activity report - cea/cea

Dap

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En couverture : SerenoMosaïque de Giovanna GalliDate : 2006Dimensions 50 cm X 50 cm

Au verso du document, liste des personnes présentes au Dapnia entre le 1er janvier 2004 et le 1er janvier 2006 pour une durée d’au moins 6 mois.

Directeur de la publication : Jean Zinn-JustinConception : François Bugeon, Yves SacquinCoordination rédactionnelle : Yves Sacquin

Comité de rédaction : François Bugeon, Guillaume Devanz, Jean-Michel Dumas, Bertrand Hervieu, Fabien Jeanneau, Pierre-Olivier Lagage, Paul Lotrus; Philippe Mangeot; Laurent Nalpas; Johan Relland; Angèle Séné; Michel Talvard; Didier VilanovaRédacteurs de la brochure : Nicolas Alamanos, Philippe André, Shebli Anvar, Éric Armengaud, Édouard Audit, Alberto Baldisseri, Pierre-Yves Beauvais, Pierre Bosland, Denis Calvet, Jean-Pierre Chièze, Olivier Cloué, Michel Cribier, Antoine Daël, Anne Decourchelles, Éric Delagnes, Guillaume Devanz, Jean-Michel Dumas, David Elbaz, Ioannis Giomataris, Pierre-François Giraud, Andreas Goergen, Andrea Goldwurm, Bertrand Hervieu, Fabien Jeanneau, Pierre-Olivier Lagage, Jean-Marc Le Goff, Olivier Limousin, Paul Lotrus, Sotiris Loucatos, Christophe Magneville, Philippe Mangeot, Patrice Micolon, Alban Mosnier, Claude Pigot, Alexandre Réfrégier, Johan Relland, James Rich, Danas Ridikas, Vannina Ruhlmann-Kleider, Laurent Schoeffel, Angèle Séné, Romain Teyssier, Sylvaine Turck-Chièze, Pierre Védrine, Christophe Yèche, Jean Zinn-Justin.

Traduction : Provence Traduction

Conception graphique et maquette : Christine MarteauMise en page version française : Christine Marteau

Mise en page version anglaise : Atefo

http://www-dapnia.cea.fr

Dépôt légal : septembre 2007 ISBN : 978-2-7272-0228-8

Commissariat à l’énergie atomique,

Direction des sciences de la matière

Département d’astrophysique, de physique des particules, de physique nucléaire et d’instrumentation associée.

Laboratory of research into the fundamental laws of the Universe.

Dapnia Activity Report

2004 - 2006

The ultimate constituents of matter 7The Standard ModelThe Standard Model 8Physics at the LHC 10Neutrinos 12Hadron structure 14

Energy content of the Universe 17Dark matter 18Dark Energy 20Antimatter and CP violation 22

Structure formation in the Universe 25Cosmology and structure formation in the Universe 26Galaxy formation and evolution 28

Structure and evolution of stars 31Formation of stars and planets 32Stellar and laboratory plasmas 34Compact objects and their environment 36Cosmic ray sources 38

Nuclear matter in extreme states 41 Quark-gluon plasma 42 Exotic nuclei 44

Innovation for detection systems 47Development of detectors 48Signal processing and real time systems 50Intensive computation and simulation 52

Magnets and accelerators 55Particle accelerators 56Superconducting magnets 58Test facilities 60

New developments for magnet and accelerator instrumentation 62

Physics for nuclear energy 65Nuclear data measurements and modelling 66Technological research for fusion energy 68

DAPNIA expertise at the service of society 71Physics and health 72Expertise in decommissioning and design of nuclear facilities 74Light sources 76Environment 78

DAPNIA publications 80

DAPNIA research themes and programmes

2

IntroductionBudget and manpower 4

3

3

Jean Zinn-JustinHead of DAPNIA

DAPNIA, a research institute devoted to the study of the fundamental laws of the Universe, is a basic research department of the CEA’s Direction des sciences de la matière. Its scientifi c activities cover the fi elds of astrophysics, nuclear physics and particle physics. With such a wide range of activities, the institute must, of course, set itself highly ambitious and together coherent goals. To that end, it can draw on a number of specifi c both scientifi c and technical assets: competence of his collaborators, pooled resources concentrated on one site, integration within the CEA, organizational structure, management-by-project culture, and, of course, its own experience and goals.

DAPNIA’s activities call for highly concentrated human skills and material resources, as well as heavy equipment built around cutting edge technologies and requiring further development work. They require a regular prospective discussion of the future development of the various research fi elds to allow for sensible medium range and long range planning.

Most of these activities are carried out as part of international programmes, in external institutions and in close collaboration with many French and foreign laboratories.

The very nature of its activities has led DAPNIA to set up a project-based structure across its line organization, something somewhat original in the world of fundamental research. The structure allows scientifi c equipment to be built more effi ciently and more reliably – from design through industrial follow-up. In addition, CEA differs from CNRS and universities in that its researchers and engineers share a common status. This brings them closer together, ensuring that the instruments developed meet optimally the demands of the scientifi c community.

All this makes it particularly advantageous for DAPNIA to be part of an organization concerned mainly with technological development work. Conversely, especially innovative technological research could hardly exist without a constant stream of new ideas from the world of fundamental research.

DAPNIA activities are focused on the nine topics listed on the opposite page. The fi rst fi ve encompass thematic fi elds of physics, while the other concern related technological developments as well as applications of DAPNIA’s expertise to other fi elds or society problems.

The choice of themes confi rms how fuzzy the boundaries have become between astrophysics, nuclear and particle physics – a development that was somewhat anticipated in the creation of DAPNIA. This brings us to another of DAPNIA’s original features – right from the beginning, it acknowledged that understanding the fundamental laws of nature meant, in particular, studying it on the smallest and largest scales possible.

We are living at a time where the scientifi c fi elds of DAPNIA are especially active with exciting developments: the discovery of dark energy after dark matter has much improved our understanding of the universe at large scales and simultaneously pointed out that we know well only about fi ve per cent of the energy content of the universe. Theory, large scale numerical simulations and observation, using instruments both on satellites and on the ground, have shed new light on the structure formation of the Universe, from galaxy clusters to stars. We anticipate from new experiments progress in the construction of the Standard Model of neutrino physics.

Enormous resources of the Institute have been devoted for more than ten years to the Large Hadron Collider construction. We hope now that the LHC, due to start operating in the summer of 2008, will reveal new physics and, in particular, provide new insight into the origin of masses of leptons and quarks.

The Institute intends also to strongly contribute to the necessary future upgrade of the accelerator as well as to the studies of future linear colliders.

If the structure of stable nuclei is well understood, a global model of the nuclear structure is still missing. In France, SPIRAL2 to the construction of which the Institute is strongly participating, should largely extend our knowledge of exotic nuclei. Finally, current and new experiments should still improve our understanding of the hadron structure.

DAPNIA has the competence and the ambition to take a visible part in these exciting developments but, of course, this requires adequate funding.

Dapnia 2004 - 2006Bu

dget

and

Man

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er

4

2006 Budget

Grant: 59 560 External resources: 11 908

Resources (k€)

Manpower: Foreign collab. and post-docs: Travels and per diem: Logistics: Programmes:

Expenditures (k€)

External resources (k€)

National Agencies: CNES: Europe: Nucl. instal. decommissioning: Internal CEA: Other:

1 7833 707 2 904

770739

2 005

Astrophysics: Particle physics: Nuclear physics and activities: Accelerators: Magnets: Other:

Repartition according to programmes (k€)

4 413 4 546 1 0483 1412 320

463

45 0101 6743 0075 846

15 931

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Laboratoire de recherches sur les lois fondamentales de l’Univers

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DAPNIA women and men in 2006

Unit

DIRSPPSPhNSApSédiSISSACMSenac

Total

Engineers, physicists and

executives

127050 807952,5666

415,5

Techniciansand

administration

2034

1758

50,5484

204,5

Total

32735497

13710311410

620

Permanent staff

Non permanent staff and external collaborators

The ultimate constituents of matter

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Only twelve elementary constituents and three

fundamental forces are enough today to describe the known matter, be it on

Earth or in the Universe.The electroweak and strong

forces are dealt with by the Standard Model, thoroughly verified using high energy accelerators and colliders. The advent of LHC, for which DAPNIA launched some flagship projects, shall certainly bring major breakthroughs in this validation process.

Electroweak force is also responsible of the asymmetries observed between matter and antimatter at the quark level: in the next future, this effect will be looked for also in the neutrino sector.

Last, nucleon structure studies give an ever more accurate description of the roles of the different constituents, and lead to a real three-dimensional view of their distributions inside the nucleon.

In those different fields, DAPNIA has contributed to major advances, which are echoed in the following pages.

Vanina Ruhlmann-Kleider

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The Standard Model

E xperiments using accelerators at the highest accessible energy can be used to perform precise tests on the Standard Model. At CERN, the LEP has obtained many results leading

to more precise knowledge in this fi eld. The degree of precision attained in measuring the mass of the W boson has been exploited to obtain an indirect upper bound for the mass of the Higgs boson through quantum corrections. The Tevatron accelerator at Fermilab (near Chicago) has yielded results on the physics and mass of the top quark. The HERA collider at the DESY research centre in Hamburg has obtained more precise measurements of inclusive cross sections, related to parton (i.e. quark and gluon) densities in the proton, offering vital physics data for the LHC. All these experiments have also included an extensive search for possible deviations from the Standard Model.

The latest LEP analysesThe LEP programme was divided into two phases: LEP1

before 1996, followed by LEP2, a higher energy phase completed at the end of 2000. Over the period 2004-2006, DAPNIA physicists taking part in the ALEPH and DELPHI experiments contributed to extensive analytical work, not only through their collabo-rative work but also within the working groups set up to combine the results of the four LEP experiments. Their work focused on two important areas: direct searches for Higgs bosons and precise measurement of the W boson mass.Quantum corrections to the Standard Model predict a re-lationship between the Z and W boson masses, the top quark mass and the Higgs boson mass. If the W and Z bo-son characteristics were precise enough to be sensitive to

quantum effects, then it would be possible to constrain the standard Higgs boson mass value to complete the direct search results. This precision level was achieved with the LEP. At high energy, the key measurement was the W boson mass. DAPNIA's physicists made a major contribution to the data analysis for this measurement. The two collaborations fi nalised their measurements in 2006. The fi nal W boson mass measurements were then combined for the fi rst time by the four experiments in the summer of 2006. The validity of the Standard Model was reconfi rmed, as the W boson mass measurements made by LEP2 and the Tevatron and the top quark mass measurement by the Tevatron were in agreement with the indirect estimations chiefl y obtained du-ring LEP1. From these results, an upper bound (with a 95% confi dence level) of 166 GeV/c2 can be deduced for the standard Higgs boson mass, completing the lower bound (with a 95% confi dence level) of 114 GeV/c2 obtained through direct searches and published in 2003. This leaves a mass window of about 50 GeV/c2 to be explored for a Higgs boson that agrees with the Standard Model without extensions.The LEP has also tried to track down supersymmetric Higgs bosons. Physicists at DAPNIA were actively involved in fi -nalising and publishing data analyses and/or the related phenomenological interpretations (see Figure 1).

Analysis work at the Tevatron Run 2 of the Tevatron experiment began in early 2001 at

higher energy and collision rate (luminosity) to learn more about the top quark and W boson and measure their mass with greater precision. DAPNIA is taking part in the DØ experiment for which the detector, commissioned at the beginning of 2002, underwent some major changes for this second run.

DAPNIA has helped to design a new trigger system, made necessary by the high luminosity, and contributed in many other ways, developing new tools and working on physical analyses. With regard to tools, the laboratory is closely involved in measuring particle jet energy and in reconstructing muon tracks using various parts of the detector.

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Figure 1. Results of direct searches for neutral, supersymmetric Higgs bosons at the LEP, in the case of maximum CP symmetry violation in the Higgs sector. The area of tested parameters is shown according to the mass of the lightest neutral boson, mH1, and tan β, parameter of the model.8

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Laboratory of research into the fundamental laws of the Universe

Exploratory and metrological themes are addressed for the analytical aspect of the laboratory's activities. Within this context, DAPNIA's DØ group took part in searching for a Kaluza-Klein graviton that decays into two muons, as predicted by a theory that assumes an additional space-time dimension. DAPNIA's physicists have also helped in the search for a supersymmetric Higgs boson in the mode where it is produced in association with a b quark, as well as for electroweak production (via charged W boson decay) of a "single" top quark. Following on from this study, the DØ collaboration brought this process to light at the end of 2006.As part of the work aimed at verifying the Standard Model, the DAPNIA group has taken part in measuring the production cross-section of the W boson decaying with a muon in the fi nal state, as well as the inclusive cross-section of jet production. This analysis work is very important with the LHC on the horizon. Other key contributions made by the group include measuring the production cross-section for top quark pairs in the electron-muon channel and top quark mass in this channel.

HERA analysesRun 2 of the HERA collider began at the end of 2003.

It has since multiplied available data on electron-proton collisions by ten compared with Run 1 and the number of collisions in positron-proton mode has doubled. Physicists from DAPNIA are taking part in the H1 experiment and have carried out many analyses made possible by the large quantity of data now available. In particular, a DAPNIA physicist coordinated all the physical analyses from the H1 experiment in 2005 and 2006.The group contributed largely to the measurement of cross-sections in neutral- and charged-current deep inelastic inte-ractions. The results were used to fi t parton density measu-rements with Standard Model parameters. Work is now underway to include jet production cross-sections, paying close attention to systematic uncertainties. These latest de-velopments are crucial in the preparation of LHC analyses, for which proton parton densities must be determined as accurately as possible.The precision measurement programme has also focused on diffractive interactions in which the proton remains vir-tually intact after the interaction. These processes account for some 10% of all inelastic collisions and therefore de-serve specifi c analysis. Here, too, DAPNIA's physicists have been very active and studies carried out teach us more about these interactions, which will be of signifi cant interest for the LHC programme. DAPNIA's H1 group also publishes work on other processes, such as elastic production of real photons. Through this work, it will be possible to measure parton densities in the nucleon according to the position of the partons in the plane perpendicular to the direction in which the nucleon is travelling.In this necessarily selective overview of DAPNIA's contributions, attention should be drawn to the development of a far-reaching search for deviations from the Standard Model. Events are studied from every possible topological angle (multiplicities, angular distributions, etc.) and statistical

analysis is carried out to determine to what extent the fi ndings agree with the Model. Deviation from the Model can still be observed for topologies comprising an isolated lepton and a missing momentum in the fi nal state – electron-jet-neutrino or muon-jet-neutrino (see Figure 2)

channels (GeV) e and XTP

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= 46DataN 6.0±= 43.0 SM N

) -1p, 341 pb± events at HERA 1994-2006 (emissTl+P

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Figure 2. Distribution in transverse momentum of the hadron system for events with isolated lepton and missing transverse momentum, compared with the Standard Model prediction.

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Physics at the LHC

The Standard Model of elementary particles provides an incredibly precise description of matter and its interactions up to the highest energy explored so far. And yet, one of its

predictions remains to be verifi ed: the electroweak symmetry-breaking mechanism, which points to the existence of a new particle called the "Higgs boson". Furthermore, several extensions of the Standard Model, such as supersymmetric models, predict the existence of new particles. These theories will be extensively tested by the Atlas and CMS experiments, presently setting up the at the LHC facility, the large hadron collider, capable of reaching an energy level of 14 TeV and scheduled to come into service in 2008. DAPNIA's physicists and engineers, who have been involved in developing the related detectors and software required and in carrying out physical analyses for more than ten years, will then be able to tap the vast discovery potential of these two exploratory and general experiments.

ATLASDAPNIA has been part of the Atlas design effort right

from the outset and has been responsible for making several detection systems. The laboratory made 12 of the 32 modules of the central electromagnetic calorimeter, which has now been installed, fi lled with argon and tested. DAPNIA is also responsible for the fi rst-level trigger system. Installation of the boards and cables is almost completed and calibration tests have begun.

In addition to this, the laboratory plays an active – if not central – part in the design, construction and installation of the toroïde magnet, which was tested at its nominal current in 2006. Other tasks with which DAPNIA has been entrusted include mapping the magnetic fi eld and aligning the central muon spectrometer. The spectrometer chambers are nearly installed and the 5800 optical lines of the alignment system are in commisionning. The magnetic fi eld measuring system demonstrated its compliance with tolerance requirements during toroïde magnet testing. Also, the alignment system could be used to measure current-related deformations of the toroïde magnet.

DAPNIA produced the reference software (Muonboy) used to reconstruct tracks in the muon spectrometer, coupled with an interactive 3D display system (Persint).

Physicists at DAPNIA have continued to develop this series of programs, in particular introducing a new tool specially designed to identify low-momentum muons, whose trajectories are diffi cult to reconstruct. The tool is used for identifying b quarks. This group is also responsible for the program used to compute chamber alignment and deformation parameters (ASAP) and is involved in the important task of making a computerised description of the muon spectrometer.

These programs have been used in analysis work where various sub-detectors can be combined with data obtained

either using muon beams or cosmic rays. They are currently used in physical analysis work, where they have validated

simulations during Atlas full-scale production and analysis exercises.

The group is involved in a number of other physics analysis tasks. One of these is aimed at detecting the top quark in order to measure its mass with greater precision than at

Figure 1. View of the trajectory of a cosmic muon recorded by the Atlas spectrometer. The magnetic fi eld effect can be seen in the curve of the trajectory. Only the detectors concerned are shown here. DAPNIA-developed software is used for reconstruction and display purposes.

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the Tevatron. Measurements to determine the accuracy of the Standard Model are also being prepared to measure the mass of the W gauge boson. Lastly, the group is also conducting research into exotic particles (Z' and W') and the Higgs boson through its decay channel to four leptons. DAPNIA is coordinating Artemis, a European network involving seven laboratories, as part of this last project. In order to assist the physicists with this analysis work, DAPNIA is helping to set up in the Ile-de-France region Tier 2, a major node in the computing grid.

CMS CMS is a compact, high-

precision detector built around a superconducting solenoid magnet. Designed in collaboration with DAPNIA/SACM, this magnet is 13 metres long and 6 metres in diameter. The magnetic fi eld in the centre of the solenoid has an unprecedented intensity of four tesla. It is here that a silicon strip tracker is incorporated, along with electromagnetic and hadron calorimeters. The solenoid return yoke, made from 11,000 tonnes of steel, is equipped with a series of very high-performance muon detectors.Right from the start of the collaboration, the CMS group at DAPNIA was closely involved in the design and optimisation of the detector, before going on to play an active part in its construction. Some members of the group occupied positions of considerable responsibility on the CMS Steering Committee.Production work on the main components of the detector is now practically completed. Only the endcaps of the electromagnetic calorimeter remain to be built. They will be ready in time for the fi rst physical data collection runs in 2008.Most of the CMS detector was assembled in the hall above ground while civil engineering work carried on below the surface. The experimental cavern and service cavern were delivered to the CMS experiment team at the beginning of 2006, when installation work began for the various services of the detector.Among the milestone events of the last three years of the CMS experiment, the assembly and testing of the superconducting coil in the summer of 2006 were successfully completed. The fi rst detector segments were also lowered into the interaction zone in 2006. This phase will continue until May 2007. The detector will be ready for the fi rst proton-proton collisions by 2008.

The CMS group at DAPNIA plays a key role in the calibration of the lead-tungstate-crystal electromagnetic calorimeter and in optimising its energy and position

resolution. This work is essential as the calorimeter must reach outstanding performance levels if it is to detect a light Higgs boson (the typical mass of which would be below 125 GeV/c2) by rare decay into a pair of photons. The

group is also interested in the production of pairs of ZZ, WZ or WW gauge bosons predicted by the Standard Model. These pairs lead to fi nal states with multiple leptons forming an unavoidable background to the signal produced by a Higgs boson as it decays into gauge bosons, in the 130 et 500 GeV/c2 energy range

Figure 2. Lowering of a CMS detector segment. The detector segments are assembled above ground before being installed in the experimental cavern.

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Neutrinos

N eutrinos are quite remarkable elementary particles which are produced in great abundance in the sun, in the atmosphere and at the core of nuclear power reactors.

DAPNIA has been interested in them for a very long time. It has now been established that although they are very light, neutrinos do not have zero mass. It remains to be determined how these masses are distributed among the three known varieties of neutrino: νe , νµ and ντ .Based on recent progress in experiments, it seems that these neutrinos could provide remote information about the fuel used in nuclear reactor cores.

First postulated in 1930, then discovered in 1956, there are three varieties – or fl avours – of neutrino, associated with three known charged leptons: the electron and its two heavier partners, the muon and the tau. Neutrinos are not only the particles that interact the least with matter, they also exhibit a unique property that allows them to metamorphose from one fl avour to another. This phenomenon is known as oscillation. Of the three parameters that characterise oscillation amplitude, two have already been measured during earlier experiments (some involving DAPNIA) and this search was awarded the 2002 Nobel Prize. Thanks to this work, we know the distance at which the maximum transformation effect is obtained for a neutrino of a given energy. The third parameter, an angle called θ13, has not yet been measured; we only know that it is small. This parameter must be measured for two crucial reasons: a) to complete the Standard Model of particle physics and b) to prepare the way for future e x p e r i m e n t a l research toward the origin of asymmetry between matter and antimatter in the Universe.

There are two ways of obtaining this measurement: by experimenting on neutrino beams from accelerators or exploiting the abundant source of antineutrinos provided by nuclear reactors. DAPNIA's physicists are preparing experiments in both areas. In France, the Double Chooz experiment carries on the tradition of experimentation in nuclear power plants, while the K2K experiment in Japan has allowed DAPNIA's teams to start preparations for a new experiment called T2K.

Double ChoozNuclear reactors are very intense sources of electronic

antineutrinos. The aim of the Double Chooz experiment, studied and launched by DAPNIA physicists, is to reveal the oscillation phenomenon governed by θ13 . In order to measure this third parameter, the experiment will measure and compare with great precision the neutrino fl uxes at two different distances from the reactor cores of the Chooz nuclear power plant in the Ardennes in the north-east of France. The challenge is to increase the sensitivity of the experiment by a factor of 10. This can only be achieved using two identical detectors, one installed 250 m from the cores, the other at a distance of 1000 m. Both detectors are shielded from cosmic radiation by a natural rock or man-

made cover. While the underground site of the previous Chooz experiment can be used again for the more distant detector, an underground laboratory must be built about 40 metres below the surface to house the detector nearer the reactor cores.

DAPNIA's physicists have proposed a novel concept where each Double Chooz detector is incorporated into a

cylinder 7 m high and 7 m in diameter. In addition, each detector is made up of four vessels fi tting one inside the other to improve antineutrino detection and select interactions more clearly. DAPNIA is in charge of making the detector

Figure 1. Double Chooz: Dapnia technicians, engineers and physicists around the 1:20 scale mock-up of the distant detector in its laboratory. (Credit CEA/Dapnia)

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core and of the technical coordination of the project as a whole. In order to validate this technical solution, a 1:5 scale mock-up was built, which has yielded a wealth of information. Long test campaigns were carried out in our laboratories on the stability of scintillating liquids as part of the studies for this work.

K2K & T2KThe second approach for measuring θ13 entails using the

intense beams of neutrinos produced by new-generation accelerators coupled to detectors weighing several hundred thousand tonnes. This method can be used not only to measure the angle, θ13 , but also, for the fi rst time ever, to determine a phase parameter, δ, associated with matter-antimatter asymmetry. With this in view, DAPNIA's physicists

have joined Japanese experiments while continuing to work on the design and promotion of a European project planned for the period 2015-2020.The K2K experiment in Japan has confi rmed the oscillation observed in atmospheric neutrinos. A beam produced at the KEK laboratory was detected 250 km away in the Super-Kamiokande detector, a vast underground tank containing 50,000 tons of water, equipped to detect the Cherenkov light produced during interactions. DAPNIA's team made a successful contribution to this spectacular result, as illustrated by the two theses defended during this period.

At the same time, DAPNIA is playing an active part in the next step, T2K, when a more intense beam of neutrinos,

being built near the J-Parc accelerator (in Tokai, Japan), will be aimed at the same Super-Kamiokande detector 300 km away. The main goal is to achieve even greater sensitivity to the mixing angle, θ13 . A detector, installed 280 m from the production target, will provide information about the beam at its starting point, while another detector 2000 m away would add to our understanding. Discussions on this second detector are still in progress.The choice of Micromegas technology for the time projection chambers of the detectors installed 280 m away is a great success for DAPNIA, further amplifi ed by the use of read-out electronics proposed by Sédi. As a result, production is underway on 72 Micromegas detectors, equipped with an ASIC chip and analog and digital boards, all developed at DAPNIA (see the chapter on detector development). In addition, DAPNIA's expertise comes into play in the safety and protection system for the superconducting magnets on the beamline.

The road to very large detectorsAfter conducting studies for a large underground detector

(Memphys) in Fréjus, DAPNIA has now joined in the effort to design a “megatonne” detector, coordinated by the European Laguna project. The detector should provide access to a wealth of physics data, ranging from supernova neutrinos to the neutrinos associated with the internal heat of the Earth and opening up new horizons for the study of nucleon decay. Designing a detector of this type calls for the use of very intense neutrino beams. European physicists are working to characterise these beams as part of the BENE programme.

