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There has been rapid progress in inertial fusion in the past few years. This progress spans the construction of ignition facilities, a wide range of target concepts and the pursuit of integrated programmes to develop fusion energy using lasers, ion beams and z-pinches.Two ignition facilities are under construction, the national ignition facility (NIF) in the United States and the laser megajoule (LMJ) in France, and both projects are progressing towards an initial experimental capability. The laser integration line prototype beamline for LMJ and the first four beams of NIF will be available for experiments in 2003. The full 192 beam capability of NIF will be available in 2009 and ignition experiments are expected to begin shortly after that time.There is steady progress in target science and target fabrication in preparation for indirect-drive ignition experiments on NIF. Advanced target designs may lead to 5–10 times more yield than initial target designs. There has also been excellent progress on the science of ion beam and z-pinch-driven indirect-drive targets.Excellent progress on direct-drive targets has been obtained on the Omega laser at the University of Rochester. This includes improved performance of targets with a pulse shape predicted to result in reduced hydrodynamic instability. Rochester has also obtained encouraging results from initial cryogenic implosions.There is widespread interest in the science of fast ignition because of its potential for achieving higher target gain with lower driver energy and relaxed target fabrication requirements. Researchers from Osaka have achieved outstanding implosion and heating results from the Gekko XII Petawatt facility and implosions suitable for fast ignition have been tested on the Omega laser.A broad-based programme to develop lasers and ion beams for inertial fusion energy (IFE) is under way with excellent progress in drivers, chambers, target fabrication and target injection. KrF and diode pumped solid-state lasers are being developed in conjunction with dry-wall chambers and direct-drive targets. Induction accelerators for heavy ions are being developed in conjunction with thick-liquid protected wall chambers and indirect-drive targets.

In the framework of research on inertial fusion, experiments on a reduced-scale prototype of the future Laser MegaJoule (LMJ) are planned in the ‘Laser Integration Line’ at CEA/DAM/CESTA. By 2005, part of these experiments will involve Deuterium–Tritium targets in which fusion reaction will result in radiation—mainly in the form of neutron flux and photon radiation from activated materials—that constitute a source of radiological exposure at the workplace. At the conception stage, an evaluation of the radiological exposures of occupational workers was performed. Different options for reducing these exposures have been studied. Results show that by modifying the composition of the staff or delaying the interventions, a reduction of the individual doses to the most exposed categories of employees from 2 to 50% to a factor 4 can be achieved, without increasing the total collective dose which can be further reduced by 10–25%. This study is a good illustration of how the ALARA principle can be implemented at the conception stage of an installation. Due to the low individual and collective exposures, the different options to reduce doses are more closely associated with staff and planning re-organisations. These options are characterised by a rather low cost and limited constraints of implementation.

The Laser Megajoule (LMJ) is a facility dedicated to inertial confinement fusion experiments. Building construction phase should start in the first half of year 2003. Use of a deuterium–tritium mixture in the experiments and high neutron yield generation induces hazards such as contamination of equipments inside the target chamber and activation of materials. Calculations have been undertaken to estimate dose rates levels in the facility. Optimization is under development on ALARA principle basis to reduce activation and workers exposure. Decontamination is an other important safety issue for LMJ; different processes are available and have to be considered (lasers, foams …). Radioactive wastes will be generated and their disposal has to be taken into account.

Neutron yield at the National Ignition Facility (NIF) or the Laser MegaJoule (LMJ) will range from 1019 for a capsule that ignites and burns well to below 1015 for one that fails to ignite. Expected image sizes in deuterium–tritium (DT) neutrons decrease with the neutron yield. At 1018–1019 yields the capsules have ignited and are burning main fuel, producing images with full width at half maximum (FWHM) of ∼100 μm which require a 200 μm field of view and would need 10 μm resolution. Marginally igniting capsules, with yields of 1017 to 1018, burn the hot spot and some main fuel. Their neutron images are smaller, ∼60 μm FWHM, and require ∼120 μm field of view, with 7 μm resolution needed. Below ∼1017, the capsule fails to ignite and a field of view of ∼100 μm suffices to image the hot spot which might be ∼30 μm FWHM with a resolution of ∼5 μm. Images in downscattered neutrons are as large or larger than the time integrated images, have ∼5% of the brightness, and require correspondingly larger fields of vie...

