S Bianco

O.-H Ellestad

P Ferreira

F Friend

P Gargiulo

R Hanania

S Henrot-Versille

A Holtkamp

P Igo-Kemenes

D Jarroux-Declais

M Jordão

B.-C Kämper

J Krause

T Lagrange

F Le Diberder

A Le Masurier

A Lengenfelder

C M Lindqvist

S Mele

S Plaszczynski

R Schimmer

J Vigen

R Voss

M Wilbers

J Yeomans

K Zioutas

Towards Open Access Publishing in High Energy Physics Report of the SCOAP 3 Working Party The SCOAP 3 Working Party *

published or not. The documents may come   L'archive ouverte pluridisciplinaire

A word from the Chair

Dear Reader This Report concerns the implementation of a process initiated by CERN's Director-General, Dr. Robert Aymar, today supported by leading actors from the particle physics community, and worked through in detail by members of an international Working Party. The initiative offers an opportunity for the cost-effective dissemination of high-quality research articles in particle physics, enabling use of the new technologies of e-Science across the literature of High Energy physics.

The particle physics community has led the academic world in disseminating preprints of research articles through large repositories. This Working Party Report offers a new opportunity for the community to add open access peer-reviewed journals to its publishing outlets through a global conversion of the main corpus of journals to the open access model. The opportunity to improve cost-effective access to peer-reviewed research is there for authors, funding agencies and publishers who respond imaginatively to the proposal.

The Working Party has done its work. It is now in the hands of the different stakeholders to use the opportunity opened up in this Report.

Hopefully the model proposed by the Working Party will inspire other disciplines to start work on the conversion of their literature to open access. However, this model can only act as an example and each subject community will have to make their own analysis and decisions to suit their publishing environment.

It has been a privilege for me to chair the Working Party and to witness the vision and the dedication to detail of its members.

Frederick Friend

London, 14 th April 2007

JISC Scholarly Communication Consultant

Honorary Director Scholarly Communication University College London f.friend@ucl.ac.uk

Synopsis Background

The goal of "Open Access" 1 (OA) is to grant anyone, anywhere and anytime, free access to the results of scientific research. The OA debate has gained considerable momentum in recent years. It is driven mostly by two factors:

• The "serials crisis" of ever-rising costs of journals, which has forced libraries to cancel a steadily-increasing number of subscriptions, curtailing the access of researchers to important scientific literature.

• The increasing awareness that results of publicly-funded research should be made generally available. This need is amplified by the transformation of research activities towards "e-Science", carried out by a global scientific community linked by strong networks.

High Energy Physics (HEP) pioneered OA through "repositories" containing collections of "pre-prints" freely accessible on the Internet. Today about 90% of HEP pre-prints are available in repositories. Thanks to the speed with which they make results available, repositories have become the lifeblood of HEP scientific information exchange. However, repositories do not perform peer review and may contain only the original versions of articles submitted to journals, and not necessarily the final, peer-reviewed, published versions.

Notwithstanding the success of repositories, there is consensus in the scientific community about the need for high-quality journals that will continue to provide:

• quality control through the peer review process;

• a platform for the evaluation and career evolution of scientists;

• a measure of the quality and productivity of research groups and institutes.

The price of an electronic journal is mainly driven by the costs of running the peerreview system and editorial processing. Most publishers quote a price in the range of 1'000-2'000 Euros per published article. On this basis we estimate that the annual budget for the transition of HEP publishing to OA would amount to a maximum of 10 Million Euros per year. In comparison, the annual list-price of a single "core" HEP journal today can be as high as 10'000 Euros; for 500 institutes worldwide actively involved in HEP, this represents an annual expenditure of 5 Million Euros.

1 http://oa.mpg.de/openaccess-berlin/berlindeclaration.html

The SCOAP 3 model

The proposed initiative aims to convert high-quality HEP journals to OA, pursuing two goals:

• to provide open and unrestricted access to all HEP research literature in its final, peer-reviewed form;

• to contain the overall cost of journal publishing by increasing competition while assuring sustainability.

In the present proposal, the publishers' subscription income from multiple institutions is replaced by income from a single financial partner, the "Sponsoring Consortium for Open Access Publishing in Particle Physics" (SCOAP 3 ). SCOAP 3 is a global network of funding agencies, research laboratories, and libraries. Each SCOAP 3 partner will recover its contribution from the cancellation of its current journal subscriptions. This model avoids the obvious disadvantage of OA models in which authors are directly charged for the OA publication of their articles.

The financing and governance of SCOAP 3 will follow as much as possible the example of large research collaborations and each country will contribute according to the number of its scientific publications. To cover publications from scientists from countries with no funding of HEP research, an allowance of not more than 10% of the SCOAP 3 budget is foreseen.

In practice, the OA transition will be facilitated by the fact that the large majority of HEP articles are published in just six peer-reviewed journals from four publishers 2 .

Five of those six journals carry a majority of HEP content. HEP has a natural overlap with related fields such as, but not limited to, astroparticle physics and nuclear physics. The five "core" journals include between 10% and 30% of articles in these disciplines, which will be naturally and logically included in the OA transition. This is in the interest of the readership and promotes the long-term goal of an extension of the SCOAP 3 model to these related disciplines.

The fractions of "broadband" journals quoted above also include publications in these related disciplines.

Of course, the SCOAP 3 model is open to any other, present or future, high-quality journals carrying HEP content. This will ensure a dynamic market with healthy competition and a broader choice.

The annual budget for the SCOAP 3 operation will be established through a tendering procedure. The tender and the subsequent contracts with publishers will address the use of OA articles, the conditions for un-bundling OA journals from existing subscription packages, and the reduction of subscription prices for "broadband" journals following the conversion of a fraction of articles to OA.

Provided that the SCOAP 3 funding partners are ready to engage in long-term commitments, many publishers are expected to be ready to enter into negotiations along the lines proposed here. The SCOAP 3 model could be implemented during 2007. Once leading funding agencies will pledge funds for the financial backing of the consortium, the tendering procedure could take place during summer and the exact budget envelope could be known by autumn. A Memorandum of Understanding for the governance of SCOAP 3 and the cost sharing could then be signed by the funding agencies; this will be followed by the establishment of contracts with publishers. OA publishing in HEP could then become reality as of the beginning of 2008.

The example of SCOAP 3 will be an important milestone in the history of scientific publishing. It could rapidly be followed by other disciplines and, in particular, by fields related to HEP such as nuclear physics or astro-particle physics.

Introduction

Access to past and current research reports is of vital importance for current and future research. A key factor in the efficiency of the research process is therefore easy and affordable access to the work of other individuals and groups working in the same area. The Open Access (OA) paradigm aims to thus empower researchers by granting anyone, anywhere and anytime, free access to the results of scientific research, in general through free availability of the electronic versions of scientific publications on the Internet.

For many academic communities, easy and affordable access to journal articles has been put at risk by the lack of price-related competition in the journals industry. The steady increase of journal prices, far above general inflation rates, has forced libraries to cancel subscriptions for journals their readers need, curtailing the access of researchers to parts of the scientific literature. In some cases universities worldwide have even reached the paradoxical extreme of being no longer able to afford the journals where their scientists publish their own work. This "serials crisis" has now reached a level that is damaging the interests of the scientific communities of readers and authors as well as those of some publishers. Although the current publishing scenario still appears stable, the very existence of some key titles is at stake at a time when the quantity of research output is expected to grow 3 . A change in the publishing model along the lines proposed in this Report would provide authors with high-quality publishing outlets at prices sustainable both for research funding agencies and for publishers.

Greater value can be achieved not only from the price-related competition the proposal in this Report will introduce into the physics publishing market, but even more from the OA paradigm itself, which will enable greater use of research results, stimulating further research built upon access to high-quality, peer-reviewed, freely available research reports. In addition, the OA model will free up text and data currently locked away in subscription journals for text-and data-mining applications.

For successful publishers, the proposal in this Report offers opportunities to attract the best authors and achieve higher impact factors. The OA model can bring the benefits of higher citations to all stakeholders in research communication, enabling Notwithstanding the success of repositories, there is a consensus in the scientific community that refereed journals will continue to fulfil important functions in future:

• to guide researchers to the most important publications in their field through the editorial scope of journals and their -perceived or establishedimportance and prestige;

• to provide quality control through peer review;

• to provide a platform for the evaluation and career evolution of scientistsmost importantly, young scientists -for which publications in refereed journals will remain an important criterion;

• to provide a measure of the quality and productivity of research groups and institutes, often used as an important criterion in decisions about future funding.

All these are important raisons d'être for journals, which repositories cannot fulfil in their present form.

The motivation for the initiative described in this Report is to produce greater value from the investment funding agencies make in supporting peer-reviewed publication of scientific results in high-quality journals. This initiative aims to maintain both the quality of journal publication and a choice for authors among publication outlets, while introducing an element of competition into the service provided by journals, linking price to value.

The HEP community has effectively spearheaded OA, first with its 50-year old "preprint culture", then with the spread of repositories in the last 15 years. It is now ready for a transition to OA publishing. Its relatively small size and its nearly complete overlap between the reader and author communities4 can be of great advantage in this pioneering process.

An appropriate model to achieve this transition of HEP publishing to OA, while maintaining quality and adding greater value, was set out by the Task Force on Open Access Publishing in Particle Physics. This tripartite task force, which comprised representatives from the author communities, from research agencies and from publishers, operated between late 2005 and early 2006. In its Report5 , published in June 2006, the task force proposed to establish a Sponsoring Consortium for Publishing in Particle Physics (SCOAP 3 ), a central body which would remunerate publishers for the peer-review service, effectively replacing the "reader-pays"model of traditional subscriptions with an "author-side" funding.

Following the task force Report and the acceptance of its model by representatives from major European stakeholders, a Working Party was established to develop a specific proposal for the creation of SCOAP 3 , which is described in this Report.