Putting neutrinos to workSo much more has been learnt about the fundamental

properties of neutrinos that applications can now be contemplated. At the International Atomic Energy Agency's request, physicists at DAPNIA are studying new ways of monitoring nuclear reactors. A nuclear reactor burns uranium-235 but also produces plutonium-239 – a favourite ingredient in making nuclear weapons. Once produced, this plutonium could be put aside for future illegal purposes. The antineutrinos emitted when a plutonium-239 nucleus fi ssions are different from those emitted during uranium-235 fi ssion. This principle could be used to identify operating modes that generate a lot of plutonium and those that do not.While Double Chooz experimentation reveals more about neutrino oscillation, the same data can be correlated to the isotope composition of the nuclear fuel to build a precious reference base for assessing the potential of this new monitoring tool. In a closely related area, DAPNIA physicists are also working to fi nd out more about the energy spectra of the antineutrinos produced by different types of fi ssion.The antineutrinos that escape from a nuclear power plant offer a quite novel way of measuring the thermal output of a reactor, as they provide an overall, instantaneous view of the entire reactor. A team of DAPNIA physicists is studying this application that now seems technically feasible

Figure 2. Energy distribution of neutrinos observed in SuperKamiokande and produced by the K2K experiment beam. Data is represented by dots with an error bar. The solid line shows data fi tted with neutrino oscillation and the dotted line the expected distribution with no oscillation. Measurements reveal a neutrino defi cit and a deformation of the spectrum in agreement with νμ oscillation.

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Hadron structure

T he DAPNIA is closely involved in studying the structure of nucleons (i.e. neutrons or protons) and describing them in terms of their components, which are known as quarks

and gluons. Its teams are helping to solve fundamental questions as to how these components defi ne the quantum numbers which characterise nucleons and are investigating the contribution of strange quarks to electromagnetic structure, as well as the part played by gluons in nucleon spin structure. The recent concept of generalised parton distribution, which should open the way to a 3D description of nucleons, announces the dawning of a new era. DAPNIA contributes actively to this progress through its theoretical and experimental work.

The measurements required for these studies are carried out at CERN (Switzerland) and Jefferson Lab or JLAB (USA), which look into how muons or electrons scatter as they interact with nucleons. The theoretical description of this scattering process involves the predominant exchange of a virtual photon, which transfers a momentum energy q to one of the nucleon's components. The resolving power of a probe of this type is proportional to 1/Q, where Q2 = -q2. From this description, it is possible to defi ne various measurable characteristics relating to nucleon structure: form factors, which describe charge distributions and magnetic moment; parton (i.e. quarks and gluons) distributions in terms of density or spin direction, according to a parameter, x, which represents the fraction of the nucleon momentum carried off by the parton; and lastly, generalised parton distributions combining the two notions above. CERN and JLAB cover complementary kinematic ranges in terms of these two fundamental variables, x and Q2.

Strange quarksIn 2004-2005, the Happex Collaboration completed

a measurement of weak form factors for a Q2 value of 0,1 GeV2. The measurement shows the contribution of strange quarks to charge distributions and magnetic moments, s

EG and sMG . The experiments were carried out in

JLAB's Hall A and yielded the most accurate measurements ever of parity-violating asymmetry in electron scattering, reaching a total systematic error of 40·10-9 and a relative systematic error of 1.9 %. DAPNIA played a major role in this programme by building electron detectors and developing a Compton polarimeter of unrivalled relative accuracy: 1 % on electron beam polarisation at 3 GeV. Strange quarks contribute very little to GE and GM (Figure 1): the strange charge radius and magnetic moment are respectively 1 % and a few % of those of the proton! These high-precision results place powerful constraints on nucleon modelling and on lattice quantum chromodynamics (QCD) calculations.

Gluons and the nucleon spinThe distribution of partons according to their spin is

measured by deep inelastic polarised lepton scattering mechanisms in which the nucleons of the target, which is also polarized, are broken. DAPNIA played a considerable part in improving the instrumentation of the Compass experiment at CERN, with the fast electronics (APV) for the RICH detector, a large drift chamber (2.0 × 2.5 m2) and the control system of the new superconducting magnet of the target. The Compass experiment is aimed at measuring gluon polarisation ΔG/G, with respect to nucleon spin. This is achieved by measuring spin asymmetry. The process used to probe the gluons is based on the fusion of a virtual photon with a nucleon gluon, giving birth to a quark-antiquark pair. This process can be revealed by detecting either the production of a pair of hadrons with large transverse momentum relative to the virtual photon or the creation of charmed particles.The second method, though very neat, suffers from statistical limitations, while the fi rst is very accurate in its statistics but calls for Monte-Carlo simulation to subtract the contribution of background to the asymmetry. The results obtained reject models where ΔG, the integral of ΔG(x), is high. The RHIC experiment in Brookhaven, Compass' rival, has not yet extracted ΔG/G from pion production asymmetries measured in polarised proton-proton collisions, but this type

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of asymmetry also rules out high ΔG values.

Compass has also yielded one of the fi rst measurements of transversely polarised quark distribution, together with the longitudinally polarised structure function g1(x), with unrivalled precision at low x values. These data place strong constraints on QCD fi tting of g1 which offer an indirect measurement of ΔG.

Generalised parton distributionsGeneralised parton distribution (GPD) combines the two

previous notions of spatial distribution and parton momentum distribution. By measuring these distributions, it would be possible, for example, to determine whether high-x partons (which are the "fastest") are at the centre or the edge of the nucleon, thus providing the fi rst-ever 3D image of the nucleon. As they link position and momentum in different directions, these distributions can provide insight into parton orbital angular momentum. More generally, they express the correlations or interferences between different states of the nucleon in terms of quarks and gluons. For experimental purposes, GPDs can be obtained through Compton scattering of the virtual photon on the proton, γ*p → γ p,

in the "hard" process known as DVCS (deeply virtual Compton scattering) and the hard exclusive production of mesons, γ*p → γ M.Two DVCS experiments were performed at JLAB, in which DAPNIA played a key part, from the development of dedicated instrumentation through to data interpretation. The experiment in Hall A, devoted to the precise measurement of the absolute cross section and its dependence on Q2, demonstrated that at Q2 values of around 2 GeV2 the cross section was dominated by the DVCS process. The Hall B experiment measured beam spin asymmetries using the CLAS spectrometer, covering a broad kinematic range, as illustrated in Figure 3. It will provide powerful constraints for GPD models.It is planned to increase the statistics of the Hall B experiment in 2008 and measure spin asymmetries of the target. DAPNIA is also involved in defi ning the DVCS programme with a future 12 GeV beam. Studies are underway using cylindrical Micromegas detectors to reconstruct tracks in the central region as part of this work. DAPNIA is also a driving force behind the defi nition of a future Compass programme aimed at obtaining lower x values than at JLAB. Starting in 2007, Compass will carry out DVCS and meson production measurements using a transversely polarised proton target, but with no recoil detector for the proton. Tests were already underway in 2006 to defi ne this detector, which should be commissioned in 2010 for use in measuring spin and beam charge (μ+/μ-) asymmetries on the proton and neutron.

Theory Theoretical work seeks to learn more about nucleon

structure and baryon resonances (structures built around 3 quarks). The aim is to propose theoretical descriptions of these resonances and identify their properties by interpreting the results of measurements where they have a signifi cant impact. Research teams have investigated the role of two-proton exchange and higher-order radiative corrections in large-momentum-transfer, elastic electron-nucleon scattering, which affects the electromagnetic form factors of the proton. The structure and decay channels

of baryon resonances are related to specifi c meson production reactions. SPhN, DAPNIA's nuclear physics unit, uses lattice QCD calculations to study nucleon structure. Another development is the proposal of an effective nuclear force model which makes a connection between nucleon quark substructure and nuclear dynamics

Figure 3. The x and Q2 kinematical range covered by the CLAS/DVCS experiment and the angular dependence of the asymmetry measured in one of the sub-ranges. The amplitude of this asymmetry is related to generalised parton distributions.

Figure 2. Members of the DAPNIA/SPhN Compass team in front of the spectrometer: the superconducting coil of the target, Micromegas detectors and drift chambers built in DAPNIA.

15

17

The energy content of the Universe

Astronomical observations show that the Universe

behaves as though it is primarily composed of dark matter and dark

energy. DAPNIA physicists and astrophysicists have participated in programs like ARCHEOPS, COSMOS and SNLS that have contributed to our understanding of these two substances. We can expect more progress from future projects like OLIMPO, PLANCK and DUNE.

So far, the objects making up the dark matter have not been identified, though programs like EDELWEISS and CAST have placed constraints on

the characteristics of hypothetical particles. More definitively, the EROS project eliminated the possibility that faint stellar objects could constitute the dark matter, drawing a long controversy to a close. Hopefully, whatever it is will be detected by ongoing experiments, in which DAPNIA teams are very active.

Last, the study of the antimatter, another enigma of our Universe, is also puzzling and can bring surprises.

James Rich


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Dark matter

For several decades now, numerous astrophysical and cosmological observations have been interpreted by assuming the existence of large quantities of 'dark matter' that cannot

be directly observed (galactic rotation curves, cluster masses, gravitational shear, distribution of large structures and fossil radiation, etc.). Understanding the nature of this dark matter is one of the major challenges of modern cosmology. Several DAPNIA experiments aim to detect dark matter and determine its properties.

Mapping the dark matter of the UniverseGravitational lenses are one of the manifestations of dark

matter at the scale of the Universe. The light from distant galaxies is defl ected by the massive structures present between them and us (nearby galaxies, and particularly galactic clusters). Dark matter dominates the mass of these objects and causes most of the associated gravitational lens effects.The spatial distribution of dark matter can be inferred by studying the deformation of background galaxies. This technique has been applied to the COSMOS survey, which combines obser-vations of the same fi eld made with different space telescopes (Hubble, XMM) and large ground-based telescopes (VLT/ESO, Subaru, MegaCam). The gravitational deformation analysis methods developed at DAPNIA, based on multiscale decom-position using wavelet packets, have allowed dark matter to be mapped in three dimensions for the fi rst time. DAPNIA teams are now actively involved in the DUNE wide-fi eld space imager pro-ject, which will enable studies with much greater resolution so as to investigate the spectra of dark matter structures at different scales and compare them with the predictions of cosmological models.

Galactic clustersThe largest concentrations identifi ed in maps of dark

matter are those hosting galactic clusters. In order to study the mass distribution in these large haloes of dark matter, we can study the spatial structure of the X-ray emission associated with the hot gas contained therein. This gas is distributed according to the gravitational potential of the dark matter.

The analysis of observations made by DAPNIA teams with the XMM-Newton satellite shows that nearby galactic clusters have density profi les in excellent agreement with the theoretical predictions of the standard, non-relativistic, 'cold' dark matter model.

DAPNIA teams now seek to study the more distant, younger galactic clusters identifi able in Canada-France-Hawaii Te-lescope data (CFHT) obtained with the MegaCam came-ra developed at DAPNIA. Only a few hundred photons are received per cluster. A wavelet-based multiscale analysis method is used to detect these weak and extended sour-ces. The distant galactic clusters identifi ed in this manner are currently being surveyed as part of the XMM-LSS X-ray observation programme.

Investigating dark matter at the scale of galaxiesDark matter also manifests itself at the galactic scale,

and galactic collisions are an ideal laboratory to study its dynamic behaviour. DAPNIA computer simulation teams have developed multigrid numerical techniques demons-trating that collisions between massive galaxies must form second-generation dwarf galaxies. According to conventio-nal models, these dwarf galaxies should not contain dark matter, and observations are now being made to confi rm this.

Figure 1. Visible matter (left) and dark matter (right) in the fi eld of the COSMOS survey.

Figure 2. Radial dark matter distribution in ten galactic clusters.

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Search for baryonic dark matterIn our own galaxy, observations with the EGRET telescope

have revealed large quantities of dark molecular gas never before detected. This dark gas has been detected near the Sun through the γ radiation created by its interaction with cosmic rays, and it may constitute a signifi cant quantity of baryonic dark matter if all galaxies contain similar proportions.

A fraction of the hidden mass in galactic haloes could also consist of massive baryonic objects with masses too low to form directly visible stellar objects. The EROS2 experiment developed by DAPNIA and conducted since 1996 at the La Silla Observatory (Chile) has searched for the signature of such objects in the halo of our galaxy via the gravitational microlensing effect on stars in the Magellan cloud. The fi nal results of the EROS2 experiment suggest that these objects constitute more than 15 % of the halo mass if their mass is comprised between 2·10-7 and 20 solar masses. They also suggest that white dwarfs account for over 10 % of the halo mass.

Direct detection of non-baryonic dark matterNone of the searches for baryonic dark matter have

yielded decisive results, so it is reasonable to assume that dark matter consists of a gas of elementary particles exhibiting little interaction with known particles. A number of extensions of the standard model predict the existence of stable particles having the necessary properties and can be tested directly with LHC instruments (refer to the section on LHC physics).

• Axions are hypothetical particles introduced to address the problem of CP symmetry violation in the strong interaction theory. The CAST experiment uses a CERN superconducting magnet pointed at the Sun to detect the X-ray emission resulting from the interaction between hypothetical solar axions and the magnet's magnetic fi eld. DAPNIA is responsible for the Micromegas detector used in this experiment. The fi rst results recently published impose limits on the axion-photon coupling constant.

• Supersymmetry models and models with additional dimensions provide natural candidates for non-baryonic, cold dark matter particles, referred to as 'WIMPs'. The EDELWEISS experiment aims to directly detect such particles by searching for galactic halo WIMP

interactions in cryogenic bolometers installed in the Modane Underground Laboratory. The fi nal results from the fi rst phase of the experiment (three bolometers) have led to the establishment of a cross section upper limit of approximately 10-6 pb for a WIMP with a mass of 100 GeV/ c2. The second phase of the experiment is currently being prepared and aims to achieve sensitivity 100 times greater. DAPNIA contributes to the technical developments and analyses.This research is being continued with the EURECA international project, which aims to investigate a large number of supersymmetric dark matter models.

Indirect detection of non-baryonic dark matter

Dark matter particles such as the neutralino (in supersymmetry) or the lighter Kaluza particle (in theories with additional dimensions) can annihilate each other in the denser regions of galactic haloes (e.g. galactic centre, Sun's core, Earth's core). The annihilation products (photons, neutrinos, etc.) are detectable, and DAPNIA contributes to the technical developments and analyses for several detection experiments (ANTARES neutrino telescope, GLAST and HESS observatories). The analysis of the photon fl ux of approximately 1 TeV received from the galactic centre (measured by the HESS observatory) has so excluded dark matter annihilation as a dominant contributor to this fl ux.

The INTEGRAL satellite has studied the galactic bulb, which is an intense source of radiation (511 keV). A possible interpretation developed at DAPNIA is that this radiation originates from the decay of dark matter particles into electron-positron pairs. The INTEGRAL satellite's observations may therefore indicate the existence of light dark matter particles with masses between 1 and 100 MeV/c2

Figure 3. Map of our galaxy showing the visible molecular gas (blue) and dark molecular gas detected by γ –ray observations with EGRET.

Figure 4. Energy spectrum of the point-like source of TeV photons in the galactic centre, measured by the HESS observatory. The colour curves correspond to 'adjustments' using non-baryonic dark matter annihilation models.

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20

Dark Energy

Recent cosmological measurements have revealed that the expansion of the Universe is undergoing acceleration. This phenomenon, referred to as ‘Dark Energy’, poses one

of the most pressing questions in fundamental physics. The Megacam instrument built by DAPNIA has been used over the last few years to derive some of the strongest constraints on this mysterious component. A probe of strong potential to elucidate the nature of dark energy is now the observation of SZ-Clusters, in which DAPNIA is committed through the Olimpo Balloon and the Planck satellite that will fl y in 2008. In the longer term, DAPNIA has a leading role in two future experiments focussing on the nature of dark energy: HSHS, a radio interferometer, and DUNE, a space mission recently proposed to ESA.

The combination of recent cosmological measurements has revealed that 76 % of the content of the Universe is composed of a mysterious component called ‘Dark Energy’ (see Figure

1). This component produces an acceleration of the expansion of the Universe at our cosmological epoch. Its existence is very diffi cult to reconcile with f u n d a m e n t a l physics whose prediction for its energy density differs by more than 30 orders of magnitude. A convenient way to study dark energy is to consider its equation of state parameter

w and its evolution. The most important question concerning dark energy is whether it is simply the cosmological constant introduced by Einstein (w = -1 at all times) or a dynamical quantity characterized by an equation of state (varying w). Another possibility is that dark energy is the consequence of a modifi cation of Einstein’s theory of gravity on large scales. The acceleration of the Universe expansion produced by dark energy has several observational effects: it affects the distance-redshift relation of distant objects and the rate of growth of cosmic structures (e.g. galaxies and clusters of galaxies). Several cosmological probes can be used to study dark energy through these two effects. Type Ia Supernovae can be used as standard candles to measure the distance-redshift relation. This relation can also be measured using the length scale of Baryonic Acoustic Oscillations (BAO) produced in the early Universe and which provides a standard rod. SZ-Cluster observations probe the evolution of the largest cosmic structure. The setting up of large galaxy cluster catalogues, combined with ground-based experiments and optical observations, should carry conclusive information on the nature of dark energy. Finally, the Weak Gravitational Lensing provides a measurement

of the distribution of matter in the Universe and is therefore sensitive to both effects of dark energy. Scientists at DAPNIA are very involved in this fi eld through their participation in present and future experiments aimed at the study of dark energy. This is done through realisations of instruments, as well as data analysis and theoretical modelling.

Current observations with MegacamSeveral of the strongest constraints on dark energy today

have been derived in the last few years with the Megacam camera built by DAPNIA and installed on the Canada-France-Hawaii Telescope (CFHT). Megacam is a wide-fi eld CCD camera covering 1 square degree. It has been used to carry out large legacy surveys with the CFHT.Figure 2 shows the constraints on dark energy derived with this instrument using Supernovae and weak gravitational len-sing. These measurements combined with BAO measurement derived with the Sloan Digital Sky Survey concur to constrain the density of dark energy to be around 76 % of the Universe critical density, and its equation of state parameter to be around -1, assuming that it is constant in time. This is consistent with a model where dark energy is explained by a cosmologi-cal constant, but further measurements are needed to rule out other models of dark energy.

Figure 1. Composition of the Universe today according to recent cosmological measurements. The Universe density is dominated by dark matter and dark energy, while ordinary matter makes up only a small fraction. Dark energy produces an acceleration of the expansion of the Universe at our cosmological epoch.

Figure 2. Current constraints on dark energy from CFHT/Megacam and the Sloan Digital Sky Survey. The constraints are expressed in terms of the fraction of Universe density in the form of dark energy (1-Ωm) and of the dark energy equation of state parameter w. Constraints from Super-novae of the SNLS survey (left) and weak lensing (right) derived from Megacam on CFHTLS are shown, along with BAO constraints from SDSS.

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Future Experiments planned at DAPNIAWhile the recent measurement described above confi rm

that the behaviour of dark energy is close to that of Einstein’s cosmological constant, more precise measurement are needed to give a defi nite answer regarding its nature. In particular, future experiments need to measure both the parameter w and its evolution with redshift to distinguish a cosmological constant from a dynamical model of dark energy. Scientists at DAPNIA play a leading role in 3 futures probes on these topics.

Olimpo and Planck SZ-cluster Surveys

The Olimpo balloon and the Planck satellite will observe the millimetre wave sky in several bands. Both are funded and are planned to fl y in 2008. DAPNIA has been involved in the instrument design and tests and preparing science. Olimpo and Planck will observe the CMB anisotropies and will provide large SZ cluster catalogues. Planck satellite will deliver, among many other scientifi c data, a full sky catalogue of the most massive clusters, mainly at low redshifts. Olimpo will observe at improved angular resolution (3’) a smaller patch of the sky (300 deg2).

Combined with ground based follow-up observations and even deeper catalogues from large ground based telescopes (APEX-SZ, ACT or SPT), SZ-cluster observations will settle on within few years if the dark energy behave as a cosmological constant, or if a dynamical model is required.

The HSHS BAO experimentAn international collaboration including physicists from

DAPNIA recently proposed the HSHS experiment which aims to perform an all-sky BAO survey with a radio interferometer. This is done by using the neutral hydrogen 21 cm spectral

line (f = 1.5 GHz) to detect galaxies and locate galaxies out to redshifts of 2. The HSHS interferometer will have angular resolution of about 1 arcmin, and a redshift resolution of about 10-3. HSHS will achieve 5 % and 25 % sensitivities, respectively, on the equation of state parameter w and on its evolution with redshift. A possible design for this novel interferometer is based on a telescope built from several 1 km long cylinders, and will benefi t from recent progress in cell phone amplifi ers. DAPNIA is involved in simulation of the instrument, as well as in the construction of a prototype of electronics chain.

DUNE: The Dark Universe ExplorerDUNE is a wide-fi eld space imager whose primary goal is

the study of dark energy and dark matter with unprecedented precision using weak gravitational lensing (see Figure 3). DUNE will simultaneously challenge all the sectors of the cosmological model, such as dark energy, dark matter, and the seeds of structures. In particular, it will reach a 1 %

and 5 % precision on the equation of state parameter and its evolution with redshift, respectively. Because weak lensing probes dark energy through both its effect on the distance-redshift relation and the growth of cosmic structures, DUNE will also be able to distinguish dark energy models from modifi cations of Einstein’s theory of gravity. Immediate secondary goals of DUNE concern the evolution of galaxies, to be studied with groundbreaking statistical power, the detailed structure of the Milky Way and nearby galaxies, and the

demographics of Earth-mass planet. DUNE is a mission with limited risks and costs, consisting of a 1.2 m telescope with a combined visible/near infrared (NIR) fi eld-of-view of 1 deg2. It will be placed in geosynchronous orbit by a Soyuz Fregat Launcher. DUNE will carry out an all-sky survey in one visible and three NIR bands which will form a unique legacy for astrophysics and cosmology. DUNE has been the object of a pre-study phase (phase 0) by the CNES. It has recently been proposed as a Medium-Class Mission to ESA’s Cosmic Vision programme. The DAPNIA/SAp is P.I. of the mission and the DAPNIA has a leading role in the payload instrument of the mission

Figure 3. Foreseen sensitivity to cosmological parameters of a short term deep SZ-cluster survey. The matter density Ωm , dark energy ΩΛ , and matter density contrasts σ8 are constrained with respect to the distri-bution of cluster numbers with redshift dN/dz . (from Holder et al.)

Figure 4. The Dark Universe Explorer (DUNE) mission is a wide-fi eld space imager which will make a full sky map of large scale structure. DUNE will place defi nite constraints on dark energy through its effect on the distribu-tion of matter in the Universe.


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Antimatter and CP violation

In the Big Bang theory, matter and antimatter appeared in equal proportions at the very beginning of the Universe. Particles and antiparticles mutually annihilated each other, but

one billionth of the baryons subsisted to form the matter of the world around us. The origin of this extraordinarily slight excess matter remains one of the major enigmas of particle physics and cosmology. One of the possible explanations is based on the 'CP violation' phenomenon, which is actively investigated through experiments focusing on the properties of K or B mesons.In addition, the behaviour of antimatter in a gravitational fi eld is another major enigma of modern physics. The Anti-Hydrogen experiment currently under preparation at DAPNIA addresses this issue.

Investigating matter-antimatter asym-metryIn 1967, A. Sakharov proposed an explanation to the

matter-antimatter asymmetry in the Universe based on a mechanism involving the 'CP violation' phenomenon fi rst observed in 1964 in weak interaction decays of neutral K0 mesons.

Although the CP violation observed up to now is too slight to explain this asymmetry, understanding the mechanisms involved remains of fundamental importance. This asymmetry is more specifi cally due to 'direct' CP violation, which refl ects the difference in decay rates between two processes conjugated by CP symmetry. The NA48 experiment conducted at CERN has addressed this issue using neutral kaon beams.

In the standard model, the Cabibbo-Kobayashi-Maskawa matrix (CKM) groups the coupling parameters of different quark families. CP violation is manifested in the values of certain complex parameters, and the mathematical properties of this matrix can be represented in the complex plane through a 'unitarity' triangle. Accurately measuring the parameters of this triangle is one of the major objectives of the BaBar experiment conducted at SLAC (California, USA), which studies B-mesons containing b quarks.

NA48 experiment: Direct CP violation in kaonsThe fi rst demonstrations of CP violation date back to

observations of neutral kaon decay. DAPNIA has always been at the forefront of experiments in this fi eld, the latest of which is the NA48 experiment conducted at CERN. In 2001, NA48 observed direct CP violation for the fi rst time. During the second phase of the experiment, high intensity kaon beams were used to successfully observe very rare kaon decays into a pion and two electrons or two muons: KS → π0e+e- and KS → π0μ+μ-.In 2003-2004, the NA48/2 programme devoted to the study of charged kaons was launched. DAPNIA has

played a leading role in the development of the KABES kaon beam spectrometer (based on the MICROMEGAS detector), which can measure kaon displacements with 1% precision at fl uxes exceeding 20 million events per second. This programme has allowed the study of direct CP violation in kaon decays into three pions, for which NA48 observes no signals at precision levels of 10-4, in agreement with standard model predictions. By studying kaon decays into a pion and two leptons (K± → π0e±ν / π0μ±ν), NA48 has measured one of the parameters of the CKM matrix and solved a unitarity problem that had remained unresolved for many years.In addition, by studying kaon decays into 2 charged pions and two leptons K± → π+π-e±ν, DAPNIA physicists have made a signifi cant contribution to the understanding of the interaction between low energy pions.

