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Since the first experiment in 2014, more and more plasma diagnostics are being deployed on the Laser MegaJoule (LMJ) facility manufactured by C.E.A/D.A.M. These diagnostics aim at measuring radiations or particles emitted during laser experiments to study high-energy physics, especially inertial confinement fusion (ICF). Different types of sensors surround the LMJ target chamber and realize the conversion of the quantities of interest to an electric signal. The signal is then transmitted via coaxial cables, acquired by a broadband oscilloscope, and digitally post-processed. Each step of this typical acquisition chain adds measurement errors and increases the global uncertainty. First, a numerical model of the digitizer alongside a specific hardware system designed to perform its metrology in situ will be presented. It computes errors sources such as offset, gain and skew, and provides a measurement of the effective number of bits (ENOB) of the digitizer. The experimental characterization of the electrical chain via its transfer function measurement will also be detailed. Finally, the numerical methods deployed to handle the inverse problem, based on deconvolution processes, will be introduced, including future developments exploiting Bayesian inferences and statistical approaches.

The Laser MegaJoule (LMJ) located at CEA-CESTA will be equipped with x-ray plasma diagnostics using different kinds of x-ray components such as filters, mirrors, crystals, detectors and cameras. To guarantee LMJ measurements, detectors such as x-ray cameras need to be regularly calibrated. An x-ray laboratory is devoted to this task and performs absolute x-ray calibrations for similar x-ray cameras running on Laser Integration Line (LIL). This paper presents the x-ray calibration bench with its x-ray tube based High Energy x-ray Source (HEXS) and some calibration results. By mean of an ingenious transposition system under vacuum absolute x-ray calibration of x-ray cameras, like streak and stripline ones, can be carried out. Coupled to a new collimation system with micrometric accuracy on aperture sensitivity quantum efficiency measurements can be achieved with reduced uncertainties.

The feasibility of efficient X-ray sources for radiography on the LMJ (Laser MegaJoule) in the multi-kJ/ns range was demonstrated on the OMEGA laser facility (Univ. Rochester) from 2002 to 2004 [1,2]. We significantly enhanced the conversion efficiency of titanium (4–6 keV), copper (8–10 keV) and germanium (9–13 keV) foils by using an optimized pre-pulse/pulse combination. Since higher X-ray energy and therefore electronic temperature need hydroconfinement, plastic cylindrical hohlraums internally coated with titanium, copper and germanium with various OMEGA beam configurations were successfully tested from 2005 to 2009 [3–5]. In addition, many shots with metal-doped aerogel (Ti, Fe, Ge) were tested on OMEGA [6].Recently we tested a new concept of “HYBRID sources” based on the combination of a thin titanium foil at the exit hole of a plastic cylinder filled with very low density SiO 2 aerogel (2 and 5 mg/cc). The benefit of the underdense medium is, first, to transport the laser energy to the titanium foil after its conversion into a supersonic ionization front and, second, to prevent foil expansion and excessive kinetic energy losses by longitudinal hydroconfinement.

We present a review of recent analysis of optical specifications for the Laser Megajoule (LMJ) plain size (40 cm × 40 cm) components. Our studies are mainly achieved using the Miro laser propagation code. The purpose of this paper is first to describe the different methods used to model the wavefronts transmitted by the components. Then, we give examples of evaluation results for the following issues: surface imperfection specification on the 1ω phase plate, surface conditioning defects tolerance on 1ω transport mirrors, Power Spectral Distribution (PSD) specifications of the transmitted wavefront and of the roughness on the components of the amplifying section.

Conference of 7th International Conference on Inertial Fusion Sciences and Applications, IFSA 2011 ; Conference Date: 12 September 2011 Through 16 September 2011; International audience; The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium microballoon. In this context an X-ray imager is necessary to diagnose the core size and shape of the DT-target in the 10-100 keV band in complement of neutron imaging system. Such a diagnostic will be composed of two parts: an X-ray optical system and a detection assembly. Each element will be affected by the harsh environment created by fusion reactions.

In this work, a 3D thermal model of the LMJ calorimeter is developed usingComsol multiphysics. The unknown thermal properties of the system are identified by comparing the model results with the measured temperature. Several model's applications, such as comparing deposition modes (electrical and optical) or defining calibration procedure, are presented. The Laser Integration Line (LIL) at Commissariat a l'Energie Atomique (CEA) near Bordeaux (France) is a prototype beam line, built to demonstrate the technology and performance of the French Laser Megajoule (LMJ) ignition facility (1). Electrically calibrated laser calorimeters are considered as the most suitable tools to perform laser energy measurements. REC calorimeter has been especially manufactured to accurately quantify the energy of laser pulses of the LIL. REC consists of an absorbing glass which is attached to an aluminium plate. The response of the calorimeter is the time dependent temperature profile measured on the rear face of the aluminium plate using an array of Peltier cells. Moreover, electrical heaters are attached to the aluminium rear face to perform electrical calibration. (cf. figure 1). The energy deposited inside the calorimeter is dissipated into the thermal mass. Obviously, modelling and analysis of the calorimeter thermal behaviour are very important issues. In this study, a three-dimensional model is developed with COMSOL Multiphysics to analyze the calorimeter response.

