They certainly started to become an element of decor in Late Antique basilicas. As in houses, curtains were used to keep insects and birds out of the building. They protected the privacy of the inner space from uninvited eyes. In areas where sunlight could be very bright, they provided a screen barrier. Most of all, however, their role was to adorn an important area and indicate a change of space: between narthex and nave, and between nave and sanctuary. Thus, curtains acted as a visual signal of the differentiated sanctity of the two spaces they demarcated.

Besides these practical roles, and their symbolic meaning, they added warmth and colours to the church. 20 In Byzantine churches, curtains added their touch to the 'passion for colour, complex variation, effects of light, contrast, and the interaction of media as essential elements in the formation of beauty', which defines Byzantine aesthetics inside churches. 21 Although, in poorer churches, 20 G. Ripoll, 'Los tejidos en la arquitectura de la antigüedad tardia. Une prima approximacion a su uso y funcion', Antiquité Tardive 12 (2004), pp. 169-82. they were probably very simple and perhaps off-white, in wealthier churches, they were embroidered with religious scenes or figures, or intricate designs. 22 In the fourth century, not everyone accepted door curtains embroidered with holy figures. Epiphanius of Salamis tore down a village church curtain on which the image of Christ had been embroidered, because he felt it was improper to let just any hand touch such a holy figure in the mundane gesture of pushing the curtain to enter the building. 23 Many of the curtains depicted on mosaics have geometrical patterns rather than figurative embroideries, which may be an indication that Epiphanius' feelings were shared. The gift of curtains and an altar cloth became an imperial tradition. The Byzantine emperors offered precious curtains to adorn churches, starting in the fourth century. According to the Chronicon Paschale, Emperor Constantius offered splendid golden door curtains for the dedication of the Hagia Sophia 24 (Fig 4 .3). In Constantinople, Empress Irene and her son gave veils and curtains of gold thread to the church of Pege, as well as precious liturgical vessels. She had herself and her son depicted in the act of offering these gifts. 25 The recording of gifts of curtains in the Liber Pontificalis ecclesiae romanae testifies that they were valued presents. 26 Above the magnificent doors of Saint Sabine, traces of the hooks holding the curtains can still be seen. Roman basilicas had different sets of curtains, which changed with the liturgical period and adorned doors, canopies and walls for certain feasts.

The presence of textiles certainly modified the acoustics of a church and avoided some of the reverberation created by marble surfaces. Textiles were also sometimes present on walls or in between columns. The mosaics of Sant'Apollinare in Classe reveal how curtains were tied around columns (Fig. 4.4). There is also archaeological evidence for the presence of curtains in between columns. In the churches of Pella, holes were drilled in the columns to fix rods and hang curtains, either to separate a space for women or simply to adorn the nave with hangings that could be tied up between the columns. 27 In any case, textiles, whether in the form of hangings or sometimes carpets, contrasted with the smooth marble slabs that adorned the lower parts of the walls and often the floors; they brought warmth to the cold marble and absorbed sounds. They modified the sensory experience of church-goers. This contrast between textile and marble or mosaic floor was certainly striking.

After pushing the curtain, the second gesture of a worshipper was very probably touching the floor in a gesture of respect for God's presence inside the church. Marble was frequently used on church floors, in churches built with significant funding. A visitor entering such a church could feel the cold marble when performing a proskynesis or when simply touching the floor in a gesture of humility. Touch was also involved in gestures of devotion, such as kissing columns, doors and icons, not to mention touching the reliquaries and the lamps above them. John Chrysostom mentions the habit of kissing the door of the church in a sermon preached at Antioch: 'Do you not see how many of you kiss even the porch of this temple, some stooping down, some grasping it with their hand and putting their hand to their mouth'. 28 The tradition of kisses and prostrations also existed in the West. Paulinus of Nola depicts the gestures of a peasant coming to petition Saint Felix: 'he prostrated himself at the doors, planted kisses on the doorposts'. Peter Brown, who has gathered some of the evidence in an article published in 1998, interprets a passage of Augustine's sermon, which mentions Christians who adore columns in churches, as referring to this practice of kissing elements of the church building. [START_REF] Brown | Augustine and a Practice of the Imperiti: Qui adorant columnas in ecclesia (S. Dolbeau 26.10. 232, Mayence 62)[END_REF] Late Antique and Byzantine Christians enjoyed contact with sacred objects or places, which they believed to be filled with the power to protect them and sometimes even cure them. They came to church in order to approach and touch the sacred. 30 Kissing icons or reliquaries achieved that goal. The power of relics was accessed by touching, even if through a reliquary. Gregory of Nyssa describes the deportment of pilgrims worshipping relics: 'those who behold them embrace, as it were, the living body in full flower: they bring eye, mouth, ear, all senses into play, and then shedding tears of reverence and passion, they address to the martyr their prayers of intercession as though they were present'. 31 The number of enkolpia, used to hold fragments of the saints' relics or a morsel of the Eucharist, is clearly linked to this desire to touch the sacred, or to have the sacred touch one's body, and through it protect one's soul. [START_REF] Pitarakis | Les croix-reliquaires pectorales byzantines en bronze[END_REF] Through touch, holiness and even divine life could be transmitted. The devotion given to objects known to have been held by the saints, such as the belt of a holy woman, [START_REF]Life of Melania the younger (61), Greek text, introduction and notes[END_REF] or even better the veil or belt of the Theotokos, [START_REF] Wortley | The Marian Relics at Constantinople', Greek, Roman and Byzantine Studies[END_REF] shows how much contact mattered.

In the case of Christ, it was not possible to have a body to divide as was done with so many of the saints' bodies, but the objects he held as a child and the instruments used to torture him were all considered very precious. [START_REF] Durand | Byzance et les reliques du Christ[END_REF] The proof of their belonging to Christ was their ability to cure. [START_REF]Lieux saints et pèlerinage d'Orient[END_REF] Among these, the favourite was undoubtedly the cross. Discovered in the fourth century, fragments of it were quickly dispersed: Macrina (d.380), the sister of Basil of Caesarea and Gregory of Nyssa, wore a piece of the cross around her neck, so that it touched her heart. [START_REF] Gregory | Vie de Sainte Macrine[END_REF] After Heraclius' victory over the Sassanians, part of the holy cross was brought to the imperial palace in Constantinople and kept in a staurothek. Each year, it was brought to the Hagia Sophia to be kissed and venerated by the Byzantine court and by the Constantinopolitans. For three days, from Thursday to Saturday, during the Holy Week before Easter, the cross was taken out of its reliquary and presented to be kissed first by the men led by the emperor, then by the empress leading the women, and finally by members of the clergy. Arculf, a Gallic bishop who travelled to the East on a pilgrimage in the 680s, told abbot Adomnan 43 44 oil, able to cure all illnesses, oozes from the wood of the cross. 38 Another relic of Christ played an important role in Constantinople: the Mandylion, a piece of cloth, which had reputedly touched the face of Jesus. [START_REF] Drijvers | The Abgar Legend[END_REF] This relic was kept in the city of Edessa, until it was brought to Constantinople in 944. [START_REF]Continuateur de Said ibn-Bitriq[END_REF] The twelfth-century manuscript illustrating the Chronicle of John Skylitzes contains the image of the emperor welcoming the Mandylion. The face of the emperor meets the face of Jesus imprinted on the piece of cloth. The image reveals that personal contact and touch was central in the gesture of devotion. 41 Byzantine pilgrimage sanctuaries provided visitors with opportunities to touch holiness. This could be in the form of oil burning in front of the tomb, hnana, 'holy dust' from the tomb, or kerote, a mixture of wax, oil and dust. At healing shrines, the sick, hoping for a cure, would anoint themselves with these sanctified medicines. Visitors would bring some oil home in little flasks, often called ampullae. Miracle stories emphasised the healing power of these products. The writer of saints Kosmas and Damian's miracles recalls stories of sick persons cured with kerote. [START_REF] Deubner | Kosmas und Damian[END_REF] Reading those texts, one could assume that access to the lamps was easy, but clerical mediation appeared to be in place in most sanctuaries. [START_REF] Marcos | Los Thaumata di Sofronio[END_REF] Members of the clergy would welcome the sick and organise the distribution of oil and of kerote. [START_REF] Caseau | Parfum et guérison dans le christianisme ancien et byzantin: des huiles parfumées au myron des saints byzantins[END_REF] Some saints, called myroblites, specialised in giving perfumed oil with curative properties. Gregory of Tours mentions the oil given by Saint Andrew at Patras, as if it was full of spices. 45 For the saint's feast, it flowed out of the tomb and reached the middle of the church. Potions and unguents were made out of it. Cyprus had many

