The ultimate constituents of matter - CEA-Irfu

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Dapnia 2004 - 2006
Activity Report
En couverture :
Sereno
Mosaïque de Giovanna Galli
Date : 2006
Dimensions 50 cm X 50 cm
Directeur de la publication : Jean Zinn-Justin
Conception : François Bugeon, Yves Sacquin
Coordination 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 Vilanova
Rédacteurs 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 Marteau
Mise 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
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.
Dapnia
Activity Report
2004 - 2006
Laboratory of research
into the fundamental laws
of the Universe.
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.
DAPNIA research themes
and programmes
Introduction
Budget and manpower
The ultimate constituents of matter
The Standard Model
Physics at the LHC
Neutrinos
Hadron structure
Energy content of the Universe
Dark matter
Dark Energy
Antimatter and CP violation
Structure formation in the Universe
Cosmology and structure formation in the Universe
Galaxy formation and evolution
Structure and evolution of stars
Formation of stars and planets
Stellar and laboratory plasmas
Compact objects and their environment
Cosmic ray sources
Nuclear matter in extreme states
Quark-gluon plasma
Exotic nuclei
4
7
8
10
12
14
17
18
20
22
25
26
28
31
32
34
36
38
41
42
44
Innovation for detection systems
47
Development of detectors
Signal processing and real time systems
Intensive computation and simulation
48
50
52
Magnets and accelerators
Particle accelerators
Superconducting magnets
Test facilities
New developments for magnet and accelerator instrumentation
Physics for nuclear energy
Nuclear data measurements and modelling
Technological research for fusion energy
DAPNIA expertise at the service of society
Physics and health
Expertise in decommissioning and design of nuclear facilities
Light sources
Environment
DAPNIA publications
2
3
55
56
58
60
62
65
66
68
71
72
74
76
78
80
Jean Zinn-Justin
Head 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 scientific activities cover the fields 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 specific
both scientific 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 fields 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 scientific equipment
to be built more efficiently 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 scientific 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 first five encompass thematic
fields of physics, while the other concern related technological developments as well as applications of DAPNIA’s
expertise to other fields or society problems.
The choice of themes confirms 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 scientific fields 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 five 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.
3
Budget and Manpower
Dapnia 2004 - 2006
2006 Budget
Resources (k€)
Grant: 59 560
External resources: 11 908
External resources (k€)
1 783
National Agencies:
3 707
CNES:
2 904
Europe:
Nucl. instal. decommissioning: 770
739
Internal CEA:
2 005
Other:
Expenditures (k€)
45 010
Manpower:
Foreign collab. and post-docs: 1 674
3 007
Travels and per diem:
5 846
Logistics:
15 931
Programmes:
Repartition according to programmes (k€)
Astrophysics:
Particle physics:
Nuclear physics and activities:
Accelerators:
Magnets:
Other:
4
4 413
4 546
1 048
3 141
2 320
463
Unit
DIR
SPP
SPhN
SAp
Sédi
SIS
SACM
Senac
Permanent staff
Total
Engineers,
Technicians
physicists and
and
Total
executives administration
12
70
50
80
79
52,5
66
6
415,5
20
3
4
17
58
50,5
48
4
204,5
Budget and Manpower
DAPNIA women and men
in 2006
32
73
54
97
137
103
114
10
620
Non permanent staff and external collaborators
5
Laboratoire de recherches sur les lois fondamentales de l’Univers
6
The ultimate constituents
of matter
O
nly
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
7
Dapnia 2004 - 2006
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 field. 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 analyses
tanβ
The 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 collaborative 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 relationship between the Z and W boson masses, the top
quark mass and the Higgs boson mass. If the W and Z boson characteristics were precise enough to be sensitive to
(d)
Excluded
by LEP
10
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
finalised their measurements in 2006. The final W boson
mass measurements were then combined for the first time
by the four experiments in the summer of 2006. The validity
of the Standard Model was reconfirmed, 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 chiefly obtained during LEP1.
From these results, an upper bound (with a 95% confidence
level) of 166 GeV/c2 can be deduced for the standard
Higgs boson mass, completing the lower bound (with a
95% confidence 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
1
0
8
Theoretically
Inaccessible
CPX
20
40
60
80
100 120 140
mH1 (GeV/c2)
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.
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.
-1
H1 Data (prelim.)
All SM
Signal
102
NData = 46
NSM = 43.0 ± 6.0
10
1
10-1
0
10
PXT
20
30
40
50
60
70
(GeV) e and µ channels
±
l+Pmiss
events at HERA 1994-2006 (e p, 341 pb )
T
Events
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 spacetime 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 final 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.
80
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.
HERA analyses
Run 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 crosssections in neutral- and charged-current deep inelastic interactions. The results were used to fit parton density measurements with Standard Model parameters. Work is now
underway to include jet production cross-sections, paying
close attention to systematic uncertainties. These latest developments 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 virtually intact after the interaction. These processes account
for some 10% of all inelastic collisions and therefore deserve specific analysis. Here, too, DAPNIA's physicists have
been very active and studies carried out teach us more
about these interactions, which will be of significant 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
findings agree with the Model. Deviation from the Model
can still be observed for topologies comprising an isolated
lepton and a missing momentum in the final state – electronjet-neutrino or muon-jet-neutrino (see Figure 2)
9
Laboratory of research into the fundamental laws of the Universe
Dapnia 2004 - 2006
Physics at the LHC
T
he 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 verified: 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.
ATLAS
DAPNIA 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, filled with argon and tested. DAPNIA is
also responsible for the first-level trigger system.
Installation of the boards and cables is almost
completed and calibration tests have begun.
either using muon beams or cosmic rays. They are currently
used in physical analysis work, where they have validated
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 field 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 field 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 difficult 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.
10
These programs have been used in analysis work where
various sub-detectors can be combined with data obtained
Figure 1. View of the trajectory of a cosmic muon recorded by the Atlas
spectrometer. The magnetic field effect can be seen in the curve of the
trajectory. Only the detectors concerned are shown here. DAPNIAdeveloped software is used for reconstruction and display purposes.
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
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
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-deFrance region Tier 2, a major
node in the computing grid.
CMS
CMS is a compact, highprecision
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 field 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 first 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 first 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 first proton-proton collisions by 2008.
Figure 2. Lowering of a CMS detector segment.
The detector segments are assembled above ground
before being installed in the experimental cavern.
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 final 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
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
11
Dapnia 2004 - 2006
12
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 flavours – 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 flavour 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
experimental
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 Chooz
Nuclear 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 fluxes 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 manmade 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
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)
cylinder 7 m high and 7 m in diameter. In addition, each
detector is made up of four vessels fitting one inside the other
to improve antineutrino detection and select interactions
more clearly. DAPNIA is in charge of making the detector
K2K & T2K
The 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 first time ever,
to determine a phase parameter, δ, associated with matterantimatter asymmetry. With this in view, DAPNIA's physicists
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 amplified by the use of readout 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.
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.
The road to very large detectors
After 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 work
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 fitted with neutrino oscillation and the dotted line the expected
distribution with no oscillation. Measurements reveal a neutrino deficit
and a deformation of the spectrum in agreement with νμ oscillation.
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 confirmed the oscillation
observed in atmospheric neutrinos. A beam produced at the
KEK laboratory was detected 250 km away in the SuperKamiokande 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,
So 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 fissions
are different from those emitted during uranium-235 fission.