The Laser Megajoule plant is a huge building that measures 300m by 100m in length, 35m in height and 25m in depth at its center. It is composed of 4 laser bays, where laser beams are generated, and a central hall where experiments are carried out. Workers have to be trained as it is described in hazard analysis and, on the basis of these analysis methods, risks are listed for every area. The adequacy of risk and training is assured with access control. Depending on the hazard analysis and in accordance with French work regulations, there are different levels of authorization to access each part of the facility. Access to workplaces is managed with one-person-airlocks. All areas of main risk are controlled by detectors on every point of access, which are managed with a supervision unit in the control room of the facility. In these areas, laser hazard is confined when operators do not need to make local beam adjustments. Most of the equipment has been preset designed to be replaced in case of dysfunction, as it reduces the need of laser adjustments. Laser beam seclusion is controlled by detectors, seals or rounds of inspection. An organization has been defined to have the assurance of risk-control, despite the co-activity between the process of experiment and the phases of assembly needed for the next beams. This includes hazard analysis for each operation, with potential co-activity, which is transcribed in intervention vouchers. The whole safety management system contributes to assuring high levels of safety when conducting the plant’s first experiments, especially with the risks posed by ionizing radiation, lasers and high voltages.The Laser Megajoule plant is a huge building that measures 300m by 100m in length, 35m in height and 25m in depth at its center. It is composed of 4 laser bays, where laser beams are generated, and a central hall where experiments are carried out. Workers have to be trained as it is described in hazard analysis and, on the basis of these analysis methods, risks are listed for every area. The adequacy of risk and training is assured with access control. Depending on the hazard analysis and in accordance with French work regulations, there are different levels of authorization to access each part of the facility. Access to workplaces is managed with one-person-airlocks. All areas of main risk are controlled by detectors on every point of access, which are managed with a supervision unit in the control room of the facility. In these areas, laser hazard is confined when operators do not need to make local beam adjustments. Most of the equipment has been preset designed to be replaced in case of dysfunction, a...

In the context of the direct-drive Laser-Megajoule (LMJ) fusion-research program, the characteristic long-wavelength nonuniformities produced by irradiating a pellet with multiple overlapping laser beams are studied with or without imperfections coming from power imbalance and pointing errors. The intensity profiles are modeled by super-Gaussian shapes. The beam pattern which minimizes the intrinsic LMJ nonuniformity is determined. It is shown the LMJ beam placement creates untractable nonuniformities from even modes. The laser imperfections create odd and low modes of nonuniformity which can dominate the even modes.

We explore two alternative irradiation schemes for the large ('outer') and small ('inner') angle beams that currently illuminate National Ignition Facility (NIF) and Laser Megajoule cavities. In the first, while the outer laser beams enter through the usual end laser entrance holes (LEH), the inner beams enter through slots along the cavity axis wall, illuminating the back wall of the cavity. This avoids the current interaction of the inner laser beams with the gold wall bubbles generated by the outer beams, which leads to large time-dependent changes in drive symmetry. Another scheme potentially useful for NIF uses only the outer beams. The radiative losses through the slots or from the use of outer beams only are compensated by using a smaller cavity and LEH.

Miró software has been used intensively to simulate the Laser Megajoule (LMJ) with the treatment of amplification, frequency conversion, and both temporal/spatial smoothing of the beam for nanosecond pulses. We show that the software is able to model most relevant aspects of the petawatt PETAL laser chain in the subpicosecond regime, from the front-end to the focal spot with a broadband treatment of the amplification and compression stages, including chromatism compensation in the laser chain, segmentation and recombination of the beams on the second compression stage, and focusing by an off-axis parabola.