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ExPERIENCING BYzANTIUM 72 myroblite saints. John the Almsgiver, patriarch of Alexandria buried in his native city of Amathonte, gave perfumed oil, bringing incorruptibility and eternal life to 'his children like a loving father'. 46 Many such miracles took place during the Arabic invasion of the island, as a testimony that the saints had not abandoned the faithful. Starting in the ninth and tenth centuries, two saints, Nicholas of Myra and Demetrius, were renowned for their gift of myron. After Thessalonika was taken in 904 and the church of Saint-Demetrius was partially destroyed, the cult was reorganised and the myron started to flow. John Staurakios, chartophylax of the church in the thirteenth century, mentions how the oil flowed out of the reliquary through tubes to reach the faithful. [START_REF] Staurakios | Analecta de unguento[END_REF] In the miracles stories of Saint Eugenios of Trebizond, a monk recalls how he saw people take some of this holy perfumed oil, rub it on themselves, and take some home. [START_REF] Rosenqvist | The Hagiographic Dossier of St Eugenios of Trebizond in Codex Athous Dionysiou[END_REF] In other churches, water was the means to convey the healing powers of the saints. Before the myron replaced it, the cult of Saint Demetrius included holy water. [START_REF] Mentzos | Τό προσκύνημα τοῡ Ἀγίου Δημητρίου Θεσσαλονίκης στά βυζαντινά χρόνια. Έταιρεία τών φίλων τοῡ λαοῡ[END_REF] Holy fountains were also frequent in sanctuaries of the Theotokos. The hagiasma of the Theotokos of Blachernai, which was a major church in the capital, attracted many people; and even when the church was destroyed, the fountain remained. Holy waters endured through the centuries and were frequented by Christians and Muslims. Close to Constantinople, however, the most famous sanctuary for healing waters was the monastery of the Theotokos of Pege. [START_REF] Janin | La géographie ecclésiastique de l'Empire byzantin. 1[END_REF] The waters of a spring reputedly blessed by the Mother of God flowed inside the church, dated to the sixth century. Two compilations of miracles performed by the Theotokos of Pege, one dating to the tenth century and a second dating to the fourteenth century, have recently been studied. [START_REF] Efthymiadis | Le monastère de la source à Constantinople et ses deux recueils de miracles. Entre hagiographie et patriographie[END_REF] As is usual in miracle stories, it matters to the writer or compiler to underline the wide influence of the sanctuary and how its fame reached all social groups from the humblest to that of the imperial family. In this case, however, a high percentage of miracles involved the aristocracy or the imperial family. Two types of healing methods took place near that hagiasma. First, mud could be made with the holy water and rubbed on the sick part of the body, following a method quite similar to miracles performed by Christ himself. Second, the water could be consumed to bring about good health. The miracle stories concern important members of the imperial family throughout Byzantine history, including the sister of Justinian's spouse Theodora, who was cured with mud; Empress Irene, healed of a haemorrhage after drinking the holy water; Zoe Karbonopsina, who was no longer sterile after benefiting from both water and mud; and later, in 1330, the sick Andronic III, who recovered after drinking the water. Some of the water was also used to bathe his forehead. The Russian pilgrims Ignatius of Smolensk and zosimus saw the church, but in 1547, when Pierre Gilles came to Constantinople, it was no longer standing. 52 From the fourteenth century, the church was known by the name of zoodochos Pege. 53 The numerous icons of the Theotokos zoodochos depicting Mary in the middle of a beautiful fountain, and sick or possessed people healed and freed by tasting the water, are a proof of its enduring popularity. 54 The church was destroyed, but the reputation of the waters blessed by the Theotokos and infused with her healing powers remained.

As we can see from this example, experiencing the sacred was not only about touch but also about taste. Touch, smell and taste were combined in the case of holy oil used in potions, or that of 'edible icons', wax or clay images of the saints believed to have curative powers. 55 Naturally, tasting bread and wine was the most frequent experience in church, at least for members of the clergy, and took place at least once for all baptised Christians. Late Antique preachers invited the faithful to touch and taste the Eucharist. 56

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ExPERIENCING BYzANTIUM 74 putting one's hands on the reliquary, but with even greater awe, touching the consecrated bread amounted to touching the body of Christ. Cyril of Jerusalem recommended that Christians appreciate the contact of their hands with the consecrated parcel holding Christ. He also told them to extend the benefit of this contact to the other senses, the eyes in particular. 57 The Church Fathers of this period emphasised this personal contact and this proximity with Christ that communion allowed. Theodore of Mopsuestia (d.428), Narsai (fifth century) and Cyrus of Edessa (sixth century) advised the faithful to kiss the Eucharistic bread before eating it. [START_REF] Of | Les Homélies catéchétiques de Théodore de Mopsueste[END_REF] Kissing the bread while acknowledging the presence of Christ in one's hands was both a gesture of devotion and one of purification of the mouth. Many of the Byzantines did not dare take communion with too many sins tarnishing their souls. They considered it risky for their salvation, so instead, they preferred to take blessed bread. [START_REF] Caseau | Sancta sanctis. Normes et gestes de la communion entre Antiquité et haut-Moyen Âge[END_REF] Clerical mediation transformed gifts of food into a sacrificial offering. In the fourthcentury compilation known as the Apostolic Constitutions, Christians were encouraged to give first fruits of wheat, wine, oil and fruits, and they were told that God would bless their fields and bring prosperity to their families. [START_REF]Les Constitutions apostoliques[END_REF] We hear of cheese, olives and wine brought to churches in the early centuries of the Byzantine Empire, but the most commonly offered food was bread. In cities such as Alexandria or Aphrodito, the wealthy had flour sent to bakers with orders to deliver bread to churches. [START_REF] Papaconstantinou | Le culte des saints en EÉgypte des Byzantins aux Abbassides. L'apport des inscriptions et des papyrus grecs et coptes[END_REF] Only a small amount of this bread was consecrated on the altar. Eventually only bread prepared by clerical hands or under clerical supervision was taken for consecration. Yet all the bread brought by the faithful was redistributed, mostly to members of the clergy, to the poor registered as beneficiaries, and as antidoron, blessed bread offered at the end of the liturgy. The eulogia breads were often marked with crosses or with religious scenes 62 (Fig. 4.5). They had religious value as blessed bread, conveying some form of communion with Christ and calling on God's blessing Sanctification by contact was an extremely important part of the early Byzantine religious experience. It remained an important feature of later Byzantine culture, but underwent significant changes. The communion experience changed at the end of Late Antiquity. The Byzantines did not feel that their hands were pure enough to hold the body of Christ any longer and they replaced communion in the hand by communion with a spoon. 63 The sensory participation of the faithful in the whole Eucharistic ritual diminished: the eventual building of an iconostasis deprived them of seeing what was taking place on the altar, while contact with the body of Christ was reduced with the abandonment of hand communion. They could still hear the invitation 'Ta Hagia tois hagiois' (the holy things for the holy people), but no longer the prayers of consecration. 64 [START_REF] Taft | The Decline of Communion in Byzantium and the Distancing of the Congregation from the Liturgical Action: Cause, Effect, or Neither?[END_REF] Many Christians related to the Eucharist offering in another way, by giving of bread and wine and by seeing, with eyes of faith, the transformation of the elements on the altar (or prosphora) into the Body and Blood of Christ, at least when, during the high middle ages, chancel barriers around the altar area did not block the view. 66 Afterwards, when the iconostasis isolated the sanctuary from the nave, their attention was often more centred on the procession of the gifts, before the consecration. [START_REF] Walter | The Origins of the Iconostasis[END_REF] Other forms of participation in the liturgical rituals or acknowledgement of the church as a sacred space also took precedence. Touching and kissing the icons or the reliquaries became common gestures of sanctification. [START_REF] Gougaud | Baiser', Dictionnaire de spiritualité[END_REF] The horos of the Council of Nicaea II in 787, decided that it was proper and good to give icons kisses and proskynesis. [START_REF] Sahas | 88). 70 Belting, Likeness and Presence[END_REF] After 843, icons were granted a specific function in church ritual: they were offered to the faithful for veneration and kissed both by the priest and by the worshippers. 70 Portable icons were changed in accordance with the church calendar and became part of the liturgy. Touching and kissing icons became a mark of the Byzantine religious culture. Pilgrimages and visits to churches included gestures of veneration towards icons and relics. Ignatius of Smolensk recalls his moves while visiting the Hagia Sophia in 1389: 'We kissed the table on which the Relics of the Passion of Christ are placed, and the [the body of] St. Arsenius the Patriarch and the table at which Abraham welcomed Christ manifest in Trinity, as well as the iron pallet on which Christ's martyrs were burned'. [START_REF] Majeska | Russian Travelers to Constantinople in the Fourteenth and Fifteenth Centuries[END_REF] To these personal gestures of devotion towards objects, one should add ritual kisses given to people. The kiss of peace was important in the early church to create a family bond between the full members of the community. The Apostolic Constitutions recall the order given by the deacon: 'Greet one another with a holy kiss' -and the members of the clergy kiss the bishop, the laymen kiss the laymen, and the laywomen kiss the laywomen. 73 The Byzantine tradition, explains R. Taft, was to exchange the peace among members of the same rank. It seems that the kiss of peace stopped being exchanged between laypeople at some point during the middle ages, after the eleventh century. By the time of Philotheos Kokkinos, patriarch of Constantinople during 1353-54 and from 1364 to 1376, only members of the clergy exchanged the kiss of peace. 74 The Book of Ceremonies lists the objects kissed by the emperor when he came to church and mentions that a kiss was exchanged by the patriarch and the emperor before the liturgy, or at different moments, such as after lunch. For the emperor, the kiss of peace was extremely ritualised. Here again the Book of Ceremonies mentions the ideal order that should be followed: 'The sovereigns, standing outside the chancel, give the kiss first of all to the patriarch, then after him to the synkellos, all the metropolitans and archbishops, and to the protopope of the Great Church, and to the dignitaries of the patriarch … then to all those of the senate, all of whom the master of ceremonies leads by the hand'. [START_REF] Porphyrogénète | Own Eyes: Liturgy as the Byzantines Saw it[END_REF] This tradition is no longer mentioned by the De Officiis of Pseudo-Kodinos in the fourteenth century. Kissing the hand of the priest (bishop or patriarch) was such an important gesture that it is depicted on late medieval paintings of the communion of the Apostles. The apostle kisses Jesus' hand, at the time he receives the bread from him. [START_REF] Ch | Customs and Practices Surrounding Holy Communion in the Eastern Orthodox Churches[END_REF] Also, kissing objects increased both during the liturgy and as a form of personal devotion. These are just a few examples of the importance of touch in Byzantine religious rituals. The Late Antique and Byzantine Christians wished to establish a personal contact with the building and its objects, as well as with the people. These numerous examples of gestures of devotion call for a revision of our too-often audio or visual-centred understanding of the religious experience of Byzantine worshippers. Instead of focusing on the gaze or on the sounds and perfumes, this paper has attempted to draw attention to two of the senses that are often neglected in the accounts of Byzantine aesthetics, but that played an important role in experiencing liturgies and devotions: touch and taste.