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 find out more about the energy spectra
of the antineutrinos produced by different types of fission.
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
13
Dapnia 2004 - 2006
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
define 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 define 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 quarks
In 2004-2005, the Happex Collaboration completed
Q 2 = 0.1 GeV
0.15 H
AP
PE
[18]
[19]
[20]
[21]
[22]
[23]
2
X-
0.1
H
0.05
GsE 0
HAPPEX-4 He
-0.05
-0.1
-0.15
-1.5
-1
-0.5
0
GsM
0.5
1
Figure 1. Happex results (black outline), shown in the G Es - GMs plane
and compared with various models and other experimental results.
14
1.5
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, G Es and G Ms . 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 spin
The 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 first 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
Compass has also yielded one of the first 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 fitting of g1 which offer an indirect
measurement of ΔG.
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.
Generalised parton distributions
Generalised 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 first-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 defining 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 definition 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 define this detector, which should be commissioned
in 2010 for use in measuring spin and beam charge
(μ+/μ-) asymmetries on the proton and neutron.
of asymmetry also rules out high ΔG values.
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 significant impact. Research teams have investigated the
role of two-proton exchange and higher-order radiative
corrections in large-momentum-transfer, elastic electronnucleon scattering, which affects the electromagnetic form
factors of the proton. The structure and decay channels
of baryon resonances are related to
specific 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.
15
16
The energy content of
the Universe
A
stronomical 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
F
or 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 Universe
Gravitational lenses are one of the manifestations of dark
matter at the scale of the Universe. The light from distant galaxies
is deflected 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 observations of the same field 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 decomposition using wavelet packets, have allowed dark matter to be
mapped in three dimensions for the first time. DAPNIA teams are
now actively involved in the DUNE wide-field space imager project, 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.
The analysis of observations made by DAPNIA teams with
the XMM-Newton satellite shows that nearby galactic
clusters have density profiles in excellent agreement with
the theoretical predictions of the standard, non-relativistic,
'cold' dark matter model.
Figure 2. Radial dark matter
distribution in ten galactic clusters.
DAPNIA teams now seek to study the more distant, younger
galactic clusters identifiable in Canada-France-Hawaii Telescope data (CFHT) obtained with the MegaCam camera 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 sources. The distant galactic clusters identified in this manner
are currently being surveyed as part of the XMM-LSS X-ray
observation programme.
Figure 1. Visible matter (left) and dark matter
(right) in the field of the COSMOS survey.
Galactic clusters
The largest concentrations identified 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.
18
Investigating dark matter at the
scale of galaxies
Dark 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 demonstrating that collisions between massive galaxies must form
second-generation dwarf galaxies. According to conventional models, these dwarf galaxies should not contain dark
matter, and observations are now being made to confirm
this.
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The
Search for baryonic dark matter
interactions in cryogenic bolometers installed in the
Modane Underground Laboratory. The final results from
the first 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.
In 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 significant quantity of baryonic
dark matter if all galaxies contain similar proportions.
Indirect detection of non-baryonic
dark matter
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 final
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
matter
None 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
field. DAPNIA is responsible for the Micromegas detector
used in this experiment. The first results recently published
impose limits on the axion-photon coupling constant.
E2 × dN/dE (TeV cm-2 s-1)
Figure 3. Map of our galaxy showing the visible molecular gas (blue)
and dark molecular gas detected by γ –ray observations with EGRET.
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 flux
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 flux.
10-11
10-12
-13
10
2004 (H.E.S.S.)
2003 (H.E.S.S.)
MSSM
KK
70% bb, 30% τ+τ-
1
10
Energy (TeV)
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.
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 electronpositron pairs. The INTEGRAL satellite's observations may
therefore indicate the existence of light dark matter particles
with masses between 1 and 100 MeV/c2
• 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
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20
Dark Energy
R
ecent 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 fly 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 difficult
to reconcile with
fundamental
physics
whose
prediction for its
energy
density
Figure 1. Composition of the Universe
differs by more
today according to recent cosmological
than 30 orders
measurements. The Universe density is
of magnitude. A
dominated by dark matter and dark
convenient way to
energy, while ordinary matter makes
up only a small fraction. Dark energy
study dark energy
produces an acceleration of the expansion
is to consider
of the Universe at our cosmological epoch.
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
modification 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 distanceredshift 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 field 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 Megacam
Several 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-FranceHawaii Telescope (CFHT). Megacam is a wide-field 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 lensing. 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 cosmological constant, but further measurements are needed to rule out
other models of dark energy.
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 Supernovae of the SNLS survey (left) and weak lensing (right) derived from
Megacam on CFHTLS are shown, along with BAO constraints from SDSS.
While the recent measurement described above confirm
that the behaviour of dark energy is close to that of Einstein’s
cosmological constant, more precise measurement are needed
to give a definite 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 fly 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 scientific 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).
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 distribution of cluster numbers with redshift dN/dz . (from Holder et al.)
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.
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 benefit from recent progress in cell
phone amplifiers. DAPNIA is involved in simulation of the
instrument, as well as in the construction of a prototype of
electronics chain.
DUNE: The Dark Universe Explorer
matter
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The
Future Experiments planned at
DAPNIA
DUNE is a wide-field 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
modifications of Einstein’s
Figure 4. The Dark Universe
theory of gravity. Immediate
Explorer (DUNE) mission is a
secondary goals of DUNE
wide-field space imager which
will make a full sky map of large
concern the evolution of
scale structure. DUNE will place
galaxies, to be studied with
definite constraints on dark energy
groundbreaking statistical
through its effect on the distribupower, the detailed structure
tion of matter in the Universe.
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) field-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
The HSHS BAO experiment
An 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
21
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Antimatter and CP violation
I
n 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 field is another major enigma of
modern physics. The Anti-Hydrogen experiment currently under preparation at DAPNIA
addresses this issue.
Investigating matter-antimatter asymmetry
In 1967, A. Sakharov proposed an explanation to the
matter-antimatter asymmetry in the Universe based on a
mechanism involving the 'CP violation' phenomenon first
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 specifically due to 'direct' CP violation,
which reflects 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 kaons
22
The 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 → π0 e + 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 fluxes 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 ± → π0 e ±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 significant contribution to the understanding
of the interaction between low energy pions.
BaBar experiment: CP violation in Bmesons
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 first observation of CP violation outside the
kaon system, and a significant confirmation 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
0.4
0.3
γ
matter
Universe
constituents
of the of
ultimatecontent
Theenergy
The
0.5
excluded area has CL > 0.95
0.6
η
accuracy of the DIRC particle identification
system used for the experiment (developed with
significant 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.
CK M
fitter
CKM 2006
εK
ms & md ,
sin2β
& Vub/V cb
γ
sol. w/ cos2β < 0
(excl. at CL > 0.95)
α
α
0.2
0.1
How does anti-hydrogen fall?
A way to test the behaviour of antimatter in a gravitational
field 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 field.
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 sufficiently '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).
0
-0.4
γ
α
-0.2
0
β
0.2
ρ
0.4
0.6
0.8
1
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.
DAPNIA is presently conducting the first 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
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 field.
As a first 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 efficient type of material for the conversion
of positrons into positroniums to be emitted in a vacuum.