The advent of high-power lasers facilities such as the National Ignition Facility (NIF) and the laser megajoule provide unique platforms to study the physics of turbulent mixing flows in high energy density plasmas. We report here on the commissioning of a novel planar direct-drive platform on the NIF, which allows the acceleration of targets during 30 ns. Planar plastic samples were directly irradiated by 300–450 kJ of UV laser light (351 nm) and a very good planarity of the laser drive is demonstrated. No detrimental effect of imprint is observed in the case of these thick plastic targets (300 μm), which is beneficial for future academic experiments requesting similar irradiation conditions. The long-duration direct-drive (DD) platform is thereafter harnessed to study the ablative Rayleigh–Taylor instability (RTI) in DD. The growth of two-dimensional pre-imposed perturbations is quantified through time-resolved face-on x-ray radiography and used as a benchmark for radiative hydrocode simulations. The ablative RTI is then quantified in its highly nonlinear stage starting from intentionally large 3D imprinted broadband modulations. Two generations of bubble mergers is observed for the first time in DD, as a result of the unprecedented long laser acceleration.

The Petawatt Aquitaine Laser (PETAL) facility was designed and constructed by the French Commissariat à l'énergie atomique et aux énergies alternatives (CEA) as an additional PW beamline to the Laser MegaJoule (LMJ) facility. PETAL energy is limited to 1 kJ at the beginning due to the damage threshold of the final optics. In this paper, we present the commissioning of the PW PETAL beamline. The first kJ shots in the amplifier section with a large spectrum front end, the alignment of the synthetic aperture compression stage and the initial demonstration of the 1.15 PW @ 850 J operations in the compression stage are detailed. Issues encountered relating to damage to optics are also addressed.

A numerical method providing the optimal laser intensity profiles for a direct-drive inertial confinement fusion scheme has been developed. The method provides an alternative approach to phase-space optimization studies, which can prove computationally expensive. The method applies to a generic irradiation configuration characterized by an arbitrary number $N_{B}$ of laser beams provided that they irradiate the whole target surface, and thus goes beyond previous analyses limited to symmetric configurations. The calculated laser intensity profiles optimize the illumination of a spherical target. This paper focuses on description of the method, which uses two steps: first, the target irradiation is calculated for initial trial laser intensities, and then in a second step the optimal laser intensities are obtained by correcting the trial intensities using the calculated illumination. A limited number of example applications to direct drive on the Laser MegaJoule (LMJ) are described.

Commissariat a l’Energie Atomique et aux Energies Alternatives has developed the ARGOS X-ray framing camera to perform two-dimensional, high-timing resolution imaging of an imploding target on the French high-power laser facility Laser MegaJoule. The main features of this camera are: a microchannel plate gated X-ray detector, a spring-loaded CCD camera that maintains proximity focus in any orientation, and electronics packages that provide remotely-selectable high-voltages to modify the exposure-time of the camera. These components are integrated into an “air-box” that protects them from the harsh environmental conditions. A miniaturized X-ray generator is also part of the device for in situ self-testing purposes.

The Laser MegaJoule (LMJ) timing system has to synchronize 176 laser beams within 40 ps to compress symmetrically the millimeter-size target in order to ignite the deuterium and tritium filled capsule despite the fact that the quadruplet laser sources are separated within the building by several hundred of meters. This kind of performance is also required for fiducial pulses used to temporally mark laser and plasma diagnostics. While the LMJ timing system is under development, a major technical challenge is to ensure a time drift of delays measurements (from 5 μs to 100 μs) to less than 2 ps peak-to-peak (pp) over 24 hours, 10 ps pp over 7 days and 30 ps pp over a month for the most precise classes. In this context, a collaboration between the CEA and the UTINAM Institute was set up in order to develop the methods and means required to reach the measurement of such time drifts. In this unusual time domain calibration — ps drift for delays of several microseconds watched over periods of several hours or days — the main problem is the control and implementation of the instruments needed to achieve such measurements. The firsts results obtained in this collaboration provided a measurement method and its associated instruments. This method was certified by an ultra stable frequency reference (MASER supervised over UTC) and very high sampling frequency digitizers (up to 160 Gs/s). In this paper, the results will be analysed and discussed in terms of stability (jitter) and accuracy (time drift of synchronization delays). The method used to supervise the facility's time drifts of the LMJ timing system will also be presented.