  21 E.S. Bolman, 'Painted Skins: The Illusions and Realities of Architectural Polychromy, Sinai and Egypt', in S.E.J. Gerstel and R. Nelson (eds), Approaching the Holy Mountain: Art and Liturgy at St Catherine's Monastery in the Sinai (Turnhout, 2010), pp. 119-40, esp. 123.

Figure

  Figure 4.2 Curtain hook in situ at the Basilica Euphrasiana, Poreč (author's photograph)

22S.

  Schrenk, Textilien des Mittelmeerraumes aus spätantiker bis frühislamischer Zeit (Riggisberg, 2004); M.-C. Bruwier, Egyptiennes. Etoffes coptes du Nil, Mariémont (Morlanwelz, 1997); Y. Bourgon-Amir, Les Tapisseries coptes du musée historique des tissus, Lyon (Montpellier, 1993); M. Flury-Lemberg, Textile Conservation and Research (Bern, 1988), pp. 396-405; M. Martiniani-Reber, Lyon, musée historique des tissus. Soieries sassanides, coptes et byzantines V e -XI e siècles (Paris, 1986). 23 Letter to the emperor Theodosius and letter to John bishop of Jerusalem, translated in Mango, The Art of the Byzantine Empire, pp. 41-3. 24 Chronicon Paschale (I), ed. B.G. Niebuhr, Corpus Scriptorum Historiae Byzantinae (Bonn, 1832), p. 544, tr. M. and M. Whitby, Chronicon Paschale 284-628 AD (Liverpool, 1989), p. 35. 25 De sacris aedibus Deiparae ad Fontem, translated in Mango, The Art of the Byzantine Empire, p. 156, also translated in A.-M. Talbot and S. Fitzgerald Johnson, Miracle Tales from Byzantium (Cambridge, MA, 2012).

  Participation in the communion ritual became quite 62 G. Galavaris, Bread and the Liturgy: The Symbolism of Early Christian and Byzantine Bread Stamps (Madison, WI, 1970).

63B.

  Caseau, 'L'abandon de la communion dans la main (IV e -xII e s.)', Mélanges Gilbert Dagron, Travaux et Mémoires 14 (Paris, 2002), pp. 79-94. 64 R.F. Taft, '"Holy Things for the Saints": The Ancient Call to Communion and its Response', in G. Austen (ed.), Fountain of Life: In Memory of Niels K. Rasmussen, O.P., NPM Studies in Church Music and Liturgy (Washington DC, 1991), pp. 87-102; B. Caseau,

Figure 4

 4 Figure 4.5 A bread stamp showing a cross and a blessing for a family reading: 'Eulogia eu ef hmas ke epi ta tekna hmvn' and 'Eulogia ku ef hmas ke epi ta tekna hmwn' (author's photograph)

From

  Experiencing Byzantium Copyright © 2013 by the Society for the Promotion of Byzantine Studies. Published by Ashgate Publishing Ltd, Wey Court East, Union Road, Farnham, Surrey, GU9 7PT, Great Britain.

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  Choricius of Gaza, Laudatio Marciani (I, 17), translated in C. Mango, The Art of the Byzantine Empire (Toronto and London, 1986), p. 61; R. Penella (ed.), Rhetorical Exercises from Late Antiquity: A Translation of Choricius of Gaza's Preliminary Talks and Declamations (Cambridge, 2009). Being ushered to the proper area in church was most probably a common experience for many Byzantines.

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	38 39 40	Paul Silentiarios, Description of the Church of Saint-Sophia, translated in Mango, The Art of the Byzantine Empire, p. 89.
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  The apocryphal Cave of Treasures imagines Noah's Arch, which symbolises the church, with two doors, one for females and one for males. A. Su-Min Ri, La Caverne des Trésors. Les deux recensions syriaques, Corpus Scriptorum Christianorum Orientalium 486, Scriptores Syri.

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	39 40 41	8 Cassingéna-Trévedy and I. Jurasz (eds), Les liturgies syriaques (Paris, 2006), pp. 229-66, esp. J.-P. Sodini, 'Archéologie des églises et organisation spatiale de la liturgie', in F. 233; W. Mayer and P. Allen, The Churches of Syrian Antioch (300-638 CE) (Leuven, 2012), p. 212.
	42
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  Commentaire de la Caverne des Trésors. Etude sur l'histoire du texte et de ses sources (Louvain, 2000), p. 242. In the 16-17 November 2012 conference on Syriac churches, Les églises en monde syriaque (Xe Table-ronde de la Société d'études syriaques), Elif Keser Kayaalp pointed out architectural examples (forthcoming in 2013, to appear within a volume of the collection Etudes syriaques). Taft, 'Women at Church in Byzantium: Where, When -and Why?', Dumbarton Oaks Papers 52 (1998), pp. 27-87, esp. 31; testimony of Paul Silentiarios at p. 34.

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	15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37	207 (Louvain, 1987), p. 52. I wish to thank F. Briquel-Châtonnet for this reference; A. Su-Min Ri, o p y
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10 R. 11 A. Karras, 'Female Deacons in the Byzantine Church', Church History 73.2 (2004), pp. 272-316; A. Karras, Women in the Byzantine Liturgy (Oxford, 2005). Nesbitt & Jackson.indb 62 6/18/2013 8:12:17 AM P r o o f C

  , pp. 31-75; M. Arranz, Admission dans l'Église des enfants des familles chrétiennes, Orientalia Christiana Periodica 49 (Rome, 1983), pp. 284-302. Taft, 'The Byzantine Imperial Communion Ritual', in P. Armstrong (ed.), Ritual and Art: Byzantine Essays for Christopher Walter (London, 2006), pp. 1-27. Canon 69; see G. Nedungatt and M. Featherstone (eds), The Council in Trullo Revisited (Rome, 1995), p. 151. Constitutions Apostoliques (II, 57, 12), ed. and tr. M. Metzger, Les Constitutions apostoliques (Paris, 1985), pp. 316-17; more examples in B. Caseau, 'La place des enfants dans les églises d'Orient (3 e -10 e siècles)', in M. Aurell and Th. Deswarte (eds), Famille, violence et christianisation au Moyen Age. Mélanges offerts à Michel Rouche (Paris, 2005), pp. 15-27.

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R. 14 15 16 R. Mainstone, Hagia Sophia: Architecture, Structure and Liturgy of Justinian's Great Church (New York, 1988), p. 231.

  Antony of Choziba, The Miracles of the Mother of God (5), ed. C. House, 'Miracula beatae virginis Mariae in Choziba', Analecta Bollandiana 8, (1888), pp. 366-7; translated in T. Vivian and A.N. Athanassakis, The Life of Saint George of Choziba and the Miracles of the Most Holy Mother of God at Choziba (San Francisco, CA, and London, 1994), p. 101-102; John Moschus, The Spiritual Meadow (196), Patrologia Graeca 87, c.3081, translated in J. Wortley, John Moschus: The Spiritual Meadow (Kalamazoo, 1992), pp. 172-4. Dynamic Splendor: The Wall Mosaics in the Cathedral of Eufrasius at Porec, (University Park, PA, 2007), p. 60.