23
24
The structure formation in
the Universe
T
he 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 numerical 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
25
The structure
formation
in theof
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matter
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The ultimate
Dapnia 2004 - 2006
Cosmology and structure
formation in the Universe
T
he study of the large-scale structures of the Universe has developed dramatically over the
past two decades, since the discovery of temperature fluctuations 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 evolution, small primordial density fluctuations grew under the effect of gravitational instability
and formed the galaxies and galactic clusters that we observe today.
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 first
stars. It also requires increasingly efficient 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 first
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
background
26
The 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 fluctuations.
DAPNIA has participated in measurements of cosmic
microwave background radiation fluctuations for over 10
years now. In particular, it was involved in the ARCHEOPS
experiment, which yielded one of the first 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).
Figure 1. Map of the cosmic microwave background observed by the WMAP satellite. (Source: NASA/WMAP)
Detecting the end of the « dark age »
This long period following the recombination period and
preceding the formation of the first stars lasted approximately
100 million years. It came to an end when the concentration
of matter due to gravitational instability was sufficient to
allow the formation of the very first stars ('Population III'
stars). These stars 'reionised' the intergalactic medium and
profoundly modified 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 gammaray 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.
The 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.
cosmic history. Their quantity, physical properties and spatial
distribution all constitute extremely valuable cosmological
probes. DAPNIA physicists have significantly 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).
matter
constituents
The The
structure
formation
in theof
Universe
ultimate
Modelling galaxy formation
Understanding the structure of the
Universe
Galaxies organise themselves at large scales within giant
clusters and filaments 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 specific status, since they are the last objects formed in
Figure 3. Dark matter distribution (projected density map)
simulated by a Horizon project team at CCRT (CEA Bruyèresle-Châtel). (Source: Christophe Pichon, CNRS/DAPNIA)
These large-scale observations of the Universe (such as those to be conducted by the DUNE satellite, DAPNIA's new
key project) should yield significant measurements of current
cosmological model parameters, supplementing cosmic microwave background observations. They will also be used
to test the general paradigm of gravitational instability in an
expanding universe
Figure 2. Primordial galaxy (projected density map) simulated by a
Horizon project team on the MareNostrum supercomputer (Barcelona Supercomputing Centre). (Source: Pierre Ocvirk, DAPNIA)
27
The structure
formation
in theof
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matter
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The ultimate
Dapnia 2004 - 2006
Galaxy formation and
evolution
O
bservational 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 influence 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 scientific 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 spectrum to study their various components (stars, gasses and dust) in their different states (neutral, 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 largescale 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 clusters
28
Galaxy 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 (intracluster 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 specific 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 contractorship of the DAPNIA), has unveiled population of galaxy
groups that was hitherto unknown.
Together, these studies show how difficult it is to understand
galaxy clusters evolution and formation without taking account of the evolution of galaxies themselves, in their environment.
Galaxies and their environment
Galaxies have thus exerted an influence 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 first 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
matter
constituents
The The
structure
formation
in theof
Universe
ultimate
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
first 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.
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.
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.
Conclusions
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.
Star formation in galaxies
DAPNIA/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
scientific 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
Work 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, quasiprimordial). 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
29
30
Structure and evolution
of the stars
T
he energy driving galaxy
evolution comes from many
sources like the formation of stars
and their explosion in supernova,
the formation of supermassive 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 multiscale 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
31
matter
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stars
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Dapnia 2004 - 2006
A
strophysicists 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 specifically Saturn rings, are the subject of spectacular
findings made using the Cassini probe.
Simulation of interstellar cloud
formation
The 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 difficulties, related to the multiphase nature of this
medium, impeded its correct treatment for years. Today,
the development of computing tools allows registering
significant progresses. Astrophysicists from SAp managed
to simulate, with very high resolution, the first stage of
the formation of a molecular cloud, with creation of cold
and rather dense cold gas condensations, in a turbulent
bidimensional and multiphase flow. 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.
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
Star formation in interstellar clouds
The 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
32
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): positionvelocity 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)
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 finest 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.
DAPNIA astrophysicists are also responsible for the scientific and technical aspects of the ArTéMis project, which
aims to produce a large-scale bolometer array submillimetric camera for ground-based telescopes, using technology
developed by the CEA for PACS. A first prototype camera
has been designed to operate at a wavelength of 450 micrometers. It was successfully tested, in March 2006, at the
focal plane of the KOSMA telescope at the Gornergrat observatory in Switzerland, then in March 2007 on the APEX
telescope, a 12 m antenna used to prepare the development of the future ALMA interferometer.
Figure 4. A surprising
view of the Saturn
F ring, taken on 29
October 2004 by
Cassini’s narrow field
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 finest details here are
about 940 metres. (photo credit: NASA/ESA)
Protoplanetary disks and planet
formation
SAp 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
Figure 3. Left: false-colour image of infrared emission at 8.6 μm, from
the matter surrounding star HD 97048, obtained by VISIR. Comparison 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)
matter
ofof
constituents
stars
ultimate and
TheStructure
evolution
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 first
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.
Planets and Saturn rings
SAp researchers are finally conducting research
into planets and, more specifically, Saturn rings (See
figure 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: first on the
unilluminated side and then the side illuminated by the
Sun. These first measurements led to surprising findings:
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
33
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M
ost 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 field 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.
The internal dynamics of stars right
to the solar core, revealed using
seismology
The 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 fluxes, the GOLF instrument
has been used to research "gravity" modes that convey
totally new information: rotation in the nuclear region
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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.
and the influence of deep magnetic fields. 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
identification 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 SoHO'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 field 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, significant 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.
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Figure 3. Photo of a GOLF-NG cell, instrumented by
the SIS. The cell is filled 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.
Figure 2. The GOLF-NG prototype being tested at the premises of Sédi.
Magnetohydrodynamic processes
simulated on large computers
3D 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 influence on the tachocline. A non-linear 3D calculation
(Figure 4) confirms the existence of non-axisymmetrical
instabilities in the poloidal field 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 plasmas
Laboratory 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-flux 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 scientific communities in astrophysics and
laser inertial fusion. The SINERGHY project is responding
to these needs with
the development of
t h re e - d i m e n s i o n a l
hydrodynamics,
massively
parallel
algorithms, the management and display
of large quantities of
data and fi nally, the
creation of a shared
library of transport
coefficients, equations
of state, and rates of
nuclear and chemical
reactions
Figure 4. 3D simulation of a portion of the solar radiative zone showing the diffusion
of the magnetic field and how the rotation of the zone changes over time.
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Compact objects and their
environment
C
ompact 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
fields, 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 fields, the physical phenomena associated to the accretion of matter and to the emission of relativistic
jets, the nature of particle acceleration in extreme magnetic
fields, nucleosynthesis processes of supernovae, the formation 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
scientific 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 benefited
from several coordinated multiwavelength observation
programmes, from the radio wave to the ultraviolet (UV)
domains.
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 possible to place strong constraints on the emission mechanisms.
In addition, a quasi-periodicity of about 22 minutes was detected in the longest X-ray flare. 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 first time, an
estimate of the black hole spin.
The supermassive black hole at the
galactic centre
One of DAPNIA's most important scientific 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. Identified 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 flares, originating close to the black hole’s horizon, were discovered and closely studied as a result
of a vast campaign of simultaneous observations performed
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Figure 1. View of the Galactic centre region at low-energy gamma
rays, as seen from the INTEGRAL observatory. The image includes 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.