BaBar experiment: CP violation in B-mesons The BaBar experiment is located near the PEP-II 'B

factory' at SLAC. It aims to conduct a complete and highly accurate study of CP violation in B-meson decays. Beyond that, another goal is to test the consistency of the standard model and possibly reveal the existence of New Physics.The PEP-II accelerator was commissioned in 1999 and quickly reached its nominal luminosity, which it now exceeds by a factor of four. By the summer of 2006, BaBar had recorded 380 million pair decays (B -B).In 2001, BaBar observed CP violation in the Β0 → J/ ψ K0, decay system and established that the sin(2β), parameter associated with the unitarity triangle is different from zero. This was the fi rst observation of CP violation outside the kaon system, and a signifi cant confi rmation of Standard Model predictions. The present BaBar measurement, of great precision, gives sin(2β) = 0,710 ± 0,039.In addition, in 2004, BaBar established the existence of direct CP violation in the B 0 (B 0)→ K+π- (K- π +)decay system. This discovery was made possible by the excellent 22

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accuracy of the DIRC particle identifi cation system used for the experiment (developed with signifi cant participation from DAPNIA).Additional studies are being conducted in parallel to measure the other angles and dimensions of the unitarity triangle. As shown in Figure 1, all BaBar measurements obtained to date are consistent and do not contradict the standard model.DAPNIA physicists actively participate in a number of leading studies, including the measurement of the angles α and γ of the unitarity triangle, the analysis of rare decay modes, and tests of T and CPT symmetry with two-lepton events.

How does anti-hydrogen fall? A way to test the behaviour of antimatter in a gravitational

fi eld consists in measuring whether gravitational forces acting on a hydrogen atom are identical to the one acting on an anti-hydrogen atom, in the Earth gravitational fi eld.

In order to weigh anti-hydrogen atoms H, they must be slowed down to less than 1 m/s. It has been proposed to use antimatter ions H+, formed by an antiproton and two positrons, since they can be suffi ciently 'cooled' prior to removal of the excess positron using a laser. H+ ions are produced by directing an antiproton beam at a very dense target of positroniums (PS), through two successive reactions: p + PS → H + e-, then H + PS → H+ + e-. The advantage of this process is that it is much easier to slow down H+ ions (charged) than H, atoms (neutral).

As a fi rst step, the method will be validated and its feasibility demonstrated by producing matter ions (H-)from positroniums. A dense positronium gas can be obtained by bombarding a suitable material with an intense beam of positrons. An experiment is being prepared at CERN to select the most effi cient type of material for the conversion of positrons into positroniums to be emitted in a vacuum.

DAPNIA is presently conducting the fi rst phase of this ambitious programme by developing a positron collector within the framework of the ANR-funded SOPHI project (Figure 2). Moreover, the development of a controllable positron source system offers many advantages for industries, particularly the electronic components industry

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Figure 1. Most recent constraints on the unitarity triangle. The coloured bands show the regions allowed by the different angular measurements: α (light blue), β (dark blue) and γ (grey). The regions surrounded in red and brown correspond to the most probable values for the peak of the triangle, taking into account constraints associated with angular and dimensional measurements, respectively.

Figure2. Example of positron transport simulation in the SOPHI system. Electrons have been sorted, and positrons (shown as coloured spiral lines) are guided by the magnetic fi eld.

23

The structure formation in the Universe

25

The imaging of the fossil radiation of the Big Bang

revolutionized cosmology during the last few years by uniquely constraining

the cosmological parameters (age and energetic density of the various components of the Universe) and the initial granularity of the Universe which lead to its present-day structures.

DAPNIA played an active role in this, both observationally (with the ARCHEOPS experiment and in the future OLIMPO and PLANCK) and theoretically. Thanks to the HORIZON Project, it played a key role in the nume-rical simulation of the structure formation of the Universe by

combining for the first time a unique sharpness at both cosmological and galactic scales.

The understanding of the physics of galaxy formation not only requires to study these extreme scales, but also the complete electromagnetic spectrum, from the hard radiation, with the X-ray emission of galaxy clusters on million light-year scales (with XMM), to the soft radiation, with the infrared emission of stars embedded in their parent dusty molecular clouds on light-year scales (ISO, VISIR, SPITZER, HERSCHEL).

The questions remain numerous in this expanding field and the future is fascinating.

David Elbaz


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T he study of the large-scale structures of the Universe has developed dramatically over the past two decades, since the discovery of temperature fl uctuations in the cosmic microwave

background by the COBE satellite team in 1992 (2006 Nobel Physics Prize). This has made our knowledge of the initial conditions of the Universe accurate enough to consider studying its dynamic evolution over the 13 to 14 billion years of its existence. In the course of this evo-lution, small primordial density fl uctuations grew under the effect of gravitational instability and formed the galaxies and galactic clusters that we observe today.

Cosmology and structure formation in the Universe

The study of this complex and non-linear mechanism, referred to as the 'hierarchical model', requires the use of high-performance, ultra-sensitive observation systems to investigate the primitive universe and the formation of the fi rst stars. It also requires increasingly effi cient computation tools to accurately calculate the model's predictions. An accurate knowledge of the initial conditions is a prerequisite to any ab initio description of galaxy formation in the Universe. The observation of the cosmic microwave background is therefore the cornerstone of modern cosmology. The study of the end of the 'dark age' and the formation of the fi rst stars or primordial galaxies is a strategic challenge for understanding galaxy formation. This aspect constitutes the 'holy grail' of current cosmology, with abundance of unanswered questions for which numerical simulation will play a key role. Other important aspects of this research include the study of our local Universe (less than one billion light years from the Milky Way), the physics of galactic clusters, and large-scale structure formation in the Universe.

Observing the cosmic microwave backgroundThe WMAP satellite has observed this fossil radiation

since 2001 and produced a map of the Universe when it was only 300,000 years. This map has allowed the precise measurement of the total density of the Universe (close to critical density). The European Planck satellite to be launched in 2008 will allow far greater precision (a few percent) in the determination of the main cosmological parameters. In addition, the study of cosmic microwave background radiation polarisation will allow the measurement of other fundamental parameters that are currently still inaccessible, thereby yielding essential information on the origin of these primordial fl uctuations. DAPNIA has participated in measurements of cosmic microwave background radiation fl uctuations for over 10 years now. In particular, it was involved in the ARCHEOPS experiment, which yielded one of the fi rst measurements of the total density of the Universe. With its acknowledged expertise in bolometer instrumentation, DAPNIA is also involved in the development of the Planck satellite and is an active participant in the OLIMPO experiment. All of these experiments also allow the investigation of galactic clusters via the Sunyaev-Zel'dovic effect (see last section).

Detecting the end of the « dark age »This long period following the recombination period and

preceding the formation of the fi rst stars lasted approximately 100 million years. It came to an end when the concentration of matter due to gravitational instability was suffi cient to allow the formation of the very fi rst stars ('Population III' stars). These stars 'reionised' the intergalactic medium and profoundly modifi ed the chemical and thermal balances in the Universe. Accurately determining the reionisation period is a fundamental aspect of current cosmology. It is also one of the main objectives of the SKA radio interferometer project, as well as DAPNIA's SVOM/ECLAIR satellite project. This French-Chinese satellite will observe gamma-ray bursts with unprecedented spatio-temporal accuracy, allowing the detection of ultraviolent phenomena referred to as 'hypernovae' and likely associated with the death of Population III stars. All these stars are believed to have disappeared. The JWST satellite to be launched in 2013 will allow the observation of the very early galaxies, within which the oldest stars currently populating our Universe were formed. Such observations of the distant Universe (more than 10 billion light years from the Milky Way) will be made possible by the MIRI infrared camera developed at DAPNIA. These primordial galaxies are the building blocks from which other galaxies were progressively assembled.

Figure 1. Map of the cosmic microwave background obser-ved by the WMAP satellite. (Source: NASA/WMAP)

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Modelling galaxy formationThe main success of the hierarchical model is its ability to

coherently explain the formation of galaxies. In a universe dominated by dark matter, galaxies grow and develop through continuous accretion of diffuse matter, punctuated with more or less violent phases involving collisions with other galaxies. The often simplistic analytical calculations performed over the past 20 years seem to indicate that this model works. In the case of numerical simulations, the situation is much less clear (angular momentum problem, missing satellites problem, cusps' problem). Is the hierarchical model in danger? The Horizon project was created in France three years ago in an effort to resolve these reliability problems with the calculation of the model's predictions. Numerical modelling of galaxy formation is generally approached using two distinct methods: cosmological simulations (e.g. Horizon simulation on MareNostrum supercomputer at Barcelona) and simulations of collisions between isolated galaxies (e.g. M31 simulation on CCRT vectorial computer at Bruyères-le-Châtel). It is now widely accepted that a synthesis between the two approaches (cosmological and galactic scale) is required in order to accurately calculate the predictions of the hierarchical model.

Understanding the structure of the Universe

Galaxies organise themselves at large scales within giant clusters and fi laments interconnected in what is referred to as the 'cosmic spiderweb'. It is crucial to understand the structure of this particular medium, as well as the internal structure of the nodes composing it, i.e. galactic clusters. These objects have a specifi c status, since they are the last objects formed in

cosmic history. Their quantity, physical properties and spatial distribution all constitute extremely valuable cosmological probes. DAPNIA physicists have signifi cantly contributed to their comprehension by studying the X-ray emission from the hot gas surrounding them (using observations from the XMM satellite in whose development DAPNIA participated).

These large-scale observations of the Universe (such as tho-se to be conducted by the DUNE satellite, DAPNIA's new key project) should yield signifi cant measurements of current cosmological model parameters, supplementing cosmic mi-crowave background observations. They will also be used to test the general paradigm of gravitational instability in an expanding universe

Figure 3. Dark matter distribution (projected density map) simulated by a Horizon project team at CCRT (CEA Bruyères-le-Châtel). (Source: Christophe Pichon, CNRS/DAPNIA)

Figure 2. Primordial galaxy (projected density map) simulated by a Horizon project team on the MareNostrum supercomputer (Barce-lona Supercomputing Centre). (Source: Pierre Ocvirk, DAPNIA)


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Observational Cosmology has reached an important turning point. After years of seeking the parameters that govern the evolution of the Universe, there seems to be increasing

consensus in acknowledging the dominant infl uence of dark matter on baryons and that of dark energy on dark matter. Paradoxically, the behaviour of the two “dark” components that make up 95% of the energy content of the Universe is easy to model (dark matter is nondissipative and subject only to gravity, while dark energy acts as an anti-gravitational factor), even though our knowledge of their nature remains highly speculative. This has led to the scientifi c community’s leaning increasingly toward what has become the conundrum that best stands up to theoretical attack: the behaviour of baryons and the origin of the light we receive from stars, galaxies and galaxy clusters. It is now acknowledged that it is not possible to understand how galaxies form and evolve without using the entire electromagnetic spec-trum to study their various components (stars, gasses and dust) in their different states (neu-tral, ionized, young/old, dense/not very dense).

Paradoxically, it is the two opposite extremes of the electromagnetic spectrum that best stand up to interpretation and yet they seem to be produced by the same physical processes (star formation and super massive black hole growth): thermal infrared, at temperatures of T ≈ 40 K, and X-rays, at T ≈ 107 K. Thanks to its substantial involvement in space-based instruments used to observe at these wavelengths, DAPNIA/SAp is one of the key players, internationally, to have discovered the existence of links between the physical scales related to these regions and which vary over 6 orders of magnitude. These scales range from the parsec (3·1016 m), for molecular clouds out of which stars are formed, observed using infrared, to the megaparsec (3·1022 m), for galaxy clusters, observed using X-rays. Future space missions in which DAPNIA/SAp is involved (Herschel, JWST, ECLAIRs and Simbol-X), are totally consistent with this observational approach, which is strengthened by numerical simulations of galaxy formation, in the framework of large-scale structures formation. The main questions that these studies try to answer are:

– How and when did the structures of the Universe form?– How and when did the stars that make up galaxies

form?

Galaxy clustersGalaxy clusters are the largest structures in the Universe

linked together by gravity. Thus, they represent ideal laboratories to study the role of physics other than gravitation in structure formation. This can primarily be done by measuring the X-ray emission of the intergalactic gas in clusters (intra-cluster medium, ICM), which gives access to its luminosity and temperature, from which the gas mass and total cluster mass can be derived as well as its specifi c entropy. Thanks to the XMM satellite, it has been possible to measure how those observational properties are related by scaling laws (clusters of different masses are similar by effecting a single transformation) with a precision never achieved before. Those scaling laws show excess entropy in comparison with predictions from theoretical models based on cold dark matter and a non-zero cosmological constant (ΛCDM),

which include only gravitational effects. DAPNIA/SAp, which played a leading role in developing the scaling laws, demonstrated that this excess entropy did not depend on the distance to the center of the cluster and that it was present in clusters of all masses. These results suggest a scenario in which galaxies inject entropy into a cluster by means of winds produced by a central active nucleus (supermassive black hole) or supernovae, after a burst of star formation, with more entropy being generated through shocks during the accretion of groups of galaxies in the cluster formation process. Groups of galaxies indeed appear to play a key role both on galaxy and cluster formation. The vast XMM-LSS (Large Scale Structure) mapping of the sky, directed by a team from DAPNIA/SAp, and combining observations from the XMM satellite and from Megacam (built under the prime contrac-torship of the DAPNIA), has unveiled population of galaxy groups that was hitherto unknown.Together, these studies show how diffi cult it is to understand galaxy clusters evolution and formation without taking ac-count of the evolution of galaxies themselves, in their envi-ronment.

Galaxies and their environmentGalaxies have thus exerted an infl uence on the largest

scale structures, but the opposite is also true. Thanks to deep imaging in the mid-infrared using NASA’s Spitzer satellite, DAPNIA/SAp physicists demonstrated for the fi rst time that star formation in galaxies is extremely sensitive to the local environment on intermediate scales between that of galaxies (30 kpc) and that of clusters (5 Mpc). Thanks to images of the deepest views of space ever taken, using a combination of X-ray (Chandra satellite), optical (Hubble Space Telescope, VLT and Keck), mid- and far infrared (Spitzer satellite) and radiowave (VLA) technology, it has been found that galaxies formed stars more rapidly when located in galaxy-dense regions (cf. Figure 1).It has unexpectedly emerged that the role of the fusion between two massive galaxies put forward in the past does not adequately explain this phenomenon and new causes must be investigated, relating the evolution of galaxies with

Galaxy formation and evolution

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the formation of large structures, such as an accelerated collapse of intergalactic gas at the time when galaxy groups formed or multiple non-fusion interactions.

To progress further in the attempt to resolve this key question in galactic history, the DAPNIA team was involved in the fi rst three-dimensional mapping of the distribution of matter in the Universe, using three ways to track matter in the Universe: visible radiation for galaxies, X-ray for hot cluster gas and groups of galaxies and gravitational shearing for total mass (mainly dark matter) which deforms images of the galaxies. Thanks to this 3D mapping of the galaxies in their environment, it is now possible to improve our understanding of how the formation and evolution of galaxies and large structures are related. Numerical simulations are an essential tool used to interpret these observations since it allows us to test hypothetical physical models that may explain the effects of environment on galaxy formation. Figure 2 shows an example taken from one of these studies where simulations served to demonstrate that the fusion of two massive spiral galaxies produced, in its “tidal arms”, dwarf galaxies that will survive after the collision and form their own stars.

Star formation in galaxiesWork at DAPNIA/SAp has helped improve our

understanding of how stars are formed, within galaxies, thanks to the study of starbursting events occurring in local galaxies with low heavy element content (and, therefore, quasi-primordial). These studies revealed a key actor: interstellar dust grains. In fact, the stars that produce the majority of light in a galaxy, those with ten times the mass of the Sun but that radiate ten thousand times more energy, are born from molecular clouds that have a lifetime comparable to that of

these stars, of around 10 million years. During this time, most of the light from the stars is absorbed by dust and then radiated in the infrared. It is therefore crucial to measure the infrared light emitted from galaxies in order to elucidate their star formation activity. However, dust is a complex element in a galaxy, where polycyclic aromatic hydrocarbon molecules mix with amorphous grains the size of a micron and produce a spectrum which is extremely complicated to decode but will serve to achieve the quantitative measurement of galaxy activity. Physicists at the SAp have discovered a number of fundamental relations linked to infrared emission which can be used for precisely this purpose, to decode this spectrum and thus reveal hidden information about the birth of the stars.

ConclusionsDAPNIA/SAp’s studies on the formation and evolution of

the galaxies thus consists in collating “multiple wavelength” observations of the Universe and, in so doing, to shed light on the physical relations that unite the processes occurring at scales encompassing six orders of magnitude but which are impossible to understand individually. The pivotal role played by the DAPNIA/SAp in terms of infrared and X-ray instrumentation is particularly well-suited to this task and the scientifi c subjects developed on the three scales mentioned above serve to optimize the progression from observation to the interpretation of these observations with a high degree of acuity

Figure 1. Three colour (BVI) image of a distant overdense region of galaxies taken by the Hubble Space Telescope. The image is focused on a spiral galaxy similar to the Milky Way but located at z = 1, i.e. 8 billion years ago. Twice the mass of the Milky Way, it has a star formation rate thirty times higher due to the surrounding galaxy overdensity.

Figure 2. Numerical simulation developed at DAPNIA/SAp showing the formation of dwarf galaxies during the fusion of two massive spiral galaxies. These galaxies (close-up, bottom left) survive after the collision. Time, T, is measured in millions of years.

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Structure and evolution of the stars

The energy driving galaxy evolution comes from many

sources like the formation of stars and their explosion in supernova,

the formation of super-massive black holes and their accretion of surrounding material. The detailed study of these phenomena goes through observing objects of our “neighbourhood”, with a multi-wavelength and multi-scale observational approach, supplemented by numerical modelling and laboratory experiments.

The galaxy components are or will even better be known thanks to the current or forthcoming programmes: star mass distribution (with HERSCHEL and APEX/ARTEMIS), Sun dynamical evolution (SOHO), accretion and jets around black holes (INTEGRAL, SIMBOL-X), cosmic ray acceleration (XMM, GLAST, HESS)…

The study of planet formation is also a quickly evolving field. Thanks to the Cassini mission, Saturn's rings are revealing their secrets; with VISIR, protoplanetary disks are unveiled. And in the near future, exoplanet images are expected from JWST.

Pierre-Olivier Lagage


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Formation of stars and planets

Astrophysicists from the DAPNIA/SAp are conducting top research, since years, on the early phases of star formation in interstellar clouds. These studies are now entering

a new phase, marked by the advent of the Herschel and ArTéMIS projects, and by the increasing role of numerical simulations. Studies into star formation are complemented by research into protoplanetary disks, around which exoplanet formation and evolution occurs. Closer to home, planets, and more specifi cally Saturn rings, are the subject of spectacular fi ndings made using the Cassini probe.

Simulation of interstellar cloud formationThe structure formation and evolution of the interstellar

medium are determined by the properties of the atomic hydrogen (HI) component of the interstellar gas. Important numerical diffi culties, related to the multiphase nature of this medium, impeded its correct treatment for years. Today, the development of computing tools allows registering signifi cant progresses. Astrophysicists from SAp managed to simulate, with very high resolution, the fi rst stage of the formation of a molecular cloud, with creation of cold and rather dense cold gas condensations, in a turbulent bidimensional and multiphase fl ow. This study established the link between turbulence and the number of formed dense structure, and allowed characterizing their mass spectrum: N(m) ∼ m-1.7, and proposing semi-analytical models explaining its behaviours.

Star formation in interstellar cloudsThe objective of star formation studies at SAp is to

understand the mechanisms by which clouds of interstellar gas contract and collapse within themselves to form protoclusters, before breaking up into prestellar cores that produce star embryos, or protostars (see Figures 1 and 2). Infrared observations have already demonstrated that the

vast majority of stars in our Galaxy are formed in clusters, but such observations can only be used to study stars that have already acquired most of their mass. Conversely, star progenitors (prestellar cores, protostars and protoclusters) are very cold objects (∼ 10 K). Their radiation is essentially contained in the band that extends from the far-infrared to the submillimetric range, in the spectral domain of “submillimetric” ground-based radio telescopes (IRAM, APEX), of the Herschel space observatory, and of ALMA, the ESO future millimetric and submillimetric interferometer in Chile. SAp research in star formation has strong ties with two experimental projects - the Herschel space telescope and the ArTéMIS bolometer camera – both of which have a European scope. The Herschel telescope is a European Space Agency mission dedicated to observing the Universe in the infrared and submillimetric ranges. Herschel will be launched in 2008 and it can boast a 3.5 m-diameter mirror

Figure1. On the left: image at 2 μm from NGC7538 a region where massive stars are formed. On the right: image taken at 1.2 mm with Mambo-2 on IRAM. Three new protostellar clusters have been detected in the south of the complex where infrared emission is quiet and submm/mm emission is intense. Massive proto-stars (+), highlighted through the detection of a methanol maser, are associated with each cluster. This region is to be studied by Herschel. (Photo credit: Minier and Motte)

Figure 2. (a) : image of the dust continuum emission at 1.2 mm from the NGC 2264-C protocluster obtained with the IRAM 30 m telescope. The principal cores are designated by CMM. (b): position-velocity diagram, along an axis passing through CMM2, CMM3 and CMM4. (c): image of the “synthetic column density” obtained through hydrodynamic simulations conducted at DAPNIA. Fragments are labelled as SIM. (d): position-velocity diagram obtained through simulations, along an axis passing through SIM2, SIM3 and SIM4. The spatial resolution of this image is identical to that of observations with the 30 m telescope. (Photo credit Peretto and André)

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making it the largest telescope ever to be sent into space. Three instruments will be on board Herschel: PACS, SPIRE and HIFI. DAPNIA is managing the construction of the PACS camera and all associated electronics, as well as part of the electronics in the SPIRE camera. A considerable proportion of Herschel’s time will be dedicated to studying star formation mechanisms. The objective will be to clarify the origin of the distribution of stellar mass distribution (IMF for Initial Mass Function). SAp researchers are leading two star-formation key programmes with Herschel: the fi rst will focus on the study of interstellar clouds close to the Solar System (Gould belt) - with a view to mapping them in a comprehensive manner - while the second will turn its attention towards more distant regions in our Galaxy, where massive stars are formed. The extremely sharp sensitivity of the Herschel imaging instruments, coupled with the spatial resolution provided by the 3.5 m mirror, will make it possible to record all prestellar cores and protoclusters in these clouds. Physical quantities, such as the objects’ temperatures and masses will also be directly derived from the Herschel observations. By cross-checking with complementary observations, this will greatly help to shed light on the origin of IMF.

DAPNIA astrophysicists are also responsible for the scien-tifi c and technical aspects of the ArTéMis project, which aims to produce a large-scale bolometer array submillime-tric camera for ground-based telescopes, using technology developed by the CEA for PACS. A fi rst prototype camera has been designed to operate at a wavelength of 450 mi-crometers. It was successfully tested, in March 2006, at the focal plane of the KOSMA telescope at the Gornergrat ob-servatory in Switzerland, then in March 2007 on the APEX telescope, a 12 m antenna used to prepare the develop-ment of the future ALMA interferometer.

Protoplanetary disks and planet formationSAp astrophysicists are also studying protoplanetary

disks, where exoplanet formation and evolution occurs. Exoplanets orbit stars other than the Sun. Over the last ten years, exoplanet research has resulted in the detection of

200 candidate planets. These planets are formed in disks of gas and dust that orbit the stars when they are young, but the exact circumstances of their formation are still unknown. To understand the processes involved, astrophysicists are studying protoplanetary disks by observing them in the mid infrared range (8.6 micrometers). At this wavelength, radiation is dominated by the emission of certain complex molecules known as PAH (Polycyclic Aromatic Hydrocarbons) which are mixed to dust. These molecules, heated by light from the central star, re-release infrared radiation that can be used to draw up a precise "map" of the surface of the disk. SAp research into these disks is conducted using the VISIR instrument (VLT Imager and Spectrometer for InfraRed, installed on the ESO’s VLT telescope in Chile), designed by DAPNIA and Astron (The Netherlands). Placed at the focal plane of a giant 8-meter diameter telescope, it makes it possible to distinguish the fi nest details currently accessible using imaging instruments. Recent VISIR images revealed an extended disk around star HD97048, a good example of a protoplanetary disk at the beginning of its life.

Planets and Saturn ringsSAp researchers are fi nally conducting research

into planets and, more specifi cally, Saturn rings (See fi gure 4). The Cassini-Huygens space probe has been in orbit around Saturn since 30 June 2004. The CIRS (Composite InfraRed Spectrometer) instrument, the result of an international collaboration of which DAPNIA was part, was able to measure the rings’temperature with a degree of precision hitherto never achieved: fi rst on the unilluminated side and then the side illuminated by the Sun. These fi rst measurements led to surprising fi ndings: the rings appear to have the same temperature on their illuminated side as on their unilluminated side. This unexpected property provides better understanding of the nature of the particles that make up the rings

Figure 3. Left: false-colour image of infrared emission at 8.6 μm, from the matter surrounding star HD 97048, obtained by VISIR. Compa-rison with the image of a star with no disk (bottom left) shows that star HD97048 is surrounded by a structure that extends for at least 370 astronomical units of length. Right: the contour of the infrared emission (in the form of an ellipse) is markedly shifted with respect to the position of the star (marked by an arrow), indicating that this structure is an inclined disk. (Photo credit Lagage and Pantin)

Figure 4. A surprising view of the Saturn F ring, taken on 29 October 2004 by Cassini’s narrow fi eld camera. Perturbation introduced by the small Prometheus satellite (visible to centre) creates "bridges" of matter that are formed between the ring and the satellite. Once these bridges are broken, a sort of scar remains that streaks the ring at the impact point. Cassini images reveal however, that any traces of destruction are eliminated in less than 3 months, as if the ring had a strange capacity of repairing itself all alone. The fi nest details here are about 940 metres. (photo credit: NASA/ESA)


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Most of the known matter in the Universe is in the form of plasma. Astrophysical phenomena affect the properties of plasma in conditions that, because of their

extremes of density, temperature or speed, are unknown on Earth. The study of some of these properties, detected in the Sun by seismology, uses the modelling of dynamic phenomena and 3D simulation. The GOLF space instrument is playing an important part in this, through the discovery of a signature for gravity modes, low-frequency waves produced by upthrust, for which scientists have been looking for more than 30 years. This signature suggests the solar core is rotating rapidly, a vestige of the period when our star was formed. Knowing how matter moves in stars opens up for investigation the vast fi eld of stellar plasmas, enriched by the successful launch of the COROT satellite. It encompasses everything from star formation to the explosion of supernovae, including the interaction of Sun and Earth.In parallel, CEA's large LIL/PETAL and LMJ lasers are proving particularly valuable for studying certain isolated phenomena such as interaction between photons and matter, hydrodynamic instability and nuclear fusion. Using numerical simulation, experiments conducted on plasma produced by lasers constitute stringent tests of the models describing their properties.