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	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21	o p y	Figure 4.1b Curtain pushed by the hand, at San Vitale,	Ravenna (author's photograph)
	18 (Private Affairs), London, 1970, pp. 423-234; B. Caseau, 'Objects in Churches: The Testimony P. Grenf. II, 111, ed. and transl. A. S. Hunt, C. C. Edgar, Select Papyri I: Non-Literay of Inventories', in L. Lavan (ed.), Late Antique Archaeology: Objects in Use (Leiden, 2008), pp. 551-79; E. Wipszycka, 'Church Treasures in Byzantine Egypt', The Journal of Juristic Papyrology 34 (2004), pp. 127-39. Figure 4.1a Curtain pushed by the hand, Mosaic of the Visitation, Basilica Euphrasiana, Poreč (author's photograph) P r o o f C 40 41 42 43 44 37 38 39 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

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Nicolas Chanon

The Compact Muon Solenoid Experiment

Recent measurements of top quark pair production and single top quark production in pp collisions at the CMS experiment are presented. These proceedings focus on the measurement of top quark pair production at 5 TeV center-of-mass energy, mesurements of top quark pair production in the full kinematic range at 13 TeV, and the measurement of single top quark production associated with a W in the lepton+jets channel at 13 TeV. The status of related measurements is briefly outlined.

Introduction

The top quark, with a mass m t ≈ 173 GeV, is the heaviest of the discovered elementary particles. Since its coupling to the Higgs boson is of order 1, the top quark plays a major role in many extensions beyond the Standard Model (SM). The LHC produces top quarks in abundance in pp collisions, owing to very large value of the gluon parton distribution function (pdf) in the proton at high momentum transfer. From Tevatron ( √ s = 1.96 TeV) to the LHC Run 2 ( √ s = 13 TeV), top quark pair (t t) and single top production profit from an increase of a factor above 100 in cross section. In addition, the large increase in delivered integrated luminosity makes it possible to perform exquisite measurements of t t and single top production.

Measurement of top quark pair cross sections at CMS

Status of top quark pair production measurements

The top quark decays to bW before it can hadronize, and the W boson can decay leptonically or hadronically. Measurements of inclusive t t cross sections ranging from √ s = 5.02 TeV to √ s = 13 TeV were performed at CMS 1 in the dilepton, lepton+jets and all-hadronic final states. Best relative precisions achieved are below 4%.

Nowadays, multi-differential cross sections are measured at the CMS experiment at 13 TeV, for instance in the dilepton channel 2 . Measurements of t t cross sections are a test of perturbative Quantum Chromodynamics (pQCD). They can be used to constrain the strong coupling constant α S , measure the top quark mass, or constrain pdfs.

In the all-hadronic final state, where the QCD background is difficult to control, measurements were performed in the boosted regime, at high top quark p T 3 .

Top quark pair production at 5 TeV

The inclusive cross section for t t process has been recently measured in the eµ channel at 5.02 TeV pp collisions, using a luminosity of 304 pb -1 of 2017 data The Drell-Yan background is estimated from data, using control regions with same flavour leptons. Single top tW and diboson processes are estimated from simulation. The t t yield is corrected for detector efficiencies, geometrical acceptance, and branching ratios. Largest systematic uncertainties arise from jet energy scale, Drell-Yan background estimation, and the estimate of the integrated luminosity. The measured cross section is σ t t = 60.3 ± 5.0 (stat) ±2.8 (syst) ±0.9 (lumi) pb. This measurement is combined with a previous measurement of t t process in the lepton+jets channel at 5.02 TeV using 28 pb -1 of 2015 data, resulting in σ t t = 62.6 ± 4.1 (stat) ±3.0 (syst+lumi) pb. The results are shown, together with other CMS t t measurements, in Fig. 1.

Measurement of top quark pair production in the full kinematic range at 13 TeV

Differential cross sections for top quark pair production are measured in the full kinematic range at 13 TeV with an integrated luminosity of 137 fb -1 , in the lepton+jets channel 5 . This measurement combines low-p T analysis (resolved top quark decay products) with high-p T analysis, where top quark decay products overlap.

At least one isolated electron or muon must be reconstructed, with p T > 30 GeV and |η| < 2.4. Resolved jets, reconstructed with the anti-k t algorithm with a parameter of 0.4, are also required to satisfy p T > 30 GeV within |η| < 2.4.

Four event categories are defined: -"2t": Among the jets, there must be at least two jets identified as b jets with a tight criterion.

-"1t1l": Among the jets, there must be one jet identified as b jets with a tight criterion, and a second jet identified with a looser criterion. In the "2t" and "1t1l" categories, the top quark system is reconstructed assuming "resolved" reconstruction, where each of the decay products are identified with a reconstructed particle in the event. A quadratic equation is solved to find missing information on the neutrino. Jets are assigned using a likelihood method.

-"BHRL" (boosted hadronic resolved leptonic): there must be one jet reconstructed with the anti-k t algorithm with a parameter of 0.8, with p T > 400 GeV and |η| < 2.4, and a jet mass m j > 120 GeV (boosted hadronic top candidate). The PUPPI algorithm is used for pileup mitigation. A neural network is used to identify the subjets arising from the top quark.

-"BHBL"(boosted hadronic boosted leptonic): a boosted hadronic top candidate must be reconstructed, accompanied with a boosted leptonic top candidate, which is reconstructed by requiring a non-isolated lepton with p T > 50 GeV close to a jet, identified with a neural network trained to identify leptons arising from a W boson against multi jet background.

The categories are exclusive. The resulting spectra are presenting a smooth transition between resolved and boosted regimes. The distributions are unfolded for detector effects within a fiducial volume as close as possible to the recontructed criteria. The systematic uncertainties are estimated by repeating the fit with varied response matrix. Figure 2 shows the differential distributions for hadronic and leptonic top p T , as an example. 3 Measurements of single top cross sections at CMS

Status of single top production measurements

Single top quark production can be produced in t channel (largest cross section at the LHC), in association with a W boson or in the s channel. Measurements in the t channel at CMS are able to provide differential cross sections as well as ratios of differential cross sections between top and antitop production 6 . The tW channel is measured differentially in the dilepton channel 7 . The s channel is yet to be observed at the LHC. In addition, measurements of single top in association with a photon or a Z boson have been performed.

Measurement of single top tW production in lepton+jets channel

The inclusive cross sestion for single top tW production is measured in the lepton+jets channel at 13 TeV for the first time, using 36 fb -1 of pp 2016 data 8 . Events with a single muon (electron) having p T > 26(30) GeV are selected. Jets with p T > 30 GeV are required to be away from leptons. Exactly one jet identified as b jet is required. Three regions are defined: 2 jets (W boson control region), 3 jets (signal region) and 4 jets (t t control region). A boosted decision tree (BDT) is trained against t t background, exploiting the difference in jet kinematics relative to the signal. The signal is extracted by a simultaneous fit in the three regions. An illustration of the BDT output is shown in Fig. 3. The result is the first observation (with more than 5σ) of tW process in the lepton+jet channel, with a cross section σ tW = 89 ± 4 (stat) ±12 (syst) pb. The largest systematic uncertainties arise from the QCD jets and W+jets background normalization, the jet eneregy scale, the b-tagging efficiency.

Summary

Recent measurements of t t and single top cross sections have been discussed. Thanks to the large number of top quark pair produced, measurements of t t cross sections are now multi-differential and extend into the boosted regime. Observations of more difficult decay channels for single top processes are now performed.

4 .

 4 Isolated leptons are required to satisfy p T > 20 (leading lepton) and p T > 10 GeV (subleading lepton) with a pseudorapidity |η| < 2.4 (2.5) for electrons (muons), and the dilepton mass must be m eµ > 20 GeV to suppress conversions and low-mass resonances. At least two jets with p T > 25 GeV within |η| < 2.4 are required.

Figure 1 -

 1 Figure 1 -Inclusive t t cross sections measured at CMS. The black dot represents the measurement described in this section 4 .

Figure 2 -

 2 Figure 2 -Differential distributions for hadronic and leptonic top pT 5

Figure 3 -

 3 Figure 3 -Boosted decision tree in the three event categories, for the muon channel 8 .


domain: phys spi

text:
Yoann Bernard-Gardy

Jean-Charles Matéo-Vélez

François Issac

Julien Jarrige

Gaël Murat

Laurent Garrigues

Denis Payan

Innovative Technique for Electrostatic Discharges Characterization on a Floating Nanosatellite Mockup

This paper presents efforts made to improve the characterization of electrostatic discharges induced by severe spacecraft surface charging events. The novelty of this work resides in the design and implementation of a test setup that provides more refined information than the techniques usually adopted and prescribed by spacecraft design guidelines. We applied the test setup to two different nanosatellite mockups. By reducing the coupling with ground-test equipment, we significantly improved the measurement precision. An application of such a setup is the evaluation and prediction of inrush currents caused on nanosatellites by electrostatic discharges induced by hazardous space weather conditions.