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
identified with Sgr A*, nor with any of the other objects of this
complex region, but it could be related to the TeV γ source detected at the centre of the Galaxy by HESS in 2004 (Fig. 2).
This source also coincides with Sgr A* but cannot be clearly
identified either. Its spectrum is not compatible with that expected 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 20200 keV band, resolving a good fraction of it as point like
Stellar black holes and microquasars
Accreting 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 explained 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 first microquasar to show apparent superluminal – or
faster-than-light – motion) in which the accretion rate varies
significantly 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 accretionejection 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* flares.
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
isolated
Unlike black holes, neutron stars have their own magnetic
field, 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
flow is dominated by the magnetic field (Fig. 3).
The most significant results in this field 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
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sources, most of which are made up of binary systems with
an accreting compact object.
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)
first 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 emissions from magnetars, including ‘soft gamma-ray repeaters’
and ‘anomalous X-ray pulsars’. These neutron stars are powered by their extremely intense magnetic fields (∼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 programmes
The 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 first 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 benefit from the laboratory's participation
to the UV-visible-IR X-SHOOTER spectrograph project, an instrument to be installed at the ESO's VLT in 2008.
The SIMBOL-X programme, the first telescope capable of focusing hard X-rays (> 10 keV) through the use of multi-layer X-ray
mirrors and the operation of two satellites in formation flying, is
also in Phase A study, as part of a French-Italian mission. SIMBOL-X main scientific objectives are the physics of compact objects and particle acceleration processes in the Universe
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Cosmic ray sources
S
tudying 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 finally 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 field 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 first step towards detecting highenergy 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 sufficiently 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
simulations
A 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 first 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
38
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
fluxes 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 fluxes 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
Figure 1. The supernova G347.3-0.5 (or RX J1713-3946), displayed in Xrays by XMM-Newton (on the left), and in γ rays by HESS (on the right).
filament-like morphology is explained by significant radiative
synchrotron losses on TeV-accelerated electrons and
induces a strongly amplified magnetic field at the shock.
Moreover, the morphology of the thermal X-ray emission
from young supernova remnants can only be explained
by significant back-reaction of cosmic rays on the shock
structure. These results are in line with models of cosmic-ray
modified 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 field weakens
and prevents any efficient 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 efficient acceleration.
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.
Extragalactic 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 flux 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 flux is too
weak for Antares but will be easily detectable by the km3
detector.
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Future instrumentation
Future instrumentation
Acceleration in pulsar wind nebulae:
observations and modelling
Observations 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 field, 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 first 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 400700 TeV.
Cosmic rays interacting with
dense matter in our Galaxy
Extragalactic 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
flux 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 flux is too
weak for Antares but will be easily detectable by the km3
detector.
For 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 finished 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 experiments. 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 3. Visualizing the trajectory
of an upward muon produced
by a neutrino, detected by
the five first Antares lines.
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Nuclear matter
in extreme states
T
hese 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
C
entral 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 plasma
The 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 confined 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 final
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 final 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 first of these experiments has identified
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 production of these particles should be suppressed, since in such
dense and 'coloured' media, quark-antiquark interactions
are screened by surrounding colour charges and become
insufficient to form bound states. This suppression was predicted in 1986, and results tending to confirm this prediction 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 experiment
The first 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 first significant data on J/ψ production
in gold-gold collisions (for which DAPNIA played a key
role) has been recently published. Figure 1 shows the nuclear modification factor (R AA), which compares J/ψ production 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 significant suppression as a function of the number of
participants, far beyond that corresponding to cold nuclear
Figure 1. Evolution of the nuclear modification factor as a function 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 fit the deuterium-gold data).
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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 experiment
For 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 significant
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 final 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 qualified at Saclay.
DAPNIA took in charge the construction of the supporting
structures for the detection components of the trajectography chambers. These structures consist of large honeycomb
panels (approximately 6 x 3 m2 for the largest ones) with
carbon fibre 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
Figure 3. Pad chamber installed at CERN.
(© Antonio Saba, www.antoniosaba.com)
groups and in the definition and implementation of the analysis 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 first proton beams at the beginning of the experiment, the first lead-lead collisions should
follow a year later
Figure 2. Exploded view of the ALICE experiment. The tracking chambers of the 'muon arm' are shown in blue.
a systematic testing phase, the detectors received from the
various partner laboratories are mounted on the supporting
structures, cabled, and installed in their final 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-micrometer spatial resolution required to separate the different 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
43
of matter
constituents
The
nuclear
matter
in extreme
states
ultimate
The
Dapnia 2004 - 2006
Exotic nuclei
T
he atomic nucleus is a many-body quantum system of strongly interacting particles, the
protons and neutrons. As a complete description of this system from first principles is not
possible, mean-field 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 nuclei
The 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 confirmed, 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 influence 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 structure
44
The 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 subshell closures in nuclei far from stability may differ significantly
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 neutronrich 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 first 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 coexistence
The 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 filled 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 flattened (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 first time for radioactive nuclei
in short-lived excited states in these experiments, and the
finding of opposite signs for the quadrupole moments directly
confirms the coexistence of prolate and oblate shapes. The
measurement of the transition strengths between the various
states allowed a quantitative analysis of the configuration
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.
The question of the heaviest chemical elements that can exist
has been a very fundamental one ever since D.I. Mendeleev
first 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
bombard mono-crystalline nickel and germanium targets
to produce by complete fusion systems with Z = 120 and
124, respectively, which then undergo fission. By observing
the trajectories of the fission fragments in the crystal lattice,
a significant proportion of long fission times (≥10 -18 s) has
been observed with respect to the fast quasi-fission process
(10 -21 s). This points to a high fission barrier and hence to an
enhanced stability of the superheavy systems.
Perspectives
The SPIRAL2 project at GANIL offers exciting opportunities
for nuclear structure physics. The Dapnia physicists are
strongly involved in defining the physics program and in
building equipment for SPIRAL2. The new facility will deliver
of matter
constituents
The
matter
in extreme
states
ultimate
Thenuclear
Spectroscopy of transactinides
Figure 1. Excitation spectra of 251Md, obtained at the University
of Jyväskylä. The γ-ray transitions shown in the upper part
of the figure are in mutual coincidence. Their regular energy
spacing is characteristic of a deformed rotating nucleus
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 difficult 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 first 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 identified 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 significant as their
location is sensitive to singleparticle 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
Figure 2. Photo du dispositif Must2 monté
pour une expérience au Ganil.
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 microelectronics 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 first exploitation of a sub-array, the
so-called AGATA-Demonstrator, at the end of 2008, in
Legnaro
Figure 3. The first AGATA triplet
of highly segmented germanium
detectors, on a test bench.
45
46
Innovation for detection
systems
F
or 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
47
Dapnia 2004 - 2006
A
s the construction of the large-scale instruments for the LHC reaches its final 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.
Micromegas
The versatility of the Micromegas gas detector suggests
there is scope for its development for experiments and
applications in a wide variety of fields. 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
Figure 2. Readout plane of the T2K TPC.
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 fine
3D granularity. Along the same lines, the first tests of a
Micromegas integrated on to a silicon wafer (InGrid) look
very promising.