Section 2 describes the SCOAP 3 model and the roles of publishers, funding agencies and libraries in the OA publishing scheme, as well as the benefits for the scientific community.

In Section 3 the HEP publication landscape is analyzed and an initial set of five "core" HEP journals is spotlighted as candidates to be entirely converted to OA. The section also treats the case of articles relevant to HEP but dispersed in several "broadband" journals, some of which are to be converted to OA on an article-byarticle basis.

Section 4 discusses an estimation of the SCOAP 3 budget envelope and presents a "fair-share" scenario for the financing of SCOAP 3 by the countries with an active HEP community. The sharing of costs is based on the affiliations of individual authors contributing to the "core" HEP journals and to selected HEP articles in "broadband" journals.

Section 5 discusses the requirements that will form the basis of a tender to be submitted by SCOAP 3 to publishers. These requirements and the subsequent contractual agreements will concern the journal infrastructure, quality and policy of the journal, along with some technical and financial aspects. The section also spells out the intended use of the articles, under OA tenets, by the author and reader communities.

A possible timeline of the actions on the road towards the full conversion of HEP publishing to OA is outlined in Section 6.

After two technical annexes, this Report is concluded by a glossary of technical terms and a list of recent public statements in favour of OA publishing from within the HEP community.

The SCOAP 3 model

The role of SCOAP 3 The SCOAP 3 consortium will act as a unique interface between the main stakeholders of the HEP scientific information market: on one side the author and reader communities, which have a large overlap, mostly represented by the same funding agencies and served by the same libraries; on the other side the publishers of highquality HEP journals. The aim of SCOAP 3 is to establish OA to HEP peer-reviewed articles along the lines of the Budapest Initiative 6 , namely "[The] free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself".

At the time of writing, SCOAP 3 is an initiative emanating from:

• several European funding agencies, among which CNRS and CEA (France), INFN (Italy), MPG (Germany) and other funding bodies from Greece, Portugal, Norway, Sweden and Switzerland;

• the two largest European particle physics laboratories, CERN and DESY;

• national and international library and other consortia such as GASCO (Germany, Austria, Switzerland), INFER (Italy), COUPERIN (France), JISC (U.K.), ABM-utvikling (Norway).

Within the next few months SCOAP 3 aims to federate similar agents worldwide.

The SCOAP 3 model will only be successful if partners from all countries contributing to HEP literature become members of the consortium. Indeed, a pillar of the model is to ensure OA to all HEP articles appearing in high-quality journals through this coordinated effort.

SCOAP 3 will be financed primarily by HEP funding agencies, laboratories and libraries, from funds currently used for journal subscriptions. However, it will also engage other bodies interested in the broad and free dissemination of scientific information. Each country will contribute to SCOAP 3 according to its share of the authorship of HEP articles as described in Section 4. For the SCOAP 3 model to be successful, it has to represent a stable, viable and sustainable alternative to subscriptions vis-à-vis its partners. It is therefore expected that the SCOAP 3 operation will follow the financial blueprints of large scientific collaborations laid down in corresponding Memoranda of Understanding.

An important asset of the SCOAP 3 model is that it will centralize all OA expenses that will therefore not have to be directly borne by authors and research groups. This contrasts with so-called "author-pays" OA options, offered by many publishers but of scarce success in HEP, which are perceived as an even higher barrier than subscription charges, in particular for theoretical physicists from small institutions who actually produce the vast majority of HEP articles.

Manuscripts from authors without academic affiliation or authors from countries with no funding of HEP research and which, therefore, cannot be reasonably expected to contribute to the Consortium at this time, will be treated like all other articles submitted for publication. This choice has obvious ethical reasons: namely not to preclude any author from the benefits of the peer-review service. In addition, it has sound practical and financial reasons: restricting OA privileges to authors from a selected set of countries would simply replace the present toll-access barriers by other limitations based on the geographical origin of authors. Conversely, if only a geographically defined subset of the HEP literature were to become available in OA, consortium members would still have to purchase the remaining subset and part of the benefits from the OA transition would thus be lost.

It is expected that SCOAP 3 will contribute to stabilizing the rising cost of access to information in the HEP domain by virtue of its representation of an important array of particle physics institutes and funding agents, by increasing the author awareness of costs and prices, by linking price to value, and by fostering new competition in the market.

One model, two implementations

A large fraction of the publications on "core" HEP subjects is published in a limited number of journals, as detailed in Section 3. Among those journals, some carry almost exclusively HEP content. SCOAP 3 aims to assist publishers to convert these "core" HEP journals entirely to OA. It is expected that the vast majority of the SCOAP 3 budget will be spent on these through a "lump-sum" payment model: SCOAP 3 pays a negotiated price for the peer-review and OA dissemination of all articles of the journal. Obviously, the entire journal will be available online to read for anyone without paying any subscription. On the other hand, some articles relevant to HEP appear in "broadband" journals that carry just a small fraction of HEP content. It is expected that the OA conversion of these articles will be sponsored by SCOAP 3 on a "pay-per-article" basis. Clearly, the subscription prices of "broadband" journals are expected to be decreased accordingly.

Conference proceedings and monographs are not within the scope of the SCOAP 3 budget. In the case of conference proceedings, OA should be realized by the conference organizers through their choice of publishing outlets.

The life-cycle of a SCOAP 3 OA article

The SCOAP 3 transition to OA aims to be transparent for authors. The life-cycle of a SCOAP 3 article may start in any country when it is submitted to one of the highquality journals that are partners of SCOAP 3 . The submission will be in all cases free of charge since the peer-review and publication costs are supported by SCOAP 3.

The journals will process the article through their peer-review system. Upon acceptance, the article will immediately be published OA on the publishers' web site and at the same time will be sent, together with all related metadata, to a repository designated by SCOAP 3 as discussed in Section 5. From there, mirror copies to other repositories will ensure the widest possible dissemination and long-term preservation of the article. This population of repositories with final versions of peerreviewed articles will become the norm within the HEP community. It will generate a new e-infrastructure for e-Science providing among other things:

• a freely accessible source of data for text-and data-mining applications;

• a comprehensive, freely available, citation index for HEP publications;

• a system to continuously measure the scientific production of individual countries, which is at the basis of sharing the costs of SCOAP 3 .

Access to previously published literature

As in most sciences, research in HEP relies heavily on previously published work. In the case of specialized journals, citations often refer to earlier articles published within the same journal or in other "core" HEP journals. Hence, it is a legitimate expectation of the reader community to have access to these earlier articles that are contained in "back-files" of the publishers. SCOAP 3 will address the access issue in two different ways, depending on the formats in which these back-files are currently preserved and made available.

• Some current journal subscriptions include access to a limited number of previous editions. These include typically the recently-digitised yearly collections of long-standing journals or the entire production in the case of new (electronic) journals. For some other titles the subscriptions cover a fixed number of years within a "sliding window". In the SCOAP 3 model, publishers will be required to provide free access to the same volume of backfiles as they presently make available in their subscription models.

• Some journals have recently made available digitised versions of their entire "historic" archive including in some cases also precursor titles. Access to these back-files is possible today through annual subscriptions or through a single "one-off" payment. In the SCOAP 3 model publishers will be invited to make an offer for providing OA to these "historic" back-files.

Roles of and benefits for publishers

In the SCOAP 3 model, the publishers will continue to have the primary responsibility of ensuring the highest standards of quality for the published articles through independent editorial boards and peer review. They will ensure the dissemination of OA articles by posting them on their web site, without any access barrier, and by feeding them to a SCOAP 3 repository.

Publishers will benefit from a more sustainable business model than the traditional subscription scheme, which is becoming increasingly fragile. Furthermore, they will continue to meet the demands and charge for "premium" services and products outside the scope of SCOAP 3 , such as: print subscriptions, re-prints of single articles, colour plates in these printed versions, collections of articles in electronic or paper form, access to metadata databases.

Roles of and benefits for funding agencies

According to the OA paradigm, the costs of scientific publications, which are predominantly those of the organisation of the peer-review process, central to science, should be shifted from the reader community to the author community. In HEP, these two communities are largely overlapping and are funded by the same entities. Funding agencies are therefore at the pivot point of the transition to OA in scientific publishing and the ultimate decision and responsibility for the operation rests with them.

Funding agencies will be the key players in financing SCOAP 3 both directly and indirectly, according to the systems of each country. Funds will come from the redirection of subscriptions that are paid directly by the funding agencies, or by additional investments in the OA transition. Funding agencies will be instrumental in engaging the national bodies paying subscriptions to publishers to re-direct those funds towards SCOAP 3 . They will also play a role of paramount importance in raising the OA awareness of their author base.

In the long run, funding agencies will profit from the savings due to the costeffective publication strategy offered by SCOAP 3 . They will also benefit from a more stable and competitive publication market. Finally, they will profit from the broader visibility under OA tenets of the research they sponsor.

Roles of and benefits for libraries

Most scientific libraries are currently federated into consortia, primarily on a national or regional basis, and their actions are often linked to the main territorial funding agencies, e.g. COUPERIN in France, grouping some 200 libraries and maintaining strong links to CNRS, INSERM and INRA. In Germany the consortia are organized at the level of the Länder and in Belgium separately for the two main linguistic communities. In the present system, these consortia negotiate with publishers; they also pool their budgets in paying access fees to electronic collections. These national and regional library consortia are considered as natural candidates for participation in SCOAP 3 .

In the OA era, libraries will continue to serve the scientific community by providing access to the entire, multi-disciplinary, scientific literature including the HEP articles to be published in OA journals. How the libraries will be involved financially regarding OA publishing will obviously vary from country to country, depending on the specific financing model chosen. Some countries might transfer parts of the current subscription budget to the research sector, earmarked for publication costs, while other countries might choose to ask their universities to pay publication costs pro rata for their affiliated authors via their libraries.

