[en] The subject of this thesis is the nuclear core of the sun. The first part is theoretical and concerns neutrino flux predictions. A precise description of the solar plasma is necessary to predict boron, beryllium and CNO cycle neutrinos. We treat here the nuclear reaction rates. They are mainly determined by the cross sections and the enhancement factors due to plasma particles, the co-called screening factors. We have discussed the various possible formalisms that could be used in stellar evolution and performed direct calculations of screened cross sections. We concluded that the screening prescriptions which have been used so far in stellar evolution should be replaced by the Mitler formalism. Next, we examine the cross section uncertainties and we show that it is possible to get a better agreement between theory and experiment. Discrepancies between the gallium experiments and the calculations suggest that we should go beyond the classical solar model. This has motivated our study on possible magnetic fields deeply buried in the solar core. We discuss here the influence of a magnetic pressure perturbation on solar evolution. In the experimental part of this work, we deal with the GOLF experiment, one of the three helio-seismological experiments on board the space probe SOHO. The purpose of this instrument is the study of the global oscillation modes in the frequency range 10^-7 to 6 10^-3 Hz with a sensitivity for frequencies higher than 2 10^-4 Hz of about 1 mm/s over 20 days of continuous integration at counting rates of 12 10⁶ cs/s. One part of this work was devoted to the precise characterization of the photomultipliers and their associated electronics in order to select them according to their intrinsic performances. This step was followed by long duration tests of three weeks simulating as well as possible the flight conditions. We show that the detection chain effectively meets the stability requirements of around 10^-7 by velocity measurement. We also show that the phototube lifetime is compatible with the expected six year mission, if the space environment does not modify the photomultiplier characteristics

[en] The main limitations on long-distance space transport is neither the energy source nor the propulsion system but appears to be the protection of cosmonauts from radiation. Cosmic radiation is made up of protons (87%), alpha particles (12%) and heavy nuclei (1%), all these particles travel through interstellar space and come from the explosion of stars at the end of their life. The earth is protected from cosmic radiation by 3 natural shields: i) the magnetic field generated by the solar wind, ii) the earth magnetic field (magnetosphere), and iii) the earth atmosphere, this elusive layer of air is equivalent to a 10 meter-high volume of water. Magnetosphere and atmosphere reduce the radiation dose by a factor 4000. According to a European directive (1996) air crews must be considered as radiation workers. (A.C.)

[en] One of the main limitations to the sensitivity of the infrared camera ISOCAM on-board the Infrared Space Observatory (ISO) comes from responsivity variations and glitches caused by the impacts of charged particles in photo-detectors. An international glitch working group has been created in order to centralize information about these phenomena and prepare for future space experiments. Results about ISOCAM glitches are presented here. The predicted glitch rate has been re-evaluated and compared to in-flight measurements. The study of temporal and spatial properties of glitches has led to a classification into 3 distinct families. These families are related to the linear energy transfer (LET) of charged particles interacting with the detectors

[en] Airix is a linear accelerator producing a 60 ns, 2 kA, 19 MeV electron beam. It has been operated in a single shot mode by the 'Commissariat a l'Energie Atomique et aux Energies Alternatives' (CEA) for flash X-ray radiography purposes for nearly 12 years. Usually each accelerating unit (a cell and its driver) delivers a 100 ns pulse of 250 kV amplitude to the beam. The test bench is used to determine the behaviour over time of the cells, the driver (high voltage generator) and the links between them (high voltage cables). We try different configurations and deal with ensuing problems. In this paper, we describe the test-bed in use, the problems we have met and how we dealt with them, and we establish the reliability performances we now expect from the accelerating units for the next decades. (authors)

[en] LIPAc is the Linear IFMIF Prototype Accelerator developed within the framework of the IFMIF project under the Broader Approach (BA) agreement signed between EURATOM and the Japanese Government in 2007. The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity neutron fluxes with appropriate energy spectrum in order to characterize materials envisioned for future fusion reactors. Because the IFMIF accelerator has to reach unprecedented performances, the feasibility is being tested through the design, manufacturing, installation, commissioning and testing activities of a 1:1-scale prototype accelerator, namely LIPAc, from the injector to the first cryomodule together with the High Energy Beam Transport line and the High Power Beam Dump. After outstanding results obtained in 2019, the LIPAc project has entered 2020 in the preparation of the third commissioning stage, i.e., validation in continuous-wave mode of the complete accelerator up to 5 MeV with its final beam dump. The validation until the nominal energy of 9 MeV will be made after the completion of cryomodule assembly. After a brief overview of the goals already achieved in the framework of the IFMIF/EVEDA program, this paper will present a synthesis of the results that have been obtained so far with the LIPAc accelerator as well as the future developments planned beyond 2020.

