CEA's participation to the LHC - Ambafrance-in.org

micefunctionalUrban and Civil

Nov 15, 2013 (3 years and 7 months ago)

72 views

CEA’s participation to the LHC




The CEA (the French Atomic Energy Commission) participates in the scientific programs of Atlas, CMS
and Alice, three out of the four main instruments at the LHC. From the eighties on, CEA’s groups were
amongst the first t
o propose concepts for the big detectors Atlas and CMS. For more than ten years, by
calculation and engineering, they took part in their conception and in their realisation, as well as in those
of essential components of the accelerator.


Simulation, expe
rimental measure and data processing

The simulations of CEA
-
IRFU’s teams first served for assessing different concepts of possible detectors,
then for refining their design. Today, the physicists of IRFU follow the development of their algorithms to
be ab
le to model most accurately the functioning of the detectors which are set up in the instruments and
of analysing the experimental data (physical appearance of the standard model, measure of the mass of
the detected particles, the search for the Higgs Boso
n and new particles).


Grid computing for LHC experiments


To be able to treat the colossal quantities of data generated by the experiments, IRFU is involved in the
grid computing LCG and Egee, which have the aim of sharing available computing resources,
whether
they are of local, regional, national or international origin. To federate research laboratories in the Paris
region around a common tool, IRFU engaged itself into the Research Grid of Ile
-
de
-
France (Grille de
Recherche Ile
-
de
-
France
-

GRIF). The p
urpose of these grids is the processing of scientific data coming
not only from experiments to LHC (grill LCG), but also of other domains of interest as the biomedical (grid
Egee) or research on fusion via a collaboration with the Research institute on mag
netic fusion (IRFM
-

Association CEA Euratom).


The accelerator


To solve the huge technological challenges of the LHC, the National Centre for Scientific Research
(CNRS), CEA and CERN collaborated closely for the construction of the accelerator. The prot
ocol of
collaboration between these three organisms had been signed on February 14th, 1996 in the presence of
the minister for research. The magnets guiding the particle beams of the LHC are working in the state of
superconductivity, which needs functionin
g at low very temperatures. The LHC is thus the largest
cryogenic infrastructure ever built in which CNRS and CEA conceived and realised with the teams of
CERN the cryogenics of super fluid helium at
-
271°C


a temperature lower than the one of interstella
r
space.


Furthermore France participated in a key part of constructing the focusing units, by conceiving quadruple
superconductors for the LHC and their assembling in their cold state. These 392 quadruple magnets, now
present in the entire tunnel, will g
uarantee the focusing of beams, in other words ensure the accuracy on
millimetre scale throughout their trajectory. These magnets are inserted in boxes with liquid helium
together with corrective magnets as well as many other components. This complex assem
blage, called
"cold mass", is encircled itself by a cryostat and a control module. The entire structure forms something
which is called a "short straight section".

CEA
-
IRFU accomplished prototypes and subsequently participated in the technology transfer an
d in
following the industrial manufacturing of the 392 cold masses of quadruples in Germany. The Institute of
nuclear physics of Orsay (CNRS/ IN2P3


Paris 11 university) participated in study and in the fabrication
of the cryostats of the short straight s
ections, from the prototypes up to industrial manufacturing. Its
contribution continued up to the monitoring of the fabrication and the assembly of the final parts present in
CERN. The first short straight section, and thus the first quadruple magnet, has
been descended in LHC's
tunnel in April, 2005.

The Institute of nuclear physics of Orsay also studied and calibrated more than 6000 thermometers to
measure and to control all superconducting elements of LHC down to a tenth of a degree. The low
temperature
division of CEA
-
INAC participated in the monitoring of the fabrication, the reception and the
installation of the low temperature units (at
-
271°C), after having conducted basic studies on them. The
same division developed the cryogenics of the experimenta
l fusion device "Tore Supra" in Cadarache.


Atlas

Very present from the initial phase of the project, CEA
-
IRFU (division of particle physics, division of
accelerators, cryogenics and magnetism, division of detector electronics and the division of system
en
gineering) largely contributed in the conception of this big detector. Particularly, IRFU's conceived and
supervised the accomplishment of the toroidal magnet of the Muon spectrometer (this magnet produces
the largest artificial magnet field on earth), the

electromagnetic calorimeter running on liquid argon and the
system in charge of the positioning of the Muon detectors.


Toroidal magnet

CEA
-
IRFU had the responsibility for the integration of eight gigantic spools of the toroidal magnet in their
cold mass and their cryostat. IRFU was also in charge of defining the assembly and the conception o
f the
tools for handling the spools of the central toroid, as well as in charge of the supervising of the assembly
in its cavern at CERN.


Muon detectors

CEA
-
IRFU is, together with the Nikhef Institute (the Netherlands), in charge of the positioning of the

muon
spectrometer chambers rooms of the central part. IRFU also contributed to the following tasks: the
conception, the realisation, the calibration and the integration of the positioning system; the determination
of the magnetic field map of Atlas (calcu
lation and measures), the software of reconstruction and of
visualisation of the trajectories of the Muons, the analysis software and the database for positioning.


Electromagnetic calorimeter

CEA
-
IRFU contributed in an essential way to the optimisation of

the central electromagnetic calorimeter
and to the development of its process of manufacturing and assembly. Ten of 32 modules were put
together and tested in CEA's Saclay center, and IRFU had the responsibility for the assembly of all
modules in CERN and

of their insertion in the cryostat. Concerning the read out electronics, IRFU took
care of the chips which give the priors to the fast triggering of the data acquisition coming from the signals
of the calorimeter. IRFU also conceived the integrated circui
t for fast read
-
out ("HAMAC"), based on
commuted capacities, which was later at the origin of a long course of study used in more than ten other
experiments.


CMS

As for CMS, CEA
-
IRFU conceived the world's largest solenoid which allows a magnetic field of
4 Tesla.
Due to this very high field intensity, the Muon spectrometer can be very compact without losing in
precision. The device also includes an electromagnetic calorimeter composed of crystals of very dense
lead tungsten, trapping electrons and photons.

CEA
-
IRFU also developed the system of monitoring of the
calorimeter, which allows to control the reliability of the obtained measures.


Solenoid

IRFU had the scientific and technical responsibility of the overall study of the cold mass, the details of
certain components and supervising the industrial fabrication (bootstraps of suspension,

heat shields,
close
-
by cryogenics, and current providers). IRFU also assured trials of critical components (electrical
junction prototypes, current providers, bootstraps of suspension, close
-
by cryogenics) and the
coordination of the assembly of the cold
mass.


Calorimeter

CEA
-
IRFU was in charge of conception, fabrication and starting operations of the calibration system, via
injection of laser light into the electromagnetic lead tungsten crystal calorimeter. IRFU's teams conducted
the R&D on photo detecto
rs as well as on crystals (75000 crystals in the final detector). CEA
-
IRFU also
studied, developed and supervised the installation, tests and the data handling of the system monitoring
the transparency of crystals and of the selective read
-
out processor. I
RFU also studied and assures the
manufacturing and implementation of the system of the super module integration of the electromagnetic
calorimeter in the CMS experiment.


Alice


The Alice group of CEA
-
IRFU is mainly interested in the study of the resonance production, which is the
signature for the creation of quark
-
gluon plasma. The inst
itute is subsequently involved in the realisation of
the «dimuons” arm and more particularly in the study and realisation of 5 stations used to monitor the
trajectories. IRFU's teams are in charge of the manufacturing of 39 out of approximately 160 detecti
on
laths, support panels, translation system of 3 stations and tools for handling cavern integration, integration
of 3 big stations and of the study of the cooling by air system.