French targets prepared for inertial confinement fusion experiments, to be shot on the Laser Megajoule facility, are organic (CHx) microshells. The microshell, that contains the deuterium–tritium mixture (DT), is placed in a gold holraum that converts the laser light into an x-ray flow. It is an indirect drive to reach ignition. This microshell, whose role is an ablator to initiate compression of the target, is fabricated by plasma polymerization of organic precursors. In these implosion experiments, it is necessary to control the preheat of the deuterium–tritium fusible mixture in the capsule, and the ablation front instability, by doping the ablator layer with a small quantity of high Z material. The germanium or bromine doping of the CHx enables the control of the microshell opacity to prevent the preheat of DT from high energetic x rays. Titanium is used to diagnostises the implosion of the target. The coating properties evolve with the amount of dopant incorporated in the CHx matrix. Evolution of the...

The cryogenic targets of the Laser Megajoule Facility (LMJ) are hollow spheres. Their internal wall is covered by a solid cryogenic fuel layer. One issue of inertial confinement fusion experiments is to guarantee the quality of the geometry of fuel layer. Cryogenic targets must be cooled at a temperature near the triple point (19 K) with a very good stability (0.2 mK) for a long time (many hours). This period is used to position the target with accuracy at the centre of an experimental vacuum vessel of 10 m diameter where the laser beams are focused. A complex cryogenic infrastructure has been imagined to insure the continuity of the cryogenic chain from the filling station located in Valduc in Burgundy to the experimental chamber installed close to Bordeaux. The design of the target and a succinct description of the infrastructure are presented. A first prototype of cryogenic grip has been built and characterised. Some experimental results are given.

This paper reviews the leading edge of the basic and applied science that use high-intensity facilities. The more than 15 000 experiments on the Nova laser since 1985 and many thousands more on other laser, particle beam, and pulsed power facilities around the world have established the new laboratory field of high-energy-density plasma physics and have furthered development of inertial fusion. High-brightness femtosecond lasers have enabled the study of matter in conditions previously unachievable on earth. These experiments and advanced calculations have established the specifications for the National Ignition Facility (NIF) and Laser MegaJoule (LMJ) and have enhanced scientific fields such as laboratory astrophysics. Science and technology developed in inertial fusion have found near-term commercial use, have enabled steady progress toward the goal of fusion ignition and gain in the laboratory, and have opened up new fields of study for the 21 st century.

The cryogenic targets of the Laser Megajoule facility (LMJ) are hollow spheres. Their internal walls are covered with a solid layer of frozen deuterium-tritium (D-T). One issue of inertial confinem...

The goal of the Laser MegaJoule project (LMJ), which started at CEA/DAM since 1995, is to achieve combustion of a DT (Deuterium-Tritium) target and to demonstrate a gain in energy of about 10. Target compression and the steps which leads to ignition and combustion are briefly described in order to explain the specifications of the laser driver. Laser architecture and milestones of the construction are presented.

Inertial fusion energy (IFE) ignition and gain facilities based on lasers, the national ignition facility (NIF/USA) and the laser megajoule (LMJ/France), will be operating in the first years (2002–2010) of the next century. The conceptual design of another ignition and gain facility, the heavy ion design of ignition facility (HIDIF), is under way in an European initiative. NIF's target emission spectra show the differences in the energy fraction of debris and X-rays between direct and indirect driven (hohlraum) targets and the importance of the angular dependence in hohlraum emissions. Emerging neutrons could limit the availability to the chamber area because of activation and produce damage in the final optics; however, the NIF/LMJ designs do not envision significant effects in routine or accident conditions. Damage from debris and X-rays to the chamber wall has been extensively analyzed, concluding on the use/choice of coating materials (B4C, B, C). Removal depths in the wall/chamber have been estimated, together with the materials deposition in areas such as final optical assembly (FOA), target positioner, and debris shields. Differences in NIF and LMJ chambers include essentially the concrete shielding sandwiches in the Al layers in the case of LMJ. The use of present technology of composite materials, instead of Al, will give a better contact dose rate in some frequent access areas of the facilities. After previous reactor concepts reported in the early 90's, additional work has been done on LIBRA-SP, HYLIFE-II and KOYO designs, establishing new approaches to protection and material consideration, together with systems such as the target injector (HYLIFE-II). The choice and disposition of materials in KOYO (SiC + HT-9), LIBRA-SP (HT-9) and HYLIFE-II (SS304) is presented for handling and disposal considerations, with clear consequences in the classification of areas for shallow land burial (SLB). The importance of uncertainties in nuclear data will be discussed, and its influence in early conclusions. The effect of neutron spectrum in accidental release emissions by activation of materials is also critical in the characterization of the components of the reactor, and will be discussed.