Stellar and laboratory plasmas

The internal dynamics of stars right to the solar core, revealed using seismologyThe SoHO satellite will continue its observations of

the Sun until the end of the decade, having already given rise to the publication of more than 2500 articles. Following a static study of the solar core through its "acoustic" vibration modes, which had an impact on the calculation of solar neutrino fl uxes, the GOLF instrument has been used to research "gravity" modes that convey totally new information: rotation in the nuclear region

and the infl uence of deep magnetic fi elds. Two pieces of research have been published by the SAp team, one on potential gravity modes formed from individual peaks leaving a certain amount of ambiguity about the identifi cation of their components, and the other on the detection to more than four standard deviations of the signature of gravity dipole modes in a frequency range very sensitive to the nature of the solar core (Figure 1). This long-awaited discovery seems to show that the solar nuclear core is rotating 3 to 5 times faster than the rest of the star, a vestige of its original state.This important result, at the limit of the capabilities of So-

HO's instruments, is encouraging the development of a new generation of instruments dedicated to this type of study. The GOLF-NG technological prototype is currently being produced and tested at DAPNIA and will constitute the ultimate probe for the magnetic fi eld of the solar radiative zone. It is designed to be able to measure speeds of less than 1 mm/s in the sun's atmosphere (Figure 2). This and other instruments of measurement are being proposed for a future ESA mission known as DynaMICCS, targeting interaction between the Sun and the Earth.Alongside this work, signifi cant modelling activity is being used to gain a better understanding of the observations and to prepare those from the COROT astro-seismology satellite launched from Baikonur in December 2006. The objective of this modelling program is to introduce dynamic processes into all the stellar plasmas to discover the missing links between the formation of stellar

systems and the explosion of supernovae.Figure 1. Signature of the presence of gravity dipole modes in data collected over more than 3000 days by the GOLF space instrument onboard SoHO.

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Magnetohydrodynamic processes simulated on large computers3D simulation of the internal dynamics of stellar plasmas

is a new activity for DAPNIA. Following the discovery of the fundamental role of the "tachocline" region, which delimits the solar radiative and convective zones with sharp horizontal shearings, the solar dynamo was studied in 2D and 3D. Other work has covered the radiative zone, looking at the deep magnetism potentially present in this region and its infl uence on the tachocline. A non-linear 3D calculation (Figure 4) confi rms the existence of non-axisymmetrical instabilities in the poloidal fi eld and of instabilities in the toroïde structures formed through the Ω effect, which were anticipated theoretically. This deep magnetism may have important consequences for the structure and internal composition of the Sun.

Laboratory plasmasLaboratory astrophysics relies on the production using

lasers of plasmas typical of those found inside stars or in the interstellar environment. The Service d’Astrophysique is engaged in performing and interpreting experiments to study the dynamics of radiative shocks and jets (v > 100 km/s)and determining the opacity of solar plasma. An understanding of the dynamics of interaction between radiation and matter in dense and hot plasmas is essential for the design, dimensioning and interpretation of high-fl ux laser experiments. The development of a radiation hydrodynamic code, HERACLES, has meant that it is possible to simulate astrophysical and experimental situations. The work of the Laser & Plasmas Institute (ILP) has highlighted the needs shared by the scientifi c communities in astrophysics and laser inertial fusion. The SINERGHY project is responding

to these needs with the development of t h ree - d im ens iona l h y d r o d y n a m i c s , massively parallel algorithms, the mana-gement and display of large quantities of data and fi nally, the creation of a shared library of transport coeffi cients, equations of state, and rates of nuclear and chemical reactions

Figure 2. The GOLF-NG prototype being tested at the premises of Sédi.

Figure 4. 3D simulation of a portion of the solar radiative zone showing the diffusion of the magnetic fi eld and how the rotation of the zone changes over time.

Figure 3. Photo of a GOLF-NG cell, instrumented by the SIS. The cell is fi lled with sodium vapour and is used to calibrate variations of Doppler speed of the displacements of Sun’s atmospheric layers. The great accuracy measurement (10-7) of those variations will allow probing the dynamics of the solar core.


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Compact objects and their environment

Compact objects (black holes, neutron stars and white dwarfs) play a major role in modern astrophysics. They are associated with the most exotic environments and violent

phenomena of the Universe. Surrounded by extremely powerful gravitational and magnetic fi elds, they appear as luminous X-ray or gamma-ray sources, thus allowing scientists to explore certain physical processes under conditions that cannot be obtained in laboratories.

Astrophysicists involved in the study of compact objects focus on a number of key issues: the validity of the theory of gravitation in strong fi elds, the physical phenomena associa-ted to the accretion of matter and to the emission of relativistic jets, the nature of particle acceleration in extreme magnetic fi elds, nucleosynthesis processes of supernovae, the forma-tion and evolution of black holes.The high energy observation programmes of compact objects carried out over the last years yielded many important results. In particular, the DAPNIA contributed to the construction and scientifi c operation of XMM-Newton (in the X-ray range between 0.1 and 10 keV), INTEGRAL (X and γ-rays from 3 keV to 10 MeV), and HESS (very high-energy gamma rays from 100 GeV to 10 TeV). This research has also benefi ted from several coordinated multiwavelength observation programmes, from the radio wave to the ultraviolet (UV) domains.

The supermassive black hole at the galactic centre

One of DAPNIA's most important scientifi c programmes concerns the study of the super-massive black hole at the centre of our Galaxy and the exploration of the high-energy phenomena occurring in its vicinity. Identifi ed with the compact radio source Sgr A*, this black hole of about 3 million solar masses is the nearest and most extensively studied of all the massive black holes in the galactic nuclei.

Two Sgr A* X-ray fl ares, originating close to the black ho-le’s horizon, were discovered and closely studied as a result of a vast campaign of simultaneous observations performed

in 2004, in X-rays with XMM and in γ-rays with INTEGRAL. One of the bursts was also observed at infrared frequencies (IR) by the Hubble Space Telescope (HST), making it possi-ble to place strong constraints on the emission mechanisms. In addition, a quasi-periodicity of about 22 minutes was de-tected in the longest X-ray fl are. This phenomenon could be related to a periodic modulation at the last stable orbit of an accretion disc around a rotating black hole. In this case, the measured period allows one to obtain, for the fi rst time, an estimate of the black hole spin.

Using all 2003-2004 INTEGRAL data on the Galactic Center, DAPNIA research teams succeeded in making the most comprehensive and accurate γ-ray map ever made of this complex region of the Galaxy (Fig. 1), and discovered a central source (IGR J17456-2901) well located at the position of the black hole.This source does not exhibit temporal variation and cannot be identifi ed with Sgr A*, nor with any of the other objects of this complex region, but it could be related to the TeV γ source de-tected at the centre of the Galaxy by HESS in 2004 (Fig. 2). This source also coincides with Sgr A* but cannot be clearly identifi ed either. Its spectrum is not compatible with that ex-pected from the decay of dark matter, and it rather reveals the presence of very high-energy particle acceleration.More broadly, the study of gamma emission from the galactic bulge and disc using INTEGRAL has provided a detailed map and spectrum of the mysterious diffuse emission at 511 keV, the electron-positron annihilation line, and led to the detection of the gamma-ray lines of the 26Al and 60Fe radionuclides, which testify the nucleosynthesis carried out by the supernovae in the Galaxy. INTEGRAL has also solved the mystery of the diffuse galactic emission in the 20-200 keV band, resolving a good fraction of it as point like

Figure 1. View of the Galactic centre region at low-energy gamma rays, as seen from the INTEGRAL observatory. The image inclu-des several accreting X-ray binary systems (the brightest of which is the black hole microquasar 1E 1740.7-2942) and the central source at the position of the supermassive black hole, Sgr A*.

Figure 2. The Galactic centre region at very high-energy gamma rays, as seen from the HESS observatory. The bright central source coincides with the supermassive black hole of the Galaxy.

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sources, most of which are made up of binary systems with an accreting compact object.

Stellar black holes and microquasarsAccreting black holes of stellar mass (roughly between

2 and 50 times the solar mass) in close binary systems are the most intense sources of low-energy gamma rays (Fig. 1) and are often observed beyond 300 keV. In these systems, the black hole captures matter from the companion star which, as it accretes, provides the energy to feed – via a disc or a hot corona – the X-ray and γ -ray emission and sometimes (in microquasars) a radio jet of relativistic particles. Black hole X-ray binary systems are INTEGRAL's priority targets. They are studied to model the accretion disc, the hot corona and the jet, as well as their mutual interactions. One of the outstanding results of DAPNIA's research efforts in this area was the detection of a high-energy component in the X-ray/γ -ray spectrum of Cygnus X-1, the prototype of black hole binary systems. This component cannot be explai-ned by the hot plasma corona and points to the presence of relativistic non-thermal electrons (i.e. electrons with an energy distribution different from that describing a gas of particles in thermal equilibrium).INTEGRAL observations and associated multiwavelength observational campaigns have also been performed for a certain number of transient or highly variable binary sources (such as the galactic black hole GRS 1915+105, which was the fi rst microquasar to show apparent superluminal – or faster-than-light – motion) in which the accretion rate varies signifi cantly during the main outbursts. This made it possible to study the behaviour and the interplay between the disc, the hot corona and the jet, as the sources evolved in different spectral states.All these results have contributed to the development of the hydro-magnetic instability model (also known as accretion-ejection model) of the disc around black holes, which SAp researchers have proposed. The model, which also explains how the accretion disc releases energy towards the hot corona, and ultimately feeds the jet, was improved, compared with data from various sources, and then successfully applied also to Sgr A* fl ares. The in-depth study performed at the SAp on another type of instability, known as the advective-acoustic instability, has shown why gas accretion on a black hole at supersonic speed is necessarily non-stationary. This instability is the cause of asymmetry in gravitational supernova explosions and can explain the mixing of elements during the explosion, the abnormal velocity distribution and the pulsar spin, and even a new supernova explosion mechanism based on acoustic energy.

Neutron stars in binary systems or isolatedUnlike black holes, neutron stars have their own magnetic

fi eld, which can be extremely powerful. In this case, the emission is characterised by a coherent pulsation (caused by the radiation cone generated at the magnetic poles of the star crossing the line of sight at each rotation): this is what is known as a pulsar. DAPNIA's astrophysicists have studied several pulsars in X-ray binary systems, where the accretion fl ow is dominated by the magnetic fi eld (Fig. 3).

The most signifi cant results in this fi eld have been obtained for "millisecond" binary pulsars, which provide a link between the neutron stars in binary systems and isolated neutron stars. Three of these objects were detected and studied for the

fi rst time in the hard X-ray range (energy greater than 10-20 keV) with INTEGRAL, and a decrease in the rotation period was discovered in one of these systems. This strengthens the hypothesis whereby fast-spinning isolated pulsars are "cannibals" neutron stars, formerly in a binary system, that have completely devoured their companion star.DAPNIA's research teams also work on the X- and γ -ray emis-sions from magnetars, including ‘soft gamma-ray repeaters’ and ‘anomalous X-ray pulsars’. These neutron stars are powe-red by their extremely intense magnetic fi elds (∼1015 G) rather than by accretion of matter. INTEGRAL detection of persistent hard X-ray emission from these classes of objects was a surprise and opens the door to a wealth of important theoretical development in neutron star modelling.

Future programmesThe DAPNIA continues its research programmes on compact

objects (with XMM, INTEGRAL and HESS) and prepares the exploitation of future γ -ray data from HESS2 (extension of HESS, scheduled for 2008) and from the space mission GLAST (10 MeV – 100 GeV, to be launched in 2007). The DAPNIA is involved in both these telescope projects, developing electronics for the fi rst and contributing to the data analysis system for the second.Looking further ahead, DAPNIA is working on the development of two new high-energy space missions planned for the period 2011-2014. The SVOM/ECLAIRs mission was approved for phase A study as part of a French-Chinese bilateral agreement. This mission is dedicated to the study of gamma-ray bursts, a domain that will also benefi t from the laboratory's participation to the UV-visible-IR X-SHOOTER spectrograph project, an instru-ment to be installed at the ESO's VLT in 2008.The SIMBOL-X programme, the fi rst telescope capable of focu-sing hard X-rays (> 10 keV) through the use of multi-layer X-ray mirrors and the operation of two satellites in formation fl ying, is also in Phase A study, as part of a French-Italian mission. SIM-BOL-X main scientifi c objectives are the physics of compact ob-jects and particle acceleration processes in the Universe

Figure 3. Artist's view of an X-ray pulsar in a close binary system like the INTEGRAL source IGR J0029+5934. (Credit: NASA/Dana Berry)


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Cosmic ray sources

Studying galactic cosmic rays was one of the original choice topics in CEA’s Service d’Astrophysique (SAp). Far from being resolved, the origin of cosmic rays raises

topical questions about the energy source capable of sustaining this population, about the acceleration mechanism at work, about the maximum energy and spectral form given to particles by this mechanism and fi nally about the required number of different accelerator types. Is it possible to reproduce the observations using a single type of energy source and acceleration mechanism? What fraction of the cosmic ray spectrum is of extragalactic origin?

Observational efforts are concentrated on searching, in potential sources of galactic cosmic rays, for the signatures of the particles (notably electrons, protons) that have been accelerated to the highest energies. Observing in X rays and γ rays is crucial to the study of accelerated particles with energies of up to 3·1015 eV. This range characterizes the following: synchrotron emission from ultra-relativistic electrons, inverse Compton scattering of these electrons in the ambient photon fi eld and γ ray emission with neutral pion decay as accelerated protons interact with protons from the interstellar medium. This last process produces an amount of neutrinos comparable to (or, in the event of γ absorption at the source, superior to) the number of γ rays. Key science results were obtained at DAPNIA using the XMM-Newton and INTEGRAL satellites, and the HESS telescope. The Antares project, initiated at DAPNIA/SPP, has taken a fi rst step towards detecting high-energy cosmic neutrinos with the successful installation and operation of 5 photodetector lines at the bottom of the Mediterranean Sea.From a modelling perspective, only the diffusive shock acceleration theory has been suffi ciently developed to be used for quantitative calculations and to account for a large number of observational constraints. Since these models have reached a certain maturity, they can now be used to assess the physical parameters of acceleration by comparing them to observations of supernova remnants. However, other available models will be compared with γ ray observations and neutrinos.

Acceleration in supernova remnants: observations, modelling and simulationsA major breakthrough in γ ray astronomy was achieved

using HESS to map the supernova remnant G347.3-0.5 in the TeV range, followed by a second remnant, Vela Junior. This produced the fi rst images at these energies using the stereoscopic system in HESS telescopes. These observations (Figure 1), along with those obtained in X-rays using the XMM-Newton satellite, made it possible to map the regions where particles are accelerated to energies in the range of 100 TeV and to characterise their spectrum. In soft γ rays, INTEGRAL was used to observe emission from Cas A - the youngest supernova remnant in our galaxy - that reached up to 100 keV (Figure 2). The presence of two radioactive decay lines implies that the 44Ti mass synthesized by the

supernova is much higher than predicted by spherically symmetric supernova nucleosynthesis models. The nature of the continuum emission - up to 100 keV - remains undetermined. In terms of producing neutrinos, supernova remnants are the most promising sources (particularly G347.3-0.5, Vela junior), as well as the galactic centre or microquasars (such as LS5039), etc. However, the neutrino fl uxes predicted by the calculations are too weak for these sources to be detected by Antares. If the observations do not completely disprove the predictions, the successor to Antares - a telescope larger than one km3 - will look for these precious fl uxes over the coming years.

Numerous observations of young supernova remnants using the XMM-Newton and Chandra satellites have shown that the emission at the shock is of synchrotron origin. Its

fi lament-like morphology is explained by signifi cant radiative synchrotron losses on TeV-accelerated electrons and induces a strongly amplifi ed magnetic fi eld at the shock. Moreover, the morphology of the thermal X-ray emission from young supernova remnants can only be explained by signifi cant back-reaction of cosmic rays on the shock structure. These results are in line with models of cosmic-ray modifi ed hydrodynamics, developed from the start of the new millennium by DAPNIA researchers. Only these models can consistently calculate both thermal and non thermal (synchrotron) emission, and they have also been integrated in a numeric hydrodynamic code. Furthermore, it has been proven that as the ejecta expand magnetic fi eld weakens and prevents any effi cient acceleration in the internal shock (that propagates through the ejecta). This is consistent with the observed high temperature of shocked ejecta that is not compatible with effi cient acceleration.

Figure 1. The supernova G347.3-0.5 (or RX J1713-3946), displayed in X-rays by XMM-Newton (on the left), and in γ rays by HESS (on the right).

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Acceleration in pulsar wind nebulae: observations and modellingObservations in X-rays and γ rays of pulsar wind nebulae

are highly complementary and provide key information to understand electron acceleration in the vicinity of pulsars. X-ray emission comes from ultra-relativistic electrons with TeV energies spiralling in the nebula magnetic fi eld, while the very high-energy γ rays are more likely to come from the inverse Compton scattering of these relativistic electrons on low-energy ambient photons.To date, the Crab nebula was the only known case of very high-energy γ ray emission in a nebula where the energy is provided by a young neutron star. HESS discovered several nebulae of this type, opening a new window through which this population of sources can be observed. The fi rst spatially resolved γ ray spectral studies revealed a softening of the spectrum towards the edges of the nebula. This effect has already been observed in the X-ray range with XMM-Newton and is a result of the cooling of ultra-relativistic electrons in the nebula. Observations of one of these nebulae with the INTEGRAL satellite up to 100 keV made it possible to estimate the maximum energy reached by electrons at between 400-700 TeV.

Cosmic rays interacting with dense matter in our GalaxyExtragalactic sources such as active galactic

nuclei emit high-energy γ rays. Since extragalactic radiation in the TeV range can be absorbed by interaction with infrared photons, the constraints concerning the neutrino fl ux are less strict. The detection (or not) of galactic and extragalactic sources and their neutrino spectrum are used to constrain the relative contributions (hadronic and leptonic) of the acceleration mechanisms at work and to interpret the spectrum of high-energy cosmic rays (knee, ankle, etc.). If we use a phenomenological prediction extrapolated from very high-energy cosmic rays, the predicted fl ux is too weak for Antares but will be easily detectable by the km3 detector.

Future instrumentationExtragalactic sources such as active galactic nuclei emit

high-energy γ rays. Since extragalactic radiation in the TeV range can be absorbed by interaction with infrared photons, the constraints concerning the neutrino fl ux are less strict. The detection (or not) of galactic and extragalactic sources and their neutrino spectrum are used to constrain the relative contributions (hadronic and leptonic) of the acceleration mechanisms at work and to interpret the spectrum of high-energy cosmic rays (knee, ankle, etc.). If we use a phenomenological prediction extrapolated from very high-energy cosmic rays, the predicted fl ux is too weak for Antares but will be easily detectable by the km3 detector.

Future instrumentationFor the detection of neutrinos, Antares will be comprised

of 12 lines some 450 m high, anchored at a depth of 2,475 meters, containing a total of 900 photomultipliers and covering 30,000 m² off the coast of La Seyne-sur-Mer. Since April 2005, 5 lines have been deployed and successfully connected, providing data found (Figure 3). Complete implementation shall be fi nished at the beginning of 2008. Design work for a detector of over a km3 is already in progress.The study of cosmic ray sources is continuing with an approach

combining the modelling and the successful use of data from XMM-Newton, INTEGRAL and HESS. Physicists have high expectations for the department’s future expe-riments. Firstly the GLAST satellite, whose launch is planned for the end of 2007, will be used to better identify γ rays produced by the interaction of accelerated protons with those in the interstellar medium. Then HESS2 will cover the energy range between HESS and GLAST. In the longer-term, the new SIMBOL-X experiment will make it possible to tackle the physics of particle acceleration in the Universe

Figure 2. Soft γ ray spectrum in energy from Cas A supernova remnant obtained by INTEGRAL/ISGRI, showing 44Ti decay lines and high-energy continuum emission.

Figure 3. Visualizing the trajectory of an upward muon produced by a neutrino, detected by the fi ve fi rst Antares lines.

Nuclear matter in extreme states

41

These pages deal with extremes of both excitation

energy and density (in the quark-gluon plasma) and isospin (for exotic nuclei).

Early in the Big Bang, when temperature and pressure conditions were too high for hadronic matter to exist, all matter was in the quark-gluon plasma state. Evidence for this scenario will be searched for in the PHENIX experiment at Brookhaven and in ALICE at the LHC.

Following studies of highly unstable nuclei new phenomena

have been discovered, such as evidence for new magic shells, showing the limits of models based on stable nuclei. The new physics opened up by these studies motivates the strong involvement of DAPNIA in accelerator projects for radioactive beams like SPIRAL2, thus continuing the progress already made with SPIRAL.

Nicolas Alamanos


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Quark-gluon plasma

Central collisions between heavy nuclei accelerated to ultrarelativistic energies are an ideal tool for investigating the behaviour of nuclear matter under extreme temperature

and density conditions. The phase transition between ordinary nuclear matter and a new state referred to as quark-gluon plasma is predicted by the fundamental theory of strong interaction. Its existence is actively sought using high-energy accelerators in Europe and the USA. DAPNIA is currently participating in two related experiments: PHENIX (BNL, USA) and ALICE (CERN, Geneva).

Quark-gluon plasmaThe goal is to study the phase transition towards a

new state of matter, referred to as quark-gluon plasma, at energies ranging from approximately 100 GeV to 10 TeV in the centre of mass of the nucleon-nucleon system (√sNN). This state is predicted by quantum chromodynamics (strong interaction theory) at temperatures beyond approximately 170 MeV, based on numerical lattice calculations. In this state, quarks and gluons are no longer confi ned to objects in a quantum colour neutral state (hadrons), and can move freely over large distances. According to cosmological theory, the Universe went through this phase transition when it was a few microseconds old. In laboratory experiments, only frontal collisions between heavy nuclei can form samples of nuclear matter subject to such conditions. The temperatures and pressures achieved are far beyond those present in atomic nuclei and could be close to those inside astrophysical objects such as neutron stars. Despite the extremely brief duration of these collisions, the reduced dimensions of the samples (approximately 400 nucleons) and the fact that detectors only observe the fi nal state, there are good theoretical reasons to believe that it is possible to study the successive states undergone by these samples, or at least their hottest and densest state. Given the strong interaction between the nucleons, only few collisions are required for the system to achieve a state close to thermodynamic equilibrium. Among the parameters that can be measured in the fi nal state, theoreticians and experimentalists seek to identify 'robust' variables preserving a record of the hottest and densest state.DAPNIA is engaged in the PHENIX experiment (at Brookhaven National Laboratory, USA) using the RHIC collider at √sNN = 200 GeV, and the ALICE experiment (at CERN, Geneva) using the forthcoming LHC collider at √sNN = 5,5 TeV. The fi rst of these experiments has identifi ed the plasma, and the second will allow a detailed study.In both experiments, DAPNIA physicists concentrate on measuring the production of 'resonant' particles composed of a quark-antiquark pair, charm for J/ψ family or beauty for ϒ family. If a quark-gluon plasma is formed, the produc-tion of these particles should be suppressed, since in such dense and 'coloured' media, quark-antiquark interactions are screened by surrounding colour charges and become insuffi cient to form bound states. This suppression was pre-dicted in 1986, and results tending to confi rm this predic-tion have already been obtained in CERN experiments at

√sNN = 17 GeV. These resonances are studied through their decay into a muon pair with opposite electrical charge, detected in wire chambers with segmented cathode pads, located on each side or inside a magnetic dipole.

PHENIX experimentThe fi rst results concerning J/ψ production were obtained

in proton-proton and deuteron-gold collisions, considered as essential reference systems for evaluating the expected suppression in gold-gold collisions. This data enabled the study of cold nuclear phenomena in the absence of plasma processes.The analysis of the fi rst signifi cant data on J/ψ production in gold-gold collisions (for which DAPNIA played a key role) has been recently published. Figure 1 shows the nu-clear modifi cation factor (RAA), which compares J/ψ pro-duction in gold-gold and proton-proton collisions. In other words, if J/ψ production is the same in both collisions, we will observe a constant ratio equal to 1. The data obtained show signifi cant suppression as a function of the number of participants, far beyond that corresponding to cold nuclear

Figure 1. Evolution of the nuclear modifi cation factor as a func-tion of collision centrality (parameter indicating the number of participating nucleons). Two sets of data selected in terms of rapidity (y) are compared with the trends expected in the absence of plasma (adjusted to best fi t the deuterium-gold data).42

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effects. The observed suppression is therefore indicative of abnormal behaviour probably due to the formation of a very dense state compatible with a quark-gluon plasma. These recent results are currently being compared with theoretical models.