I. Introduction

S PACECRAFT surface charging is the result of a complex inter- action between the space environment and the satellites [START_REF] Hastings | Spacecraft-Environment Interactions[END_REF][START_REF] Garrett | Guide to Mitigating Spacecraft Charging Effects[END_REF]. The main contributors to spacecraft charging are electrons with an energy of a few kiloelectron volts. During geomagnetic substorms, they are responsible for negatively spacecraft charging levels down to hundreds and sometimes thousands of volts. This effect is partly mitigated by secondary electron emission from spacecraft surfaces, including electrons generated by environmental electron impacts and by ultraviolet light from the sun. Insulators and conductors do not emit the same number of electrons; this depends on their electrical properties, which lead to electrical potential difference buildup on satellite surfaces. Electrostatic discharge (ESD) triggering depends on the nature of the surface materials and on how they are bound to each other (clamping or gluing). The charge and energy released during discharge depend on both the spacecraft and its environment. The geosynchronous Earth orbit (GEO) and middle Earth orbit (MEO) are known to generate a significant ESD risk with many associated anomalies [START_REF] Fennell | Spacecraft Charging: Observations and Relationship to Satellite Anomalies[END_REF][START_REF] Anderson | Spacecraft Charging Anomaly on a Low-Altitude Satellite in an Aurora[END_REF][START_REF] Ferguson | Plasma Conditions During the Galaxy 15 Anomaly and the Possibility of ESD from Subsurface Charging[END_REF][START_REF] Ahmad | Diagnosing Low Earth Orbit Satellite Anomalies Using NOAA-15 Electron Data Associated with Geomagnetic Perturbations[END_REF]. Low Earth orbit (LEO) charging issues occur in the auroral ovals during auroral electron injections [START_REF] Anderson | Characteristics of Spacecraft Charging in Low Earth Orbit[END_REF][START_REF] Eriksson | Charging of the Freja Satellite in the Auroral Zone[END_REF]. ESDs have been detected in GEO, MEO, and LEO [START_REF] Koons | Summary of Environmentally Induced Electrical Discharges on the P78-2 (SCATHA) Satellite[END_REF][START_REF] Shimizu | Solar Array Electrostatic Discharge Current and Image Captured in Orbit[END_REF]. To face this risk, the space industry design guidelines define how to evaluate and prevent the effects of the charging environment [START_REF] Purvis | Design Guidelines for Assessing and Controlling Spacecraft Charging Effects[END_REF][START_REF]Mitigating in Space Charging Effects-A Guideline[END_REF][START_REF]Spacecraft Charging[END_REF][START_REF]Space Systems-Space Solar Panels-Spacecraft Charging Induced Electrostatic Discharge Test Methods[END_REF]. One common approach consists of performing numerical simulations by assuming worst-case conditions [START_REF]Assessment of Space Worst Case Charging Handbook[END_REF][START_REF] Mandell | Nascap-2k Spacecraft Charging Code Overview[END_REF][START_REF] Roussel | SPIS Multitimescale and Multiphysics Capabilities: Development and Application to GEO Charging and Flashover Modelling[END_REF][START_REF] Thiébault | SPIS 5.1: An Innovative Approach for Spacecraft Plasma Modeling[END_REF][START_REF] Muranaka | Development of Multi-Utility Spacecraft Charging Analysis Tool (MUSCAT)[END_REF]. The guidelines also define ground-test setups and protocols to represent the main interactions between the environment and sensitive equipment. They were initiated at a time when almost all satellites were medium to large spacecraft. With the advent of small satellites (microsatellites, nanosatellites, CubeSat, etc.), most of the guidelines have been tailored in order to reconsider the capacity of the test methods to fit small satellite configurations. A typical example concerns ESDs on solar arrays. On the one hand, solar panel power buses are much lower than on large telecommunications spacecraft. Therefore, the risk of sustaining secondary arcing can generally be neglected. Only very limited solar cell degradations are expected in the future unless power bus voltages increase. On the other hand, the reduced size of nanosatellites increases the proximity of ESD sites and sensitive components, such as electronics boards. In particular, reducing the electrical wiring length automatically produces higher overvoltage levels on electronics board I/O by direct injection of transient signals. In addition, the ESD radiative component couples more easily with harnesses and with the frame, leading to more or less severe electromagnetic coupling (EMC), depending on the attention given to this aspect by spacecraft engineers. That is the reason why ESD on solar panels could be as detrimental on nanosatellites because they are on telecommunication satellites. There is thus a need to reconsider how to test ESD/EMC effects on small satellites. The inrush current flowing in the spacecraft frame and harnesses when an electrostatic discharge occurs is a key parameter; this current depending on many parameters including the ESD location and the spacecraft architecture. The best method to replicate the inrush current is the "test-asyou-fly" approach. Performing an ESD test at spacecraft scale is impossible in practice for most satellites, except for small satellites that can fit vacuum chamber dimensions. The experimental protocol is not straightforward, however. One major concern is the necessity to limit the electromagnetic interferences between the spacecraft and the ground-test setup. Classical techniques use high negative voltage supply to charge the test coupon through a capacitor component that mimics the spacecraft capacitance with respect to its environment. The coupon is then immersed in a dense plasma, irradiated with an electron beam, or illuminated with an ultraviolet source to represent LEO, GEO, and MEO charging environments. When the differential voltage of an insulator exceeds a given threshold, an ESD occurs. Its physics is described by the cathode spot theory. Electrons flow from the negatively charged component capacitor to the cathode spot, then to vacuum, and finally to the grounded tank walls, closing the electrical circuit loop. The absolute capacitance of GEO/MEO large satellites is about a few nanofarads. That of nanosatellites in LEO is rather on the order of a few tens of picofarads. Such a low value is often overpassed by the parasitic capacitance of the test setup, which in the end significantly distorts the measurement of the blowoff and flashover currents with respect to flight conditions. The blowoff (BO) is the current flowing from the negatively charged nanosatellite to the ambient space environment at the very beginning of the ESD ignition. The most adapted geometrical configuration for blowoff triggering is the so-called triple point, i.e., the junction between a conductive material connected to the structure, an insulator, and vacuum. A triple point increases the ESD occurrence because it locally enhances the electric field [START_REF] Cooke | Introducing the Passive Anode Surface Emission Cathode[END_REF]. This situation is particularly risky for insulators with a large secondary electron emission yield under electron impact or when the insulator is facing the sun. Both situations result in less negative potential than that of the conductive materials because with such an insulator, more electrons are emitted than collected on its surface from the environment. This results in the so-called inverted potential gradient (IPG). The flashover is a plasma bubble that expands from the structure and discharges positively charged dielectrics [START_REF] Sarrailh | Plasma Bubble Expansion Model of the Flash-Over Current Collection on a Solar Array-Comparison to EMAGS3 Results[END_REF][START_REF] Toyoda | Flashover Discharge Measurement with Uniform Surface Charging and Modeling of Current Waveform[END_REF][START_REF] Hoffmann | AFRL Round-Robin Test Results on Plasma Propagation Velocity[END_REF][START_REF] Okumura | Flashover Discharge on Solar Arrays: Analysis of Discharge Current and Image[END_REF][START_REF] Monnin | Flash-Over Propagation Simulation Upon Spacecrafts Solar Panels[END_REF].

The main objective of this paper is to show the feasibility to perform ESD tests on nanosatellite models under charging conditions representative of flight environments and with limited disturbance from the test setup itself. We first aim at demonstrating the feasibility to evaluate the BO current. Another objective of this paper is to collect preliminary information on the flashover (FO) current.

Section II presents the experimental setup used to characterize ESDs on two nanosatellite mockups. Section III describes typical results obtained in vacuum chamber under electron and vacuum ultraviolet (VUV) irradiation. Section IV is a discussion around the definition of new test protocols. Section V summarizes the work and presents some perspectives.

II. Experimental Setup A. Overview

The tests reported in this paper are performed in the JONAS vacuum chamber located at ONERA's Toulouse center in France [START_REF] Mateo-Velez | Ground Plasma Tank Modeling and Comparison to Measurements[END_REF]. This cylindrical chamber is 3.4 m long along the horizontal axis and 1.85 m in diameter. The nanosatellite mockups are mounted one by one at the center of the chamber with nonconducting nylon wiring. The onboard electronics used to monitor the events on the nanosatellite mockup are connected to the laboratory acquisition system with optic fibers. As a result, the mockups are electrically floating with respect to the ground. Two additional panels are mounted on the mockup: one on each side. They are insulated from the mockup platform by nonconducting Teflon® brackets and screws. The panels consist of dielectric coupons fixed on a conductive substrate, hence producing numerous triple points. To test the technique on a large variety of arrangements, we used several panels made of different triple-point assemblies. The orientation of the mockup faces and the position of the two panels are defined in Fig. 1. The rear side was exposed to UV irradiation, whereas the front side was exposed to electron gun bombardment.