Thermo-mechanical deformation of Neodymium doped glass slabs during high-power laser shots strongly affects the beam wave-front. The thermally distorted phase profile is corrected with an adaptative mirror on the French Ligne d'Integration Laser (LIL), the 8-beam prototype of the Laser Megajoule (LMJ). Nitrogen cooling of the flash lamps reduces the delay needed to reach thermal equilibrium between two shots by optimizing the slab relaxation back to their original shape. The wave-front is measured before, during, and after a shot with a Shack-Hartmann wave-front sensor. To predict and control the phase profile during cooling, phase dynamics is computed from the thermo-mechanical properties of the slab. Numerical results and measurements are in good qualitative and quantitative agreement.

This paper presents recent studies of the propagation of high-power laser beams like Laser Integration Line (LIL) and Laser MegaJoule (LMJ) beams, when interactions occur with environmental pollution particles and component defects. The studies are mainly achieved with the CEA-DAM MIRO beam propagation code. The highest intensifications in the downstream propagation are obtained for phase objects like dielectric particles, scratches or laser damage rather than for amplitude objects like metallic particles. Dramatic amplification of Kerr nonlinear effect leading to beam self-focusing inside the component is predicted depending on the particle size. The effect of statistical distributions of end-of-line phase defects on the LIL/LMJ 0.351-μm-wavelength focal spot intensity and size is quantified.

The use of the Laser MegaJoule facility within the shock ignition scheme has been considered. In the first part of the study, one-dimensional hydrodynamic calculations were performed for an inertial confinement fusion capsule in the context of the shock ignition scheme providing the energy gain and an estimation of the increase of the peak power due to the reduction of the photon penetration expected during the high-intensity spike pulse. In the second part, we considered a Laser MegaJoule configuration consisting of 176 laser beams that have been grouped providing two different irradiation schemes. In this configuration the maximum available energy and power are 1.3 MJ and 440 TW. Optimization of the laser–capsule parameters that minimize the irradiation non-uniformity during the first few ns of the foot pulse has been performed. The calculations take into account the specific elliptical laser intensity profile provided at the Laser MegaJoule and the expected beam uncertainties. A significant improvement of the illumination uniformity provided by the polar direct drive technique has been demonstrated. Three-dimensional hydrodynamic calculations have been performed in order to analyse the magnitude of the azimuthal component of the irradiation that is neglected in two-dimensional hydrodynamic simulations.

The possibility of enhanced mirrors for laser megajoule reflectors has been studied, and preliminary samples have been realized with magnetron sputtering technology. Spectral measurements of improved reflectivity and cosmetics analysis are presented.

We report on new developments in micro-optics technologies used at LETI for the collective fabrication of very-low-threshold plano-concave stable micro-cavities in laser materials and refractive silica microlenses. Among the range of industrial applications, diode-pumped microchip lasers are used as pulse generators in the Laser Megajoule front end. With this aim, the beam of the microchip lasers has been coupled into a polarization-maintaining single-mode optical fibre through a silica microlens with a coupling efficiency of better than 70%.

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.

We present direct-drive target design studies for the laser mégajoule using two distinct initial aspect ratios (A = 34 and A = 5). Laser pulse shapes are optimized by a random walk method and drive power variations are used to cover a wide variety of implosion velocities between 260 km/s and 365 km/s. For selected implosion velocities and for each initial aspect ratio, scaled-target families are built in order to find self-ignition threshold. High-gain shock ignition is also investigated in the context of Laser MégaJoule for marginally igniting targets below their own self-ignition threshold.

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.