MAPS (Monolithic Active Pixel
Sensors)
Figure 1. The Piccolo detector.
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 amplification 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.
48
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 sufficiently 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 specification:
• 5 cylindrical layers of pixels (r = 15 mm to 60 mm), i.e.
approximately 800 million pixels;
• Signal reading time: 20 μs for the first 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
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.
Bolometry
The PACS project
Figure 3. ILC vertex detector.
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 first detection of charged particles with MAPS was
performed in Strasbourg in 1999. The first 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 detectors
Work 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 gammaray 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
The 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 first 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).
Innovation
for detection
matter
ofsystems
ultimate constituents
The
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 sufficient to withstand
500 kilorads and 5·1010 neutrons/cm² in 5 years.
Massive ionization-heat bolometers for
EDELWEISS2
On 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 scientific potential
associated with the production of around 100 detector of this
type to be evaluated
Figure4.
Prototype
of the
HiMAPS-1
(Mimosa8)
chip.
49
Dapnia 2004 - 2006
Signal processing and real time
systems
I
n 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.
ASICs
Although 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 fine 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 (ApplicationSpecific 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
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 first two groups,
the AFTER ASIC, developed for the T2K neutrino oscillation
experiment, includes 72 preamplification and filtering
channels and an analogical memory. It is the largest circuit
(500,000 transistors) ever to be designed at DAPNIA.
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.
Figure 1. SAM - multi gigahertz sampler for the
HESS-2 experiment. This chip integrates 80,000
transistors on a reduced surface of 11 mm².
50
and digital circuits capable of integrating, for example,
sequencers or signal processing functions. Generallyspeaking their parameters can be configured. ASICs
designed at DAPNIA are classified 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 field of analogical 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
MAPS, part of the third group, connect a detector and its
front-end electronics on a single substrate. For the first 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 MAPSbased 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 timeframe to read the 65,000 channels in the RICH detector of
the COMPASS experiment.
Using FPGAs for real-time acquisition
and processing
The 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 fields: 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
In the field of acquiring and processing data from highlysegmented experimental devices producing a massive
data flow, 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.
Figure 3. One of the CMS Selective Readout Processor boards.
Real time systems
Acquisition
The T2K experiment represents a particularly strong commitment
from DAPNIA in the field 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.
Innovation
for detection
matter
ofsystems
The
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.
MATACQ
Based on an analogical memory developed in collaboration between
IN2P3/LAL and DAPNIA, the MATACQ card digitizes analogical signals on a 12 bits dynamic range,
at a frequency of 2 GHz. It is manufactured and sold under license by
two industrial partners. One hundred
copies of this card are currently used
worldwide, mostly in research laboratories.
Electronics for space systems
DAPNIA is also developing electronic
functions that are crucial for the implementation
of innovative detection systems for scientific space
instrumentation. These detection systems meet the diverse
requirements of the various scientific 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 final delivery.
Finally, DAPNIA teams are involved in new projects, such as the
design and production of the scientific processing unit on the
ECLAIRs satellite and for the high energy γ -ray camera on the
SIMBOL-X satellite
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.
51
Dapnia 2004 - 2006
Intensive computation and
simulation
P
hysics 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 highenergy physics experiments
Distributed applications (i.e. applications running on
networked computers) are playing an increasing role in
DAPNIA's scientific 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 scientific community, facilitating software maintenance
on centralised servers, and managing massive data flows
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 field 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.
Software development and Web technology
Expertise 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
scientific data. These tools include specific middleware
(e.g. real-time processing simulation for CMS experiments),
software development frameworks, and tools to exchange
and distribute scientific data. A very successful example
would be PHOCEA, the web portal configuration environment
developed at DAPNIA and adopted by numerous CEA
departments and external laboratories.
52
Computational grids for LHC
experiments and other fields
DAPNIA 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
scientific data from LHC experiments (LCG project), as well
as data from other fields 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.
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.
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.
Innovation
for detection
matter
ofsystems
The
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 first 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 processing
Ground 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.
Specific analysis tools must therefore be developed to
ensure optimal use of existing and future instruments.
Figure 3. Visualisation of HERACLES data by the SDvision
software: Simulation of turbulences in the interstellar medium.
With this objective in mind, the 'Multiresolution' joint
research programme (DAPNIA/SEDI-SAP) develops
Parallel computation, visualisation
and software development for the
numerical simulation of astrophysical
plasmas
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.
DAPNIA'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 significant 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 significant efforts on
DAPNIA's part to develop and generalise software tools
and methods intended for the international astrophysics,
geophysics and plasma physics communities
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 filtering, 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).
53
54
Magnets and accelerators
T
he 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 R3BGlad 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
55
Magnets
and accelerators
of matter
constituents
The ultimate
Dapnia 2004 - 2006
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
final 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
RFQ corresponding to one-fifth 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 specifications (accelerator field of
11 MV/m and surface electric fields 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 qualification module is currently being assembled
in the laboratory.
High-intensity proton injector (IPHI)
and high-intensity proton linacs
Figure 1. First cavity with β = 0.07, intended for
the SPIRAL2 superconducting accelerator.
56
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
first 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
The 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 rigidified 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
EURISOL and beta beams
The 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-defined flavour,
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.
Figure 2. HIPPI : Prototype of the proton
superconducting cavity with β = 0.5.
Advances in electron and positron
collider technology
Ongoing 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 fields as high as possible.
Figure 3. Schematic lay-out of an accelerator system for
neutrino production using the beta-beam method.
of matter
constituents
Magnets
and accelerators
The ultimate
platform in Saclay (SUPRATech project). This source will be
used to test the high-power HF couplers needed to produce
the accelerator field 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.
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.
ILC
In 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 first cavities treated
led to exceptional gradients (up to 42.5 MV/m). This
significant progress is also due to the optimisation of
the vacuum curing process, which ensures a very high
quality factor under high field conditions and extends
the field limit.
Cavities subjected to very high surface fields undergo
deformations due to radiation pressure, causing a
disturbance of the accelerator field. 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
Clic
The CERN CLIC project is based on High Frequency
(12 GHz) resonant copper cavities. Each branch of the
system consists of two linacs. The first 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),
57
Magnets
and accelerators
of matter
constituents
The ultimate
Dapnia 2004 - 2006
D
DAPNIA has acquired significant 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 LHC
Within 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 first 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 figures: Length: 3 m – Average coil radius: 0.04 m
– Field gradient: 223 T·m – Parasitic components with
respect to reference field < 10 -4 – Mechanical production
tolerance: 20 μm – Electromagnetic dispersal force:
110 tons per metre – Number of quadrupoles: 408.
ATLAS toroid
DAPNIA 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 configuration. Industrial
production of magnet components lasted from 2002 to
Figure 2. General view of the ATLAS central toroid, in the cavern.
58
Figure 1. Lowering of the first quadrupole cold
mass in the LHC tunnel (19 April 2005).
2004. In 2004, the first 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 figures: 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 field: 1.25 T.
The 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 qualification 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 field
the framework of the 6th R&D Framework Programme. This
innovative magnetic design includes active shielding and
gradual trapezoid-shaped flat coils matching the required
beam acceptance. The stored energy and magnetic
field 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 final project.