B. 2U-Like Model

The 2U-like model is a box made of 5-mm-thick aluminum plates. Its size is 265 × 130 × 91 mm. panel configurations used with this mockup. Details are given in Table 1. The panel substrate is conductive and located at the front. It is made of copper in configurations 1 to 4 and of graphite in configurations 5 and 6.

C. 8U-Like Model

The 8U-like model is composed of a frame made of a 5-mm-thick aluminum plate. Its dimensions are 300 × 200 × 145 mm. Three aluminum panels and three printed circuit board (PCB) panels are attached to the frame. The PCB panels are made of 1.6-mm-thick epoxy coated with 100-μm-thick copper. The faces located at the front and at the rear are made of PCB panels with dimensions of 200 × 145 mm. The rear face is covered by two sheets of Teflon with dimensions of 80 × 110 × 0.5 mm that are separated by a gap of 40 mm. The face oriented in the -Z vertical direction is made of aluminum, and its dimensions are 300 × 200 × 2 mm. The face oriented in the +Z direction is made of PCB, and its dimensions are 300 × 200 mm. The right and left sides are made of aluminum, and their dimensions are 300 × 145 × 3 mm. PCB and aluminum panels are electrically connected to each other and connected to the frame. Figure 3 schematically presents the two panel configurations used with the 8U mockup, i.e., configuration 7 and configuration 8. Details are given in Table 2. On configurations 7 and 8, and from outside toward the mockup structure, the four first alumina patches are glued with a dielectric glue. The next two patches are glued with conductive H20E, and the last two patches are glued with Duralco 127 graphite. The generated triple points are of two kinds. For half of them, the glue is masked by the insulator. For the second half, the glue overflows from the patch to the substrate junction. The panel's front side is made of graphite.

D. Model Instrumentation

A shunt resistor R shunt of 4.7 Ω connects each panel's substrate to the structure, see Fig. 4. A 100-mm-long and 1-mm-diameter wire made of copper is fixed outside the mockup at the center and perpendicular to the surface located at the right of the mockup. It is electrically connected to the structure through a resistor R ant of 100 kΩ. The mockup embeds the electronic board of a Picoscope® PS4227 with a bandwidth of 100 MHz, a sampling rate of 250 MS/s, and 12 bit input channels. This board digitalizes the signals from the analog inputs of channel 1 and channel 2. Channel 1 measures the voltage drop across one of the two shunt resistances. The instrumented panel is located on the right. Channel 1 thus detects the current flowing between the frame and the right panel. Channel 2 measures the wire voltage at the R ant terminals. This device detects the mockup potential variations through high-impedance measurement. This part of the measurement chain is not treated in this paper. The electronic board is connected to the data acquisition system through an optical fiber. A battery mounted inside the mockup powers the electronics. The test setup is thus electrically floating with respect to the ground. It is located at a distance of at least 60 cm from any grounded element inside the tank.

E. Current Paths

The current monitored by channel 1 integrates both BO and FO currents flowing by the instrumented right panel. The FO plasma bubble expanding from the cathodic spot can reach other parts of the mockup [START_REF] Toyoda | Flashover Discharge Measurement with Uniform Surface Charging and Modeling of Current Waveform[END_REF][START_REF] Hoffmann | AFRL Round-Robin Test Results on Plasma Propagation Velocity[END_REF][START_REF] Monnin | Flash-Over Propagation Simulation Upon Spacecrafts Solar Panels[END_REF]. Depending on the location and duration of the cathode spot, the measurement can produce different signals. shows three different situations. The situation in Fig. 5a corresponds to a BO that occurs on the instrumented right panel. The measurement includes the electron currents flowing from the structure, from the left panel to the right panel, and (in the end) to vacuum. This current evacuates the negative charges of the mockup frame. The situation in Fig. 5b corresponds to a BO that occurs outside the instrumented right panel. The measured current is composed of the current flowing from the right panel to the cathode spot located either on the mockup or on the left panel. This current also discharges the negative potential of the mockup. The situation in Fig. 5c corresponds to a FO that expands from the cathode spot located on the right panel, to the mockup frame, and to the left panel. The measured current is composed of a BO current (as in the situation in Fig. 5a) and of a second component associated to the return current when the plasma gets to the mockup and to the left panel. In addition to discharging the negative potential of the mockup, this current partly or fully discharges the insulators with a positive voltage with respect to the mockup frame. The last situation, which is not represented here for the sake of conciseness, is when a FO expands from a cathode spot located on the mockup or on the left panel. is used to negatively charge the mockup. It is located at a distance of 1.6 m from the model's front side. It is powered by an EGPS-4104C power generator and by a Glassman PS/FJ30N04.0 voltage generator. The dielectric differential charging is obtained with a VUV lamp (Hamamatsu 30 W L2D2/ L7296). This VUV lamp is located at a distance of 2 m from the model's rear side. The energetic photons skip electrons out from surfaces, making them tend to 0 V with respect to the tank.

Measurements

A set of complementary chamber instruments aims to monitor extra parameters. It includes a video camera to observe the ESD's onset location. A wire antenna is mounted on the JONAS chamber wall and connected to an oscilloscope (Lecroy WaveRunner 640Zi) with an input impedance of 1 MΩ to detect electrical transients inside the chamber. We have also used a three-dimensional translating arm equipped with different instruments: 1) a contactless electrostatic potential kelvin probe (KP) to map the rear side potential with respect to the ground (using TREK 17284-189B), 2) a 1 cm 2 copper patch (PA) located on the rear of the kelvin probe to evaluate the photoemission flux induced by VUV light (this current is measured with a Keithley 2410 ammeter), and 3) a Faraday cup (FC) located under the kelvin probe to monitor the electron beam current density (this current is measured with a Keithley 6485 picoammeter).

The software used are LabView and Pico6. All results are posttreated with Python 3.8 and associated NumPy, Matplotlib, and pandas libraries.

G. Calibrations 1. Electron Beam

The electron beam current density profiles are measured in the absence of the nanosatellite mockups for beam energies of 5.5, 10, and 20 keV, as well as for different injected currents. An example of the X-Y-Z profiles is presented in Fig. 7 with a maximal current density of 200 pA∕cm 2 in absolute value. During the tests, the maximal current density ranged from 100 pA∕cm 2 up to 150 nA∕cm 2 . Under a 5.5 keV electron beam with a current density of 200 pA∕cm 2 , the mockup equilibrium potential scaled from -105 0 to -3100 V with respect to the ground, depending on the panel configurations. This is the result of materials with different secondary electron emission yields.

VUV

The photoelectron emission current density is mapped at the rear side of the model. It is almost uniform and scales from 0.5 up to 1.0 nA∕cm 2 . This is representative of sun exposure at 1 astronomical unit [START_REF]Mitigating in Space Charging Effects-A Guideline[END_REF].

ESD Threshold

The main difficulty when using a floating mockup is to measure the time evolution of the structure during ESDs. Indeed, the KP must be located far enough from the mockup to reduce its interference with The ringing parasitic oscillations observed on the current are related to the measurement setup and not to the physical phenomenon itself. The resonance frequency of this circuit is about 10 MHz. This is related to the LC (inductor L and capacitor C connected together) circuit composed a 2 m copper cable in series with the C mes capacitor. We clearly see those oscillations during the ESD onset (time < 2 μs) and after the ESD has stopped (2 μs < time < 5 μs). The oscillations are about 25% of the signal amplitude, which illustrates the drawbacks associated with this type of measurement, as well as the necessity to improve the test setup.

III. Results

A. ESD Main Characteristics

A total number of 130 ESDs have been obtained with an electron current density ranging from 0.1 to 150 nA∕cm 2 and with the electron beam energy ranging from 5 to 15 keV. Figures 9 and10 the ESD waveforms measured on the 2U-like and 8U-like mockups, respectively. The current is positive when the ESD occurs on the right panel and negative when it occurs anywhere else (on the left panel or on the mockup). The current generally follows a bimodal time evolution: a fast dynamic blowoff with a high current peak, followed by a slower flashover with a lower but longer current.