Relationships between subsurface damage (SSD) depth and peak to valley surface roughness (Rt ) have been widely studied and present a major interest for an easy assessment of the SSD depth. We seek the relation between SSD depth and other surface roughness parameters using the Abbott-Firestone curve on a large campaign of grinding tests (with different abrasive grain size, grinding speed and grinding mode). The results reveal that the Abbott-Firestone parameter Mr2 , which can be linked to the volume fraction of valley in the roughness profile, is more accurate than Rt for an assessment of the SSD depth and that the relationship between Mr2 and the SSD depth varies when changing the grinding mode. Keywords: subsurface damage, surface roughness, Abbott Firestone, fused silica glass 1. INTRODUCTION Many studies tried to define an empi rical relationship between subsurface damages and surface roughness because these damages under surface, mainly due to the manufacturing steps, limit greatly the lifetime of optical components in high energy laser applications such as Laser Megajoule (LMJ) or National Ignition Facility (NIF)

International audience; Estimating the vulnerability is a key challenge for plasma diagnostics designed to operate in radiative background associated with megajoule 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.

High-power, single longitudinal mode, single-polarization beam generates from a polarization maintaining double-clad Yb-doped silica fiber laser is more applicable for inertial confinement fusion (ICF) applications. The laser beamlets that converge on a target originate from a low power fiber laser in the master oscillator room (MOR). The laser seed signal amplifies through several cascaded amplifier chains in the front-end system. Today, the most famous fusion facilities, including National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL), Ligne d’Integration Laser- Laser Megajoule (LIL-LMJ) and OMEGA utilize fiber-based lasers. In this paper, we have compared various pumping modes comprising end-pumped master oscillator-power amplifier (MOPA) configuration and distributed sidepumped multifiber series fiber laser for scaling up the power of large-mode area (LMA) Yb:silica fiber laser for forward pumping regime.

This paper describes the main features of the Laser Megajoule (LMJ), an equivalent project in France to the NIF project in USA. It has been sized to achieve ignition of a small amount of DT and to produce fusion energy in a laboratory with a significant gain, by imploding small capsules filled with a DT mixture. The paper explains the main issues to design the target area because of the large emissions of neutrons, x-rays and debris due to the explosion of the target. We show that Phebus in France as well as Nova in USA can be used as test beds to study the threats expected on the first wall of the target chamber due to the large burst of neutrons, x-rays and shrapnels emitted from the exploding target. 10 refs., 11 figs., 1 tab.

High-resolution, high-sensitivity X-ray imaging is a real challenge in laser plasma diagnostic to attain reliable data in high-energy density plasma experiments. In this context, ultra-high-intensity lasers generate hot and dense plasma but only in a small volume. An experiment has been performed at the LULI2000 laser facility to diagnose such plasma conditions from thermal spectroscopic data. To image the emission zone plasma's Al Heβ, a Fresnel-lens-based X-ray imager has been developed. It features a 846 μm-diameter Fresnel Phase Zone Plate (FPZP) and a Pd/B4C multilayer mirror (thickness d = 5.1 nm). This association can be used between 1500 eV and 2100 eV. The FPZP's efficiency was measured on a synchrotron facility (SOLEIL) and its spatial resolution in a laser facility (EQUINOX). The mirror reflectivity was measured on the synchrotron facility BESSY II. With experimental conditions, the system resolution reaches 3.8 ± 0.6 μm with an adequate efficiency in the 1800 eV-1900 eV energy range with a solid angle of 9 × 10-6 sr. Consequently, a FPZP is an excellent optics setup for high-resolution quasi-monochromatic X-ray imaging and provides a good collection angle. Bragg-Fresnel lenses, based on the principle of FPZP and mirrors, are currently designed for an X-ray imager at the Laser MegaJoule facility.

The first experiments on the National Ignition Facility (NIF) in the US started and will be followed by the Laser MegaJoule (LMJ) in France. Such facilities will provide unique tools for inertial confinement fusion (ICF) physics & for basic science. A petawatt short pulse laser (ps) is being added to the ns pulse beams of the LMJ. This is PETAL (PETawatt Aquitaine Laser), under construction on the LMJ site near Bordeaux (France). The Petal+ project is aiming at the design and construction of diagnostics dedicated to experiments with PETAL and LMJ laser beams. Within Petal+, three types of diagnostics are under study: a proton spectrometer, an electron spectrometer and a large-band X-ray spectrometer. The first goal of these diagnostics will be to characterize the secondary radiation and particle sources produced with PETAL. They will also be used for experiments using both ns and ps beams. In the present paper emphasis is put on the charged-particle diagnostics.

