[en] We present numerical simulations of strongly two-dimensional laser experiments. First, it is concerned to restitute the direct driven implosion of microballoons irradiated with the two beams of Phebus laser facility at 0.53 μm wavelength and 3.2 TW power. In the second experiment, we study the impact between two foils. The accelerated foil is irradiated at 0,35 μm wavelength with a power of 20 GW. The numerical simulations are realized with the two - dimensional lagrangian FCI 2 code. The X-ray diagnostics are simulated with the DXFCI 2 code. In spite of numerical difficulties, principally close to the laser axis and the target interfaces, calculations have been carried out for a sufficient long time to provide results in accordance with the experiment. A simulation of the implosion of 600 μm in diameter microballoons made with an absorption rate of 40 % provides a neutron yield as well as X-ray emission peaks in agreement with the experiment. In the plane target case, it is shown that, for 80 μm in diameter focal spot, the 2D effects occurring in the acceleration of the foils influence in a preponderant way the energy transfer between these two foils

[en] The existence Rayleigh-Taylor instabilities, in laser heated plasmas, is shown. By means of the acceleration of flat three-layered Au-Al-Au targets, a mixing zone, under the concept of Rayteigh-Taylor instabilities, is observed. The Al emission spectra is obtained, by heating the back of the target with a laser beam. A phase difference exists betwen the main laser beam and the applied one. The spectrum allows the analysis of the Au-Al mixture. The evaluation of the mixture composition is given and the role of the radiating heating is underlined

[en] We present the one-dimension diffusive mixing model Medic-2F which simulates the interpenetration of shell and fuel and its effects in a laser Megajoule (LMJ) capsule. This model needs only the time evolution of the mixing lengths over and under the interface and the expression of wrinkling of this interface. We have compared Medic-2F simulations to the simulations given by the radiation hydrodynamic code FCI2 applied to 3 LMJ targets. The results show a good agreement concerning hydrodynamic quantities particularly fuel mass fraction and YOC temporal evolution. We have also made a parametric study concerning the YOC sensitivity to the gas-filled density, this study shows a qualitative agreement between the 2 simulations, the quantitative agreement is not so good but is promising about the ability of Medic-2F to perform parametric studies around a LMJ target with high mode perturbations within 1 hour Cpu-time per each run

[en] A base-line capsule design for the Laser MegaJoule facility is optimized by radially grading the Ge dopant in plastic ablator. A one dimensional robustness study is performed to optimize the implosion and the entropy deposition. Then, the tolerance versus the ablator roughness is examined for modes over 10 through direct two-dimensional simulations. The stability is significantly higher than that of an uniformly doped design. (authors)

[en] The results of the experiments carried out on a laser system are reported. The work is performed in order to investigate the problem of target instability under ablative acceleration and to get direct evidence of Rayleigh-Taylor instabilities. Tri-layer experiments assert the validity of X-ray spectroscopy measurements as experimental method to investigate the problem. A mixing zone is evidenced and general trends of mixing development versus target acceleration are coherent with numerical simulations. Results obtained with optical smoothing demonstrate that the apparent mixing is not due to large scale illumination non uniformities. Numerical simulations confirm that Rayleigh-Taylor instability seems to be the dominant process responsible for the mixing. Benefit of time resolved spectroscopy appears attractive and gives a real knowledge of the mixing layer

[en] To characterize the hydrodynamic flows in laser accelerated targets, we define two Reynolds numbers. Transport coefficients are computed within the frameworks of the One Component Plasma model for strongly correlated plasmas, and of the Braginskii formula for plasmas dominated by small angle scattering. Configurations with laser energies ranging from 100 J to 2 MJ are investigated. It appears that flows are generally in non-linear regimes except for a target imploded with a 2 MJ laser where turbulence probably occurs. Natural diffusion effects appear to be small. (author)

[en] In the frame of a CEA/US DOE collaboration, convergent experiments have been done on the Nova laser. Numerical simulations with our 2D Lagrangian code FCI2 led the analysis and correctly reproduced the experimental data. From single mode 2D perturbations, ablation front Rayleigh-Taylor instability growth is computed. Moderate and high convergence ratios are addressed. The shrinking of the wavelength plays a prominent role for small convergence ratio and weakly nonlinear hydrodynamics

[en] Mixing experiments have been performed using Si/Al/Au trilayer targets accelerated with laser beams smoothed by random phase plates. The Al-Au mixing is detected by heating the rear of the target with a probe beam and observing the Al line emissions. A null-mix experiment has been performed with Si/Al/Si, which is stable according to Rayleigh and Taylor, in order to check that the probe beam does not induce a specific mixing. Simulations with a hydrocode have been made to characterize the main features of the target when the instabilities occur. In the case of Si/Al/Au targets, the Al emission indicates a mixing of Al and Au for a driver irradiance as low as 10¹³ W/cm² and that most of the Au is mixed with Al. (author). 30 refs, 14 figs, 1 tab

[en] Numerical simulations of strongly two dimensional laser experiments are presented. The first experiment concerns the simulation of the direct driven implosion of microballoons irradiated with the two beams of the Phebus laser facility at 0.53 μm wavelength and 3.2 TW power. In the second experiment the impact between two foils is studied. The accelerated foil is irradiated at 0.35 μm wavelength with a power of 20 GW. The numerical simulations are realized with the two dimensional Lagrangian FC12 code. The X-ray diagnostics are simulated with the DXFC12 code. In spite of numerical difficulties, principally in the vicinity of the laser axis and the target interfaces, calculations have been carried out for a sufficiently long time to provide results in accordance with the experiment. A simulation of the implosion of 600 μm diameter microballoons made with an absorption rate of 40% provides a neutron yield and X-ray emission peaks in agreement with the experiment. In the plane target case it is shown that, for an 80 μm diameter focal spot, the two dimensional effects occurring in the acceleration of the foils influence substantially the energy transfer between these two foils. (author). 5 refs, 2 figs

[en] Convergent ablation experiments with gas-filled rugby hohlraum were performed for the first time on the OMEGA laser facility. A time resolved 1D streaked radiography of capsule implosion is acquired in the direction perpendicular to hohlraum axis, whereas a 2D gated radiography is acquired at the same time along the hohlraum axis on a x-ray framing camera. The implosion trajectory has been measured for various kinds of uniformly doped ablators, including germanium-doped and silicon-doped polymers (CH), at two different doping fraction (2% and 4% at.). Our experiments aimed also at measuring the implosion performance of laminated capsules. A laminated ablator is constituted by thin alternate layers of un-doped and doped CH. It has been previously shown in planar geometry that laminated ablators could mitigate Rayleigh Taylor growth at ablation front. Our results confirm that the implosion of a capsule constituted with a uniform or laminated ablator behaves similarly, in accordance with post-shot simulations performed with the CEA hydrocode FCI2. (paper)