The transition to OA will allow libraries to move towards new services, directed towards e-Science, which could not be developed under the subscription model with its permission barriers. In addition, the library community will play a fundamental role in the long-term archiving of the OA articles.

The scope of SCOAP 3

The definition of HEP articles

The notion of HEP is usually linked to the theoretical and experimental study of particles produced at accelerators of ever-increasing energies. Its definition has evolved to include subjects traditionally closer to fields like nuclear physics, astroparticle physics and cosmology. Different authors, journals and funding agencies focus on different parts of the HEP "spectrum".

In order to be successful, SCOAP 3 has to target the subset of HEP literature that addresses the broadest possible HEP authorship and readership. A minimal set of common interest, the "core" HEP subjects, includes theory and phenomenology of elementary particles, their experimental investigations, quantum-field theory, and lattice-field theory. These are loosely related to the hep-th, hep-ph, hep-ex, and hep-lat categories of the arXiv.org repository; however, these categories often also carry content in cognate disciplines. The scope of SCOAP 3 should be clearly extended to cover ancillary subjects such as experimental techniques as well as mathematical and numerical methods related to HEP.

The DESY classification

The documentation group of the DESY Library has a long tradition of selecting and classifying pre-prints, journal articles, monographs and conference contributions of relevance to the HEP community for their inclusion in the popular SPIRES database.

Their established procedure can be used to define an extension of the "core" areas of HEP towards a wider definition of HEP literature.

Subjects primarily associated with other fields but clearly connected to HEP include:

• nuclear physics (high energy nuclear reactions, relativistic heavy ion scattering, hyper-nuclei, double beta decay, neutrinos, quarks, gluons, QCD, meson production, meson-and hyperon-induced reactions);

• astrophysics (neutrino mass, flavour and oscillation, very high energy cosmic radiation, air showers, strange stars, postulated particles, dark matter candidates);

• gravitation and cosmology (quantum gravity and cosmology, field-theoretical models, higher dimensions, super-gravity, quantum aspects of black holes, string and brane models, inflation, gravitational waves);

• border areas including atomic physics, quantum physics, condensed matter, antimatter and fundamental constants.

As the borders between these related disciplines are not well defined, part of the literature in these connected fields will naturally be included along with the "core" HEP subjects by the selection of HEP journals along the lines discussed in the following.

The HEP publishing landscape

The DESY classification presented above has been used to select all articles relevant to HEP and published in peer-reviewed journals in 2005, excluding conference proceedings, editorials and other material outside the scope of SCOAP 3 . About 8'500 articles are selected; these are published in about 150 journals 7 . Of these articles, 5'200 deal with "core" HEP topics of theory and phenomenology of elementary particles, their experimental investigations, quantum-field theory, and lattice-field theory. The vast majority of these articles concern phenomenology and theory and have on average between two and three authors. Publications on experimental results, often authored by up to 800 researchers, account for less than 10% of the total.

7 Only journals with more than 10 articles relevant to HEP are considered to count the total number of articles.

Table 1 presents the most popular HEP journals, their publishers, their ISI impact factor (IF 8 ), the total number of articles published in 2005 9 (N tot ), the number of articles that satisfy the DESY HEP-article definition (N HEP ), and the number of "core" HEP articles (N core ). The last two columns show the fractions f HEP and f core of DESYtagged HEP articles and "core" HEP articles, respectively. Only journals with N HEP >100 are shown; they are ordered by N core . About 75% of the HEP articles in its broader definition, and about 85% of the "core" HEP articles, are carried by just six journals from four publishers.

Candidate journals for conversion to OA in the SCOAP 3 model

A recent study 10 analysed about 5'000 "core" HEP articles submitted in 2005 to the arXiv.org repository in the hep-ex, hep-lat, hep-ph, hep-th categories and subsequently published in peer-reviewed journals. Almost 90% of the articles appeared in the top six peer-reviewed journals listed in Table 1.

Five out of these six journals carry a majority of HEP content; these are:

• Physical Review D (published by the American Physical Society),

• Physics Letters B (Elsevier),

• Nuclear Physics B (Elsevier),

• Journal of High Energy Physics (SISSA/IOP),

• European Physical Journal C (Springer).

SCOAP 3 aims to assist publishers to convert these "core" HEP journals entirely to OA.

As described in the last column of Table 1, these five "core" journals include up to 30% of articles in nuclear physics, astro-particle physics and other subjects beyond the "core" HEP topics. These articles will be naturally and logically included in the OA transition along the proposed scheme. This is in the interest of the HEP readership and promotes the long-term goal of an extension of the SCOAP 3 model to these related disciplines.

The sixth journal, Physical Review Letters (American Physical Society), is a "broadband" journal that carries only a small fraction (10%) of HEP content. In summary, taking the DESY classification as the reference, the five "core" HEP and two "broadband" journals together covered in 2005 about 4'200 articles tagged as belonging to the "core" HEP subjects and about 5'300 articles in the broader HEP definition. The full conversion to OA of the five "core" HEP journals and the partial conversion of the two "broadband" journals would cover over 80% of the "core" HEP subjects and over 60% of the entire HEP literature, including all related subjects.

The financing of SCOAP 3

In the era of electronic journals, the price of a journal is mainly driven by the costs of running the peer-review system, by editorial costs for copy-editing and typesetting, by the cost for electronic publishing and access control, and by subscription administration. Most publishers today quote a cost, from reception of the manuscript to final publication, in the range of 1'000 -2'000 Euros per published article 12 . This includes the cost of processing articles that are eventually rejected, the fraction of which varies substantially from journal to journal. The SCOAP 3 model will eliminate the costs of access control and subscription administration.

The annual budget for a transition of HEP publishing to OA can be estimated from this figure and from the fact that the five "core" HEP journals, which cover a large fraction of the HEP literature, as discussed in Section 3, publish about 5'000 articles per year. Hence, we estimate that the annual budget for a transition of HEP publishing to OA would amount to a maximum of 10 Million Euros per year.

Another indication which corroborates this estimate is that the costs to run a "core" HEP journal such as Physical Review D amount to 2.7 Million Euros per year 13 and it covers about one third of all HEP publications.

A "fair-share" scenario for the financing of SCOAP 3 is to distribute these costs among all participating countries on a pro-rata basis, taking into account the relative fraction of authorship of HEP articles. To cover publications from scientists from countries that cannot be reasonably expected to contribute to the consortium at this time, an allowance of not more than 10% of the SCOAP 3 budget is foreseen.

The fraction of HEP authorship of each country is estimated using a recent study 14 of the authorship of articles in the seven journals spotlighted for conversion to OA as discussed in Section 3. and Nuclear Instruments and Methods in Physics Research A. A total sample of about 11'300 articles was considered. For each article, all authors were uniquely assigned to a given country. In this context CERN was treated as an additional "country".

In about 5% of the cases, authors were found to have multiple affiliations, often in different countries, reflecting the intense cross-border tradition of HEP. In these cases, the ambiguity in the assignment of authors to countries was solved by using the following guiding principles:

• If one of the multiple affiliations of an author is CERN, the author is assigned to CERN.

• If one of the multiple affiliations of an author is a HEP laboratory, the author is assigned to the host nation of that laboratory.

• The remaining multiple-affiliation cases were resolved by assigning the author to the country with the largest per capita gross domestic product 15 . If among the multiple affiliations there were two or more HEP laboratories, the same principle was applied by considering the per capita gross domestic products of the corresponding host countries.

The results from this study are summarized in Table 3 and Figure 1. The contribution of CERN and the CERN Member States 16 is 41.0% while that of the United States is 24.3%. The countries with the next-largest shares are Japan with 7.1% and China with 5.6%.

The determination of the pro-rata fractions for all participant countries will be repeated every year and whenever a change of the scope of SCOAP 3 makes it necessary.

15 International Monetary Fund, World Economic Outlook Database, September 2006. 16 The CERN Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, the Slovak Republic, Spain, Sweden, Switzerland and the United Kingdom.

The tendering requirements

This Section describes the selection criteria for journals and the requirements that will form the basis of the contracts with the selected publishers. Financial and transition aspects are addressed at the end.

Selection criteria

1. Journal scope. SCOAP³ will select among existing or future journals interested in publishing HEP articles, as discussed in Section 3.

2. Journal standing. The high quality of the journals is of paramount importance in the SCOAP³ model. For well-established journals criteria such as, but not limited to, the ISI impact factor will be used to assess the journal standing. For new journals, criteria such as the profile of the editorial board or the size of the author and reader base will be considered.

3. Peer-review process. Rigorous, high-quality peer-review is a central component of the SCOAP³ model. SCOAP³ will require journals to ensure an independent peer-review process of the highest standard, of a reasonable duration. The acceptance and rejection rates, which contribute to indicating journal quality, have to be made available for assessment and monitoring purposes.

Requirements

The OA tenets of "open and unrestricted access to research literature" apply throughout the life of a scientific result and, of course, also in the remote future. The contracts to be signed with publishers shall, inter alia, include the following conditions:

1. The articles shall be made available on an irreversible OA basis; 2. There shall be immediate and free access via the internet to the publisherformatted full text of the articles and the corresponding metadata, as published on the publisher's Web site; 3. Publishers shall deliver to a repository designated by SCOAP 3 the final version of the articles as well as the corresponding metadata and interoperable usage statistics as detailed in Annex 1 and Annex 2, respectively; 4. There shall be free transfer of the articles and the corresponding metadata to any further repository, through the intermediary of the repository designated by SCOAP 3 ; 5. There shall be free extraction and re-using of the figures (e.g. in conference presentations and further articles), tables and numerical data (e.g. for reinterpretation or statistical combination with other results) included in the articles;

6. There shall be free use of the articles and corresponding metadata for textand data-mining applications; 7. Authors shall be free to post pre-prints and post-prints to subject and institutional repositories; 8. Publishers shall pro-actively support publisher-independent long-term preservation through repositories and national libraries; 9. Upon the acceptance of an article, publishers shall transmit the corresponding metadata to crossref.org; 10. Publishers shall accept direct submission to their journals from selected subject and institutional repositories, such as arXiv.org, SPIRES, CDS, HAL, etc.