ALICE experimentFor the past 10 years, DAPNIA has worked on the

design and development of the large pad chambers for the ALICE muon spectrometer (Figure 2). Given their signifi cant dimensions (up to 6 m in height), a modular design was adopted for the three largest stations. After an initial R&D phase leading to the fi nal design of the detectors, DAPNIA devoted two years to the production of the chambers, which began in 2003. During this key phase, DAPNIA engineers and physicists participated in the development of procedures describing all production steps. These procedures were then applied in the four partner laboratories involved in the construction. A total of forty chambers were produced and subsequently qualifi ed at Saclay.DAPNIA took in charge the construction of the supporting structures for the detection components of the trajectogra-phy chambers. These structures consist of large honeycomb panels (approximately 6 x 3 m2 for the largest ones) with carbon fi bre skins to ensure good rigidity and low thermal expansion. Pulsed-air cooling simulations (conducted by DAPNIA) have been successfully completed. DAPNIA is also responsible for the integration of the large chambers (stations 3, 4 and 5). The detectors are currently being installed in the ALICE pit at CERN (Figure 3). After

a systematic testing phase, the detectors received from the various partner laboratories are mounted on the supporting structures, cabled, and installed in their fi nal location. The on-site commissioning phase has already begun and will continue until the start of the experiment.DAPNIA has also participated in the software development, particularly for the alignment and electronics calibration. These two aspects are essential for achieving the 100-mi-crometer spatial resolution required to separate the diffe-rent resonances, particularly those of the ϒ family. Analysis methods are currently being tested in the computation grid.DAPNIA teams also participate in the physics working

groups and in the defi nition and implementation of the ana-lysis programmes to be used at the start of the experiment. Given the low luminosity expected at the beginning, J/ψ physics will be given initial priority, followed by ϒ physics. After the production of the fi rst proton beams at the begin-ning of the experiment, the fi rst lead-lead collisions should follow a year later

Figure 3. Pad chamber installed at CERN. (© Antonio Saba, www.antoniosaba.com)

Figure 2. Exploded view of the ALICE experiment. The trac-king chambers of the 'muon arm' are shown in blue.

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Exotic nuclei

The atomic nucleus is a many-body quantum system of strongly interacting particles, the protons and neutrons. As a complete description of this system from fi rst principles is not

possible, mean-fi eld and shell models are used to describe the nuclear structure. Advances come from a constant interplay between nuclear structure theory and experiments that test the models under extreme conditions, such as extreme ratios between protons and neutrons, extreme mass, spin, or deformation. The nuclear physicists of Dapnia use radioactive beams delivered by the SPIRAL facility at GANIL to study exotic nuclei under extreme conditions and thereby test the validity and limitations of the nuclear models. These studies are complemented by experiments at other facilities like the Legnaro National Laboratory (Italy) or the University of Jyväskylä (Finland). An important aspect of this work is the development of new detectors and other instruments that make these experiments possible. Many of the experiments performed in the last three years lead the way into the future, which holds exciting new opportunities with the construction of the next-generation radioactive beam facility SPIRAL2.

Light exotic nucleiThe binding and excitation energies of light weakly-bound

nuclei are crucial benchmarks for microscopic nuclear models. The drip-line nucleus 8He has the highest N/Z ratio amongst all known bound nuclei, and its spectroscopy can help to clarify the isospin dependence in microscopic calculations. In an experiment using the 8He beam from SPIRAL and the particle telescopes of the Must array, the structure of 8He and resonances in unbound 7He were investigated. While the expected neutron-skin structure of 8He was confi rmed, the observation of a very low-lying resonance in 7He represents a challenge for most theoretical models. The analysis in the coupled reaction channel framework revealed that the inclusion of the neutron pick-up channel leading to 7He has a profound infl uence on the elastic proton scattering. The result showed that this general coupling effect is important to understand the spectroscopic information for exotic nuclei.

Evolution of the shell structureThe stability of nuclei depends strongly on their shell

structure, and the occurrence of large gaps between the levels is responsible for enhanced stability at the so-called magic numbers. It has become evident that shell and sub-shell closures in nuclei far from stability may differ signifi cantly from those of stable nuclei, in particular for very neutron-rich nuclei. The experimental evidence of changing shell structures for very neutron-rich nuclei along the N = 8, 20 and 28 isotopic sequences can be explained by the monopole part of the nucleon–nucleon interaction. In an experiment using the 26Ne beam from SPIRAL, a cryogenic deuterium target, and the EXOGAM and VAMOS spectrometers, two excited states were observed below the neutron-separation threshold in 27Ne, showing the lowering of negative-parity states in the chain of N = 17 isotopes with decreasing proton number. This is consistent with the emergence of a new shell closure at N = 16 as the N = 20 closure vanishes for very neutron-rich nuclei. The evolution of the shell structure for N = 16 isotopes was also investigated for the very proton-rich nucleus 36Ca, produced with the double-fragmentation technique at

GANIL. The measured excitation energy of the fi rst 2+ state is almost 10 % lower than in the mirror nucleus 36S, for which the role of protons and neutrons is interchanged. The result gives insight into the nature of the state and the role of the tensor interaction.

Shape coexistenceThe shape of an atomic nucleus is governed by a delicate

interplay of the macroscopic liquid-drop properties of nuclear matter and microscopic shell effects. In nuclei with partially fi lled shells the valence nucleons tend to polarize the nucleus towards a non-spherical, deformed mass distribution, thereby minimizing the energy of the system. The quadrupole deformation is the most important deviation from spherical shape, and the charge distribution of the protons in the nucleus is described by the electric quadrupole moment. Since the nucleons can occupy different orbitals polarizing the nucleus in different ways, various shapes can coexist in the same nucleus. Elongated (prolate) and fl attened (oblate) shapes have been predicted to coexist in the light krypton isotopes. The nuclides 74Kr and 76Kr have been studied in Coulomb excitation experiments with radioactive beams from SPIRAL and the EXOGAM spectrometer. Electric quadrupole moments were measured for the fi rst time for radioactive nuclei in short-lived excited states in these experiments, and the fi nding of opposite signs for the quadrupole moments directly confi rms the coexistence of prolate and oblate shapes. The measurement of the transition strengths between the various states allowed a quantitative analysis of the confi guration mixing in the wave functions, which represents a stringent test of the nuclear structure models. Lifetimes of excited states in 74Kr and 76Kr have been measured at Legnaro, complementing the Coulomb excitation experiments. A new experimental program has been started at GANIL to study the development of deformation and shape coexistence in neutron-rich argon isotopes by Coulomb excitation, which will give also insight into the weakening of the N = 28 shell closure for neutron-rich nuclei. The investigation of the shape coexistence phenomenon in light lead and bismuth isotopes was continued in experiments at Jyväskylä.

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Spectroscopy of transactinidesThe question of the heaviest chemical elements that can exist has been a very fundamental one ever since D.I. Mendeleev fi rst ordered the elements into a periodic system. Nuclei beyond Z = 104 are only bound because shell effects compensate for the Coulomb repulsion. Nuclear models predict the existence of a ‘superheavy’ island of stability corresponding to the shell closure at the next magic

numbers after 82 for protons and 126 for neutrons. Theoretical approaches rely on extrapolations and do not yield consistent predictions. The direct observation of superheavy nuclei is extremely diffi cult because of the tiny production cross sections. An alternative approach is to study in detail the collective and single-particle excitations in the nuclei of the deformed region around Z = 102 and N = 152. Dapnia physicists have played a leading role in experiments at Jyväskylä that found rotational structures for the fi rst time in the odd-proton nuclei 251Md (Z = 101) and 255Lr (Z = 103). In addition to the collective rotational band, excited metastable structures were established in 254No (Z = 102) and identifi ed as two- and four- quasiparticle states. In complementary experiments performed at Jyväskylä and GANIL, the single-particle structure and decay properties of 255Lr, 251Md, and 247Es

(Z = 99) were investigated and the spin and parities of the ground and excited states deduced. These states are highly signifi cant as their location is sensitive to single-particle levels above the shell gap predicted at Z=114, and thus provide a microscopic benchmark for superheavy elements.In another approach, a uranium beam was used to

bombard mono-crystalline nickel and germanium targets to produce by complete fusion systems with Z = 120 and 124, respectively, which then undergo fi ssion. By observing the trajectories of the fi ssion fragments in the crystal lattice, a signifi cant proportion of long fi ssion times (≥10-18 s) has been observed with respect to the fast quasi-fi ssion process (10-21 s). This points to a high fi ssion barrier and hence to an enhanced stability of the superheavy systems.

PerspectivesThe SPIRAL2 project at GANIL offers exciting opportunities for nuclear structure physics. The Dapnia physicists are strongly involved in defi ning the physics program and in building equipment for SPIRAL2. The new facility will deliver

exotic radioactive and stable beams with unprecedented intensities. Major advances are expected for studies using direct reactions to investigate the structure of exotic nuclei, for studies of nuclear shapes and high-spin states using gamma-ray spectroscopy, and for the exploration of the heaviest elements. The Dapnia is a major contributor to the construction of large new instruments like for example the Super Separator Spectrometer S3 to make the best use of the high–intensity stable beams from the driver accelerator of SPIRAL2. Other instruments are being constructed which will be available already on a shorter time scale. These include the MUST2 telescopes for light charged particles and a new detector array for the focal plane of the VAMOS spectrometer (MUSETT). Both detectors use a highly integrated micro-electronics developed at Dapnia.The Dapnia is an important partner in the AGATA collaboration and contributes to various aspects of the construction of this next-generation gamma-ray spectrometer. The project has entered a crucial phase with the commissioning and fi rst exploitation of a sub-array, the so-called AGATA-Demonstrator, at the end of 2008, in Legnaro

Figure 1. Excitation spectra of 251Md, obtained at the University of Jyväskylä. The γ-ray transitions shown in the upper part of the fi gure are in mutual coincidence. Their regular energy spacing is characteristic of a deformed rotating nucleus

Figure 2. Photo du dispositif Must2 monté pour une expérience au Ganil.

Figure 3. The fi rst AGATA triplet of highly segmented germanium detectors, on a test bench.

Innovation for detection systems

47

For years, developments of new detectors have contributed to

new discoveries, sources of upheavals in sciences and technologies.

Generally the invention results from a specific physics problem, rather than from a concern of technological development. For particle detection, the way from cloud chambers to multiwire proportional counters is paved with inventions carrying physics discoveries.

The recent discovery of Micromegas detector and its development are at the origin of numerous applications in physics and already become promising in the biomedical

domain.The detector is at the heart of the

experimental device, but associated electronics as well as sophisticated acquisition, large volume data storage and analysis are essential components to cope with high event rates.

DAPNIA excels in these fields and acquired, thanks to its detectors and their equipment, a worldwide reputation.

Ioannis Giomataris

Dapnia 2004 - 2006In

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Development of detectors

As the construction of the large-scale instruments for the LHC reaches its fi nal phase, DAPNIA is already preparing for the future with an ambitious program of research

and development, both for the future linear collider and for the next observation satellites or underground experiments searching for dark matter.

MicromegasThe versatility of the Micromegas gas detector suggests

there is scope for its development for experiments and applications in a wide variety of fi elds. The stability and robustness of this detector, the work done to reduce background noise (use of materials with low radioactivity, reduction of the detection threshold), and the excellent energy resolution for low energy X-rays, have enabled it to make a sizeable contribution, for example, to the CAST solar axion research experiment.Neutron and photon detection is made possible by the addition of an entry window conversion material. This change may mean that the detector needs to be sealed for working in hostile environments. This is the case with the Piccolo project, a neutron detector designed for installation in the core of a hybrid reactor, which can operate at high temperatures, and also with the photo-detector project, for which very strict conditions of cleanliness are required.A new manufacturing process known as "Micromegas bulk" has been developed and promises new applications

because of the ease of producing large surface areas and varied geometries (cylindrical, for example). DAPNIA has chosen to use this technique for producing the readout planes of the three TPCs (Time Projection Chambers) in the T2K experiment, which will each consist of 12 large-scale detectors (34x36 cm2) tiled to reduce the dead zones. As part of the development of a large TPC for the ILC (International Linear Collider), a resistive coating applied to the 2.3 mm-wide detection pads has made it possible to achieve a spatial resolution of 50 μm (collaboration with the University of Carleton, Ottawa).For Super-KABES (NA48 experiment, CERN), by reducing the amplifi cation space to 25 μm, the plan is to reduce the signal rise time to 5 ns to allow operation at 20 MHz on a given strip.

Finally, Micromegas has been coupled with a MEDIPIX2/TIMEPIX chip (in collaboration with CERN in Geneva and Nikhef in Amsterdam), opening the way for very fi ne 3D granularity. Along the same lines, the fi rst tests of a Micromegas integrated on to a silicon wafer (InGrid) look very promising.

MAPS (Monolithic Active Pixel Sensors)The ambitious physics program for the future ILC (planned

for 2015) demands a long and complex program of preliminary R&D to enable the detector associated with the collider to achieve the planned precision. The proposed vertex detector is designed to signal the presence of heavy quarks (charm and beauty) through the existence of secondary vertices a few millimetres at most from the primary vertex of the collision. This detector has to have a measurement precision smaller than 2 μm at each point to be able to separate charm and beauty suffi ciently clearly to measure with precision the branching ratios, in the decay of the Higgs boson, into quark-antiquark b-b and c-c pairs.SEDI is involved with the IPHC in Strasbourg in the study and prototyping of a vertex detector constructed using very fast MAPS based on CMOS technologies.The vertex detectors required for the study of heavy quarks must meet the following specifi cation:

• 5 cylindrical layers of pixels (r = 15 mm to 60 mm), i.e. approximately 800 million pixels;

• Signal reading time: 20 μs for the fi rst layer, 50-100 μs for the next layers, with a spatial resolution of less than 2 μm;

• The thickness of the sensor and CMOS must be

Figure 1. The Piccolo detector.

Figure 2. Readout plane of the T2K TPC.

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approximately 50 μm maximum and the total quantity of material must not exceed a thousandth of a radiation length per layer;

• Resistance to radiation must be suffi cient to withstand 500 kilorads and 5·1010 neutrons/cm² in 5 years.

At present, only the MAPS-CMOS detectors appear to have the potential to achieve the required performance (the CMOS have the advantages of the CCDs while being much faster and more resistant to radiation).The fi rst detection of charged particles with MAPS was performed in Strasbourg in 1999. The fi rst fast digitization was successfully performed by the prototype of the DAPNIA HiMAPS-1 (MIMOSA-8) in 2005, with a reading speed of 20 μs at 100 MHz for a matrix of 128x32 pixels.

CdTe detectorsWork is being done on cadmium telluride (CdTe) detectors

in a research project that is a legacy of the development of the INTEGRAL/ISGRI instrument.The aim is to improve the performance of X-ray and gamma-ray spectral imagers. To do this, the teams at DAPNIA have used matrices of CdTe detectors with segmented electrodes (pixels of 0.5 to 1 mm), their associated low-noise ASIC electronics (IDEF-X) and hybridization techniques, to form elementary detection modules that will be the future building blocks of large-scale space cameras (of the order of 100 cm2).The 2004-2006 period was devoted to developing three versions of the IDEF-X multichannel electronics (16 to 32 channels). At the same time, detector test-benches were set up (for measuring ultra-low currents and spectrometer performance) and 3D modelling of pixel detectors was

undertaken. These combined efforts meant that elementary modules of 64 and 256 channels could be produced, using the manufacturing facilities of the company 3D-Plus. These developments are now an integral part of the ECLAIRs and SIMBOL-X space missions. The application of this work to efforts to combat the NRBC threat is currently under way.

BolometryThe PACS projectThe HERSCHEL satellite will be launched by ARIANE-V

during 2008. With its 3.5 m mirror cooled to 80 K, it will open up new windows for the observation of the Universe well beyond far infrared. These spectrum bands, hidden by the Earth's atmosphere in ground-based observations, are essential for understanding among other things the mechanisms of galaxy and star formation. The project to develop large matrices of bolometers completely covering the focal plane of a telescope emerged in 1997 following results produced at shorter wavelengths by the ISO satellite. DAPNIA, with LETI, then proposed a new focal plane concept, which has been widely taken up by other groups. This has led to the production for the PACS camera of a set of two focal planes that are highly sensitive (close to background noise), and cover the ranges 60-130 μm (over 2048 pixels) and 130-210 μm (over 512 pixels) respectively. This makes it the largest bolometer camera in operation in the world. For the fi rst time on this type of detector, this camera is using a cold multiplexing system that considerably reduces the number of connections needed between the focal plane and the electronics produced by DAPNIA. To achieve the desired performance, this camera is cooled to 300 mK by a cryorefrigerator supplied by DSM/SBT in Grenoble. These technologies are now being used to produce a camera with a very large focal plane (4 kilopixels) to equip the largest terahertz ground telescopes (12 m) (ArTéMis project, launched in early 2006).

Massive ionization-heat bolometers for EDELWEISS2On the basis of experience acquired in the development of

the cryogenic detectors for EDELWEISS1, SEDI has produced a series of 23 "ionization-heat" bolometers operating at 20 mK, with the constraint of reducing the radioactivity of the detectors and their immediate environment as far as possible. With masses of between 320 and 350 g, these detectors, which simultaneously measure ionization and heat, are the largest currently in operation. These detectors allow for a rejection rate of the order of 1000 for particles produced by residual radioactivity.The new EDELWEISS2 experiment of which this is part, could ultimately lead to the deployment of thirty times more detectors than EDELWEISS1. 2007 should enable the scientifi c potential associated with the production of around 100 detector of this type to be evaluated

Figure 3. ILC vertex detector.

Figure4. Prototype

of the HiMAPS-1

(Mimosa8) chip.


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Signal processing and real time systems

In order to meet experimental physics requirements, DAPNIA maintains a high level of expertise in each link of the acquisition chain, with particular emphasis on microelectronics,

analogical and digital electronics and real time systems.

ASICsAlthough data processing chains are now largely digital,

front-end systems - which convert detector signals into electric quantities - remain analogical. For systems requiring a small number of channels, progress made on off-the-shelf circuits leads to ever faster data processing with increased performance. Increasingly fi ne detector segmentation leads to an increasing number of electronic channels, which itself entails the use of readout microelectronics. In addition to the miniaturization aspect, the use of ASICs (Application-Specifi c Integrated Circuit) reduces the electric power consumption and the price-per-unit of an electric channel. Although they are essentially comprised of analogical functions, today’s modern ASICs are mixed analogical

and digital circuits capable of integrating, for example, sequencers or signal processing functions. Generally-speaking their parameters can be confi gured. ASICs designed at DAPNIA are classifi ed into three main groups: analogical memories, ultra-low noise circuits, ultra-low consumption circuits and MAPS (Monolithic Active Pixel Sensors).DAPNIA has over ten years expertise in the fi eld of analo-gical memories for the high-frequency acquisition of signals with a large dynamic range. SAM, the latest memory designed at DAPNIA, digitizes signals from the HESS-2 experiment at a frequency of one gigahertz and with 12-bit precision. 6,000 copies have been produced so far.The second group contains IDEF-X circuits developed for

CdTe detector-based gamma spectrometry for use in space: the last prototype is designed for the SVOM/ECLAIRs satellite. Acting as a bridge between the fi rst two groups, the AFTER ASIC, developed for the T2K neutrino oscillation experiment, includes 72 preamplifi cation and fi ltering channels and an analogical memory. It is the largest circuit (500,000 transistors) ever to be designed at DAPNIA.

MAPS, part of the third group, connect a detector and its front-end electronics on a single substrate. For the fi rst time, rapid electronics performing highly developed processing tasks have been integrated onto the chips Mimosa 8 and 16 and, as a result, have demonstrated that a MAPS-based trajectograph is feasible for the future colliders. DAPNIA also has considerable expertise in testing and implementing embedded ASICs. New ultra-low noise electronics, based on APV chips designed at the Rutherford Appleton Laboratory, were produced in a very short time-frame to read the 65,000 channels in the RICH detector of the COMPASS experiment.

Using FPGAs for real-time acquisition and processingThe steps that follow the analogical processing of detector

signals are generally performed by digital systems. Today, the production of basic logic functions, data processing and data transfer tasks is essentially based on the use of logic circuits that are programmable in-situ, and on FPGAs (Field Programmable Gate Arrays). Operating these commercial components covers two of DAPNIA’s application fi elds: embedded systems in harsh environments and very high-speed data acquisition systems.As part of the Antares project, 350 acquisition boards composed of a processor and an FPGA as well as 60 Ethernet switching boards have been developed and integrated. All boards produced meet the reliability and quality assurance constraints required for embedded systems. These boards

Figure 1. SAM - multi gigahertz sampler for the HESS-2 experiment. This chip integrates 80,000 transistors on a reduced surface of 11 mm².

Figure 2. Front-end card used to read RICH detector from the COMPASS experiment. Each motherboard (at top) hosts 4 daughterboards (at bottom) integrating an APV chip processing 128 channels.

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constitute the acquisition nodes for the distributed architecture of underwater detectors. Using its experience from the Antares project, DAPNIA is involved in a European underwater detector project KM3Net.

In the fi eld of acquiring and processing data from highly-segmented experimental devices producing a massive data fl ow, the Selective Read-out Processor (SRP) project is implementing 200 very high-speed optical liaisons (1.6 Gbit/s). This system is used to process data from the CMS experiment’s electromagnetic calorimeter in real-time, using highly-developed design boards: FPGA with several million gates, parallel optic readers, dense and complex printed circuits. An important milestone was reached with the functional validation of this system.

Real time systemsAcquisition

The T2K experiment represents a particularly strong commitment from DAPNIA in the fi eld of data acquisition. DAPNIA's area of responsibility covers all electronic elements of Micromegas detectors equipping three Time Projection Chambers (TPC) and representing a total of 120,000 channels. This project relies particularly on DAPNIA expertise in analogical microelectronics and is based on a large skill base in systems architecture, the design of complex analogical and digital boards as well as encompassing the electrical, mechanical and thermal integration of these elements.

So far, the project has seen the installation and development of the acquisition system for the research experiment into dark matter ‘EDELWEISS2’ for an initial phase with 21 bolometers. Principal contributions from DAPNIA are the design and production of the electronics providing the global synchronization of the system, and the grouping of digital data, as well as the development of software providing real-time data acquisition, processing and storage.

Furthermore, DAPNIA is designing and producing the on-line second level trigger system of the HESS-2 experiment. An original development, based on an FPGA battery including a processor, is currently being studied to carry out image processing operations while respecting particularly tight constraints in terms of the processing rate.

Electronics for space systemsDAPNIA is also developing electronic

functions that are crucial for the implementation of innovative detection systems for scientifi c space instrumentation. These detection systems meet the diverse

requirements of the various scientifi c subjects and cover the entire electromagnetic spectrum, from gamma, X, visible and infrared rays to submillimetric waves. Operating such detectors often requires using cryogenic devices and developing the associated electronics.Developments conducted at DAPNIA as part of the HERSCHEL mission are a perfect illustration of these requirements. For example, the SPIRE instrument, an electronic unit including 350 ultra-low noise (a few nV/√Hz) channels and with a large dynamic range (20 bits) was designed in collaboration with the Jet Propulsion Laboratory, responsible for bolometer manufacturing. In the context of the PACS instrument, an analogical electronic system was developed to operate bolometer matrices produced by CEA/LETI. Apart from the 160 analogical processing channels, it includes polarization functions for the detector and the cryogenic system. Temperature measurements (10 μK resolution at 300 mK) were the subject of developments in collaboration with the low temperature department at DSM/DRFMC (Grenoble). To ensure effective communication between this unit and the rest of the instrument, an interface was integrated onto the ESA SpaceWire standard by DAPNIA and distributed in the PACS consortium. The electromagnetic compatibility of these units was validated in DAPNIA before fi nal delivery.Finally, DAPNIA teams are involved in new projects, such as the design and production of the scientifi c processing unit on the ECLAIRs satellite and for the high energy γ -ray camera on the SIMBOL-X satellite

Figure 3. One of the CMS Selective Readout Processor boards.

MATACQ Based on an analogical memory de-veloped in collaboration between IN2P3/LAL and DAPNIA, the MA-TACQ card digitizes analogical si-gnals on a 12 bits dynamic range, at a frequency of 2 GHz. It is manu-factured and sold under license by two industrial partners. One hundred copies of this card are currently used worldwide, mostly in research labo-ratories.


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Intensive computation and simulation

Physics experiments are making an increasing use of electronic data processing. Information technology and numerical techniques have become essential, be it to

operate increasingly complex instruments, to perform simulations for data analysis and the interpretation of physical phenomena, or to share the acquired knowledge. Through its expertise and technological innovations, DAPNIA actively contributes to the development of information technologies for physics applications.

Distributed applications for high-energy physics experimentsDistributed applications (i.e. applications running on

networked computers) are playing an increasing role in DAPNIA's scientifi c activities. The choice of a distributed application may be motivated by multiple needs: execution of data analyses for different sites, sharing of results within the scientifi c community, facilitating software maintenance on centralised servers, and managing massive data fl ows from a large number of detectors.The techniques used at DAPNIA to develop such applications rely on 'open source' products based on the Java language or on middleware (see below) developed by the high-energy physics or astrophysics community. These applications have been used successfully in a large number of experiments.Examples include the light curve and astrophysics image servers for the EROS and XMM experiments, the simulation data access servers for the ODALISC and HORIZON radiation-matter interaction programmes, and the supernova analysis server for the SNLS experiment. Other more recent applications have been developed within the framework of the CERN ATLAS experiment, such as the optical line monitoring server for the muon spectrometer chamber alignment system, and the magnetic fi eld mapping and geometric correction servers for the trajectography systems. Distributed applications allow scientists to forget about software engineering so as to better concentrate on the algorithmic aspects of analysis programmes.