Key figures: Superconducting dipole with active
shielding and 6 flat coils – Field at centre: 2.4 T - Field
integral: 4.8 T·m – Field on conductor < 6.36 T – Stored
energy: 24 MJ – Leakage field: 20 mT at 30 cm from
cryostat.
of matter
constituents
Magnets
and accelerators
The ultimate
CMS
CLAS-DVCS solenoid
Within 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 field 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
scientific objectives. The first data collection campaign for
the DVCS project was conducted from March to June 2005,
and the second campaign is scheduled for early 2008.
Key figures: Outside diameter: 0.912 m – Inside
diameter: 0.23 m – Length: 0.3 m – Current: 534 A
– Field at centre: 4.65 T.
Figure 3. CMS solenoid ready to be cooled. The current
cable feedthrough system can be seen in the top left.
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 figures: 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 magnet
Following 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 'butterfly' design was adopted within
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 fluid transfer of the magnet.
11.7 T magnet for NEUROSPIN
As 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
field 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.
59
Magnets
and accelerators
of matter
constituents
The ultimate
Dapnia 2004 - 2006
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 definitive specifications 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 figures: Magnet
with active shieldingField
at
centre:
11.7 T – Maximum
field 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
development
All projects such as ATLAS, CMS, NEUROSPIN and
many others require significant R&D. This R&D addresses
the technical concepts to be investigated and verified (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 flow. At DAPNIA, this led up to the
development of the thermosiphon used to cool the CMS.
Heat transfer mechanisms in superfluid 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 fields,
and has been
subject to specific
Vacuum chamber
research for several
years now. This
60 K screen
new
generation
of superconductors
requires extensive
Compensating
thermal treatments
coil
for
tools
and
materials.
The
development
of
an
Main coil
accelerator magnet
prototype (currently
in progress) constiHelium
tutes the final and
evacuation in
case of quench
most
complex
phase of R&D on
Nb3Sn. Research on ceramic insulators compatible with
the specific thermal treatments required for this material is
also currently in progress
Figure 5. Exploded view of the ISEULT magnet,
designed to produce a magnetic field of
11.7 T on an effective diameter of 0.9 m.
Test facilities
T
he cryogenic test facilities for R&D are an important tool used to characterize and
qualify phenomena and materials in fields 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 final 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.
60
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 flow 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
fields 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
Figure 1. CMS: test of the phase separator at Saclay
connected to a cryogenic loop reproducing the
operation of the magnet in thermosiphon mode.
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 finally 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 field 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 field 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
fields. 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 quarterwave 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 fitted 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, fitted
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 specific 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
metres in length, with currents of up to 20,000 amperes at a
minimum temperature of 1.8 kelvin in superfluid 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 qualified for the construction of
W7X.
Figure 2. Cryostat for traction tests at
the temperature of liquid helium.
61
Magnets
and accelerators
of matter
constituents
The ultimate
Dapnia 2004 - 2006
New developments for magnet and
accelerator instrumentation
P
erformance 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 flexibility, 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 cuttingedge developments in the fields of electronics, PLCs,
adaptative monitoring software and in new technologies
validations.
Web technologies
Generalization 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 specific
equipments, for the purpose of archiving data and
sending telephone or electronic alarms, according to
operator-defined 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 flexible access to this
technology.
An original web interface called « Anibus », based on the
multi-platform Java language, gives a fast and flexible 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 fieldbus, 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
configuration.
Interoperability and application to
control/command architectures
62
Fieldbus 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 specific needs of the projects.
Different technologies coming from industry or custom
developments are set on superconducting magnets;
simplification 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)
Figure 1. The analogical “bufferized” acquisition board
MIVA, embedded in the shared instrumentation interface.
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 figure 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 fieldbus 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.
Physics 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 figure 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.
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
of matter
constituents
Magnets
and accelerators
The ultimate
Developments dedicated to
cryomagnetic systems
Figure 3. Liquid He level measurement
unit for four channels with FIP fieldbus.
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 figure 3)
sends on the WORLDFIP network the status and
the measured value of each gauge. The display
is multilingual and has been made more userfriendly. One or several gauges can be put into
standby manually or via the WORLDFIP fieldbus
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 flow-chart of the
superconducting magnet safety system.
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 finalised which will soon make it possible to
validate connectors at temperature as low as -150 °C.
63
64
T
he 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).
Alban Mosnier
65
Dapnia 2004 - 2006
Nuclear data measurements
and modelling
D
APNIA 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, fission, 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, designdecommissioning of nuclear installations, nuclear medicine, etc.
Figure 1. Domain in type and energy
of the studied reactions.
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 fission-tocapture 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.
In situ transmutation studies with
Mini-INCA
Thanks to the availability of high neutron fluxes at the
ILL reactor (Grenoble, France), the transmutation of minor
actinides is studied in situ. A strong effort was the development
of microscopic fission-chambers able to withstand high
neutron fluxes (∼1015 n·cm-2·s-1) and to measure without
ambiguities the fission rates of any actinide in reference to
a known fission 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. fission 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 fission 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
66
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
210 Po 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
Figure 2. The calorimeter
of the n_TOF experiment
at CERN.
Photonuclear reaction studies
High 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-fission delayed neutrons (DN) have
been undertaken in collaboration with CEA/DIF/DPTA
employing the ELSA electron accelerator. For this purpose the
high efficiency 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 define the mass of fissile materials but also to provide
isotopic composition of mixed samples (see Fig. 3).
The experiments are accompanied by the modelling efforts,
matter
ofenergy
constituents
for nuclear
The ultimate
Physics
Figure 3. Measured decay curve of photo-fission
DNs in the case of a mixed sample: both old and new
parameterizations are plotted for comparison.
which include actinide evaluations of photonuclear cross sections, fission fragment yields, neutron multiplicities and their
energy distributions. Evaluations obtained for 235U, 238U,
237Np, 239Pu, 240 Pu and 241Am nuclei up to 20 MeV were incorporated, in collaboration with LANL (USA), into the newly
released ENDF/B-VII data library. New evaluations, extended up to 130 MeV and complemented by the photo-fission
DN parameters obtained at DAPNIA will be provided to the
European JEFF data file.
Spallation reaction studies
Reactions, 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 crosssections 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 first experiment (Fe +
p) has permitted for the first 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 significantly improved
and validated on a wide set of experimental data. In
particular, INCL4 now produces data on high-energy
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 defined by the number of
fragments, at Z ≥ 3 and Z = 2, observed in coincidence.
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.
MEGAPIE
In 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 first 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
flux monitoring. For this purpose, a dedicated neutron
detector was developed, which was composed of a few
micro fission-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 flux is correlated with
the primary proton beam intensity, i.e. the fission chambers
functioned as expected in a very hostile environment
Modelling
Finally, 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
67
Dapnia 2004 - 2006
Technological research for
fusion energy
T
he 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 specific 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.
ITER
In 2006, the ITER experimental fusion reactor project
was officially 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
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 field dipole for a conductor
test facility, thermohydraulic analyses of toroïdal coils and
cooling systems, and cryogenic fluid distribution studies.
IFMIF-EVEDA
Figure 1. The ITER ACB (Auxiliary Cold Box for
magnet structures). View of the complex cryogenic distribution box ensuring part of the cooling
and temperature control of ITER magnets.
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.
68
ITER-type reactors use the energy transported by the
neutrons produced in a fusion reaction. The neutron flux
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 fluxes 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 fluxes
while preserving sufficient 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 flux 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
matter
ofenergy
constituents
for nuclear
The ultimate
Physics
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.