Any re-use of the articles and the corresponding metadata shall of course acknowledge the authors and the published reference.

Financial aspects

1. Payment model. The decision upon a lump sum payment or the pay-perarticle model will be made according to whether the journal in question publishes mostly HEP articles ("core" HEP journal) or only some HEP articles ("broadband" journal). Conference proceedings and monographs are outside the scope of SCOAP³, as discussed in Section 2.

2. Visibility of OA fraction. In the case of "broadband" journals, the fraction of articles with HEP content converted to OA has to be explicitly visible.

3. Access to back-files. Some current subscriptions include access to a limited number of previous editions of journals. Publishers will be required to provide free access to the same volume of back-files as they presently make available in the subscription model, with the same modalities of the OA articles whose peer-reviewing costs have been covered by SCOAP 3 . In addition, publishers will be invited to submit an offer for granting similar permanent access to "historic" back-files, the digitised version of all the issues of a journal.

Transition aspects

1. Journal licence packages. In the case of a "core" HEP journals (where an entire journal is converted to OA) that is part of a large journal licence package, the publisher will be required to un-bundle this package and to correspondingly reduce the subscription cost for the remaining part of the package.

2. Partially-converted journals. For "broadband" journals (where only the conversion of selected HEP articles is paid by SCOAP³), the subscription costs are required to be lowered according to the fraction supported by SCOAP³.

For journals of this kind that are part of a licence package, the reduction should be reflected in a corresponding reduction of the package subscription cost.

3. Library subscriptions. In the case of existing long-term subscription contracts between publishers, libraries, and funding agencies, publishers are required to reimburse the subscription costs pertaining to OA journals or to the journal fractions converted to OA. To avoid administrative complications, libraries may forgo individual reimbursements as a contribution to SCOAP³.

The next steps

The SCOAP 3 Working Party was mandated by leading European HEP funding agencies, HEP laboratories and library consortia to explore the possibility of converting HEP scientific publishing to OA. This Report presents a model to achieve this transition, timely and effectively, for the benefit of all stakeholders: authors, readers, funding agencies, libraries and publishers.

The next step towards OA publishing in HEP is the acceptance of the model proposed in this Report by the entities that mandated its preparation.

The fundamental pillar of the SCOAP 3 model is the federation of HEP funding agencies and library consortia worldwide. HEP is a worldwide scientific enterprise and the conversion to OA of its literature, with all the ethical, scientific and financial benefits it implies, can only be achieved in a global co-ordinated process. A crucial step towards OA publishing in HEP is therefore the search for a worldwide consensus around the model proposed in this Report, aiming to federate HEP funding agencies and library consortia in Europe, the Americas and Asia, with a proactive stance in exploring possible funding channels.

Once sufficient funds will have been pledged towards the establishment and the operation of SCOAP 3 , a tendering process will take place, hopefully during summer 2007. Provided that the SCOAP 3 funding partners are ready to engage into long-term commitments, most publishers are expected to be ready to enter into negotiations along the lines presented in this Report.

The outcome of the tendering process will allow, after a few months, the complete SCOAP 3 budget envelope to be precisely known, as well as the contribution expected from each country. A Memorandum of Understanding for the governance of SCOAP 3 and the initial cost sharing will then be signed by funding agencies and leading national and international library consortia. Contracts with publishers will be established in order to make Open Access publishing in High Energy Physics a reality at the beginning of 2008, when the flow of experimental and theoretical publications on data from the LHC program will start.

The conversion of the HEP scientific publishing to the OA paradigm, along the lines presented in this Report, will be an important milestone in the history of scientific publishing. The SCOAP 3 model could be rapidly generalized to other disciplines and, in particular, to related fields such as nuclear physics or astro-particle physics.

Annex 1: Technical requirements for metadata

The data set Metadata provided by the publishers will serve two purposes:

• to relay bibliographic information to (meta) search engines;

• to gather data for cost-sharing accounting within SCOAP 3 .

The bibliographic information must be sufficiently comprehensive to allow the correct citation of the item to be made; it should also include a persistent pointer to the full-text version of the item. The information datasets must be guaranteed to be correct and complete.

The minimum set of data must have the following items included: title; author (one author per field); affiliation (with obvious correlation to author); ISSN; journal title, volume; issue; page (first, last) or article number and number of pages; publication year; publisher; DOI. Furthermore, the following set of supplementary information are desirable: URL; resource type; copyright; PACS; (author-defined) keywords; abstract; publication date; external reference (e.g. the arXiv.org number if the article is contained in that repository); citations; date of acceptance; date of submission.

For accounting purposes within SCOAP 3 it must be possible to automatically extract all authors from the metadata and to relate them to their affiliations. The affiliation descriptors (names, addresses) have to be standardized to facilitate the identification of SCOAP 3 participants.

Transport formats

Since internationally accepted exchange formats such as MARC-XML and Dublin Core are not ideally suited for transporting all the information specified above, stable formats defined by the publishers will be accepted.

Character encoding must be Unicode. The textual contents of all data must be identical to the published version, e.g. special characters in author names which are uniquely represented in Unicode. The title must be identical to that in the printed version; e.g. mathematical formulas, equations, symbols etc. are represented in submit the publication to a repository. "Green" OA envisages the maintenance of subscriptions for the access to peer-reviewed journals.

"Hybrid model": Within the usual subscription scheme, this model implies that authors pay a supplement to the publisher for making their articles available OA. In the context of SCOAP 3 , the hybrid model implies that the Consortium is sponsoring OA for those articles of a "broadband" journal that are recognized as relevant to HEP. However, the subscription price of these journals will be lowered to reflect the fraction of OA articles, whereas in current experimental hybrid models this is rarely the case.

High Energy Physics (HEP):

The field of particle physics dealing mainly with the study of elementary particles and their interactions.

Impact factor (IF):

A quantitative tool for ranking, evaluating, categorizing, and comparing journals. It is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period. The IF of a journal is calculated by dividing the number C of citations during year Y to articles published in the years Y-1 and Y-2 by the number P of articles published in the years Y-1 and Y-2; IF=C/P. Journal articles: Quality-controlled articles appearing in scientific journals, describing scientific results, peer-reviewed by specialists of the field and copy-edited by the journals.

Long-term archiving:

The preservation of the content of electronic or paper journals aimed to ensure the published articles are available and accessible on extremely long time scales, possibly irrespectively of the long-term future of particular publishing companies.

Memorandum of Understanding (MoU):

Document describing the terms for sharing the costs and responsibilities within large, multi-institutional collaborations, typical of HEP experiments. In the context of this Report, it is the document to be signed by the SCOAP 3 members, describing the governance and cost sharing, and acting as a legally binding document for all participants.

Open Access (OA): Immediate, free and unrestricted online access to digital scholarly material, primarily peer-reviewed scholarly journals. OA was made possible by the advent of the Internet. OA removes price barriers such as subscriptions, licensing fees, pay-per-view fees, and permission barriers in the form of copyright and licensing restrictions.

Open Access journals: Journals that publish peer-reviewed articles and make the approved, final, versions freely available on the Internet. The production costs of OA journals are met with author-side funding through publication charges or sponsoring.

Open Access Movement:

A loosely connected worldwide movement of scholars, research libraries, funding agencies, some publishers and other stakeholders of the scholarly research process in favour of the broadest possible dissemination of, and free access to, the results of scientific research.

Peer review:

The process by which the quality of an article submitted for publication is verified. It is organized by the publisher but performed by specialists (peers) of the field. The result of peer reviewing is either the acceptance of the article for publication or its rejection. During the process, authors are often advised to modify their manuscript before publication.

Post-prints:

Author-generated versions of pre-prints including all modifications added during the peer-review process.

Pre-prints: Articles describing scientific results, made available by the authors prior to the formal publication in peer-reviewed journals; it is today the vehicle for rapid exchange of information within some scientific fields.

Pre-print culture:

The habit, well established in the physics community, of depositing (even preliminary) results in the form of pre-prints in repositories with Internet access, and making use of the pool of pre-prints already available for rapid communication and feedback. These are all "subject" repositories, containing articles of relevance for a given field.

Research centres and universities often have their own institutional repositories (e.g. publications@DESY).

Re-prints:

Printed version of single articles published in peer-reviewed journals, provided by publishers. The first few copies are usually free of charge while authors can purchase additional copies.

Serials crisis:

The spiralling of subscription costs above the general inflation rate, which is observed today in scientific literature and forces libraries to cancel subscriptions of important "core" journals, depriving their users of access to valuable information.

Subscription model:

The current paradigm in scientific publishing in which the reader (or an institutional library on his behalf) pays a subscription fee for receiving printed copies of journals or getting electronic access to them (if available). It is also called the "reader-side funding" model. This is an immensely exciting prospect and one that SPARC Europe fully supports.

Statements in favour of the OA publishing policy

We wish CERN and its partners every success with this hugely important effort.

• Peteris ZILGALVIS, Head of Unit, Governance and Ethics European Commission, Research Directorate-General, Science, Economy and Society Directorate, November 3, 2006

The European Commission is favourable to experimentation with new publishing models such as SCOAP 3 seen as a pilot project for future developments in scientific publishing.

• Springer Publishing Company, November 1, 2006

The EPJ publishers are prepared to move the EPJ journals to "OA-only" seeking sponsoring models and the cooperation with funding agencies and consortia that guarantee long term financial support of OA publishing at realistic article processing fees and compatible with the efficiency and flexibility of the present system of dissemination of scientific content and metadata.