Eighty-seven ESD waveforms have been detected on the 2U-like model. The highest current magnitude reached 400 mA. The ESD duration ranged from about 1 μs up to 15 μs (which is the output duration limit during these tests). The average duration was about 8 μs. Forty-three ESD waveforms have been detected on the 8U-like mockup. The highest current magnitude reached 500 mA. ESDs lasted from about 1 μs up to 9 μs (which was the time duration limit during these tests). The average duration was about 4 μs, but one can notice that some FOs obviously exceeded the acquisition time. That means that FOs with durations greater than 20 μs have probably occurred during the tests. The curve shapes obtained with the 2U-like and 8U-like mockups are comparable even though the BO appears to last longer on the largest mockup. We have observed ESDs on all panel configurations. The panels equipped with alumina sheets bound with the conductive H20E glue had the highest ESD occurrence level. The next paragraphs show a few typical examples. 8 with the aforementioned "classical" setup. The noise-to-signal ratio is less than 5%.

B. Typical Results on 2U-Like Mockups

Figure 12 presents the surface potential profiles at two consecutive times. The curve in blue is the last profile measured shortly before the ESD occurred (typically a few seconds to a few tens of seconds). From the left to the right (i.e., from 0 to 550 mm), the rear side elements are the left panel (from 0 to 200 mm), the mockup (from 200 to 350 mm), and the right panel (from 350 to 550 mm). Because ESDs are spurious events, it was not possible to control the time lapse between the last profile and the ESD occurrence. The profile is thus an approximation of the surface potential just before the ESD. The curve in red is the profile measured a few tens of seconds after the ESD occurred, which is the time necessary to switch the electron gun and the VUV lamp off manually (as soon as an ESD is detected) and then to move the KP from its waiting position to the mockup location. The profile scan lasts about 1 min. The structure potential with respect to the ground reference potential is measured at two locations free of insulators, i.e., at x 200 and 350 mm. This potential evolves at a timescale much faster than the experimental time resolution because the mockup electrical capacitance with respect to the ground walls is small (about a few tens of picofarads). A more reliable information is contained in the insulator differential charging because 1) this differential charging actually triggers ESDs and 2) it evolves at a timescale of a few minutes due to both high capacitance and low conductivity. Consequently, we present the spatial distribution of the differential charging instead of the absolute potential with respect to the ground. The ESD associated with the profiles presented in Fig. 12 is the result of triple points in the IPG situation. Insulators are positively charged with respect to the mockup structure. That ESD did not significantly reduce the insulator differential potential. Therefore, one can suggest that it was mainly composed of a BO current. The potential profiles do not allow us to assess with precision where the ESD occurred because no significant change is observed before and after the ESD. The analysis of video camera recordings has shown that the ESD location is on the left panel.

Figure 13 is the current evolution of an ESD that occurred on the right panel in configuration 2. It was composed of a bimodal BO and FO structure. The BO is similar to the BO of Fig. 11. It occurred on the right panel, as indicated by the positive current and confirmed by the video camera. The maximal current of 400 mA is reached after about 150 ns, and the BO current ends after around 500 ns. It is followed by a FO current with a magnitude of 30 mA on average, which lasts up to 8 μs and then suddenly stops. This phenomenon is the expansion of the plasma bubble generated at the cathode spot. During its expansion, it progressively discharges the dielectrics nearby the cathode spot as long as the cathode spot remains. The electrons flow through this conductive path and recombine with the positive charges stored at the surface of the charged insulators. Part of this current loops locally on the panel where the ESD occurred. When the duration of the cathode spot is long enough, the plasma bubble expands to the other mockup surfaces. The flashover of the ESD presented in Fig. 13 lasts a bit less than 8 μs. Given the size of the mockup, this duration is consistent with previous works [START_REF] Sarrailh | Plasma Bubble Expansion Model of the Flash-Over Current Collection on a Solar Array-Comparison to EMAGS3 Results[END_REF][START_REF] Toyoda | Flashover Discharge Measurement with Uniform Surface Charging and Modeling of Current Waveform[END_REF][START_REF] Hoffmann | AFRL Round-Robin Test Results on Plasma Propagation Velocity[END_REF][START_REF] Okumura | Flashover Discharge on Solar Arrays: Analysis of Discharge Current and Image[END_REF][START_REF] Monnin | Flash-Over Propagation Simulation Upon Spacecrafts Solar Panels[END_REF].

The surface potential maps shown on Fig. 14 suggest that the considered ESD occurred on the right panel. Before the charging process, the maximal potential difference was 1600 V at the junction between the inner dielectric of the right panel and the structure. After the ESD, the potential difference decreased to 500 V. The flashover significantly discharged the right panel.

IV. Discussion

From the large variety of triple-point configurations tested in this work, those involving alumina appear to have the highest probability to trigger ESDs. Seventy-three ESDs over a total number of 130 have been triggered these panels. Their locations have been deduced from the electrical transient waveforms, from the electric potential profiles, and from the video camera. We have measured the total secondary electron emission of alumina under electron impact. The second crossover is greater than 10 keV. That confirms that the secondary electron yield of alumina is very large [START_REF] Balcon | Secondary Electron Emission on Space Materials: Evaluation of the Total Secondary Electron Yield from Surface Potential Measurements[END_REF]. The alumina sample thickness is either 150 or 250 μm, depending on the configurations. This thickness does not seem to play a major role. In addition, the ESDs obtained with the 8U-like mockup all occurred at the triple point involving the conductive glue and alumina. The combination of a conducting glue and a high secondary electron emission yield insulator is thus favorable to ESD generation.

Regarding the blowoff discharges, the events are, on average, shorter on the 2U-like mockup than on the 8U-like mockup. We believe it is the result of different insulator attachments to the conductive part rather than of the mockup size and shape. The configurations with conducting adhesive tapes as in the 8U-like mockup are more representative of assemblies such as solar cells. Configurations with adhesive tapes are more representative of multilayer insulators bindings.

The flashover is, on average, shorter on the 8U-like mockup than on the 2U-like. Levels are, however, similar: about a few tens of microamperes for both models. The relative sizes of the mockup and of the panels (for which the sizes are identical on the 2U and 8U models) may increase or decrease the flash-over duration, depending on the size of the covering insulators and on their distance to the ESD cathode spot.

Regarding the 8U mockup, the current measured on R shunt terminals reaches a maximal amplitude of 200 mAwhen the ESD occurs on the instrumented right panel. The dissipated charge varies from 50 to 100 nC. When an ESD occurs out of the instrumented panel, the peak current and the charge dissipated during the BO range, respectively, from 15 to 35 mA and from 2 to 20 nC. In both cases, the potential difference generated through the resistor R shunt remains lower than 1 V, and thus has very little impact on the discharge dynamics, meaning the measurement is not intrusive at all. We have double checked this by using a Pearson probe instead of R shunt .

We can propose a simple and easy reasoning to understand at first order the reason how the maximal peak current measured on the wire connecting the structure to the right panel is affected by the location of the ESD. We assume a uniform electric field around the mockup. Applying the Gauss theorem to each surface element S element leads to

E n × S element Q element ∕ε0
with E n as the component of the electric field normal to the surface. The net charge Q element stored on each conductive parts is proportional at the first order to its surface. Assuming that the net charge is totally evacuated at the end of the blowoff and that the blowoff has the same time evolution, whatever the surface element, one can directly relate the current to the surface of each element. The charge exchanged between the structure and the instrumented panel varies with ESD localization. Q total is defined as the total charge emitted by the cathode spot; that reaches the space environment during the ESD blow-off. During the tests we measure Q shunt ; that is defined as the total charge flowing between the spacecraft structure and the instrumented panel. When an ESD occurs on the instrumented panel, the charge Q shunt transferred to the instrumented panel is the sum of the charges released by the non-instrumented panel and spacecraft structure surfaces. When an ESD occurs anywhere else, the charge Q shunt transferred from the instrumented panel to the structure involves the surface of that panel only. Given the actual elements sizes, the relation between Q total and Q shunt writes:

Q total ≈ 15 13 Q sh unt
when an ESD occurs on the instrumented panel, and

Q total ≈ 15 2 Q sh unt
when an ESD occurs elsewhere. From this model, on average, the ESDs located on the right panel produce a blowoff current 6.5 times greater than ESDs produced anywhere else, which is consistent with the current magnitudes presented earlier. Considering this model, the actual net charge dissipated during the blowoff varied from 60 to 110 nC during the tests presented in this paper. The capacitance of the mockup with respect to the tank wall has been computed by numerical simulation. It lies between 20 and 50 pF. Combining this with the aforementioned net charge dissipation leads to a potential drop of 2 to 5 kV during the blowoff. These values are compliant with the electron beam energy of 5 to 10 keV used during the tests and with the potential difference measured between the insulator and the mockup frame.

In general, and as observed in Figs. 12 and 13, the IPG level varies from 500 to 1500 V. Accounting for the mockup capacitance computed earlier in this paper, the energy dissipated during the ESD ranges between 1 to 25 μJ under the tests conditions used in this work.