Computational grids for LHC experiments and other fieldsDAPNIA participates in the LCG and EGEE international

computational grid programmes, which are based on the sharing of local, regional, national and international computational resources. These grids are used to process scientifi c data from LHC experiments (LCG project), as well as data from other fi elds of interest, including biomedical data (EGEE project). DAPNIA is actively involved in the GRIF regional research grid project, whose purpose is to federate the activities of research laboratories in the Paris area.

DAPNIA participates in project steering, administration and implementation tasks, and is also actively involved in grid management, middleware deployment and user support activities. In addition, the valuable experience acquired by DAPNIA's computational grid team in the course of the EGEE project is being made available to the controlled fusion community through a collaboration with the CEA's Department of Research on Controlled Fusion (DRFC) in Cadarache, France.

Figure 1. Plot of the monthly evolution of computing time provided by the GRID in France. Early in 2005 the capacity was around 3,000 hours per month. Beginning 2007, about 1,500,000 hours are provided monthly to the GRID, two third of it being used by LHC experiments, the experiment D0 being the main user of the remaining. Globally the evolution in France reached a factor 500. Another 100 factor is necessary to be fully ready for LHC.

Software development and Web technologyExpertise in software development is essential for the needs of physics science in large laboratories such as DAPNIA. The purpose of this activity is to develop software tools allowing the production and management of high added value applications used to operate instruments and analyse scientifi c data. These tools include specifi c middleware (e.g. real-time processing simulation for CMS experiments), software development frameworks, and tools to exchange and distribute scientifi c data. A very successful example would be PHOCEA, the web portal confi guration environment developed at DAPNIA and adopted by numerous CEA departments and external laboratories.

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The LCG project should be operational prior to the launching of the LHC experimental programme. It must be noted that France is lagging behind other European countries and the USA, particularly in terms of analysis resources. As a result, the fi rst objective of the GRIF project is to become a Tier-2 distributed centre. Given its involvement in the LHC programme, DAPNIA is set to play a leading role in the GRIF project.

Astrophysical image processingGround and space-based observations of astrophysical

objects provide increasing quantities of data. The images obtained are disturbed by atmospheric turbulence and limitations in telescope imaging performance, as well as intrinsic limitations associated with the telescope aperture (primary mirror diameter) and potential optical aberrations. Specifi c analysis tools must therefore be developed to ensure optimal use of existing and future instruments.

With this objective in mind, the 'Multiresolution' joint research programme (DAPNIA/SEDI-SAP) develops

methods and algorithms making the best possible use of existing knowledge of image formation mechanisms. The wavelet transform technique allows the separation of image components corresponding to different spatial scales (hence the term 'multiresolution'). Possible applications include fi ltering, deconvolution, form detection and data compression. These techniques are used in various research areas, including the detection of dark matter via the gravitational lens effect or Sunyaev-Zel’dovich effect, the characterisation of internal structure and dynamics of stars (asteroseismology) and the characterisation of the cosmic microwave background (CMB).

Parallel computation, visualisation and software development for the numerical simulation of astrophysical plasmasDAPNIA's Computational Astrophysics programme

(COAST) was launched in 2005 to develop, optimise, parallelise and manage software tools for numerical simulation in astrophysics. The results achieved so far include the development of the SDvision visualisation software (to analyse hydrodynamic simulation data), the creation of the ODALISC opacity database (to model laser and astrophysical plasmas), and the implementation of common tools for software version management. Its expertise in various areas (cosmology, interstellar medium, protoplanetary discs, stellar physics, hot laser plasma physics) and its signifi cant experience in numerical analysis and software development have led DAPNIA to play a leading role in several national collaborations such as the HORIZON, ODALISC, MAGNET and SINERGHY projects. These projects will require signifi cant efforts on DAPNIA's part to develop and generalise software tools and methods intended for the international astrophysics, geophysics and plasma physics communities Figure 2. Visualisation of RAMSES data by the SDvision

software: Simulation of the formation of cosmological structures in the Universe, showing the gravitational concentration of dark matter and baryonic matter to form galactic clusters.

Figure 3. Visualisation of HERACLES data by the SDvision software: Simulation of turbulences in the interstellar medium.

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Magnets and accelerators

The past period witnessed the accomplishment of a very

important contribution of Dapnia to LHC: delivery of the 360 cold masses

of the quadrupoles, surface test of the CMS solenoid, assembly and test of the ATLAS toroïde in the cavern.

The competences of our teams in cryogenics and magnetism are unanimously recognized, and gave us the opportunity to take part in these scientific and technical challenges, namely the ISEULT magnet and the R3B-Glad spectrometer. Concerning accelerators, SACM teams achieved very high accelerating fields and proton intensities.

The next few years are also full of expectations, with the completion of IPHI, the SOPHI accelerator, the injector and the cryomodules of SPIRAL2, the launching of IFMIF-EVEDA…

Until 2010, DAPNIA, regarding its activities on accelerators, cryomagnetism and instrumentation, will continue to live very rich hours, at the level of the European scientific ambitions of CEA/Saclay and the accompanying communities.

Antoine Daël


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Particle accelerators

P article accelerators are used to produce high-energy particle beams (elementary particles or different types of nuclei) in laboratories. These beams can be focused on a

target (or the centre of a detector, in the case of a collider), providing physicists with intense and controlled collisions for matter science research. DAPNIA/SACM teams design and develop accelerator technologies for present and future experiments, from particle sources to fi nal beam focusing systems, along with copper or superconducting radiofrequency cavities giving energy to the particles.

SPIRAL2

Research on exotic nuclei at GANIL (Caen, France) is to be pursued with the SPIRAL2 accelerator currently under construction. SPIRAL2 is a high-intensity deuteron and ion linear accelerator with a charge/mass ratio of up to 1:3, producing a 40 MeV continuous deuteron beam with intensity

of up to 5 mA. DAPNIA was strongly involved in detailed design phase activities, ranging from system architecture and beam dynamics analyses to the design of the source, radiofrequency quadrupole (RFQ), adaptation sections and fi rst section of the superconducting accelerator. From 2004 to 2006, prototypes of the main accelerator components were designed, built and tested by DAPNIA/SACM teams. Experimental tests of the 5 mA Electron Cyclotron Resonance (ECR) deuteron source with permanent magnets demonstrated its performance and reliability. A section of the

RFQ corresponding to one-fi fth of the total length was tested at HF power of 50 kW. These tests served to validate the original design (without solder and with removable plates), demonstrating its frequency stability under realistic operating conditions. DAPNIA teams in Saclay were entrusted with the responsibility to build and assemble the injector (deuteron source, LEBT and RFQ). A superconducting cavity adapted for particles with relative velocity β = v/c = 0,07 was also designed, built and subsequently tested in a vertical cryostat, yielding results exceeding specifi cations (accelerator fi eld of 11 MV/m and surface electric fi elds of 55 MV/m). DAPNIA/SACM teams were assigned the construction and testing of 12 complete cryomodules, each comprising a cavity with β = 0,07. A qualifi cation module is currently being assembled in the laboratory.

High-intensity proton injector (IPHI) and high-intensity proton linacsThe collaboration between CEA and CNRS/IN2P3

on the IPHI project (high-intensity proton injector) has been expanded to include the participation of CERN. Once tested in Saclay, IPHI will constitute the head system of LINAC4, the future high-current proton injector (3 MeV) for the LHC. The construction of the RFQ cavity is being pursued with the installation of sections 2 and 3 and the machining of the remaining sections. The installation of the 2.4 MW HF power continuous source, and that of the HF network is completed. The SILHI source reliably produced a continuous 95 keV, 130 mA beam. Experiments aimed at understanding the beam dynamics in the Low-Energy Beam Transport system (LEBT), located directly downstream of the source, are being conducted in association with numerical modelling. These dynamics need to be perfectly understood in order to control the beam parameters at the RFQ input.Future proton accelerators usable as LHC injectors or for intense neutrino sources require controllable superconducting cavities adapted to ultrarelativistic protons (β comprised between 0.4 and 1). The CARE-HIPPI programme addresses this issue. A rigidifi ed 5-cell cavity with β = 0,5 and operating at 700 MHz has been developed to demonstrate the stabilisation of radiation pressure effects on frequency. This cavity is now completed and will be tested in the CRYHOLAB horizontal cryostat under conditions very close to those of an accelerator.

A 1 MW pulsed microwave source is currently being installed on the superconducting cavity testing and characterisation

Figure 1. First cavity with β = 0.07, intended for the SPIRAL2 superconducting accelerator.

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platform in Saclay (SUPRATech project). This source will be used to test the high-power HF couplers needed to produce the accelerator fi eld in the cavity and to power the proton beam. Couplers operating at up to 1 MW in pulsed mode were designed during the development of the cavity and are now being built.These developments are also of interest for the EURISOL project, since the possibility of delivering a 5 MW proton beam on a spallation target is currently being considered for the production of radioactive beams.

EURISOL and beta beamsThe European EURISOL project is investigating the

possibility of using the β radioactivity of 6He and 18Ne ions (which form a beta beam when accelerated) to produce intense neutrino sources. In an accelerator ring of this type (to be designed at DAPNIA), those ions disintegrate into 6Li and 18F nuclei, emitting neutrinos with a well-defi ned fl avour, energy and, in the straight sections, direction. The control of beam injections and losses in such a high-current ring is of primordial importance. Given its expertise in the numerical simulation of beam dynamics, DAPNIA is actively involved in the design of this new type of ring system.

Advances in electron and positron collider technologyOngoing developments for linear electron accelerators

aim to meet the highest performance requirements. The energy levels sought range from 500 GeV for the International Linear Collider (ILC) to several TeV for the Compact Linear Collider (CLIC). This will require lengths of tens of kilometres and accelerator fi elds as high as possible.

ClicThe CERN CLIC project is based on High Frequency

(12 GHz) resonant copper cavities. Each branch of the system consists of two linacs. The fi rst linac produces a 'drive beam' with very high power but low energy. Specialised HF structures are used to transfer this energy to a second linac that accelerates the main beam at very high energies. A prototype of these linacs, referred to as CTF3 (CLIC Test Facility phase 3),

is intended to validate this innovative concept at a low energy level. DAPNIA/SACM is responsible for the design and construction of the linac to accelerate the main CTF3 beam. The preassembly of the accelerator and the construction of the HF dephasers used in the power distribution network are currently in progress.

ILCIn the case of the superconducting technology adopted

for the ILC, preparing the inner surfaces of the pure niobium cavities is essential for obtaining high gradients. Electropolishing has led to gradients of approximately 40 MV/m for 1.3 GHz cavities, but problems concerning the reproducibility of the treatment have been encountered. An electropolishing bench has been installed at DAPNIA within the scope of the CARE-SRF programme to optimise the treatment process on single-cell cavities. The fi rst cavities treated led to exceptional gradients (up to 42.5 MV/m). This signifi cant progress is also due to the optimisation of the vacuum curing process, which ensures a very high quality factor under high fi eld conditions and extends the fi eld limit.Cavities subjected to very high surface fi elds undergo deformations due to radiation pressure, causing a disturbance of the accelerator fi eld. This instability

can be controlled by means of a tuning system equipped with a piezoelectric component capable of correcting the cavity frequency during HF pulses. Such a system has been designed and successfully tested within the scope of the CARE-SRF programme.The control of the beam orbit is crucial for limiting the luminosity losses. To this purpose, Beam Position Monitors (BPMs) with reentry cavities and HF processing circuits have been developed by DAPNIA/SACM teams. They have been tested on the FLASH accelerator at DESY, achieving a resolution of less than 10 microns

Figure 2. HIPPI : Prototype of the proton superconducting cavity with β = 0.5.

Figure 3. Schematic lay-out of an accelerator system for neutrino production using the beta-beam method.


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Superconducting magnets

DDAPNIA has acquired signifi cant expertise in the design and construction of superconducting magnets for physics experiments, from quadrupole electromagnets

for particle beam control to huge electromagnets used in large detectors. DAPNIA's expertise ranges from laboratory prototyping to technology transfers and monitoring of industrial series production. The ATLAS and CMS detector magnets and the approximately 400 quadrupole magnets constructed for the LHC at CERN are the most representative achievements of the recent period. Beyond the LHC, other systems have recently been developed (e.g. for JLAB and GSI) or are currently being designed (e.g. for the NEUROSPIN and R3B projects). These activities require expertise in electromagnetism, cryogenics and mechanics.

Superconducting focusing quadrupoles for LHCWithin the framework of France's participation in

the construction of the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland), DAPNIA designed, developed and validated the fi rst quadrupole prototypes and subsequently supervised the technology transfers and industrial production. Series production was performed by Accel, who delivered the last quadrupole in 2006. This delivery ended a 15 year period of very close collaboration between Dapnia and CERN. From 2004 to 2006, DAPNIA monitored the industrial production of the approximately 400 quadrupoles (requiring very rigorous processes and extremely high mechanical accuracy) with a success rate of 99.8%.

Key fi gures: Length: 3 m – Average coil radius: 0.04 m – Field gradient: 223 T·m – Parasitic components with respect to reference fi eld < 10-4 – Mechanical production tolerance: 20 μm – Electromagnetic dispersal force: 110 tons per metre – Number of quadrupoles: 408.

ATLAS toroidDAPNIA designed the ATLAS central toroidal magnet

(also for the LHC) and monitored its construction. This magnet consists of 8 large superconducting coils 25 m long and 5 m wide, in star confi guration. Industrial production of magnet components lasted from 2002 to

2004. In 2004, the fi rst coil was assembled and tested (at 22,000 amperes). In 2005, the other seven coils were assembled and tested, and teams at Saclay simultaneously developed the helium coolant and energy supply ring. Finally in 2006 the toroid was assembled in the cavern, at a depth of 100 metres, and successfully tested at up to 21,000 A. Key fi gures: 30 km of superconducting wire – 8 magnets composing a torus with inside diameter: 10 m , outside diameter: 20 m – Length: 25 m – Nominal current: 20,000 A – Test current: 21,000 A – Stored energy: 1.1 GJ – Mean toroidal fi eld: 1.25 T.

Figure 1. Lowering of the fi rst quadrupole cold mass in the LHC tunnel (19 April 2005).

Figure 2. General view of the ATLAS central toroid, in the cavern.

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CMSThe development, assembly and validation of the CMS

solenoid, the largest superconducting solenoid in the world, was completed during the recent period. DAPNIA teams at Saclay performed qualifi cation tests for the tie rods (total of 30), 20 kA cables and phase separator under real operating conditions. DAPNIA teams also supervised the production of strategic components and their assembly at CERN. Surface tests were successfully completed in 2006 (the magnet reached its nominal fi eld

of 4 T after being cooled to 4 K and progressively supplied with current up to 19,141 A). Quick discharge tests were performed so as to validate the quench-back cylinder and subsequently homogenise the magnet transition using Eddy current heating. Key fi gures: Diameter: 7 m – Length: 12.5 m – Field at centre: 4 T – Operating current: 19,500 A – Stored energy: 2.6 GJ – Expansion forces to be contained: 600 tons/m².

R3B-GLAD magnetFollowing the completion of the detailed design of a

large acceptance magnetic spectrometer (5th European R&D Framework Programme), the decision to construct the R3B-GLAD magnet was adopted in October 2005. This magnet will deviate proton beams (up to 40º) and heavy fragments, without stopping neutrons produced with particles. Several coil and shielding designs were investigated, and the 'butterfl y' design was adopted within

the framework of the 6th R&D Framework Programme. This innovative magnetic design includes active shielding and gradual trapezoid-shaped fl at coils matching the required beam acceptance. The stored energy and magnetic fi eld in the region containing the target (at the front of the magnet) are minimised. In 2006, proposals concerning the accommodation of high magnetic stresses (300 to 400 tons/m), thermosiphon cooling and magnet protection systems were adopted for the fi nal project.Key fi gures: Superconducting dipole with active shielding and 6 fl at coils – Field at centre: 2.4 T - Field integral: 4.8 T·m – Field on conductor < 6.36 T – Stored energy: 24 MJ – Leakage fi eld: 20 mT at 30 cm from cryostat.

CLAS-DVCS solenoidWithin the framework of a collaboration with the Thomas

Jefferson Laboratory (JLAB, USA), DAPNIA designed, developed and delivered a superconducting solenoid for the Deeply Virtual Compton Scattering (DVCS) experiment. This magnet is in operation since February 2005 in the centre of the toroidal fi eld of the CLAS detector (CEBAF Large Acceptance Spectrometer). The innovative magnetic compensation system used to cancel interaction between the detector and solenoid allows the two magnets to operate independently. In addition to the DVCS experiment for which it was initially designed, this magnet is also used by JLAB physicists for other experiments with complementary scientifi c objectives. The fi rst data collection campaign for the DVCS project was conducted from March to June 2005, and the second campaign is scheduled for early 2008.Key fi gures: Outside diameter: 0.912 m – Inside diameter: 0.23 m – Length: 0.3 m – Current: 534 A – Field at centre: 4.65 T.

11.7 T magnet for NEUROSPINAs part of the NEUROSPIN centre for nuclear magnetic

resonance imaging and spectroscopy, the ISEULT medical imaging programme requires a magnet providing a 11.7 T fi eld inside a room temperature bore 900 mm in diameter and intended for clinical studies on humans. DAPNIA is responsible for the development of this innovative magnet.

Figure 3. CMS solenoid ready to be cooled. The current cable feedthrough system can be seen in the top left.

Figure 4. CLAS-DVCS solenoid equipped with instrumentation at the CLAS detector input. The vertical cylinder behind the solenoid is the cryostat controlling the energy, temperature and fl uid transfer of the magnet.

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Vacuum chamber

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Test facilities

The cryogenic test facilities for R&D are an important tool used to characterize and qualify phenomena and materials in fi elds of physics dealing with low temperatures,

magnets and accelerators. For the projects, the test facilities allow checking the validity and scope of conceptual innovations. They are also used as a fi nal resource for validating critical components of complex assemblies, or the assemblies themselves. These test infrastructures for superconducting cavities are an integral part of the SUPRATECH platform supported by the Île-de-France region, which includes the facilities of DAPNIA at Saclay and IN2P3 at Orsay.

Figure 5. Exploded view of the ISEULT magnet, designed to produce a magnetic fi eld of 11.7 T on an effective diameter of 0.9 m.

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SACM has about ten such facilities, equipped for mechanical, electrical and thermal characterization of materials at low temperature, or for observing and measuring the properties of liquid helium fl ow under different conditions. Activity in the test facilities is split between R&D and project needs. Temperatures from 1.6 to 300 kelvins and magnetic fi elds from 0 to 17 teslas are covered. The R&D experimental means were used extensively for the study of the thermosiphon

in the CMS project, as were the characterization facilities for projects involving niobium-tin, such as ITER, NED, ISEULT, Nb3Sn quadrupole and R3B. Approximately two hundred superconductor samples have been characterized in three years, both for the internal needs of DAPNIA projects and for the requirements of industry (Alstom).

For the accelerator magnets (dipoles and quadrupoles), the test capacity extends to 0.8 metres in diameter and 10

Following the feasibility studies, a white book was prepared for June 2004. The project implementation phase at DAPNIA and the various collaborations required for the industrial production of the conductor and coils have led to the establishment of the defi nitive specifi cations for the state-of-the-art conductor, the magnet and its components. Several prototypes, including a test station with an 8 T magnet, are currently being developed to validate the concepts and processes to be implemented for ISEULT.Key fi gures: Magnet with active shielding- Field at centre: 11.7 T – Maximum fi eld on conductor: 11.92 T – Mass of superconducting wire: 60 tons – Stored energy: 340 MJ – Inside diameter: 0.9 m – Outside diameter: 4.5 m – Length: 5 m.

Research and developmentAll projects such as ATLAS, CMS, NEUROSPIN and many others require signifi cant R&D. This R&D addresses the technical concepts to be investigated and verifi ed (to ensure optimal implementation) and the acquisition of a better understanding of the physics of phenomena involved or materials used. One of the main axes of R&D in thermal

technology and cryogenics concerns the hydrodynamics of two-phase helium fl ow. At DAPNIA, this led up to the development of the thermosiphon used to cool the CMS. Heat transfer mechanisms in superfl uid helium in porous media are also being investigated, since they will probably be used in cooling systems for niobium-tin magnets. This new-generation material (Nb3Sn) is intended to replace

the niobium-titanium in electromagnets with high current densities and magnetic fi elds,

and has been subject to specifi c research for several years now. This new generation of superconductors requires extensive thermal treatments for tools and materials. The development of an accelerator magnet prototype (currently in progress) consti-tutes the fi nal and most complex phase of R&D on

Nb3Sn. Research on ceramic insulators compatible with the specifi c thermal treatments required for this material is also currently in progress

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metres in length, with currents of up to 20,000 amperes at a minimum temperature of 1.8 kelvin in superfl uid helium. This test infrastructure, after a long renovation period, was brought back into service at the end of 2006, for the purpose of testing the Nb3Sn quadrupole.The two cryostats of the W7X facilities can each accommodate two magnets of 4 metres in diameter simultaneously. These magnets are cooled to 4.5 kelvins in supercritical helium, and supplied with a current of 17,500 amperes. The tests have done their job, revealing a number of production problems that sometimes meant going back to the companies that made them, and have therefore led to several tests on the same coil. At the end of 2006, around twenty coils have been qualifi ed for the construction of W7X.

The vertical cryostat, 8 metres deep, has made it possible to validate critical components of the CMS project: the current leads, the 30 titanium suspension bolts that hold the solenoid, and fi nally the phase separator, which manages the operation of the solenoid thermosiphon.

For NEUROSPIN, SACM is in the process of setting up a new test facilities that will be able to produce a magnetic fi eld of 8 teslas in a useful diameter of 0.6 metres. This future test infrastructure should make possible to validate the concepts put forward for the 11.7 teslas magnet of the ISEULT project. Studies for the SEHT facilities (Station d'Essais Huit Teslas) began in early 2006 and the program is planned to start in early 2008.

In the fi eld of radiofrequency superconductivity, surface and thermal treatments are of prime importance for obtaining the highest accelerator gradients and the lowest dissipation. Chemical treatments for niobium are initially being studied and optimized on samples, and the laboratory has a dedicated cryostat for measuring the RRR (Residual Resistivity Ratio) for this. RF tests on single-cell cavities should then be performed in one of the two vertical cryostats available at SACM for superconducting cavities. Here, the cavities performances are measured at low RF power, at a temperature between 1.6 K and 4.2 K. The cryostats are shielded to avoid perturbating fi elds. The single-cell cavities at 1.3 GHz for high gradients research are evaluated in a vertical cryostat at an average

rate of 50 tests per year. Improvement of the performance of the cavities using a baking process has been validated in a vertical cryostat. The size of the CV1 cryostat means it can accommodate large cavities, and most of the cavities developed at SACM. In particular, the prototype quarter-wave cavity for SPIRAL2 was validated in this cryostat, in 2004 and 2005. The horizontal cryostat CryHoLab is used for testing cavities under conditions as close as possible to those in an accelerator. The cavities are fi tted inside with their helium vessel and can be supplied with RF using a power coupler. Cavities as diverse as a 5-cell cavity at 704 MHz for protons and a 9-cell cavity for electrons have been tested in CryHoLab. Validation of cold tuning systems (SAF, Système d’accord à froid) on a cavity can only be performed in a cryostat of this type. The SAF of the CARE-SRF program, fi tted to a 9-cell TTF cavity, was successfully tested in CryHoLab in 2006. A new medium-sized cryostat is being designed for the reliability testing of specifi c components of SAF, such as motors and gearboxes in vacuum conditions. The test platform includes continuous RF power sources of the IOT type (Inductive Output Tube), and pulsed power sources, a 1.5 MW 1.3 GHz klystron of to supply the electron cavities in the CARE-SRF program, and a 1.2 MW 704 MHz klystron of for the proton cavities and the power couplers in CARE-HIPPI.

All this equipment was transported in 2005 to the main site at Saclay. The helium condenser will now allow the

vertical cryostats to be supplied, in addition to CryHoLab. The system is planned to restart in 2007

Figure 1. CMS: test of the phase separator at Saclay connected to a cryogenic loop reproducing the operation of the magnet in thermosiphon mode.

Figure 2. Cryostat for traction tests at the temperature of liquid helium.


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New developments for magnet and accelerator instrumentation

Performance needs combined with growing complexity of physics experiments require adaptation and technical innovations. DAPNIA is involved in the development of control/

command systems that ensure a high level of reliability, availability and fl exibility, including advanced communication between heterogeneous systems with an ergonomic interface for users.

Magnets and accelerators require advanced technologies with a strong involvement of the DAPNIA as far as instrumentation is concerned.The high level of expertise and experience acquired working on projects of different size using diverse technical means, allows creating tools that will be reusable with the view of performance and cost.These needs and ability lead DAPNIA to invest for cutting-edge developments in the fi elds of electronics, PLCs, adaptative monitoring software and in new technologies validations.

Web technologiesGeneralization of web technologies enables

different systems to communicate together in accordance with a standard established independently from the operating system, and provides an interface with humans through an Internet browser.This potential is used by teams to develop original solutions for the monitoring, on-site or remotely, of one or several elements of an accelerator or a large-scale instrument.At the heart of this supervision is the FBI software application, which is being constantly upgraded. It is capable of communicating with PLCs, or specifi c equipments, for the purpose of archiving data and sending telephone or electronic alarms, according to operator-defi ned rules.In parallel, a WorldFIP library with a high abstraction level, available in C, Java and LabView, has been developed to give an easy and fl exible access to this technology.An original web interface called « Anibus », based on the multi-platform Java language, gives a fast and fl exible access to creation and broadcasting of system monitoring windows.Web technologies are not only embedded in PCs but also in custom equipments as FIP@ACS. It is a gateway designed by DAPNIA to enable communication between two fi eldbus, MODBUS and WORLDFIP. Its originality lies in its incorporation of a web server, accessible via the FIP messaging function, which can be used to modify its confi guration.