Shock ignition [1] is an approach to direct-drive inertial confinement fusion (ICF) in which the stages of compression and hot spot formation are partly separated. The fuel is first imploded at lower velocity than in conventional ICF. Close to stagnation an additional intense laser spike drives a strong converging shock, which contributes to hot spot formation. Shock ignition shows potentials for high gain at UV laser energy below 1 MJ, and could be tested on the National Ignition Facility [2] or Laser Megajoule. Due to the lower implosion velocity, issues related to hydrodynamic instabilities are relaxed. On the other hand, the interaction of the laser spike with the plasma occurs in a regime where parametric instabilities are expected to become relevant.

The laser Megajoule (LMJ) facility is designed to provide the experimental capabilities to study High Energy Density Physics (HEDP). The LMJ is part of the Simulation Program, which combines improvement of physics models, high performance numerical simulation, and experimental validation. Since the operational commissioning of the LMJ, in October 2014, several experimental campaigns have been achieved. They have demonstrated the good performances of LMJ and demonstrated its aptitudes to perform experiments for the Simulation Program. The PETAL project consists in the addition of one short-pulse (ps) ultra- high-power, high-energy beam (kJ) to the LMJ facility. The first high energy test shots in the compressor stage of PETAL, performed in May 2015, have reached a power of 1.2 PW. PETAL will offer a combination of a very high intensity multi-petawatt beam, synchronized with the nanosecond beams of the LMJ. This combination will expand the LMJ experimental field in HEDP. LMJ-PETAL is open to the academic communities; the first experiments are planned in 2017.

The laser Megajoule (LMJ) is a high energy laser facility (176 UV beam lines) designed for High Energy Density Physics. The end of the year 2014 was devoted to the progressive commissioning of the LMJ to achieve the first experimental campaign with 8 beams. This paper describes the alignment system developed in order to focus the laser beams and point the plasma diagnostics on the target. Alignment performances have been validated at very low power (1J front end shots) on an active target supporting a CCD sensor. Additional high power pointing shots have been performed to complete the characterization. We have demonstrated beam to target positioning accuracy < 52μm rms which is the LMJ requirement.

The laser Megajoule (LMJ), developed by the French Commissariat a l'Energie Atomique et aux Energies Alternatives (CEA), will be a cornerstone of the French Simulation Program, which combines improvement of physics models, high performance numerical simulation, and experimental validation. The LMJ facility is under construction at CEA CESTA near Bordeaux and will provide the experimental capabilities to study High-Energy Density Physics (HEDP). One of its goals is to obtain ignition and burn of DT-filled capsules imploded, through indirect drive scheme, inside rugby-shape hohlraum. The PETAL project consists in the addition of one short-pulse (ps) ultra-high-power, high-energy beam (kJ) to the LMJ facility. PETAL will offer a combination of a very high intensity multi-petawatt beam, synchronized with the nanosecond beams of the LMJ. This combination will expand the LMJ experimental field on HEDP. This paper presents an update of LMJ & PETAL status, together with the development of the overall program including targets, plasma diagnostics and simulation tools.

Laser-plasma interaction is a major issue for achieving ignition in inertial confinement fusion schemes, and still a major concern for the upcoming french laser megajoule (LMJ) program. In order to mitigate the deleterious effects due to laser-plasma instabilities (LPI), clearly evidenced during the recent US National Ignition Campaign conducted on the National Ignition Facility, we use the LIL facility as a demonstrator for LPI studies. In this article, we focus on preliminary results regarding the propagation of a typical LMJ quadruplet through gas-filled hohlraums. Results on hohlraum energetics will then be discussed.