SCOAP 3 8

 3 The IF of a journal is calculated by dividing the number C of citations during year Y to articles published in the years Y-1 and Y-2 by the number P of articles published in the years Y-1 and Y-2; IF=C/P. 9 Values of N tot may differ slightly from those obtained by alternative methods, e.g. through queries to popular databases, since, in the present study, articles not relevant for the scope of SCOAP 3 , e.g. conference proceedings and editorials which are not always tagged in the databases, have been removed by hand 10 S. Mele et al., JHEP 12 (2006) S01; arXiv:cs.DL/0611130. aims to sponsor the conversion to OA of this fraction on an article-by-article basis. In addition, SCOAP 3 intends to sponsor the conversion on an article-by-article basis of the HEP-related part (about 25%) of Nuclear Instruments and Methods in Physics Research A (Elsevier), which is a popular "broadband" journal in instrumentation and measurement techniques 11 .

  HEP articles in the 2 broadband journals 295 41% of N H (B) N H (C)+N H (B) HEP articles in core and broadband journals 62% of N H (T) N C (C)+N C (B) "Core" HEP articles in core and broadband journals 81% of N C (T)

Figure 1 :

 1 Figure 1: Contributions by country to the HEP scientific literature published in journals spotlighted in Section 3 for conversion to OA. Co-authorship is taken into account on a prorata basis, assigning fractions of each article to the countries in which the authors are affiliated. The last cell aggregates contributions from countries with a share below 0.3%. This study is based on all articles published in the years 2005 and 2006 in the five HEP "core" journals: Physical Review D, Physics Letters B, Nuclear Physics B, Journal of High Energy Physics and the European Physical Journal C, and the HEP articles published in two "broadband" journals: Physical Review Letters and Nuclear Instruments and Methods in Physics Research A, tagged as described in Section 3. A total sample of almost 11'300 articles is considered Countries with individual contributions less than 0.8% are aggregated in the "Other countries" category. (From J. Krause, C.M. Lindqvist and S. Mele, http://doc.cern.ch/archive/electronic/cern/preprints/open/open-2007-014.pdf)

"

  Pro-rata" sharing of costs (in the SCOAP 3 model): Cost sharing between countries, calculated according to the fractional number of authors affiliated to a given country and contributing to publications in HEP. Repositories: Electronic databases where preprints and journal articles describing the results of scientific research are stored. They do not perform peer-review but simply make the author-deposited contents freely available. They may contain at once pre-prints before peer-review and author-produced post-prints very close to the final journal articles. Notable examples are arXiv.org, initiated at Los Alamos and now at Cornell; the SPIRES database, born at Stanford and now numbering many contributors among which DESY in Hamburg; and the CERN Document Server.

SCOAP 3 :

 3 Sponsoring Consortium for Open Access Publishing in Particle Physics. It is envisaged as a central network of funding agencies, research laboratories and libraries, mandated to collect funds for financing OA in the field of HEP, to negotiate prices with publishers, and to remunerate them for their OA journals.

(

  In reverse order of date) • The following statement was approved by the ALICE, ATLAS, CMS, LHCb and TOTEM Collaboration Boards in February-March 2007: We the ALICE / ATLAS / CMS / LHCb / TOTEM Collaboration strongly encourage the usage of electronic publishing methods for ALICE / ATLAS / CMS / LHCb / TOTEM publications and support the principle of Open Access Publishing, which includes granting free access of our ALICE / ATLAS / CMS / LHCb / TOTEM publications to all. Furthermore, we encourage all ALICE / ATLAS / CMS / LHCb / TOTEM members to publish in easily accessible journals, following the Open Access Paradigm. -The ALICE Collaboration represents over 1'000 physicists, engineers and technicians from 104 institutions and 30 countries; -The ATLAS Collaboration represents about 1'800 physicists including about 400 students from 150 universities and laboratories spread over 35 countries; -The CMS Collaboration represents about 2'000 scientists and engineers including 400 students from 159 institutions spread over 35 countries; -The LHCb Collaboration represents about 600 physicists from 46 universities and other institutions spread over 14 countries; -The TOTEM Collaboration represents about 135 physicists from 20 universities and other institutions spread over 14 countries. • Prof. Torsten AKESSON, Chairman of the European Commission for Future Accelerators (ECFA), Dec 1, 2006 ECFA is in general positive towards a transition to Open Access publishing. The aim should be to implement it synchronous with the first articles from LHC. • Prof. Dr. Metin MARIK, President of the Balkan Physical Union, November 3, 2006 The Balkan Physical Union considers the Open Access Initiative to be a very positive step for scientific progress. • Dr. David C PROSSER, Director, SPARC Europe, November 3, 2006 CERN is at the forefront of both thinking about open access and its implementation.

•

  Prof. Albrecht WAGNER, Chairman of the Board of Directors, Deutsches Elektronen-Synchrotron DESY, October 20, 2006 DESY fully supports Open Access Particle Physics and we would like to see it realized within a short time scale. It is of great importance for DESY to be actively and constructively involved in the forthcoming discussions aiming at establishing a Sponsoring Consortium. • Prof. Gregor HERTEN, Chair of the Commission of Particles and Fields (C11) of the International Union of Pure and Applied Physics (IUPAP), August 2, 2006 C11 supports the transition to OA publishing, in agreement with the IUPAP mandate to guarantee free access to scientific results.

Table 2

 2

	Journal	Publisher	IF N tot N HEP N core f HEP	f core
	Phys. Rev. D	APS	4.8 2285 2101	92% 72%
	JHEP	SISSA/IOP	5.9	859	859	100% 98%
	Phys. Lett. B	Elsevier	5.3	957	862	90% 77%
	Nucl. Phys. B	Elsevier	5.5	522	481	92% 89%
	Phys. Rev. Lett.	APS	7.5 3836	407	11%	7%
	Eur. Phys. J. C	Springer	3.2	331	272	82% 71%
	Mod. Phys. Lett. A	World Scientific 1.2	281	216	77% 49%
	Phys. Rev. C	APS	3.6	853	298	35% 16%
	Class. Quant. Grav.	IOP	2.9	491	255	52% 18%
	Int. J. Mod. Phys .A	World Scientific 1.5	878	143	16% 10%
	J. Math. Phys.	AIP	1.2	446	108	24% 17%
	Phys. Atom. Nucl.	Springer	0.9	220	106	48% 33%
	JCAP	SISSA/IOP	6.7	156	128	82% 37%
	Gen. Rel. Grav.	Springer	1.6	190	103	54% 11%
	Nucl. Instrum. Meth. A Elsevier	1.2 1371	312	23%	1%

summarises these numbers.

The remaining 3'300 articles, tagged by the DESY classification as being of interest to the HEP community, not published in the journals mentioned above are scattered over some 140 other journals. Of these articles, 980 are related to gravitation and cosmology, 685 to astrophysics, 450 to nuclear physics, 120 to instrumentation and detector technology, and 115 to general theoretical physics.

It is important to note that the SCOAP 3 model is not intended to be limited to the journals spotlighted by this study but is open to all existing and future high-quality journals carrying HEP content, within budgetary limits. This will ensure a dynamic market with competition and choice.

Table 1 :

 1 Summary

of the most popular HEP journals: their publishers, ISI impact factors (IF), the total number of articles published in 2005 (N tot ), the number of articles which satisfy the DESY HEP-article definition (N HEP ), and the number of "core" HEP articles (N core ). Only journals with N HEP >100 are shown; they are ordered by N core . The last two columns show the fractions f HEP and f core of HEP and "core" HEP articles, respectively.

Table 2 :

 2 Numbers of articles in different categories published in 2005 in the five "core" HEP journals that are proposed for entire conversion to OA and into the two "broadband" journals that are proposed to be partially converted to OA, as discussed in Section 3.

Table 3 :

 3

			Share of HEP				Share of HEP
	Country	Scientific Publishing Country		Scientific Publishing
	United States			24.3% Netherlands			0.9%
	Germany			9.1% Portugal				0.9%
	Japan			7.1% Taiwan				0.8%
	Italy				6.9% Mexico				0.8%
	United Kingdom			6.6% Sweden				0.8%
	China			5.6% Belgium				0.7%
	France			3.8% Greece				0.7%
	Russia			3.4% Denmark				0.6%
	Spain			3.1% Australia				0.6%
	Canada			2.8% Argentina				0.6%
	Brazil			2.7% Turkey				0.6%
	India				2.7% Chile				0.6%
	CERN			2.1% Austria				0.5%
	Korea			1.8% Finland				0.5%
	Switzerland			1.3% Hungary				0.4%
	Poland			1.3% Norway				0.3%
	Israel				1.0% Czech Republic			0.3%
	Iran				0.9% Remaining countries			3.1%
	Physics Research A, tagged as described in section 3. A total sample of almost 11'300 articles
	is	considered	(From	J.	Krause,	C.M.	Lindqvist	and	S.	Mele,
	http://doc.cern.ch/archive/electronic/cern/preprints/open/open-2007-014.pdf).

Contributions by country to the HEP scientific literature published in journals spotlighted in Section 3 for conversion to OA. Co-authorship is taken into account on a prorata basis, assigning fractions of each article to the countries in which the authors are affiliated. The last cell aggregates contributions from countries with a share below 0.3%. This study is based on all articles published in the years 2005 and 2006 in the five HEP "core" journals: Physical Review D, Physics Letters B, Nuclear Physics B, Journal of High Energy Physics and the European Physical Journal C, and the HEP articles published in two "broadband" journals: Physical Review Letters and Nuclear Instruments and Methods in

This situation is typical of many fields of science, opposite to the very different sizes of the author and reader communities e.g. in the medical and law publishing markets.