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 final 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 file 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
69
70
DAPNIA expertise
at the service of society
D
APNIA’s know-how and
expertise in physics instrumentation 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
71
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Dapnia 2004 - 2006
Physics and health
F
or more than a century, medicine and biology have benefited fully from advances
in physics and from instruments developed for this field. 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 specific 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
benefited from the department's experience in running
large projects and in activation and radiological protection
calculations.
NEUROSPIN
DAPNIA 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-field 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 financial support from
the French Agence de l’innovation industrielle.
The development of an imaging system of this kind, based on
a main field of 11.7 teslas, in a 900 mm aperture, constitutes
an impressive feat. This field is at the furthest extreme of
72
Figure 1. Model of the 11.7 teslas magnet for NEUROSPIN.
possibilities for using traditional superconductors (niobiumtitanium), and raises some tricky problems as regards field
uniformity and control of the leakage and protective fields.
The gradient magnets and radiofrequency antennas also
create some difficult problems when it comes to mechanical
strength, materials, controlling noise and heating.
The scale of the resources deployed and the difficulties to
be resolved make this a flagship project for the department
in the interdisciplinary field of physics and medicine.
The characteristics of this MRI imager are explained in the
chapter on superconducting magnets.
Hadrontherapy
Some 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.
Protontherapy
The therapeutic efficacy 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 refitting 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 financed by the Institut Curie.
In addition, DAPNIA has performed biological protection
dimensioning calculations for the CPO's new installation.
Instrumentation
Figure 2. Comparison of CPO experimental data
with the simulation, concerning the delivery of doses at different depths. Note the perfect match
with the curves using evaluated nuclear data.
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 efficacy 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 benefit 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 imaging
In 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 fixed 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
DAPNIA/SEDI
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 first biological
validation tests are
Figure 3. Global view of the ART facility.
very encouraging,
The counter and the pump are visibnle, aside
and the project,
the small rodent installed in the micro PET.
which has already
been financed 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
matter
DAPNIA The
expertise
at constituents
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ultimate
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 subunits and to the generic effort to document the programs.
Modelling
The department is participating in the international GATE
collaboration (GEANT4 Application for Tomographic
73
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Expertise in decommissioning and
design of nuclear facilities
S
ENAC (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.
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.
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. flux
measurements performed during reactor operation),
– comparing activation calculation results with data
from analysis of samples taken at the facility under
study.
Activation studies for reactor
decommissioning
When 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 define
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 flux,
– calculating material activation by taking into account
the reactor operating history and the metallurgical
composition of the materials (including impurities).
- Reactor core description
- Incident beam description
Figure 1. Flowchart illustrating the activation studies.
74
Figure2. RAPSODIE Reactor: Graphical display of the changes in specific
activity in the SERCOTER concrete.
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
define:
– 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.
-728.6 cm
152 Eu
- 934.3 cm
154
Eu
152
Eu
-1140.0 cm
154
Eu
152 Eu
154 Eu
Calculations
280
89
93
29
26
8
Measurements
220
45
56
11
17
3
Tableau 1. RAPSODIE Reactor: comparison between calculated
specific activity values and the specific activity of samples taken on-site.
New facilities design consultancy
These studies may have various objectives:
a) For a specific 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 biological shielding optimization,
– optimization of the biological shielding around a carbon degrader, for the protontherapy centre in Orsay.
b) For new facilities (covered by French regulations
on "installations classified 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 verification 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.
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DAPNIA The
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Activity (in kBq/g)
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.
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 healthrelated consequences of a radioactive
release into the environment in the event
of an operating incident
Figure 3. ARRONAX Project (Nantes):
map of the vaults and cyclotron, showing
simulated neutron flux in a vault.
75
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76
Light sources
T
he 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
and is extracted by a set of HOM couplers whose geometry,
at SACM for the SOLEIL synchrotron, which will comprise
layout and quantity are optimised to obtain the damping
four superconducting accelerator cavities in its ring, and for
required for system operation. Like the cavities, these HOM
the SLS and ELETTRA synchrotron radiation systems (Swiss
couplers are superconductors and only operate correctly if
and Italian, respectively), which are equipped since 2002
cooled to 4 K with liquid helium.
with Super-3HC cavities for beam stabilization.
SOLEIL cryomodules
The SOLEIL cavities operate at a frequency of 352 MHz and
A cryomodule prototype was developed during the
are equipped with power couplers to provide the electron
SOLEIL detailed design phase (APD) and tested at CERN in
beam with RF energy from an external source. The SuperDecember 1999. These tests showed that the cryomodule
3HC cavities are passive cavities operating at 1.5 GHz, and
meets the operating specifications of the SOLEIL system,
it is the electron beam itself that provides the electromagnetic
provided a few
energy allowing
modifications
them to suppress
are
made.
certain
beam
Modifications were
instabilities and
performed in 2004
lengthen
the
under
SACM
electron bunch so
responsibility, in
as to increase the
collaboration with
beam lifetime.
SOLEIL and CERN
The technology
teams: complete
used for these two
disassembly
of
types of cavities is
cryomodule,
similar and based
cleaning and testing
on the RF structure
of superconducting
developed
by
cavities in vertical
Alban Mosnier in
cryostat (to check
1992 for very high
for absence of
electron current
performance
systems, whose
degradation during
main applications
tests),
complete
are
storage
reassembly
of
rings (B-Factory
cryomodule,
at SLAC, USA)
and RF power
and synchrotron
validation tests at
radiation systems.
Figure 1. Assembly of HOM coupler on SOLEIL cryomoCERN.
dule in CERN clean room (Operator: J.P. Poupeau)
Cryomodule operation on the SOLEIL
This RF structure is
ring was validated in early 2005 and
composed of two
confirmed the expected improvement in
superconducting
performance: decrease in static cryogenic consumption
RF niobium cavities cooled to 4 K and very strongly coupled
(50 W) and better overall thermal stability, very good
for all modes except the fundamental accelerator mode,
filtering of fundamental mode by dipolar HOM couplers,
allowing the generation of very intense accelerator fields
accelerator field in cavities (Emax > 11 MV/m), and
while inhibiting the development of higher order modes
maximum power withstood by RF couplers (180 kW
(HOMs) potentially detrimental to beam stability. The RF
reflected power).
power of these HOMs can be deposited by the beam itself
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 specific services and expertise
for construction-related activities and for RF power tests
at CERN.
Super-3HC
cryomodules
Figure 2. Assembly of HOM couplers on Super3HC cryomodule in DAPNIA clean room, Orme
des Merisiers site (Operator: Y. Gasser)
The
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 Super3HC cryomodule. Several
facilities could benefit from this system, which is currently
unmatched in the industry
matter
DAPNIA The
expertise
at constituents
the service of
of society
ultimate
The cryomodule was installed on the SOLEIL ring in
December 2005, cooled to 4 K in May 2006, and the
first beam was accelerated in June 2006. During the
implementation phase, the intensity quickly reached 300
mA, corresponding to phase 1 nominal operation.
77
the service of
at constituents
matter
of society
expertise
DAPNIA The
ultimate
Dapnia 2004 - 2006
78
Environment
S
ince 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 stations
The specifications 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;
- finally, 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 flow and 0.05 °C for temperature.