[en] The gamma-ray telescope IBIS, on board the INTEGRAL satellite, features a coded-mask aperture, active and passive shields and two detector arrays. The first one (ISGRI) is an assembly of 16384 CdTe detectors (4x4 mm large, 2 mm thick) operating at room temperature. ISGRI covers the lower part (15 keV-1 MeV) of the IBIS energy range (15 keV-10 MeV). Detectors are arranged on polycells, each including 16 crystals, connected to their front-end electronics (ASICs). Each of the eight independent ISGRI modules are made of 128 polycells. The ASICs contain a low noise charge-sensitive preamplifier and feature pulse rise-time measurement in addition to the standard pulse height measurement. This permits to compute a charge loss correction based on the charge drift time. After application of this correction, a spectral resolution around 7.5% at 122 keV is obtained with the ASICs. Today, 16 polycells have been mounted on the first representative ISGRI module. This module has been interfaced with the entire ISGRI data-processing electronics and forms the engineering model of ISGRI. After a presentation of the scientific context, this paper describes the ISGRI design with particular emphasis on the detectors, the polycells performances and the module assembly. gamma-detection

[en] The need for a neutron source to characterize the materials used in future power fusion reactors is accepted in the European Fusion Program since some years ago. It is currently considered that the construction and operation of a facility with such an objective is in the critical path for demonstration of a prototypical fusion power plant. This situation led the EU to initiate activities for the engineering design of IFMIF-DONES (‘International Fusion Materials Irradiation Facility-DEMO Oriented Neutron Source’). The R&D work in support of IFMIF-DONES design is currently carried out in the context of a “EUROfusion” Consortium Work Package in direct collaboration with “Fusion for Energy” organization. The main objective of these activities is to consolidate the design as well as the technological base necessary to build IFMIF-DONES in a reasonable short period of time. On the other hand, the IFMIF/EVEDA project (‘Engineering Validation and Engineering Design Activities’) is part the EU-Japan Bilateral Agreement ‘Agreement on the Broader Approach to Fusion’ framework, which aims to provide real operational data of subsystem prototypes of IFMIF-DONES. This article presents the current state of the engineering design of IFMIF-DONES.

[en] Low energy positron beams are of major interest for fundamental science and materials science. IRFU has developed and built a slow positron source based on a compact, low energy (4.3 MeV) electron linac. The linac-based source will provide positrons for a magnetic storage trap and represents the first step of the GBAR experiment (Gravitational Behavior of Antimatter in Rest) recently approved by CERN for an installation in the Antiproton Decelerator hall. The installation built in Saclay will be described with its main characteristics. The ultimate target of the GBAR experiment will be briefly presented as well as the foreseen development of an industrial positron source dedicated for materials science laboratories.

[en] During the EVEDA (engineering validation and engineering design activities) phase of the International Fusion Materials Irradiation Facility (IFMIF) project, a 125 mA/9 MeV linear prototype accelerator (LIPAc) has to be built, tested and operated in Rokkasho-mura (Japan). Involved in this project for several years, CEA-Saclay designed the injector of this accelerator which is composed of an electron cyclotron resonance ion source, delivering a 140 mA deuteron beam at 100 keV, and a low energy beam transport (LEBT) line to match the beam for the injection into the radio-frequency quadrupole. In this paper, the components of the LIPAc injector are described.

The commissioning of the ion source and LEBT with beam started in November 2014. The different phases of the commissioning are explained and some noticeable experimental results obtained with a beam at 100 keV are presented. (paper)

[en] For the first time in the history of high energy astronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and its in-flight behavior and performances. Having a sensitive area of 2621 cm² with a spatial resolution of 4.6 mm, a low threshold around 12 keV and an energy resolution of ∼ 8% at 60 keV, ISGRI shows absolutely no signs of degradation after 9 months in orbit. All aspects of its in-flight behavior and scientific performance are fully nominal, and in particular the observed background level confirms the expected sensitivity of 1 milli-Crab for a 10⁶ s observation. (authors)