R. Voss et al., Report of the Task Force on Open Access Publishing in Particle Physics, CERN; http://library.cern.ch/OATaskForce_public.pdf

http://www.soros.org/openaccess/read.shtml

Another "broadband" instrumentation journal of interest is the Journal of Instrumentation (SISSA/IOP), which could be converted, in the same scheme. It is not included in this study since it only started publishing in 2006, with 44 articles and a HEP fraction of 50%.

HTML or (La)TeX. Additional title versions (plain ASCII, different language) may be supplied.

Annex 2:

Specifications for providing interoperable usage statistics

Publishers should provide COUNTER compliant statistics (Release 2 for journals), on the article level, enhancing the granularity of Release 2. These should be provided either as web-service using the SUSHI XML schema (NISO draft standard), or using OAI PMH and OpenURL Context Objects (NISO Z39.88-2004).

Publishers should allow SCOAP³ to forward COUNTER compliant statistics to aggregating services of consortia, universities or scientific societies without additional costs. Aggregating services should be allowed to merge the statistics provided with statistics from disciplinary or institutional repositories.

Glossary "Author-side funding" model:

A publishing model alternative to the "reader-side funding" model, currently prevailing. With "author-side" funding, authors bear the costs incurred in the publication of their articles, usually through their funding agencies. OA models are by definition "author-side funding" models. However, in the publication scheme discussed in this Report, the publication charges are paid by the SCOAP 3 consortium; hence, authors do not have to directly deal with publication costs.

"Broadband" journals: Journals containing articles from a broad range of fields, as opposed to "core" journals containing articles relevant to a very specific field.

"Core" journals: Journals devoted mainly to articles dealing with subjects of a specific field. In this Report, the expression "core" HEP journal is used to designate journals mostly containing articles relevant to the field of HEP.

e-Science:

Computationally intensive science that is carried out in highly-distributed network environments, or science that uses large data sets that require the application of grid computing. In a larger sense, e-Science also indicates technologies that enable distributed collaboration. HEP is a discipline with a well-developed e-Science infrastructure due to its need for adequate computing facilities for the analysis of results and storage of data originating from the CERN Large Hadron Collider as well as its widely-distributed collaborative nature.

"Gold" OA: A way to achieve Open Access to scientific reports warranting free information availability on the public Internet, permitting any user to read, download, copy, distribute, print, search, or link to the full text of peer-reviewed articles, crawl them for indexing, pass them as data to software, or use them for any other legal purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the Internet itself (source: Budapest declaration http://www.soros.org/openaccess/read.shtml) "Green" OA: A way to achieve Open Access to scientific reports through the author submission of pre-prints and post-prints to repositories where they are accessible through the Internet to any reader. In some disciplines some journals require a certain "embargo" following the article publication for the author to be allowed to


Benoît Lelandais
email: benoit.lelandais@cea.fr

Marie-Pierre Oudot
email: marie-pierre.oudot@cea.fr

Benoit Combemale
email: benoit.combemale@inria.fr

Fostering Metamodels and Grammars within a Dedicated Environment for HPC The NabLab Environment (Tool Demo)

Keywords: HPC, DSL, Grammar, Metamodel, Compilers

Advanced and mature language workbenches have been proposed in the past decades to develop Domain-Specific Languages (DSL) and rich associated environments. They all come in various flavors, mostly depending on the underlying technological space (e.g., grammarware or modelware). However, when the time comes to start a new DSL project, it often comes with the choice of a unique technological space which later bounds the possible expected features.

In this tool paper, we introduce NabLab, a full-fledged industrial environment for scientific computing and High Performance Computing (HPC), involving several metamodels and grammars. Beyond the description of an industrial experience of the development and use of tool-supported DSLs, we report in this paper our lessons learned, and demonstrate the benefits from usefully combining metamodels and grammars in an integrated environment.

CCS Concepts • Software and its engineering → Domain specific languages; Model-driven software engineering; • Computing methodologies → Massively parallel and high-performance simulations;

Introduction

In the field of High Performance Computing (HPC), addressing the major challenges of software productivity and performance portability is becoming necessary to take advantage of emerging extreme-scale computing architectures. There is a growing demand for new programming environments to improve scientific productivity, facilitate design and implementation, and optimize large production codes with higher-level programming abstraction. In this context, the numerical-analysis specific language NabLab improves applied mathematicians productivity and enables new algorithmic developments for the construction of hierarchical and modular high-performance scientific applications.

NabLab results from a longstanding effort at CEA (French Atomic Energy Commission) to develop advanced tools and methods to support the development of ever more complex simulation codes. To this end, software engineers have studied the use of workbenches proposed in recent decades to develop Domain-Specific Languages (DSLs) and rich associated environments (e.g., editor, analysis and optimization tools, or compiler). They all come in various flavors, mostly depending on the underlying technological space (e.g., grammarware or modelware). Grammar-based language workbenches have been first proposed, together with associated frameworks supporting efficient language manipulation [START_REF] Aho | Compilers: Principles, Techniques, and Tools[END_REF]. More recently, metamodel-based language workbenches have emerged with a rich ecosystem to develop modeling environments including tools directly usable by domain experts [START_REF] Combemale | Engineering Modeling Languages[END_REF]. NabLab takes advantage of all of these approaches, first to develop compilers optimized for different low-level architectures, and more recently to address the intrinsic complexity of simulation codes themselves by supporting the design and validation activities.

Beyond the description of an industrial experience of the development and use of tool-supported DSLs, this tool demonstration paper also reflects our main lessons learned from developments involving different technological spaces. In particular, we discuss the benefits from usefully combining metamodels and grammars in an integrated environment to leverage complementary ecosystems.

The rest of the paper is structured as follows. Section 2 provides an overview of the modeling environment, which is described later in Section 3 with the technical architectures

Overview of the NabLab Environment

In this section we introduce both the NabLab and the Nabla open-source Domain Specific Language (DSL), and the corresponding development environment for numerical-analysis.

Nabla1 aims at writing out numerical-analysis algorithmic sources in order to generate optimized code for different runtimes and architectures [START_REF] Camier | Improving performance portability and exascale software productivity with the nabla numerical programming language[END_REF] called backends (cf. Fig. 1, right). Nabla is dedicated to applied mathematicians and physicists, who are the language users in our context. The DSL allows the conception of multi-physics applications, and is based on different concepts: no central main function, a multi-tasks based parallelism model and a hierarchical logical time-triggered scheduling. A Nabla source file is divided into two parts: on the one side the declarations of options, functions and variables (cf. Fig. 2, left) and, on the other, the definition of small unit functions called jobs (cf. Fig. 2, right). One can observe that jobs are tagged with a '@' directive and a number representing a hierarchical logical time (HLT), their relative triggering time. Jobs with a higher logical time wait for a previous one to be finished before being scheduled. Two jobs with the same logical time are triggered in parallel. This new dimension to parallelism is explicitly expressed to go beyond classical programming models. Control and data concurrencies are combined consistently to achieve statically analyzable transformations and efficient code generation. The Nabla compiler holds these effective generation stages for different architectures (e.g., CUDA2 , Legion [START_REF] Bauer | Legion: Expressing locality and independence with logical regions[END_REF] and Okina in Fig. 1). While the Nabla syntax is close to numerical-analysis concepts, the concept of HLT is related to the optimization domain thus bringing the DSL closer to the solution space, i.e., requiring the DSL user to map a given problem in terms of the way it is eventually implemented.

With the increasing complexity of simulation codes, there is a pressing need for high-level abstractions with which language users can directly reason about their problems, and generative approaches dealing with implementation details (e.g., HLT). NabLab has been developed in this context, with the main objective of providing abstraction and tools that help language users to design and validate their simulation codes and to translate them into Nabla programs to be further efficiently compiled for different architectures. The syntax of NabLab is strongly inspired by Nabla, but has been developed as a separate external DSL with its own high-level abstractions, and comes with a rich development environment that supports DSL users in the design and validation of their specifications. A textual editor (cf. Fig. 3, center) proposes contextual code completion, code folding, syntax highlighting, error detection, quick fixes, variable scoping, and type checking. The environment also provides a model explorer, a dedicated outline view (cf. Fig. 3, left), and a contextual LaTeX view (cf. Fig. 3, bottom). A debugging environment under construction will provide variable inspection, plot display and 2D/3D visualization. When the code has no error, the NabLab compiler can automatically generate a LaTeX report, and efficient implementations thanks to the associated compilation chain.

To bridge the abstraction gap between NabLab and Nabla, an Intermediate Representation (cf. IR in Fig. 1) has been introduced into the compilation chain to offer the relevant structure for performing analysis and optimisations. For instance, a NabLab program is composed of jobs whose execution does not sequentially start at the beginning of the program. To highlight the execution flow of the program and detect unintended cycles, a data flow graph is computed and displayed on a graphical diagram (cf. Fig. 3, right). This data flow graph is also used to automatically infer the '@' directives required to generate an optimized Nabla program, compiled further to the different low-level backends supported by Nabla. Alternatively, the IR has recently been supporting the implementation of additional code generators to high level execution platforms (e.g., JVM).

Implementation and Retrospective

This section focuses on design and technology choices for the development of the NabLab environment, and reports on the experiences of language users and designers.

The Nabla Toolchain

The Nabla toolchain is composed of three main parts: the frontend, a Flex3 /Bison4 parser that reads a set of input files, the middle-end that provides a collection of steps e.g., instrumentation, performance, analysis, validation and verification or data layout optimizations, and the backends that holds the effective generation stages for different targets or architectures like Arcane [START_REF] Grospellier | The Arcane development framework[END_REF], CUDA, Legion or Okina, a standalone backend which generates fully-vectorized C/C++ source files.

A dozen hydrodynamic applications have been written with Nabla (structured/unstructured meshes, explicit/implicit schemes), and the users help to gradually evolve the syntax of the language to better match the different algorithms.