Three stations have already been installed at their observation sites and the fourth is currently being produced. The stations 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 measuring station at an altitude of 4517 m.
Figure 2. The
second generation CO2
measuring rack.
79
matter
DAPNIA The
expertise
at constituents
the service of
of society
ultimate
Scientific publications
Dapnia 2004 - 2006
Bibliometric statistics
Year
2004
2005
2006
500
517
514
Scientific publications with impact factor
450
489
468
Scientific publications with impact factor > 0.5
441
463
464
Scientific publications with impact factor >= 5
151
156
141
Expected impact
4,28
4,37
4,41
Intellectual production
This production includes all the papers published by DAPNIA members, and all their other professional
activities. This includes:
- References of papers in scientific 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 scientific responsibilities, awards, patents, science popularisation works.
Those data are reviewed in the annexe of the present Activity Report 2004-2006.
80
See also complete list of DAPNIA publications
on the CD-Rom report, or on the DAPNIA
website.
The Standard Model
Aktas 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), 715-748
Schael 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), 547-587
Abazov V.M. et al. (D0 Coll.)
Evidence for production of single top quarks and
first direct measurement of Vtb
Phys.Rev.Lett.Vol. 98 (2007), 181802
Hadron structure
Ageev 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 matter
Massey R., et al. (Aussel H., Pires S., Refregier A.,
Starck J.-L.)
Dark matter maps reveal cosmic scaffolding
Nature 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
DUNE: the Dark Universe Explorer
Space 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 first year data set
Astron. 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 α
Phys. 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 universe
Astron. Astrophys. Vol. 445 Num. 1 (2006), 1
Schanne S., et al. (Cordier B. ; Limousin O. ; Paul J.)
The ECLAIRs micro-satellite mission for gamma-ray
burst multi-wavelength observations
N.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 universe
Bournaud F.; Duc P.-A.
From tidal dwarf galaxies to satellite galaxies
Astron. 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 Xray cluster sample over the D1 CFHTLS area.
M.N.R.A.S Vol. 372 Num. 2 (2006), 591-608
Peretto N., Andre P. ; Belloche A.
Limits on the Macho Content of the Galactic Halo
from the EROS-2 Survey of the Magellanic Clouds
Probing the formation of intermediate - to high-mass
stars in protoclusters. A detailled millimeter study of
the NGC 2264 clumps.
Dark energy
Lagage P.O., Doucet C. ; Pantin E. ; Habart E. ; Duchêne
G. ; Ménard F. ; Pinte C. ; Charnoz Z. S. ; Pel J.W.
Réfrégier A. et al. (Boulade O., Boulade S., Cara C.,
Claret A., Magneville C. Palanque-Delabrouille N.;
Schimd, C.; Sun, Zhihong)
Anatomy of a flaring proto-planetary disk around a
young intermediate-mass star
Science Vol. 314 (2006), 621
Tisserand P., et al.
of matter
publications
constituents
The ultimate Scientific
Main Publications
81
Dapnia 2004 - 2006
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 telescopes
Proc. of the SPIE, Vol 6275 (2006), 10 1117/12 671133
Charnoz S., et al. (Deau E., Brahic A.)
Raabe 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.
Cassini discovers a kinematic spiral ring around
Saturn
Science Vol. 310 (2005), 1300
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.
R A. García et al. (S. Turck-Chièze, S. Mathur)
Tracking solar gravity modes: the dynamics of the
solar core
Science, Vol. 316 (2007), 1591
Shell gap reduction in neutron rich N=17 nuclei.
Phys. Lett. B Vol.633 Num. 1 (2006) 33-37
Brun A.S., Browning M.K. ; Toomre J.
Simulations of core convection in rotating A-type
stars: Magnetic dynamo action
Astrophys. J. Vol. 629 (2005), 461
Degerli Y., Besançon M. ; Fourches N. ; Li Y. ; Lutz P. ;
Orsini F. ; et al.
Bouquet S., Chieze J. ; THAIS F. ; et Al.
Observations of laser driven supercritical radiative
shock precursors
Phys. Rev. Lett. Vol. 92 Num. 22 (2004), 5001
Compact objects and their environment
Ferrando P. et al. (Arnaud M. ; Goldwurm A. ; Laurent P. ;
Lebrun F. ; Limousin O.)
Simbol-X: mission overview
Proc. 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 outburst
Lebrun F. et al. (Goldwurm A. ; Terrier R.)
Compact sources as the origin of the soft gammaray emission of the milky way
Nature Vol. 428 Num. 6980 (2004), 293
Cosmic ray sources
Aharonian 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 J1713.7-3946
Astronomy and Astrophysics Volume 427 (2004), 199
Grenier I.; Casandjian J.M., Terrier, R.
Unveiling Extensive Clouds of Dark Gas in the Solar
Neighborhood
Science, Vol. 307 (2005), 1292
Miceli, M.et al. (Decourchelle, A.; Ballet, J.)
82
Exotic nuclei
The X-ray emission of the supernova remnant W49B
observed with XMM-Newton
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
camera
Astrophys. 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 systems
Delagnes 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.
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 al
Fast readout of the COMPASS RICH CsI-MWPC
photon chambers.
N.I.M. A Vol. 567 Num. 1 (2006), 104-106
Intensive computation and simulation
Pierre M., Pacaud F. ; Duc P. ; Le Fevre J.P. ; et al.
The XMM Large Scale Structure: a well-controlled Xray cluster sample over the D1 CFHTLS area.
M.N.R.A.S Vol. 372 Numéro 2 (2006), 591-608
Baudouy B., Juster F.P. ; Allain H. ; Prouzet E. ; Larbot
A. ; Maekawa R.
Heat transfer through porous media in static
superfluid helium.
Cryogenics Engineering Conf. and Int. Cryogenic Materials
Conf. (CEC/ICMC - 2005), Keystone, Etats-unis, 29/08/2005 02/09/2005 Cryogenics Engineering 51A, AIP, Ed. J. G.
Weisend, (2005) pp. 409-416
Nuclear data measurements and modelling
Armbruster 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
of matter
publications
constituents
The ultimate Scientific
IDeF-X ASIC for Cd(Zn)Te spectro-imaging systems.
IEEE Trans. Nucl. Sc. Vol. 52 Num. 5 part 3 (2005) ,
1595- 1602
Aerts G., Andriamonje S., Berthoumieux E., Dridi W.,
Gunsing F., Pancin J., Perrot L., Plukis A. et al.
Neutron capture cross section of 232Th measured
at the n_TOF facility at CERN in the unresolved
resonance region up to 1 MeV.
Phys. Rev. C Vol.73 Num. 5 (2006) 054610
Pomarede D., Thooris B., Audit E., Teyssier R.
Numerical simulations of astrophysical plasmas
Proc. 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
datasets
Proc. 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.
Mosnier 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
Vedrine 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
83
En couverture :
Sereno
Mosaïque de Giovanna Galli
Date : 2006
Dimensions 50 cm X 50 cm
Directeur de la publication : Jean Zinn-Justin
Conception : François Bugeon, Yves Sacquin
Coordination 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 Vilanova
Rédacteurs 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 Marteau
Mise 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
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.
Dapnia 2004 - 2006
Activity Report

The ultimate constituents of matter - CEA-Irfu

Transcription

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