Lasers can now deliver short and very intense pulses capable of producing hot and dense plasmas. The diffusion of such lasers has allowed studying the behaviour of ionized media in novel ways. Ion acceleration through laser plasma interaction is a recent research subject and its fast-paced progresses highlight the mastering of high power laser systems and the better understanding of the physics of high intensity laser plasma interaction. Short and intense laser pulses have also permitted the development of areas of research like harmonic generation, hard X-ray radiation sources, energetic particles sources and inertial confinement fusion. These researches have lead to numerous applications in transdisciplinary domains: material science, development of X-UV lasers, surface treatments, chemistry and biology are just a few examples. Large national programs are focused on these topics like the National Ignition Facility in California, the Laser Megajoule and the Apollon laser in France.

The path to successful inertial confinement fusion (ICF) requires to observe and control the micro balloon deformations. This will be achieved using X-ray microscope among other diagnostics. A high resolution, high energy X-ray microscope involving state-of-the-art toroidal mirrors and multilayer coatings is described. Years of experiments and experience have led to a small-scale X-ray plasma imager that proves the feasibility of all the features required for a LMJ diagnostic: spatial resolution of 5μm, broad bandwidth, millimetric field of view (FOV). Using the feedback given by this diagnostic, a prototype for the Laser MegaJoule (LMJ) experiments has been designed. The experimental results of the first diagnostic and the concepts of the second are discussed.

International audience; CMOS image sensors (CIS) are promising candidates as part of optical imagers for the plasma diagnostics devoted to the study of fusion by inertial confinement. However, the harsh radiative environment of Megajoule Class Lasers threatens the performances of these optical sensors. In this paper, the vulnerability of CIS to the transient and mixed pulsed radiation environment associated with such facilities is investigated during an experiment at the OMEGA facility at the Laboratory for Laser Energetics (LLE), Rochester, NY, USA. The transient and permanent effects of the 14 MeV neutron pulse on CIS are presented. The behavior of the tested CIS shows that active pixel sensors (APS) exhibit a better hardness to this harsh environment than a CCD. A first order extrapolation of the reported results to the higher level of radiation expected for Megajoule Class Laser facilities (Laser Megajoule in France or National Ignition Facility in the USA) shows that temporarily saturated pixels due to transient neutron-induced single event effects will be the major issue for the development of radiation-tolerant plasma diagnostic instruments whereas the permanent degradation of the CIS related to displacement damage or total ionizing dose effects could be reduced by applying well known mitigation techniques.

International audience; We review the advantages and limitations for the integration of optical fibers in the radiative environment associated with Megajoule class lasers as Laser Megajoule (LMJ) in France or National Ignition Facility (NIF) in the USA. Optical fibers present numerous advantages, like their electromagnetic immunity, for integration in these facilities devoted to the fusion by inertial confinement studies. Despite these advantages, it is also well-known that optical fibers suffer from a degradation of their macroscopic properties under irradiation, limiting their transmission capability. We studied the major mechanisms governing the amplitude of this degradation, focusing our discussion on the transient radiation-induced attenuation (RIA) phenomena that is often the limiting factor for LMJ applications. The amplitude and growth and decay kinetics of RIA are affected by different parameters related to the fibers themselves but also depend on the application and irradiation characteristics. We particularly investigated the fiber transient radiation responses when the optical links have to operate during the pulsed and mixed environment associated with ignition shots. Our study shows that, if the same parameters affect the fiber sensitivity for steady state and transient irradiations, the radiation tolerances of the different classes of waveguides strongly differ, implying dedicated experiments for LMJ facility needs.

International audience; The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium filled microballoon [1]. 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.

Laser Megajoule (LMJ), a €3 billion research facility completed late last year near France9s Atlantic coast, is a dead ringer for the world9s leading laser fusion lab, the National Ignition Facility (NIF) in California. The similarities are no coincidence. Both sites were designed for the same purpose—to train scores of powerful laser beams on a single target, subjecting it, for an instant, to outlandish extremes of temperature and pressure. The two labs collaborated extensively and, like NIF9s, LMJ9s primary purpose is military: replicating nuclear explosions in miniature so that weapons scientists can ensure their bombs will detonate if needed without having to test them. The French facility, like its U.S. counterpart, will also pursue a sideline in inertial fusion energy research: crushing capsules of hydrogen isotopes with laser pulses so that the isotopes fuse into helium, releasing vast stores of energy that might one day be harnessed in a power plant. But some key design differences may give LMJ a better chance of achieving fusion energy than NIF has.