Nabla users appreciate the language for prototyping new numerical schemes and test new software stacks. They also appreciate the Open-Source nature of the project to collaborate with students and universities. However, while they like the compactness and mathematical rendering of the UTF8 syntax, they express the need for an advanced dedicated editor. They also identify the complexity to compose big applications in providing the HLT, particularly the difficulty to extend an existing program and to detect unintended job cycles. They point out that this task should be hidden for applied mathematicians. On a more general level, they say that they can develop, debug and test a simple mini-application with a basic editor, but it becomes tricky to follow the same development process on larger applications.

Nabla language designers are used to working with the grammar-based Flex/Bison tools and C/C++ language. Many tools and code examples are available. This grammar-based approach is broadly used in the field of optimizing compilers. However, language designers point out that providing tools and editors with this technology stack is not easy.

The NabLab Environment

NabLab is based on the Eclipse Modeling Framework5 (EMF) [START_REF] Steinberg | EMF: eclipse modeling framework[END_REF] and its ecosystem: the textual editor and the outline are based on Xtext 6 , and the data flow graph is displayed through a Sirius diagram 7 . NabLab corresponds to 5 KLOC of Xtend, including both all editor capabilities (e.g., validation, scoping, typing and quick fixes) as well as the graph construction.

NabLab brings some changes to Nabla: explicit declaration of external functions and required connectivities, mesh variables definition on connectivities, explicit naming of iterators and generalization of reductions (i.e., integration of reductions, like sums, inside a loop). These modifications avoid any ambiguity on iterators and variables, enabling syntactic validation rules (e.g., loop patterns correctness). NabLab also increases the level of abstraction to bring the language closer to the problem space (e.g., the metamodel no longer requires users to explicitly provide HLTs on jobs).

To bridge the gap between NabLab and Nabla, we introduce a numerical analysis specific Intermediate Representation (IR). This IR is implemented as an Ecore metamodel, automatically instantiated when a valid NabLab file is saved (cf. Fig. 1). As NabLab metamodel hides the tricky notion of HLT to mathematicians, this data is automatically inferred by synthesizing in and out variables for each job. This data flow is presented in a Sirius diagram (cf. right view in Fig. 3). Once the data flow is correct and does not present cycles anymore, the shortest path to each job is computed and its value stored in the IR model. Several transformation and optimization passes are defined on the IR (e.g., variable default values replaced by initialization jobs, inner reductions transformed in loop patterns, or jobs tagged with a HLT). After these transformation steps, the IR is very close to the solution space and it becomes the source of the last Model To Text transformation to generate Nabla code (or alternatively multi-threaded Java programs). Thanks to this IR, the code generation is easier, the compilation chain is modular and the concerns are well separated.

Thanks to the Java code generator, users get directly executable code in the Eclipse environment, including validating mathematical algorithms without having to connect to a calculator and independently of the performance. A debugging environment is still under development. The goal is to be able to execute the code step by step by examining not the generated code but the initial NabLab code owned by the user. For such a purpose, information is accumulated throughout the compilation chain into a trace model (i.e., using annotations).

Language designers appreciate Xtend for its high level functions, support for model manipulation (e.g., lambda) and code generation (e.g., template). Xtext greatly facilitates the creation of a DSL, providing architecture and design patterns to develop various required tools. Language designers also appreciate the rapidly evolving EMF ecosystem, always providing new cutting-edge technologies.

Discussions

Fostering Metamodels and Grammars

The Nabla grammar-based approach uses the C++ language and time-honored technologies like Flex/Bison. This approach is well known and appreciated by the optimization community for its proximity to execution architectures (e.g., processor co-design). The NabLab metamodel-based approach uses the EMF ecosystem that offers several tools to build a user-friendly environment with rich textual editors and graphical diagrams. The NabLab metamodel provides an extra abstraction level to stay close to the problem space. To avoid mixing the concerns, notions related to optimization are deliberately omitted and the metamodel remains close to the mathematical expression.

The numerical analysis IR has been created to bridge the gap between the mathematicians needs and the optimization needs. Additionally, the IR helps in separating the stakeholders (e.g., teams working on software engineering tools and those working on optimization) and software life cycles. The NabLab metamodel can evolve independently to satisfy mathematicians and physicists and take into account new numerical formulations while the Nabla compilation chain evolves towards new optimization strategies.

Looking Ahead

The seamless integration of NabLab and Nabla allows us both to generate Java code using the same technology stack (Java API) and to target lower level backends like CUDA or FPGA. In the past decade, the HPC community explored various programming models providing abstractions for both parallel execution of code and data management, such as Kokkos 8 . Regarding such frameworks, it appears relevant to raise the generation at the level of the IR, since the gap is limited. We are currently working on such a proof of concept, to check if optimization stakeholders can directly interact with the IR. Hence, two issues remain. The first is to identify up to what level of abstraction of the backend we are able to generate from the IR and what criteria determine whether the generation is more relevant from the IR or from the Nabla code. The second is to determine which changes in the technology stack are ready to accept the HPC optimization stakeholders (e.g., should we offer them a C++ API for IR, for example using EMF4CPP 9 or is it conceivable that they use the traditional EMF technology stack with the Java API?).

Related Work

The use of DSLs for scientific computing and computational science has a long-standing history [START_REF] Orchard | A computational science agenda for programming language research[END_REF], especially to address various specific concerns (e.g., architecture [START_REF] Allan | A component architecture for high-performance scientific computing[END_REF], stencil codes [START_REF] Membarth | Towards domainspecific computing for stencil codes in hpc[END_REF], deployment on parallel platforms [START_REF] Arkin | Model-driven approach for supporting the mapping of parallel algorithms to parallel computing platforms[END_REF] or cloud platforms [START_REF] Bunch | Neptune: A domain specific language for deploying hpc software on cloud platforms[END_REF], etc.), or even specific application domains (e.g., fluid dynamics [START_REF] Macià | Saiph: Towards a dsl for high-performance computational fluid dynamics[END_REF]). More recently, problem-specific DSLs for HPC has been explored in the context of MDE [START_REF] Bruel | MDE in Practice for Computational Science[END_REF][START_REF] Palyart | Improving scalability and maintenance of software for high-performance scientific computing by combining MDE and frameworks[END_REF], incl. applications in the web and the cloud [START_REF] Simm | Se in es: Opportunities for software engineering and cloud computing in environmental science[END_REF].

In this area of application particularly relevant for DSLs, as far as we know, this tool demonstration paper is the first to report an industrial experience on the combination of grammars and metamodels in a complete modeling environment for numerical analysis and HPC. This demonstration takes a language engineering point of view, to document the pros and cons of the different technological spaces involved.

Conclusion and Perspectives

The development of NabLab over Nabla, usefully combining metamodels and grammars, is an interesting experience from both a technical and a social point of view. While the respective complementary ecosystems offer advanced features for developing industrial-grade environments, this integration facilitates collaboration between optimization experts and development team.

Future work includes debugging and results visualization capabilities (e.g., step-by-step execution, variables inspection, curves, mesh visualization). We also plan to investigate using the LLVM compiler infrastructure 10 for low-level source code generation. Finally, another challenge consists in coupling Modane [START_REF] Lelandais | Modane: A design support tool for numerical simulation codes[END_REF] and NabLab to describe both the architectural and behavioral aspects of simulation codes. Indeed, Modane is a DSL developed to design the static part of a numerical simulation code while NabLab focuses on the dynamic part. Thus, the modeling toolchain could meet our need to facilitate adaptation to the continuous hardware evolution.

A Demonstration Outline

During this demonstration, we will exhibit the capabilities provided by the Nabla programming language and the edition, design and generation services integrated in the NabLab environment.

The demonstration will be divided into two parts: first we will present the resulting environment, with a demonstration of a program example, and all the facilities provided by the tooling. Second, we will review the architecture of the NabLab environment with a focus on building the modular compilation chain around the IR.

A.1 NabLab Runtime Environment

For this demonstration, we will take as an example the use case of a resolution of a 2D hydrodynamics problem using Glace [START_REF] Carré | A cell-centered lagrangian hydrodynamics scheme on general unstructured meshes in arbitrary dimension[END_REF], a cell-centered lagrangian scheme.

We will show the possibilities offered by the Eclipse environment to help the user write his numerical code model. We will also show the graph deduced from the model and Java and Nabla codes generated. Then we will present the result of the Java execution. Concerning Nabla, we will limit ourselves to the generated code and show the results obtained on the HPC cluster. Finally, we will show a use case based on an increased complexity model to discuss the contributions but also the limits of the graphical interface.

The working environment for mathematicians using NabLab consists of an Eclipse configured with the following components: a model explorer, a textual editor, an outline and a latex view as shown in Fig. 4.

A.1.2 Textual Editor

The textual editor is a specific editor whose syntax highlighting can be defined in a dedicated setting menu (cf. Fig. 5).

NabLab editor offers several useful facilities for end-users:

• Contextual completion proposal. This proposal simplifies the writing for end-users. Only valid instructions are proposed and they do not have to write UTF8 characters (cf. • Syntactic errors highlighting and quick-fixes. Errors are marked with a red cross and an explanatory message is displayed. Eclipse quick-fixes functionality has been used to help users to solve the problem when it is possible. For example, in the following example, the iterator used is misfit (we loop over cells with a j iterator and the r iterator is used as reference for the volume variable). A message is displayed to warn about the unresolve reference to iterator r (cf. Fig. 7) and a quick-fix proposes to replace this reference by one of the available iterators (cf. Fig. 7). This solves the problem immediately. The editor is contextually linked with:

• an outline which offers a synthetic view of the jobs in the NabLab file and allows you to simply move around them (cf. window at the bottom left in Fig. 4). • a LaTeX view which displays a representation in the form of a latex equation for each selected expression (cf. bottom view in Fig. 4). • a tooltip which exposes for the selected expression, the inferred type (cf. Fig. 8).