Interoperability and application to control/command architecturesFieldbus scope of application is extending, due to

installations being more and more heterogeneous. This

situation led to the idea of gateways as FIP@ACS. A study of a gateway based on OPC technology has also be realized. Performances and limits have been evaluated taking into account the specifi c needs of the projects.Different technologies coming from industry or custom developments are set on superconducting magnets; simplifi cation of cabling and cost reductions have led DAPNIA to study a new architecture of the instrumentation based on the concept of “shared instrumentation interface”. This interface, built on an industrial PC architecture (Windows XPe), acquires data and information from the magnet safety system at a low frequency (1 kHz), and offers the possibility to record at a higher rate (up to 50 kHz)

the same information if triggered by an external event. This has been made possible through the development of a special PCI card that stores the data (see fi gure 1), giving access to measurements with less constraint and thus avoiding a real-time operating system. This interface can broadcast data through the Internet but also through the WORLDFIP fi eldbus and soon also through PROFIBUS. The system's reliability and low cost have been key factors in the development of this new technology. It will be implemented in the SEHT test facility to characterise the elements of the ISEULT magnets, and in the R3B experiment on the GSI site. Another 32 channel isolated digital acquisition board will be developed for those two projects.

Figure 1. The analogical “bufferized” acquisition board MIVA, embedded in the shared instrumentation interface.

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Developments dedicated to cryomagnetic systemsPhysics experiments make massive use of superconducting

magnets cooled to cryogenic temperatures (MRI, Tokamaks, polarised hydrogen targets, detectors…). The protection of the equipment and the management of the vast amount of energy stored in the magnets require monitoring and protecting them in the event of an accidental change from superconducting to resistive state (quench). For many years, DAPNIA has been developing complex electronics systems that analyze in real-time the behaviour of the magnets and trigger the safety devices if there is a problem. A new version of these systems, with on-line integrated control of the electronics, has been set up on one of the test facilities of the department. This new system (see fi gure 2) will be deployed in several projects (ISEULT, R3B and for a group of 28 bending magnets of the T2K accelerator). Concerning the current developments, the ISEULT project for medical imaging, the instrumentation design engineers have to take greater account of the human factor in addition to the basic parameters for developments in electronics. The impact of damage caused by a malfunction can go beyond the simple hardware damage normally taken into account in physics experiments.Challenges for future magnet safety systems will be to increase the electrical insulation needed between the measurement point and the data processing (JT60-SA, ITER), and to improve safety, so as to limit installation downtime.

Other elements, in each installation, are subjected to harsh constraints. Electrical connectors are validated in the industry for temperatures above 50 °C. An innovative test bench is being fi nalised which will soon make it possible to validate connectors at temperature as low as -150 °C.

Such cryogenic temperatures are reached using liquid helium (- 269 °C) which is stored on site. It is mandatory to know at any time the liquid He level inside a cryostat, or in a thermally insulated tank. DAPNIA has a long experience in liquid He level measurement, and at present more than a hundred units (all versions) for He level measurement have been installed in laboratories all over the world. A new “smart” version, more simple to use and more autonomous, integrates a microcontroller running four separate

measurement channels instead of a single one. This microcontroller, the « brain » of the measurement unit, computes mean values taking into account the length of cables, detects defaults, makes an automatic calibration of the gauges, and displays the calibration values and the current level of liquid as a percentage. This equipment (see fi gure 3) sends on the WORLDFIP network the status and the measured value of each gauge. The display is multilingual and has been made more user-friendly. One or several gauges can be put into standby manually or via the WORLDFIP fi eldbus to provide maximum protection for personnel handling them. This new version has been delivered on one installation and others have been pre-ordered

Figure 2. Schematic fl ow-chart of the superconducting magnet safety system.

Figure 3. Liquid He level measurement unit for four channels with FIP fi eldbus.

Physics for nuclear energy

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The DAPNIA contributions to the R & D for nuclear energy

are related to physics, in the core of the reactors, and to accelerators, for what concerns material studies.

DAPNIA always played a major part in the field of neutronics, applicable as well to energy production than to waste incineration. Through its spallation studies programme, at GSI or at PSI (with MegaPie), it helps to better understand the processes involved in the future facilities using high power beams (ADS, EURISOL, or even ESS).

Within the framework of the “broad approach” negotiated around ITER, the IFMIF-EVEDA project aims at qualifying advanced materials withstanding extreme conditions, which are very much needed for the successors of ITER. For the irradiation of the materials, the chosen neutron source uses the (D-Li) stripping reaction, and requires a very powerful accelerator. DAPNIA will lead the design and construction of this facility, before its installation in Rokkasho (Japan).

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Nuclear data measurements and modelling

DAPNIA is continuing a programme of basic research on nuclear reactions, where neutrons, photons and protons interact with various target nuclei in a wide energy

range. Research on spallation, fragmentation, fi ssion, neutron capture and nuclear decay is the driving force of a number of our present and future projects. It allows for a better and more precise modelling of complex systems, as required for nuclear energy, transmutation of nuclear waste, non-proliferation, non-destructive characterization of waste packages, design-decommissioning of nuclear installations, nuclear medicine, etc.

In situ transmutation studies with Mini-INCAThanks to the availability of high neutron fl uxes at the

ILL reactor (Grenoble, France), the transmutation of minor actinides is studied in situ. A strong effort was the development of microscopic fi ssion-chambers able to withstand high neutron fl uxes (∼1015 n·cm-2·s-1) and to measure without ambiguities the fi ssion rates of any actinide in reference to a known fi ssion cross section as 235U. These detectors were used to monitor the irradiation of a 237Np sample during 50 days, for transmutation rate studies (e.g. fi ssion of 238Np and capture cross-sections on 238Pu). The improved data analysis methods, taking into account the correlated errors inherent to the complexity of the transmutation chains, allowed to obtain major capture and fi ssion cross sections important in the incineration of 241Am and in the Th-U fuel cycle. In parallel, some perturbative methods were developed to evaluate the impact of nuclear data uncertainties on different waste transmutation scenarios.

Neutron reaction measurements at GELINA and CERN Precise neutron reaction measurements have regained

the interest mainly due to the programs related to nuclear technology but also thanks to the research on stellar nuclear-synthesis. For example, through the neutron capture on 209Bi the production of a dangerous alpha emitter as 210Po was studied at GELINA (JRC Geel, Belgium). These data are crucial for future spallation neutron sources using liquid PbBi targets as MEGAPIE (see below). Equally, the capture measurements on 206Pb were done at a similar

demand. At CERN (Geneva, Switzerland) a 4π calorimeter of BaF2 (see Fig. 2), where DAPNIA provided the photomultipliers, became operational in 2004. Other DAPNIA responsibilities were the pulse shape analysis and the discrimination of fi ssion-to-capture events. This device has permitted the neutron capture measurements for a number of actinides (e.g. 233U, 234U). Finally, the 236U(n,γ) reaction was also measured at GELINA. The knowledge of nuclear data for these uranium isotopes is crucial for the

development of an innovative Th-U fuel cycle.

Photonuclear reaction studiesHigh energy photon induced reactions are essential

for non-destructive nuclear waste characterization (e.g., the INPHO project) or nuclear material detection. The PhotoNuc project at DAPNIA aims providing accurate basic nuclear data and evaluations to respond to this request. Measurements of photo-fi ssion delayed neutrons (DN) have been undertaken in collaboration with CEA/DIF/DPTA employing the ELSA electron accelerator. For this purpose the high effi ciency DN detector was designed and constructed at DAPNIA. Up to now the determination of DN yields and group parameters have been extracted for 238U, 232Th and 235U at several energies. Thanks to the improved quality of these data, the detection of DNs can now be used not only to defi ne the mass of fi ssile materials but also to provide isotopic composition of mixed samples (see Fig. 3).The experiments are accompanied by the modelling efforts,

Figure 1. Domain in type and energy of the studied reactions.

Figure 2. The calorimeter of the n_TOF experiment at CERN.

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which include actinide evaluations of photonuclear cross sec-tions, fi ssion fragment yields, neutron multiplicities and their energy distributions. Evaluations obtained for 235U, 238U, 237Np, 239Pu, 240Pu and 241Am nuclei up to 20 MeV were in-corporated, in collaboration with LANL (USA), into the newly released ENDF/B-VII data library. New evaluations, exten-ded up to 130 MeV and complemented by the photo-fi ssion DN parameters obtained at DAPNIA will be provided to the European JEFF data fi le.

Spallation reaction studiesReactions, where light particles are produced from high

energy protons interacting with heavy nuclei, are generally called spallation reactions. These reactions occur in space due to interactions of energetic cosmic rays. In laboratory, they are produced using accelerators, giving neutrons sources for accelerator driven systems (ADS), nuclear waste transmutation or radioactive ion beam (RIB) production. The study of spallation in DAPNIA aims at acquiring a deep understanding of the reaction mechanism through experimental investigations in order to develop reliable nuclear models that can be used in simulation codes.Experiments at the FRagment Separator (FRS) of GSI (Germany) provided a unique set of isotopic cross-sections of spallation residues. A new programme has been launched at GSI, namely the SPALADIN experiment, to provide information on the de-excitation stage of the reaction by measuring in coincidence spallation residues and evaporated light particles. The fi rst experiment (Fe + p) has permitted for the fi rst time to decompose the whole reaction cross-section into partial de-excitation channels (see Fig. 4). The comparison with “standard” evaporation models has shown that additional mechanisms are necessary to reproduce the data. The FAIR/R3B project, where a complete kinematical reconstruction of the reaction for heavy systems will be possible, will extend those studies. Thanks to DAPNIA’s collaboration with Liege University and GSI, spallation models describing the reaction into two stages: the intranuclear cascade (INCL4) followed by de-excitation (ABLA), have been signifi cantly improved and validated on a wide set of experimental data. In particular, INCL4 now produces data on high-energy

composite particles. The INCL4-ABLA combination has been implemented into the high-energy transport code MCNPX, used in a wide domain of applications, and an implementation in GEANT4 software is under way.

MEGAPIEIn 2006 the MEGAPIE (Megawatt Pilot Experiment, PSI,

Villigen, Switzerland) international project has successfully accomplished all its objectives. The liquid PbBi target was irradiated for the fi rst time during 4 months at the 800 kW proton beam power without any incident. This step was essential for further development of high power liquid metal targets to be used for high intensity neutron sources, ADS, RIB (e.g. the EURISOL project) or neutrino factories. Within MEGAPIE, DAPNIA was in charge of neutron fl ux monitoring. For this purpose, a dedicated neutron detector was developed, which was composed of a few micro fi ssion-chambers imbedded inside the liquid PbBi at different distances along the beam axis. An important R&D program was carried out in 2004-2005, during which the performance of prototype detectors has been tested at ILL reactor, and a precise theoretical model describing the operation of these detectors was developed and validated. The preliminary data gathered at MEGAPIE show that the increase of the measured neutron fl ux is correlated with the primary proton beam intensity, i.e. the fi ssion chambers functioned as expected in a very hostile environment

ModellingFinally, it is noticeable that the expertise gained in the study

of nuclear reactions and in the reliability of the physics models implemented into high-energy transport codes is also used to assess the uncertainty of the simulations made to design complex nuclear systems. For example, full scale Monte Carlo simulations for the MEGAPIE target were compared with the available measurements (see above). Equally, DAPNIA coordinates modelling task within the EURISOL (6th PCRD) project in terms of maximizing the RIB production, while minimizing radioprotection constraints

Figure 3. Measured decay curve of photo-fi ssion DNs in the case of a mixed sample: both old and new parameterizations are plotted for comparison.

Figure 4. Production of spallation residues in the reaction Fe + p at 1 A·GeV, versus their atomic number Z, and for different de-excitation modes defi ned by the number of fragments, at Z ≥ 3 and Z = 2, observed in coincidence.

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Technological research for fusion energy

The decision to build the ITER experimental fusion reactor in Cadarache, France, was adopted in June 2005 and was followed by the implementation of a 'broader approach'

agreement between Europe and Japan, which provides for the construction of two large additional facilities: the JT60-SA superconductor Tokomak facility (in Japan) and the IFMIF high-intensity accelerator facility (to study the effects of radiation on materials to be used in future fusion reactors). From 2004 to 2006, DAPNIA actively participated in CEA/DSM research on specifi c and highly technical aspects of the ITER project. Due to its technological expertise in high-intensity beams and sources, DAPNIA has eventually focused on the IFMIF project.

ITERIn 2006, the ITER experimental fusion reactor project

was offi cially launched in the CEA Cadarache site (southern France). This project falls within the scope of a large-scale R&D programme aiming to build and operate an electrical

production facility by the year 2050 and including an intermediate phase to build and test a demonstration facility (referred to as 'DEMO') by the year 2040.

CEA/DSM research activities conducted in collaboration with the Département de recherche sur la fusion contrôlée (DRFC/STEP), the Département de recherche fondamentale sur le matière condensée (DRFMC/SBT) and DAPNIA include the development of a coil mockup with an innovative resin and the characterisation of high critical temperature superconductors for the DEMO facility. These activities also include responses to RFPs for the European Fusion Development Agreement (EFDA), the design of a high magnetic fi eld dipole for a conductor test facility, thermohydraulic analyses of toroïdal coils and cooling systems, and cryogenic fl uid distribution studies.

IFMIF-EVEDAITER-type reactors use the energy transported by the

neutrons produced in a fusion reaction. The neutron fl ux in the DEMO facility will be so intense that the reactor's structural materials will undergo ten displacements of each atom during the planned operating time. Such fl uxes seem incompatible with the mechanical resistance of the materials presently used. It is therefore essential to develop, test and validate new alloys capable of withstanding these fl uxes while preserving suffi cient qualities. This is the goal of the International Fusion Materials Irradiation Facility (IFMIF) currently under development.IFMIF is a large-scale test facility whose objective is to produce a 14 MeV neutron fl ux through interaction between a high-intensity deuteron beam and a lithium target so as to generate over 20 displacements per atom and per year in a half-litre sample. The high intensity deuteron beam required (250 mA of D+ ions accelerated at 40 MeV) must be produced by two linear accelerators working in parallel. Such accelerators have never been built.A prototype development phase referred to as EVEDA (Engineering Validation and Engineering Design Activity phase) is required prior to the construction of the IFMIF accelerator facility. During this phase, an accelerator consisting of a 125 mA deuteron source, a radiofrequency quadrupole cavity (RFQ), a drift tube linac (DTL) and a beam dump block will be built, assembled and tested.The sharing of responsibilities between Europe and Japan for EVEDA was decided in 2006 during negotiations for

Figure 1. The ITER ACB (Auxiliary Cold Box for magnet structures). View of the complex cryoge-nic distribution box ensuring part of the cooling and temperature control of ITER magnets.

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the 'broader approach' agreement. The IFMIF-EVEDA programme spreads over a period of six years. The accelerator subsystems will be built in Italy, Spain and France, and the fi nal system will be assembled and tested in Rokkasho, Japan.The IFMIF-EVEDA project team is composed of 16 engineers, 8 of which are European. It will be based in Rokkasho-Mura and will coordinate the entire project. The team responsible for the development and construction of the prototype accelerator and the preparation of the IFMIF construction fi le will be based at DAPNIA in Saclay. A new department has been created for this purpose: the Service d’ingénierie IFMIF-EVEDA (SIIEV). DAPNIA is responsible for the construction of various subsystems, including the injector and the DTL

Figure 2. Basic diagram of the IFMIF-EVEDA prototype accelerator. The source, the low-energy beam transport system (LEBT, labelled Injector), the adaptation section and the drift tube linac (DTL) will be designed and developed at DAPNIA.

DAPNIA expertise at the service of society

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DAPNIA’s know-how and expertise in physics instru-

mentation give it the capacity to address some of the questions that

our society is facing at the beginning of this XXIst century.

This is the case for some crucial stakes for the future generations, such as the increasing need for energy, the climate changes, the new nanotechnologies and the medicine of tomorrow.

This chapter presents DAPNIA’s involvement in projects related to these

questions, like the modelling of particle-matter interactions applied to radiation protection and nuclear waste management, the realization of stations to measure the concentration of carbon dioxide, the developments of superconductive cavities for the new generation synchrotrons, and finally the contribution of physics to medical imaging, the use of radioelement and radiotherapy.

Pierre Védrine


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Physics and health

For more than a century, medicine and biology have benefi ted fully from advances in physics and from instruments developed for this fi eld. Particle physics has made a

particular contribution to medical imaging, the use of radioactivity for research, diagnosis and treatment, and radiotherapy.Within its areas of expertise, DAPNIA can provide solutions to specifi c problems that arise in the biomedical world, for which industry cannot provide an appropriate response.

Over the last few years, DAPNIA has launched various collaborations with the biomedical community to share its know-how in detector physics, modelling, electronics and superconducting magnets. This community has also benefi ted from the department's experience in running large projects and in activation and radiological protection calculations.

NEUROSPINDAPNIA has played an active part in the construction

of the NEUROSPIN neuro-imaging center by providing assistance to the prime contractor, the Direction des sciences du vivant (DSV), for the construction and equipment of the centre. Currently the department is involved in the development of ultra high-fi eld imagers as part of the ISEULT program. This programme is being run as a collaboration between DAPNIA, the University of Freiburg and two companies, Siemens and Guerbet, which specializes in tracers for imaging. The programme receives fi nancial support from the French Agence de l’innovation industrielle. The development of an imaging system of this kind, based on a main fi eld of 11.7 teslas, in a 900 mm aperture, constitutes an impressive feat. This fi eld is at the furthest extreme of

possibilities for using traditional superconductors (niobium-titanium), and raises some tricky problems as regards fi eld uniformity and control of the leakage and protective fi elds. The gradient magnets and radiofrequency antennas also create some diffi cult problems when it comes to mechanical strength, materials, controlling noise and heating. The scale of the resources deployed and the diffi culties to be resolved make this a fl agship project for the department in the interdisciplinary fi eld of physics and medicine.The characteristics of this MRI imager are explained in the chapter on superconducting magnets.

HadrontherapySome cancer tumours can be treated using proton or

light ion beams. The way these particles lose energy (Bragg peak) favours the localized irradiation of target tumours and the protection of healthy surrounding tissues.

ProtontherapyThe therapeutic effi cacy of proton beams for treating

brain and eye tumours has been proven, particularly in paediatrics, with the risk of induced secondary cancers being minimized. Only two centres are in operation in France, in Nice and Orsay.The Orsay Protontherapy Centre (CPO) has launched a refurbishing with the installation of a new accelerator and the refi tting of the beam lines and treatment rooms. Currently, the CPO can only treat 300 patients per year, though demand is evaluated at 3000 patients per year in France. The new installation should make it possible to extend the service to treat 600 patients per year. However, there is still a bottleneck when it comes to controlling the quality of the beams before the treatment of each patient. This is an essential operation; the doses delivered must be controlled with a precision of approximately 2%. At present, it takes quite a long time to check the beams and there is a risk of inaccuracy. In collaboration with the CPO, DAPNIA has undertaken a complete modelling of the beam lines using the Monte-Carlo simulation softwares used in particle physics (MCNP, GEANT4). The models supplied allow much faster and more precise adjustment of the beams for each patient, and better productivity for the installations. This project has been partially fi nanced by the Institut Curie. In addition, DAPNIA has performed biological protection dimensioning calculations for the CPO's new installation.

Figure 1. Model of the 11.7 teslas magnet for NEUROSPIN.

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Iontherapy

Radiotherapy using a beam of carbon ions is about to receive clinical recognition for some types of cancer. Two centres are in operation in Japan, and four are under construction or are planned in Europe. This technique puts to good use the precision of ion dose delivery and the biological effi cacy of the highly ionizing particles. However, the equipment required, based on a 25 m diameter synchrocyclotron and several beam lines, is much more complex and expensive than a cyclotron. DAPNIA has maintained an ongoing relationship with the French ETOILE project team in Lyon, and has begun a preliminary study to evaluate the feasibility and impact of a rotating beam delivery system, with superconducting magnets. This system, which allows patients to be given radiotherapy through multiple incidences, is made considerably less cumbersome by the use of superconducting magnets. There are many problems still to be solved concerning the geometry of the coils, conductor characteristics, cryogenics, dynamic performance and stability of the structures. The benefi t in terms of investment and operating cost needs to be evaluated but the major imperative remains the reliability and absolute safety of the system in clinical use.Furthermore, within the "Biomedical imaging modelling and instrumentation" research group, in which DAPNIA and CNRS/IN2P3 are participating, a continuous watch of PET camera projects associated with ion beam therapy is maintained. These cameras, by viewing the distribution of β+ isotopes produced in situ by the impact of the beam, will allow on-line control of the doses given and of compliance with treatment plans. In view of the low beta activity produced and the presence of the beam, new electronic and data acquisition architectures will need to be developed, as part of the INNOTEP project.

Nuclear imagingModelling The department is participating in the international GATE

collaboration (GEANT4 Application for Tomographic

Emission). This collaboration is a joint effort to develop a computing platform for modelling nuclear imaging instruments. It is based on the GEANT4 Monte-Carlo software developed by Cern. A public version was made available to the community in 2004. The department has contributed to the development of dynamic modelling sub-units and to the generic effort to document the programs.

InstrumentationIn collaboration with the Service hospitalier Frédéric Joliot

(SHFJ) of the DSV, DAPNIA is developing an instrumentation system associated with the PET imaging of small animals, as part of the ART project (Analysis of the physiological parameters of rodents using PET imaging). Imaging of small animals, particularly rodents (rats and mice), is a technique used increasingly widely for studying metabolism, human diseases, and molecules for therapeutic or diagnostic use. The extreme sensitivity of PET at molecular level makes it a particularly valuable tool. It is often necessary to obtain information both on the sites where the molecules are fi xed and metabolized and also on the kinetics of these phenomena. To do this, it is essential to know how the radioactivity injected into the animal changes in the blood system. Manual methods used in laboratories, which are delicate and time-consuming, are not suitable for animals undergoing imaging and may introduce experimental bias and cause operators to receive unnecessary radiation.

The instrument developed at D A P N I A / S E D I allows automatic sampling and on-line measurement during imaging. It consists of a sampling pump associated with a silicon diode detector arranged around a thin-walled tube connected to the catheter implanted in one of the animal's arteries. The system is controlled by a computer through a USB interface developed at the laboratory for other applications.The fi rst biological validation tests are very encouraging, and the project, which has already

been fi nanced under a "small animal imaging" joint project of CEA and CNRS, has received support under the CEA's cross-cutting programme Techno-Santé for assistance to technology transfer

Figure 2. Comparison of CPO experimental data with the simulation, concerning the delivery of do-ses at different depths. Note the perfect match with the curves using evaluated nuclear data.

Figure 3. Global view of the ART facility. The counter and the pump are visibnle, aside the small rodent installed in the micro PET.


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The studies undertaken have mainly focused on:• Calculating the activation of reactor internals in

preparation for the decommissioning process and determining their radiological characteristics to identify working methods and waste processing procedures, or to prepare the statutory documents required by the Safety Authority prior to clean-up operations;

• Radiological optimisation for the design of facilities using particle beams and for preparing the documentation required by regulation.

Activation studies for reactor decommissioningWhen planning to dismantle reactor internals, it is vital

to carry out an accurate assessment of the radiological characteristics of the various materials in order to defi ne disassembly operations and the technical provisions required to manage the risk of external exposure and to plan for waste conditioning (optimisation of disposal, selection of conditioning methods).These studies involve the following stages:

– 3-D modelling of the core and reactor block structures,

– calculating the spatial and energy distribution of neutron fl ux,

– calculating material activation by taking into account the reactor operating history and the metallurgical composition of the materials (including impurities).

This process is illustrated in Figure 1.At each stage, calculation results must be validated by:

– comparing the results of calculated spatial and energy distribution with experimental data (e.g. fl ux measurements performed during reactor operation),

– comparing activation calculation results with data from analysis of samples taken at the facility under study.

An illustration of the validation of activation studies performed for the decommissioning of the RAPSODIE reactor is shown in Figure 2 and Table 1. The modelling results are compared with samples taken from the SERCOTER concrete.DAPNIA/SENAC has carried out studies on the ULYSSE, SILOE, MELUSINE and RAPSODIE reactors in order to defi ne:

– the disposal methods for waste generated by dismantling work (LLW/ILW or VLLW storage or disposal),

– the container types required for their conditioning,– the various possible working scenarios and the

optimisation studies required under the ALARA approach, based on radiological data.

Figure 1. Flowchart illustrating the activation studies.

Figure2. RAPSODIE Reactor: Graphi-cal display of the changes in specifi c activity in the SERCOTER concrete.

74

Expertise in decommissioning and design of nuclear facilities

SENAC (French acronym for "Nuclear decommissioning and design expertise") was set up to draw on the experience obtained by the teams involved in decommissioning the

SATURNE and ALS accelerators operated by the CEA Direction des sciences de la matière in Saclay.Since 2005, DAPNIA/SENAC has aimed to use this know-how to provide project teams with an integrated response to their problems, on projects that combine modelling of interactions between particles and matter with radiological protection and waste management issues.