V. Conclusions

The technique presented in this paper significantly refines the ESD characteristics measurement. It is very well adapted to ESD tests on nanosatellite models. The main recommendation is to perform the measurements on a floating object to get rid of parasitic capacitive and inducting coupling between that object and the rest of the test setup. This implies to embed an acquisition board with an autonomous power supply and to achieve data acquisition through an insulated communication link (like in the present work, an optical fiber). The time resolution then only depends on the acquisition board performance and on the embedded sensors. No additional signal filtering is required to remove ringing. Such a setup is useful to extrapolate the on-ground results to flight conditions and to predict the effects of ESDs in an operational context.

The results obtained with an electron beam and a VUV source are applicable to outside of LEO. Some aspects of spacecraft charging in LEO auroral arcs are nevertheless very similar to charging conditions in GEO. This is because the plasma sheath size around a highly negatively charged spacecraft in LEO gets much larger than the spacecraft dimensions.

The test setup presented in this paper represents part of this situation (i.e., the long sheath) but fails to mimic the plasma behavior: especially the ram and wake effects. It is planned to perform tests in conditions more representative of LEO, including exposure to plasma. The difficulty resides in the capacity to operate the plasma source without deteriorating the electron gun performances. Complementary numerical simulations could be used to assess charging in LEO plasma as well.

This work finds a particular application in the definition and realization of protections of nanosatellites against the ESD risk. High-fidelity inrush current patterns can be deduced from a set of dedicated tests under vacuum using a reduced nanosatellite mockup. Such results can be used to specify the EMC tests. The released energy on the order of a few tens of microjoules suggests that such ESDs can generate some undesired effects, such as bitflips on electronics. In addition, the cable lengths are significantly smaller on nanosatellites with much lower resistive and inductive losses from the ESD site to sensitive electronics. Cables are possibly less shielded as well. All this would suggest reevaluating the risks with regard to ESD electromagnetic coupling on nanosatellites.

Ultimately, nanosatellites carrying miniaturized versions of the instrumentation designed in this work would provide actual ESD characteristics. They could be directly compared to on-ground test results to validate and improve our understanding of the multiphysics and multiscale problem of satellite charging, discharging, and coupling with systems.

An evolution of this experiment would consist of generating ESDs with two separate electron guns: one to negatively charge the structure, and the other one for differential charging instead of the VUV source. It would be representative of a spacecraft in eclipse. The test setup could also upgraded with a real-time and contactless measurement of the mockup potential to assess the predischarge potential.

The following protocol could be proposed to perform qualification of ESDs on nanosatellites:

1) Obtain the ESD threshold using the classical method, which involves a capacitor, a voltage generator to charge the mockup, and a plasma source and/or an electron gun and/or a VUV source to charge the insulators.

2) Perform a precise characterization of the transient signals on a floating mockup using the present test setup with its proposed adaptations.

Finally, extending the techniques with an additional measurement of the flashover current and with more complex mockup geometries would help validate recent flashover models and numerical simulation tools in the nanosatellite context [START_REF] Sarrailh | Plasma Bubble Expansion Model of the Flash-Over Current Collection on a Solar Array-Comparison to EMAGS3 Results[END_REF][START_REF] Toyoda | Flashover Discharge Measurement with Uniform Surface Charging and Modeling of Current Waveform[END_REF][START_REF] Hoffmann | AFRL Round-Robin Test Results on Plasma Propagation Velocity[END_REF][START_REF] Monnin | Flash-Over Propagation Simulation Upon Spacecrafts Solar Panels[END_REF]. In return, the simulation would provide complementary information on the flashover expansion.

Figure 2

 2 schematically presents six

Fig. 1 Fig. 2

 12 Fig.12U-like mockup mounted in the JONAS vacuum chamber. It is fixed to the tank walls with insulating wires. The optic fiber communication link between the onboard electronics and the acquisition system is the yellow wire below the mockup.

Figure 5

 5

Fig. 3

 3 Fig. 3 Rear side of the panels used with the 8U-like mockup. The dotted line represents the region scanned by the contactless voltage probe.

FFigure 6

 6 Figure 6 schematically represents the mockup installed in the JONAS chamber. An electron gun (Kimball Physics EGF-4104A)

Fig. 4 Fig. 5

 45 Fig. 4 Schematics of the electronic setup installed in the mockup.

Figure 8

 8 presents a typical time evolution of an ESD obtained on the 2U-like mockup equipped with a left panel in configuration 3 and a right panel in configuration 4. The ESD occurred at the triple point between Teflon and copper. The ESD threshold was about -1500 V. It lasted 2 μs. It only partially discharged the 100 pF capacitor with a residual mockup potential of -800 V at the end of the ESD.

  present

Fig. 6

 6 Fig. 6 JONAS chamber test setup. The wire connecting the mock-up to the ground electrical circuit is mounted only during calibration tests including the ESD threshold measurements.

Fig. 7

 7 Fig. 7 Electron beam current density profiles as a function of the distance from the chamber center. The X-Y-Z axes are defined in Fig. 6.

Fig. 8

 8 Fig. 8 Typical ESD current and voltage transient during ESD threshold calibration tests on the 2U-like nanosatellite. The results show oscillations induced by the charging circuit.

Figure 11

 11 Figure 11 presents the time evolution of an ESD that occurred on the mockup structure or on the left panel in configuration 1 under a 12 keVelectron flux of 100 nA∕cm 2 and VUV flux. The current peak of -140 mA was reached at around 150 ns. The ESD lasted about

Fig. 9

 9 Fig. 9 ESD current waveforms measured on the 2U-like mockup.

Fig. 10 ESD

 10 Fig. 10 ESD current waveforms measured on the 8U-like mockup.

Fig. 11

 11 Fig. 11 Current evolution of an ESD that occurred on the 2U-mockup structure or on the left panel in configuration 1, under a 12 keV electron beam with a current density of 100 nA∕cm 2 and under VUV flux.

C

  Figures 15 and 16 show the current evolution of two ESDs that occurred on the 8U-like mockup. The first one occurred either on the mockup structure or on the left panel in configuration 7. The second one occurred on the right panel in configuration 8. Both present characteristics and shapes are comparable to those previously presented on the 2U-like mockup. The BO lasts about 1 μs and reaches a peak magnitude after about 500 ns. The highest peak currents are lower than in the 2U configurations. They are about -40 mA for the negative values (to be compared to -140 mA) and 200 mA for the positive values (to be compared to 400 mA). The FO lasts about 6 μs, which is comparable to the 8 μs duration of the ESD presented in Fig. 13.

Fig. 13

 13 Fig. 13 Current evolution of an ESD that occurred on the right panel in configuration2 of the 2U-mockup, under a 12 keV electron beam with a current density of 100 nA∕cm 2 and under VUV flux.

Fig. 14

 14 Fig. 14 Surface potentials measured before and after the ESD presented in Fig. 13.

Fig. 15

 15 Fig. 15 Current evolution of an ESD that occurred on the 8U-mockup structure or on the left panel in configuration 7, under a 9 keV electron beam with a current density of 150 nA∕cm 2 and under VUV flux.

Table 1

 1 Characteristics of the panels used with the 2U-like mock-up a

	Panel		Substrate
	Configurations	Dielectrics (at the rear)	(at the front)
	1	×2 Teflon FEP	200 × 10 × 2 mm raw
		(100 × 100 × 0.1 mm)	PCB with copper
			layers on each side
			connected to each
			other.
	2	×2 Teflon PTFE	Bounded with
		(100 × 100 × 0.1 mm)	Kapton ® scotch on
			corners
	3	×3 Conf 1 Teflon SSM

(200 × 100 × 0.1 mm) 4 Teflon PTFEa sin Conf2 Alumina39 × 39 × 0.25 mm Alumina39 × 39 × 0.125 mm PEEK90 × 40 × 0.15 mm 5 ×2Alumina 80 × 60 × 0.15 mm PEEK panels 200 × 80 × 6.5 mm. Front side covered with graphite plate. Rear side covered with 2 μm thick gold layer. PEEK 80 × 60 × 0.15 mm bounded with 3M TM dielectric epoxy glue 2216 6 ×2PEEK80 × 60 × 0.15 mm) a FEP is fluorinated ethylene propylene, PTFE is polytetrafluoroethylene, SSM is secondsurface mirror, PEEK is polyetheretherketone and PCB is printed circuit board.

Table 2

 2

Characteristics of the panels used with the 8U-like mock-up Panel configuration Dielectrics (at the rear) Bonding Substrate (at the front) 7 Alumina 8× 37 × 37 × 0.25 mm 4× glued with 3M TM dielectric epoxy glue 2216 2× glued with EPO-TEK® conductive H20E 2× glued with DURALCO®127 epoxy glue dopped with graphite 200 × 80 × 2 mm aluminum panels with 2 μm gold deposit 8 Alumina 8× 37 × 37 × 0.15 mm

Acknowledgments

Part of this work was funded by the National Center for Space Studies Research and Development program. This work was performed in the frame of the Charging On CubeSat (CROCUS) program of ONERA.