Figure 8. NabLab Editor tooltype

The NabLab metamodel does not require the user to enter the logical times (@) but deduces them from the calculation of a data flow graph. This data flow is derived from input / output variables for each job.

A.1.3 IR Metamodel

The IR metamodel is defined within the EMF framework in the Ecore format. When a valid file is saved in the textual editor, Xtext automatically triggers the generator. An IR model corresponding to the source code is then created.

During IR instantiation, the generator picks up the position of each model element in the source file and stores it as an annotation. Thus, it is possible to keep the link between IR and Nabla elements.

Each code generator stores a list of transformation steps to apply to the IR model before triggering model-to-text generation steps. Some of those steps are shared between Nabla and Java generators while others are dedicated to the Nabla language. The steps can be very simple, like UTF8 characters replacement (for languages that do not tolerate them), and others quite complex, like the inner reductions removals. Reductions are mathematical reduction operations on collections like sum or min/max. Inner reductions mean reductions inside reductions or loops. This step consists of replacing these inner reductions by loops. Figure 9 shows an example of IR model before and after this transformation step.

The last transformation step is in charge of calculating the HLT of each job. NabLab provides services for jobs to get input and output variables. They are used to build a data flow graph. The shortest path for each job is calculated using the JGraphT library 11 and stored in the IR model When all transformation steps have been applied, the textual generator starts from the last IR model, i.e. the model resulting from the last transformation step. Code generators are written with Xtend using templates. 11 JGraphT, https://jgrapht.org

A.1.4 Data Flow Graph

The corresponding graph is obtained using Sirius (cf. Fig. 10). An outline (cf. window at the bottom left in Fig. 10) shows the entire graph and allows the user to zoom in on a specific part in the main window. For more legibility, filters are used to hide/show the layers presenting the initialization jobs of the variables or those which correspond to the copies of variables of a time n at time n + 1. On this graph, all the cycles are highlighted. Java code produced is multithreaded using ParallelStreams (cf. Fig. 11). A main program is also generated which repeats a certain number of iterations of a loop in which the jobs are called iteratively depending on their computed logical time. So this code is directly executable in Eclipse with the Run As Option. The generated Java code contains VTK calls to record the state of each variable as the simulation goes on. For the moment, ParaView 12 and gnuplot 13 are used to visualize execution results and we plan to have an integrated visualization environment in the near future. Similarly, an upcoming version of the environment will allow the user to specify (probably using an execution model attached to the numerical model) which variables he wishes to dump.

A.1.6 Simple LaTeX Generator

A very simple generator is provided to allow users to get the LaTeX formula of the jobs (cf. Fig. 12) using JLatexMath library.

Figure 12. Simple LaTeX Generation

A.1.7 Nabla Code Generator In the same way as for the Java generation, a Nabla code generator is triggered. Having a look at Nabla file to compare with the equivalent NabLab model, we can see that logical times have been computed thanks to the data flow (cf. Fig. 13). We can also observe the creation of all initialization jobs as it is not possible in the Nabla language for scheduling reasons to specify an initial value for a variable.

The compilation chain that allows to generate code for different backends from the Nabla file has not yet been integrated into the Eclipse environment. However, it is possible 12 ParaView, https://www.paraview.org 13 Gnuplot, http://www.gnuplot.info to explicitly call the Nabla compilation chain with the Nabla file.

A.1.8 Monai Use Case

For the last part of this demonstration of Eclipse NabLab environment, we will briefly show an industrial use case: the 1993 tsunami runup onto Monai Valley, Japan, benchmark from the NOAA (National Oceanic and Atmospheric Administration) center for tsunami research 14 .

The numerical model is much more complex and the graph is quite difficult to read. But in the end, we were able to reproduce exactly the results of the real simulation code as shown in Fig. 14. The first part is in charge of the NabLab language and is composed of the fr.cea.nabla project, the Xtext project containing the grammar, the validation rules, the type inference, and the LaTeX and IR generators. The validation rules are

Figure 1 .

 1 Figure 1. Seamless integration of NabLab and Nabla and the experience report of both developers and users. In Section 4, we discuss several design and technology choices, leading to open questions for the SLE community. Section 5 reflects on related work and Section 6 concludes the paper and outline prospects for the future.

Figure 2 .

 2 Figure 2. Example of Nabla source file

Figure 3 .

 3 Figure 3. NabLab Integrated Development Environment

Figure 5 .

 5 Figure 5. Nabla Syntax Coloring parameter window

Figure 4 .

 4 Figure 4. NabLab environment

  Fig 6).

Figure 6 .

 6 Figure 6. NabLab Editor Contextual proposal

Figure 7 .

 7 Figure 7. NabLab Editor Error Highlighting and Quick-fix mechanism

Figure 9 .

 9 Figure 9. Example of IR transformation

Figure 10 .

 10 Figure 10. NabLab Data Flow Graph

Figure 13 .

 13 Figure 13. Example of Nabla Code Generation

Figure 11 .

 11 Figure 11. Example of Java Code Generation

Figure 14 .

 14 Figure 14. Simulation of tsunami runup onto Monai Valley

Numerical Analysis Based LAnguage, https://www.nabla-lang.org

NVIDIA CUDA, https://docs.nvidia.com/cuda

Flex: the fast lexical parser, https://github.com/westes/flex

GNU Bison, https://www.gnu.org/software/bison

EMF, https://www.eclipse.org/modeling/emf

Xtext, https://www.eclipse.org/Xtext/

Sirius, https://www.eclipse.org/sirius

Kokkos, https://github.com/kokkos

EMF for C++, https://code.google.com/archive/p/emf4cpp

The LLVM Compiler Infrastructure, https://llvm.org

 1. Used technologies implemented in Xtend for a seamless integration in the Xtext generated code. The type inference follows the type provider pattern as explained in book [START_REF] Bettini | Implementing Domain Specific Languages with Xtext and Xtend -Second Edition[END_REF].

The second part consists of 2 projects in charge of the IR and the language generators. The fr.cea.nabla.ir project contains the IR Ecore metamodel, the IR transformation rules and the Java and Nabla generators. The Java generated code is based on basic types and mesh capabilities defined in the fr.cea.nabla.javalib project.

The third part is in charge of the environment and is composed of 2 main projects. The first one fr.cea.nabla.ui is initialized by Xtext and is in charge of the textual editor and the LaTeX view. It contains the tooltips management (hovers), the content assist, the quickfixes, the outline and the syntax coloring. The second one fr.cea.nabla.sirius holds the Sirius graph description and its Xtend services. The other projects of this part are just generated by EMF and Xtext.

Table 1 presents the overall technologies used in the NabLab environment. The first line is dedicated to technologies and tools used by optimization stakeholders while the second line represents those used by tool developers. The C++ Kokkos generation is obtained both by the Nabla tool-chain and by the NabLab direct generation.


Bouderbala Manale
email: bouderbala.manale@gmail.com

Bossoufi Badre

Lagrioui Ahmed

Taoussi Mohammed

Alami Aroussi Hala

Yasmine Ihedrane

IMAT3E'18 International Meeting on Advanced Technologies in Energy and Electrical Engineering Power Control of Wind Generator Using PI Regulator 1*

Recently, the wind power represents an important potential. In order to exploit this potential efficiently, the wind turbine must operate at different speeds when the wind speed changes. To deal with that, this study presents essentially the modeling and power control of Wind Energy Conversion Systems (WECS) based on Doubly Fed Induction Generator

(DFIG) by using the vector control, this later relies on PI regulator [START_REF] Ackermann | An Overview of Wind Energy-Status 2002[END_REF]. Firstly, the model of the wind energy conversion systems is shown. Then, the control system is applied to ensure that our objective is achieved. This control consists of two parts: the first is to maximize the energy extracted from the turbine using the MPPT strategy (Maximum Power Point Tracking), the second part is to control the DFIG's power using the PI regulator. Finally, the results will be presented in Matlab/Simulink environment.

The WECS process transforms wind energy into mechanical energy by the turbine and, into electrical energy by the generator. It consists of wind, turbine, multiplier and generator [START_REF]Backstepping Adaptive Control of DFIG-Generators for VariableSpeed Wind Turbines[END_REF]. The following diagram illustrates the modeling of the WECS:

IMAT3E'18 International Meeting on Advanced Technologies in Energy and Electrical

Engineering

The MPPT control is used to extract the maximum power. It is based on the adjustment of the turbine rotation speed that allows the maximum power to be extracted [START_REF] Alami | Speed control of the doubly fed induction generator applied to a wind system[END_REF]. After the orientation of the fluxes, the expressions below are showing the relationship between the currents and the rotor voltages that will be applied:

(

The expressions of the powers are expressed as follows:

(3)

In order to control the machine powers, this command acts directly on the voltages by applying a PI regulator on each axis and neglecting the coupling terms between the two axes. The WECS is validated using the software Matlab / Simulink, to prove the efficiency of the vector control. So, we will apply a wind profil (fig. 3). From the fig. 4 and fig. 5, we notice that the stator powers follow the setpoint during all the variations of the random wind speed. Moreover, the fig. 6 shows that the stator currents have sinusoidal shape without harmonics. We conclude that, the FOC control combined to the MPPT strategy is simple to implement, give good results and allows controlling the active and reactive powers easily.

Figure 1 :

 1 Figure 1: WECS model

  Field-oriented control (FOC) is a technique for controlling AC electrical machines, based on the DC machine principle, which is characterized by a natural decoupling between flux and currents, in order to simplify the control of the machines [4]. This control consists of aligning the flux of the rotor (or stator) on one axis of the Park reference. In our case, we orient the flux along the axis d. So we have : and (1)

Figure 2 :

 2 Figure 2: Direct Control of active and reactive powers of DFIG

Figure 3 :Figure 6 :

 36 Figure 3: Wind Speed(m/s) Figure 4: Stator Active Power(W) Figure 5: Stator Reactive Power(Var)