- Reactor core description- Incident beam description

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New facilities design consultancy These studies may have various objectives:a) For a specifi c equipment item: improving geometric or

physical characteristics to enhance performance or radiological protection for workers and public. In this framework we can mention for example:

– optimisation of beam characteristics and target design for the production of 211At isotope in the ARRONAX project,

– support, in the design of the SOPHI project, for biolo-gical shielding optimization,

– optimization of the biological shielding around a car-bon degrader, for the protontherapy centre in Orsay.

b) For new facilities (covered by French regulations on "installations classifi ed for the protection of the environment" (ICPE) or "basic nuclear installations" (INB)): studies allowing the preparation of the technical documentation required by the authorities to demonstrate compliance with regulations concerning protection of the environment and workers. For the ARRONAX project in Nantes, the studies were focused on the verifi cation of the following issues:

– wall design (dimensions), with respect to the risk of external exposure outside the building (Figures 3 and 4),

– activation of the various components, with a view to future decommissioning operations,

– design of the ventilation system for the irradiation vaults.

These studies were used to put together the support documents required for authorization, comprising:

– a safety study to verify that all non nuclear risks are fully managed,– an impact study to verify the health-related consequences of a radioactive release into the environment in the event of an operating incident

Tableau 1. RAPSODIE Reactor: comparison between calculated specifi c activity values and the specifi c activity of samples taken on-site.

Figure 3. ARRONAX Project (Nantes): map of the vaults and cyclotron, showing simulated neutron fl ux in a vault.

Figure 4. ARRONAX Project (Nantes): model of the neutron dose rate in an irradiation vault. This study shows that concrete thickness of 4.7 m is required in order to limit the rate to the maximum authorised dose for public exposure.

Calculations 280 89 93 29 26 8

Measurements 220 45 56 11 17 3

Activity (in kBq/g)

-728.6 cm - 934.3 cm -1140.0 cm

152 Eu 154 Eu 152 Eu 154 Eu 152 Eu 154 Eu


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Light sources

The superconducting cavity technology developed by DAPNIA/SACM applies to accelerators other than those used in nuclear or particle physics. This technology is

particularly well-suited for the very high intensity electron beams needed to achieve the high luminosities required for physics experiments and has therefore been adopted for a large number of recent synchrotron radiation facilities. Superconducting cavities are used to accelerate the electron beam circulating in the accelerator ring so as to compensate the energy lost as synchrotron radiation in the course of each turn. However, they are also used to eliminate certain instabilities in the beam and thereby increase its lifetime in the ring.

These two types of applications have been implemented at SACM for the SOLEIL synchrotron, which will comprise four superconducting accelerator cavities in its ring, and for the SLS and ELETTRA synchrotron radiation systems (Swiss and Italian, respectively), which are equipped since 2002 with Super-3HC cavities for beam stabilization.The SOLEIL cavities operate at a frequency of 352 MHz and are equipped with power couplers to provide the electron beam with RF energy from an external source. The Super-3HC cavities are passive cavities operating at 1.5 GHz, and it is the electron beam itself that provides the electromagnetic energy allowing them to suppress certain beam instabilities and lengthen the electron bunch so as to increase the beam lifetime.The technology used for these two types of cavities is similar and based on the RF structure developed by Alban Mosnier in 1992 for very high electron current systems, whose main applications are storage rings (B-Factory at SLAC, USA) and synchrotron radiation systems.

This RF structure is composed of two superconducting RF niobium cavities cooled to 4 K and very strongly coupled for all modes except the fundamental accelerator mode, allowing the generation of very intense accelerator fi elds while inhibiting the development of higher order modes (HOMs) potentially detrimental to beam stability. The RF power of these HOMs can be deposited by the beam itself

and is extracted by a set of HOM couplers whose geometry, layout and quantity are optimised to obtain the damping required for system operation. Like the cavities, these HOM couplers are superconductors and only operate correctly if cooled to 4 K with liquid helium.

SOLEIL cryomodulesA cryomodule prototype was developed during the

SOLEIL detailed design phase (APD) and tested at CERN in December 1999. These tests showed that the cryomodule meets the operating specifi cations of the SOLEIL system,

provided a few m o d i f i c a t i o n s are made. Modifi cations were performed in 2004 under SACM responsibility, in collaboration with SOLEIL and CERN teams: complete disassembly of c r y o m o d u l e , cleaning and testing of superconducting cavities in vertical cryostat (to check for absence of p e r f o r m a n c e degradation during tests), complete reassembly of c r y o m o d u l e , and RF power

validation tests at CERN.Cryomodule operation on the SOLEIL ring was validated in early 2005 and confi rmed the expected improvement in

performance: decrease in static cryogenic consumption (50 W) and better overall thermal stability, very good fi ltering of fundamental mode by dipolar HOM couplers, accelerator fi eld in cavities (Emax > 11 MV/m), and maximum power withstood by RF couplers (180 kW refl ected power).

Figure 1. Assembly of HOM coupler on SOLEIL cryomo-dule in CERN clean room (Operator: J.P. Poupeau)

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The cryomodule was installed on the SOLEIL ring in December 2005, cooled to 4 K in May 2006, and the fi rst beam was accelerated in June 2006. During the implementation phase, the intensity quickly reached 300 mA, corresponding to phase 1 nominal operation.

SOLEIL is the main contractor for a second cryomodule to be built by Accel (Germany). The order was signed in October 2005, with delivery scheduled for the summer of 2007. SACM provides specifi c services and expertise for construction-related activities and for RF power tests at CERN.

Super-3HC cryomodulesThe two Super-3HC cryomodules have operated perfectly since their installation on the SLS and ELETTRA rings in 2002. They are now key operating components of these systems, particularly for ELETTRA. A few maintenance operations are performed on a regular basis (approximately every 18 months) to replace the tuning system reducers (subject to high stresses in ELETTRA, and much less so in SLS).Accel has applied for the industrial transfer of this Super-3HC cryomodule. Several

facilities could benefi t from this system, which is currently unmatched in the industry

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Figure 2. Assembly of HOM couplers on Super-3HC cryomodule in DAPNIA clean room, Orme des Merisiers site (Operator: Y. Gasser)


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Environment

Since 2003, DAPNIA has been involved with LSCE (Laboratory of Climate and Environmental Sciences) in a project to make and install instruments to measure the

carbon dioxide concentration in the air, known as Caribou. The project is driven by LSCE, which is running a program to gain a proper understanding of how the carbon cycle works, to try to anticipate potential changes. DAPNIA was chosen for its expertise in remote control/command and for the quality of its mechanical and electrical work. The laboratory is responsible for the design, production and installation of these instruments.

CO2 measuring stationsThe specifi cations for the Caribou stations are:

- accuracy of measurement of CO2 rate in the air of 0.1 ppm;

- autonomous and continuous operation;

- a remote monitoring and control/command system;

- fi nally, periodic and automatic data transmission.

The concentration is measured using the principle of comparing CO2 concentrations in a reference gas and the gas being studied. To calculate the absolute value of the concentration, the system uses a set of standard bottles that are used to periodically calibrate the instrument and to calculate its transfer function. A control gas is used to measure any potential drift of the instrument and to trigger a repeat of the calibration procedure when necessary. The two gases to be compared must have the same thermodynamic characteristics in real time. For this, fuzzy logic regulation is used to obtain the necessary performance in terms of accuracy of measurement: 0.1 hectopascal for pressure, 0.1 ml/min for fl ow and 0.05 °C for temperature.Three stations have already been installed at their observa-tion sites and the fourth is currently being produced. The sta-tions at Biscarrosse (Landes, France) and Hanle (Ladakh, India, shown in Figure 1), were installed in 2005 and are operational and giving data. The station at Trainou (Loiret, France) has been operational since the end of 2006. The fourth station will be installed in August 2007 at Ivittuut in Greenland

Figure 1. The astronomical observatory at Hanle in India, the highest CO2 measu-ring station at an altitude of 4517 m.

Figure 2. The second gene-ration CO2 measuring rack.78

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Scientifi c publications

2004

500

450

441

151

4,28

2005

517

489

463

156

4,37

2006

514

468

464

141

4,41

Year

Scientifi c publications

Scientifi c publications with impact factor

Scientifi c publications with impact factor > 0.5

Scientifi c publications with impact factor >= 5

Expected impact

Bibliometric statistics

Intellectual production

This production includes all the papers published by DAPNIA members, and all their other professional activities. This includes:

- References of papers in scientifi c publications, conference proceedings, books, reports;- Theses and “habilitation” papers defended in the laboratory.

And also- Presentations in conferences or seminars, organisation of conferences, schools, workshops;- Pedagogical activities, participation to thesis jury, post-doc contracts;- External scientifi c responsibilities, awards, patents, science popularisation works.

Those data are reviewed in the annexe of the present Activity Report 2004-2006.

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Main PublicationsSee also complete list of DAPNIA publications on the CD-Rom report, or on the DAPNIA website.

The Standard ModelAktas A., et al. (H1 coll.)Measurement and QCD analysis of the diffractive deep-inelastic scattering cross section at HERA.Eur. Phys. J. C Vol. 48 Num. 3 (2006), 715-748Schael S. ; et al. (ALEPH Coll., DELPHI Coll., L3 Coll., OPAL Coll., LEP Working Group for Higgs Boson Searches)Search for neutral MSSM Higgs bosons at LEP.Eur. Phy. J. C Vol. 47 Num. 3 (2006), 547-587Abazov V.M. et al. (D0 Coll.)

Evidence for production of single top quarks and fi rst direct measurement of Vtb Phys.Rev.Lett.Vol. 98 (2007), 181802

Hadron structureAgeev E.S. et al. (Ball J., Bedfer Y., Bernet C., Burtin E., D'hose N., Kunne F., Le goff J., Magnon A., Marchand C., Marroncle J., Neyret D., Panebianco S., Pereira H., Platchkov S., Procureur S., Thers D.)Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs.Phys. Lett. B Vol. 633 Num. 1 (2006), 25-32

Munoz Camacho C. et al. (Beaumel M., Garcon M., Sabatie F.)Scaling tests of the cross section for deeply virtual Compton scattering.Phys. Rev. Lett. Vol.97 Num. 26 (2006), 262002

Dark matterMassey R., et al. (Aussel H., Pires S., Refregier A., Starck J.-L.)Dark matter maps reveal cosmic scaffoldingNature Vol. 445 (2007), 286

Sanglard V. et al. (EDELWEISS coll.)Final results of the EDELWEISS-I dark matter search with cryogenic heat-and-ionization Ge detectors.Phys. Rev. D. Vol. 71 Num. 12 (2005) , 122002/1-122002/16

Hamadache C., Afonso C. ; Aubourg E. ; Bareyre P. ; Charlot X. ; Coutures C. ; Glicenstein J.F. ; Goldman B. ; Gros M. ; De kat J. ; Lesquoy E. ; Le Guillou L. ; Magneville C. ; Milsztajn A. ; Palanque - Delabrouille N. ; Rich J. ; Spiro M. ; Tisserand P. ; Vigroux L. ; Zylberajch S. ; et al.Galactic Bulge microlensing optical depth from EROS-2.Astron. Astrophys. Vol. 454 Num. 1 (2006), 185-199

Tisserand P., et al. Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic CloudsAstron. Astrophys. Vol. 469 (2007), 387

Dark energyRéfrégier A. et al. (Boulade O., Boulade S., Cara C., Claret A., Magneville C. Palanque-Delabrouille N.; Schimd, C.; Sun, Zhihong)

DUNE: the Dark Universe ExplorerSpace Telescopes and Instrumentation I: Optical, Infrared, and Millimeter.; Proc. of the SPIE, Vol. 6265 (2006)

Astier, P.; et al. (Aubourg, E., Palanque-Delabrouille N., Rich, J.) The Supernova Legacy Survey: measurement of ΩM, ΩΛ and w from the fi rst year data setAstron. Astrophys. Vol. 447 (2006) 31

CP violation Aubert B. et al. (Babar Coll.)Study of the decay B0(B0)→ρ+ρ-, and constraints on the Cabibbo-Kobayashi-Maskawa angle αPhys. Rev. Lett. Vol. 93 Num. 23 (2004), 231801/1-231801/7

Aubert B. et al., (Babar Coll.)Limit on the B0→ρ0ρ0, branching fraction and implications for the Cabibbo-Kobayashi-Maskawa angle α.Phys. Rev. Lett. Vol. 94 Num. 13 (2005), 131801/1-131801/7

Batley J.R., Bloch-Devaux B. ; Cheshkov C. ; Cheze J. ; DeBeer M. ; Derre J. ; Marel G. ; Mazzucato E. ; Peyaud B. ; Vallage B. ; et al.Search for direct CP violation in the decays Κ±→3π±.Phys. Lett. B Vol. 634 Num. 5 (2006), 474-482

Cosmology and structure formation in the Universe

Rasera Y., Teyssier R.The history of the baryon budget. Cosmic logistics in a hierarchical universeAstron. Astrophys. Vol. 445 Num. 1 (2006), 1Schanne S., et al. (Cordier B. ; Limousin O. ; Paul J.)The ECLAIRs micro-satellite mission for gamma-ray burst multi-wavelength observationsN.I.M. A Vol. 567 Num. 1 (2006), 327

Galaxy formation and evolution

Elbaz D. et al. (Daddi, E.; Le Borgne, D.) The reversal of the star formation-density relation in the distant universeAstron. Astrophys. Vol. 468 Num. 1 (2007), 33-48

Bournaud F.; Duc P.-A.From tidal dwarf galaxies to satellite galaxiesAstron. Astrophys. Vol. 456 (2006), 481

Pierre M., Pacaud F. ; Duc P. ; Le Fevre J.P. ; et al.The XMM Large Scale Structure: a well-controlled X-ray cluster sample over the D1 CFHTLS area. M.N.R.A.S Vol. 372 Num. 2 (2006), 591-608

Formation of stars and planetsPeretto N., Andre P. ; Belloche A.Probing the formation of intermediate - to high-mass stars in protoclusters. A detailled millimeter study of the NGC 2264 clumps.Astron. Astrophys. Vol. 445 Num. 3 (2006), 979-998

Lagage P.O., Doucet C. ; Pantin E. ; Habart E. ; Duchêne G. ; Ménard F. ; Pinte C. ; Charnoz Z. S. ; Pel J.W.Anatomy of a fl aring proto-planetary disk around a young intermediate-mass starScience Vol. 314 (2006), 621

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Talvard M. et al. (Andre P. ; Rodriguez L. ; Minier V. ; Boulade O. ; Doumayrou E. ; Dubreuil D. ; Durand G. ; Gallais P. ; Horeau B. ; Lagage P.O. ; Le pennec J. ; Lortholary M. ; Martignac J. ; Schneider N. ; Veyssiere C. ; Walter C. ; Agnese P.)ArTeMiS: Filled bolometer arrays for next generation submm telescopesProc. of the SPIE, Vol 6275 (2006), 10 1117/12 671133

Charnoz S., et al. (Deau E., Brahic A.) Cassini discovers a kinematic spiral ring around SaturnScience Vol. 310 (2005), 1300

Stellar and laboratory plasmasR A. García et al. (S. Turck-Chièze, S. Mathur)Tracking solar gravity modes: the dynamics of the solar coreScience, Vol. 316 (2007), 1591

Brun A.S., Browning M.K. ; Toomre J.Simulations of core convection in rotating A-type stars: Magnetic dynamo actionAstrophys. J. Vol. 629 (2005), 461

Bouquet S., Chieze J. ; THAIS F. ; et Al.Observations of laser driven supercritical radiative shock precursorsPhys. Rev. Lett. Vol. 92 Num. 22 (2004), 5001

Compact objects and their environmentFerrando P. et al. (Arnaud M. ; Goldwurm A. ; Laurent P. ; Lebrun F. ; Limousin O.)Simbol-X: mission overviewProc. of the SPIE Vol. 6266 (2006)

Falanga M., Goldoni P. ; Goldwurm A. ; et Al.INTEGRAL and RXTE observations of accreting millisecond pulsar IGR J00291+5934 in outburstAstron. Astrophys. Vol. 444 Num. 1 (2005), 15-24

Lebrun F. et al. (Goldwurm A. ; Terrier R.)Compact sources as the origin of the soft gamma-ray emission of the milky wayNature Vol. 428 Num. 6980 (2004), 293

Cosmic ray sourcesAharonian F., Goret P. ; et Al.High-energy particle acceleration in the shell of a supernova remnant.Nature Volume 432 Numéro 7013 (2004), 75-77

Cassam Chenai G., Decourchelle A. ; Ballet J. ; Sauvageot J. ; DUBNER G. ; giacami E.XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source observations of SNR RX J1713.7-3946Astronomy and Astrophysics Volume 427 (2004), 199

Grenier I.; Casandjian J.M., Terrier, R. Unveiling Extensive Clouds of Dark Gas in the Solar NeighborhoodScience, Vol. 307 (2005), 1292

Miceli, M.et al. (Decourchelle, A.; Ballet, J.)The X-ray emission of the supernova remnant W49B observed with XMM-NewtonAstron. Astrophys. Vol. 453 (2006), 567

Exotic nucleiRaabe R., Sida J.L., Charvet J.L., Alamanos N., Drouart A., Gillibert A., Heinrich S., Jouanne C., Lapoux V., Nalpas L. et al. No enhancement of fusion probability by the neutron halo of 6He.Nature Vol.431 Num. 7010 (2004) 823-826

Chatillon A., Theisen C., Bouchez E., Clement E., Dayras R., GÖRGEN A., Korten W., Le coz Y., Simenel C. et al.Spectroscopy and single-particle structure of the odd-Z heavy elements 255Lr, 251Md and 247Es.Eur. Phys. J. A Vol.30 Num. 2 (2006) 397-411

Obertelli A., Gillibert A., Alamanos N., Auger F., Dayras R., Drouart A., Keeley N., Lapoux V., Mougeot X., Nalpas L., Pollacco E., Skaza F., Theisen C. et al.Shell gap reduction in neutron rich N=17 nuclei.Phys. Lett. B Vol.633 Num. 1 (2006) 33-37

Development of detectorsDegerli Y., Besançon M. ; Fourches N. ; Li Y. ; Lutz P. ; Orsini F. ; et al.Performance of a fast binary readout CMOS active pixel sensor chip designed for charged particle detection.IEEE Trans. Nucl. Sc. Vol. 53 Num. 6 part 2 (2006), 3949-3955

Dirks B., Blondel C. ; Daly F. ; Gevin O. ; Limousin O. ; Lugiez F.Leakage current measurements on pixelated CdZnTe detectors.N.I.M. A Vol. 567 Num. 1 (2006), 145-149

Sanglard V., Chardin G. ; Charvin P. ; Deschamps H. ; Fesquet M. ; Fiorucci S. ; Gerbier G. ; Gros M. ; Herve S. ; Karolak M. ; De lesquen A. ; Mallet J. ; Mosca L. ; Navick X.F. ; Schoeffel L. ; Villar V. ; et al.Final results of the EDELWEISS-I dark matter search with cryogenic heat-and-ionization Ge detectors.Phys. Rev. D. Vol. 71 Num. 12 (2005), 122002/1-122002/16

Billot N., Agnese P. ; Augueres J.L. ; Beguin A. ; Bouere A. ; Boulade O. ; Cara C. ; Cloue C. ; Doumayrou E. ; Duband L. ; Horeau B. ; Le Mer I. ; Le pennec J. ; Martignac J. ; Okumura K. ; Sauvage M. ; Simoens F. ; Vigroux L. ; Reveret V.The Herschel/PACS 2560 bolometers imaging cameraAstrophys. J. (2006), 10 1117/12 671154 ; Eds. SPIE, Proc. 6265, 11 (2006)

Giomataris I., De Oliveira R. ; Andriamonje S. ; Aune S. ; Charpak G. ; Colas P. ; Giganon A. ; Rebourgeard P. ; Salin P.Micromegas in a bulk.N.I.M. A Vol. 560 Numéro 2 (2006), 405-408

Signal processing and real time systemsDelagnes E., Degerli Y. ; Goret P. ; Nayman P. ; Toussenel F. ; Vincent P.SAM: a new GHz sampling ASIC for the H.E.S.S.-II front-end electronics.N.I.M. A Vol. 567 Num. 1 (2006), 21-26

Limousin O., Gevin O. ; Lugiez F. ; Chipaux R. ; Delagnes E. ; Dirks B. ; Horeau B.82

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Anvar S., Gachelin O. ; Kestener P. ; Le provost H. ; Mandjavidze I.FPGA-based system-on-chip designs for real-time applications in particle physics.IEEE Trans. Nucl. Sc. Vol. 53 Num. 3 part 1 (2006), 682-687

Abbon P., Delagnes E. ; Deschamps H. ; Kunne F. ; Magnon A. ; Neyret D. ; Panebianco S. ; Rebourgeard P. ; et alFast readout of the COMPASS RICH CsI-MWPC photon chambers.N.I.M. A Vol. 567 Num. 1 (2006), 104-106

Intensive computation and simulationPierre M., Pacaud F. ; Duc P. ; Le Fevre J.P. ; et al.The XMM Large Scale Structure: a well-controlled X-ray cluster sample over the D1 CFHTLS area. M.N.R.A.S Vol. 372 Numéro 2 (2006), 591-608

Pomarede D., Thooris B., Audit E., Teyssier R. Numerical simulations of astrophysical plasmasProc. of the 6th IASTED Int. Conf. on Modeling, Simulations, and Optimization (MSO2006), Gaborone, Botswana, September 11-13, 2006, ed. H. Nyongesa, 507-058, Acta Press, ISBN:0-88986-618-X

Pomarede D., Audit E., Teyssier R., Thooris B.Visualization of large astrophysical simulations datasetsProc. of the Conf. on Computational Physics (CCP2006), Gyeongju, Republic of Korea, August 29-31, 2006, ed. J.S. Kim, Computer Physics Communications, 177 (2007) 263

Starck J.L., Pires S. ; Refregier A.Weak lensing mass reconstruction using wavelets.Astron. Astrophys. Vol. 451 Num. 3 (2006), 1139-1150

Particle acceleratorsMosnier A., Farabolini W., Duperrier R., Bogard D., Curtoni A., Authier M., Roux R., Girardot P., Delferrière O., Dispau G., Jablonka M., Jannin J.L., Luong M., Peauger F., Simon C.The probe beam linac in CTF3.10th European Particle Accelerator Conference (EPAC - 2006), Edimbourg, Royaume-uni, 26/06/2006 - 30/06/2006 Proc. (2006), 679-681

Visentin B., Charrier J.P. ; Gasser Y. ; Regnaud S.'Fast Argon-Baking' process for mass production of niobium superconducting RF cavities.10th European Particle Accelerator Conference (EPAC - 2006), Edimbourgh, Royaume-uni, 26/06/2006 - 30/06/2006Proc. (2006), 381-383

Superconducting magnetsVedrine P., Arnaud M. ; Levesy B. ; Mayri C. ; Pabot Y. ; Rey J. ; Sun Z.Manufacturing and integration progress of the ATLAS barrel toroid magnet at CERN.IEEE Trans. on Applied Superconductivity Vol. 14 Numero 2 (2004), 491-494 18th Int. Conf. on Magnet Technology (MT - 2003), Iwate, Japon, 20/10/2003 - 24/10/2003

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Nuclear data measurements and modellingArmbruster P. et al. (Boudard A., Leray S., Volant C.)Measurement of a complete set of nuclides, cross sections, and kinetic energies in spallation of 238U 1A GeV with protons.Phys. Rev. Lett. Vol.93 Num. 21 (2004) 212701

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En couverture : SerenoMosaïque de Giovanna GalliDate : 2006Dimensions 50 cm X 50 cm

Au verso du document, liste des personnes présentes au Dapnia entre le 1er janvier 2004 et le 1er janvier 2006 pour une durée d’au moins 6 mois.

Directeur de la publication : Jean Zinn-JustinConception : François Bugeon, Yves SacquinCoordination rédactionnelle : Yves Sacquin

Comité de rédaction : François Bugeon, Guillaume Devanz, Jean-Michel Dumas, Bertrand Hervieu, Fabien Jeanneau, Pierre-Olivier Lagage, Paul Lotrus; Philippe Mangeot; Laurent Nalpas; Johan Relland; Angèle Séné; Michel Talvard; Didier VilanovaRédacteurs de la brochure : Nicolas Alamanos, Philippe André, Shebli Anvar, Éric Armengaud, Édouard Audit, Alberto Baldisseri, Pierre-Yves Beauvais, Pierre Bosland, Denis Calvet, Jean-Pierre Chièze, Olivier Cloué, Michel Cribier, Antoine Daël, Anne Decourchelles, Éric Delagnes, Guillaume Devanz, Jean-Michel Dumas, David Elbaz, Ioannis Giomataris, Pierre-François Giraud, Andreas Goergen, Andrea Goldwurm, Bertrand Hervieu, Fabien Jeanneau, Pierre-Olivier Lagage, Jean-Marc Le Goff, Olivier Limousin, Paul Lotrus, Sotiris Loucatos, Christophe Magneville, Philippe Mangeot, Patrice Micolon, Alban Mosnier, Claude Pigot, Alexandre Réfrégier, Johan Relland, James Rich, Danas Ridikas, Vannina Ruhlmann-Kleider, Laurent Schoeffel, Angèle Séné, Romain Teyssier, Sylvaine Turck-Chièze, Pierre Védrine, Christophe Yèche, Jean Zinn-Justin.

Traduction : Provence Traduction

Conception graphique et maquette : Christine MarteauMise en page version française : Christine Marteau

Mise en page version anglaise : Atefo

http://www-dapnia.cea.fr

Dépôt légal : septembre 2007 ISBN : 978-2-7272-0228-8

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