[en] The scope of this project intends to record spatially resolved images of core shape and size of a DT micro-balloon during Inertial Confinement Fusion (ICF) experiments at Laser Mega Joule facility (LMJ). We need to develop an X-ray imaging system which can operate in the radiative background generated by an ignition shot of ICF. The scintillator is a part of the imaging system and has to gather a compromise of scintillating properties (scintillating efficiency, decay time, emission wavelength) so as to both operate in the hard radiative environment and to allow the acquisition of spatially resolved images. Inorganic scintillators cannot be used because no compromise can be found regarding the expected scintillating properties, most of them are not fast enough and emit blue light. Organic scintillators are generally fast, but present low X-ray absorption in the 10 to 40 keV range, that does not permit the acquisition of spatially resolved images. To this aim, we have developed highly lead-loaded and red-fluorescent fast plastic scintillators. Such a combination is not currently available via scintillator suppliers, since they propose only blue-fluorescent plastic scintillators doped with up to 12%w Pb. Thus, incorporation ratio up to 27%w Pb has been reached in our laboratory, which can afford a plastic scintillator with an outstanding Z_eff close to 50. X-rays in the 10 to 40 keV range can thus be detected with a higher probability of photoelectric effect than for classic organic scintillators, such as NE102. The strong orange-red fluorescence can be filtered, so that we can eliminate residual Cerenkov light, generated by γ-ray absorption in glass parts of the imaging system. Decay times of our scintillators evaluated under UV excitation were estimated to be in the range 10 to 13 ns. (authors)

[en] The implosion of an inertial fusion target generates a flux of X-radiation that is characteristic of target heating and thus important to know. The harsh radiation environment implies that measuring instruments should be away from the target which imposes the conversion of X-rays into visible light (380 - 780 nm) easier to carry. The new scintillator should operate in a spectral range away from the blue to avoid detecting Cerenkov light. A plastic scintillator has been selected: a matrix of polystyrene will make the conversion X-ray to UV radiation. This matrix will contain molecules of 2.5-diphenyloxazole and of Nil to assure the conversion of UV into red light through a cascade of absorption-emission processes. Di-isopropyl-ethylamine molecules are also present to accelerate fluorescence. (A.C.)

[en] Multilayer mirrors with enhanced bandwidth were developed with special performances for dense plasma diagnostics and mainly for high spatial resolution x-ray imaging. The multilayer coatings are designed to provide broadband x-ray reflectance at low grazing incidence angles. They are deposited onto toroidal mirror substrates. Our research is directed at the development of non-periodic (depth graded) W/Si multilayer specifically designed for use in the 1 to 30 keV photon energy band. First, we present a study for a 5 to 22 keV x-ray spectral window at 0.45 degrees. grazing angle. The goal is to obtain a high and constant reflectivity. Second, we have modeled a broadband mirror coating for harder x-rays in the range from 10 to 30 keV, with a non-periodic structure containing 300 W/SiC layers with periods in the range from 0.8 to 4 nm, designed for 0.35 degrees grazing incidence angle. (authors)

[en] A Velocity Interferometer for Any Reflector (VISAR) [1, 2] and a Streaked Optical Pyrometer (SOP) [3] were implemented on the 'Ligne integration Laser' (LIL) facility. Spatial resolution as good as 10 μm in the target plane and velocity resolution as good as 0.1 km/s can be achieved. Several campaigns were performed in 2010 involving various experimental setups and physical processes: Boron EOS, Pre-compress H₂ with special setup of diamond anvil cell and Shock coalescence. This feedback will be of a great help for the Laser Megajoule facility (LMJ) VISAR design. (authors)

[en] Estimating the vulnerability is a key challenge for plasma diagnostics designed to operate in radiative background associated with mega-joule class laser facilities. Since DT shots at OMEGA laser facility reproduce the perturbing source expected during the first 100 nanoseconds of a typical DT shot realized at National Ignition Facility (NIF) and Laser MegaJoule facility (LMJ), vulnerability of diagnostic elements such as optical relays or optical analyzers were experimentally studied and, if necessary, hardening approaches have been initiated to authorize their use at higher radiative constraints. Other facilities such as nuclear reactor or accelerator have been also used to estimate vulnerability issues as radiation induced emission of glasses or damage in multilayer coatings. (authors)

[en] Presented is a new mitigation technique to improve the radiation tolerance of CMOS image sensors to the radiation constraints associated to the fusion by inertial confinement experiments at mega-joule class laser facilities. Using the global reset mode, results acquired at the OMEGA facility show the efficiency of this technique to reduce by more than 70% the number of white pixels induced by the mixed 14 MeV neutron and gamma-ray pulse. (authors)

[en] This system intends to record spatially resolved images of core shape and size of a DT micro-balloon during fusion experiments for the Megajoule Laser. It must operate in the radiation background generated by fusion reaction. It consists of a scintillator imaged by an optical relay system on a CCD camera. The latter lies in a shielded area far from the experiment chamber. This design proposes a simple solution for the optical relay, based on Maksutov objectives. The main requirements affect the scintillator (short duration emission), and the optical relay (length of 15 meters, no Cerenkov radiation production, spatial resolution better than 10 μm in the object plane). Spatial resolution and performances to radiative background have been measured on a system shorter than 15 meters, with a YAG:Ce scintillator. Pinhole images have been obtained on the plasma laser facility EQUINOX at CEA/DIF. Hardening measurements have been achieved at the ELSA facility

[en] The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium filled micro balloon. In this context an X-ray imaging system is necessary to diagnose the core size and the shape of the target in the 10-100 keV band. Such a diagnostic will be composed of two parts: an X-ray optical system and a detection assembly. The survivability of each element of this diagnostic has to be ensured within the mixed pulse consisting of X-rays, gamma rays and 14 MeV neutrons created by fusion reactions. The design of this diagnostic will take into account optics and detectors vulnerability to neutron yield of at least 1016. In this work, we will present the main results of our vulnerability studies and of our hardening-by-system and hardening-by-design studies. (authors)

[en] This imaging system aims at recording images of the core size and shape of an imploding deuterium-tritium (DT) microballoon on LMJ inertial confinement fusion (ICF) experiments. Image acquisition is difficult due to the harsh surrounding created by the fusion reaction, which affects system specifications. This one is made of a scintillator, an optical relay, and a CCD camera shielded from the surrounding. The system was tested on different facilities at CEA/DIF, where a spatial resolution of 120 μm was achieved and gamma dose up to 20 rad effects were measured. Setup and performed test are described.

[en] We use the LIL (Ligne d'Integration Laser) facility to study the coalescence of two planar shocks in an indirectly-driven planar sample of polystyrene. This experiment represents the preliminary stage of the future shock-timing campaign for the Laser Megajoule (LMJ). The main objectives are to validate the experimental concept and to test the numerical simulations. We used a gold spherical hohlraum to convert into X-ray the 351 nm wavelength laser pulse and to initiate the two shocks in the sample. To access time resolved shock velocities and temperature, we used two rear-side diagnostics: a VISAR (Velocity Interferometer System for Any Reflection) working at two different wavelengths and a streaked optical self-emission diagnostic. We observed the coalesced shock, in good agreement with the numerical simulations. We also observed a loss of signal during the first nanoseconds probably due to sample heating from the hohlraum X-ray flux. (authors)