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.

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.

This paper investigates statistical properties of hot spots when speckle patterns are generated by the superimposition of multiple laser beams in a 2 cone and a 3 cone Laser MegaJoule configuration in the zone where all the beams overlap. Three different cases of polarizations are investigated: P polarization, S polarization and the case of Double Polarization Smoothing (DPS). It is found that the sizes of the speckles depend on the choice of the polarization and that DPS seems to be the best option in both configurations. It is shown that the longitudinal radius of the hot spots in a 2 cone configuration is bigger than in a 3 cone configuration.

We present a review of direct-drive shock ignition studies done as alternative for the Laser Mega-Joule to achieve high thermonuclear gain. One-dimensional analysis of HiPER-like Shock-ignited target designs is presented. It is shown that high gain can be achieved with shock ignition for designs which do not ignite only from the laser compression. Shock ignition is achieved for different targets of the fast ignition family which are driven by an absorbed energy between 100 kJ and 850kJ and deliver thermonuclear energies between 10-130 MJ. Shock-Ignition of Direct-Drive Double-Shell non-cryogenic target is also addressed. 2D results concerning the LMJ irradiation geometry are presented. Few systematic analyses are performed for the fuel assembly irradiation uniformity using the whole LMJ configuration or a part of the facility, and for the ignitor spike uniformity. Solutions for fuel assembly and shock ignition on LMJ using 2D calculations are presented. It is shown that high-gain shock-ignition is possible with intensity of each quad less than 1e15 W/cm2but low modes asymmetries displace the ignitor power in the spike towards higher powers.

While for decades, energy production relying on laser inertial fusion has been a strong motivation for the development in Europe of a few high-energy laser facilities and dedicated scientific programs, the HiPER initiative launched in 2004 fostered an ambitious large-scale coordinated European program toward inertial fusion energy. Anticipating the successful demonstration of fusion ignition and gain at the National Ignition Facility (NIF) in the USA, scientists and engineers from across Europe are developing the case for a next generation laser fusion facility, HiPER, to be constructed in Europe. The single-facility build strategy of HiPER (High Power Laser Energy Research Facility) aims at first demonstrating some key elements of a fusion reactor in a high rep-rate few-second cycle mode, before addressing energy production on a high rep-rate continuous mode in a second area. It has been known for almost hundred years that stars produce their energy by fusion of light elements, starting from fusion of hydrogen nuclei into helium. However, the conditions in which such a fusion process can be used to produce energy on a large scale in a controlled manner are so difficult to reach on Earth that a fusion-based power plant is still to be designed. The easiest fusion reaction is that of D and T producing a 4 He nucleus and a neutron with respective energies of 3.5MeV and 14.1MeV. In this case, in addition to an almost unlimited quantity of available D atoms, the radioactive waste generated from a fusion energy plant due to neutron activation of the fusion chamber will be short-lived and can be recycled within a 100-year period with appropriate choice of existing materials. Moreover, a fusion energy plant produces no carbon during the electricity generation cycle, even if there will be a carbon footprint associated with the construction of plant and delivery of materials. If successfully developed, fusion energy may thus provide a sustainable, low carbon, environmentally acceptable, safe and secure commercial energy source without the long-lived radioactive waste associated with conventional nuclear power plants. In the case of laser inertial fusion, a mg-mass of D-T fuel is enclosed inside a mm-size microsphere directly irradiated by powerful laser beams (direct drive) or by x-rays generated inside a laser-irradiated high-Z cavity (indirect drive). The expansion of the heated outer part of the microsphere generates a compression of the inner part of this shell and of the fuel. If sufficiently compressed, the heating of the core of the fuel leads to the conditions necessary for the start of fusion reactions and possibly to the ignition of a large fraction of the fuel. After more than fifty years of fruitful research programs and development of dedicated laser and experimental facilities, it is now believed that a laser energy close to 1 to 2MJ should be sufficient to lead to fuel ignition and energy gains between the input laser energy and the energy produced by fusion reactions of the order or larger than 10. The demonstration of high gains in the indirect-drive scheme is expected in the next few months or years on the NIF (National Ignition Facility) in the USA and on the LMJ (Laser MegaJoule) in France, two facilities at the MJ level.

In preparation of the first ignition attempts on the Laser Megajoule (LMJ), an experimental program is being pursued on OMEGA to investigate LMJ-relevant hohlraums. First, radiation temperature levels close to 300 eV were recently achieved in reduced-scale hohlraums with modest backscatter losses. Regarding the baseline target design for fusion experiments on LMJ, an extensive experimental database has also been collected for scaled implosions experiments in both empty and gas-filled rugby-shaped hohlraums. We acquired a full picture of hohlraum energetics and implosion dynamics. Not only did the rugby hohlraums show significantly higher x-ray drive energy over the cylindrical hohlraums, but symmetry control by power balance was demonstrated, as well as high-performance D2 implosions enabling the use of a complete suite of neutrons diagnostics. Charged particle diagnostics provide complementary insights into the physics of these x-ray driven implosions. An overview of these results demonstrates our ability to control the key parameters driving the implosion, lending more confidence in extrapolations to ignition-scale targets.