Solid-state dynamics experiments at very high pressures and strain rates are becoming possible with highpower laser facilities, albeit over brief intervals of time and spatially small scales. To achieve extreme pressures in the solid state requires that the sample be kept cool, with T sample Ͻ T melt . To this end, a shockless, plasma-piston "drive" has been developed on the Omega laser, and a staged shock drive was demonstrated on the Nova laser. To characterize the drive, velocity interferometer measurements allow the high pressures of 10 to 200 GPa (0.1 to 2 Mbar) and strain rates of 10 6 to 10 8 s Ϫ1 to be determined. Solid-state strength in the sample is inferred at these high pressures using the Rayleigh-Taylor (RT) instability as a "diagnostic." Lattice response and phase can be inferred for single-crystal samples from time-resolved X-ray diffraction. Temperature and compression in polycrystalline samples can be deduced from extended X-ray absorption fine-structure (EXAFS) measurements. Deformation mechanisms and residual melt depth can be identified by examining recovered samples. We will briefly review this new area of laser-based materials-dynamics research, then present a path forward for carrying these solid-state experiments to much higher pressures, P Ͼ 10 3 GPa (10 Mbar), on the National Ignition Facility (NIF) laser at Lawrence Livermore National Laboratory.

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The first measurements and numerical simulations of fusion neutrons from the gas–pusher interface of indirectly-driven inertial confinement fusion implosions have been performed using hydrogen-filled capsules made with a deuterated inner layer. Nonlinear saturation of the growth of hydrodynamic perturbations in high linear growth factor (≃325) implosions was varied by adjusting the initial surface roughness of the capsule. The neutron yields are in quantitative agreement with the direct simulations of perturbation growth, and also with a linear mode superposition and saturation model including enhanced thermal loss in the mixed region. Neutron spectra from these capsules are broader than expected for the calculated ion temperatures, suggesting the presence of nonthermal broadening from mass motion during the fusion burn.

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Few-joule table-top lasers can generate pressures up to the 100 kbar range in solid materials by propagating a low-intensity beam through a transparent dielectric, which confines the ablation pressure, onto an ablation layer in contact with the material of interest. This technique has application in studies of material dynamic behavior and material processing. Development and application of physically based models of this process have lagged experiment. In this article the particulars of a detailed computational model incorporated into a two-dimensional radiationhydrodynamics code are presented. The model accounts for the initial absorption onto a metal surface, low-intensity photoionization absorption in neutral vapor, collisional ionization, recombination, dielectric breakdown, band gap collapse, electron conductivity, thermal transport, and constitutive properties of the materials. The model shows that most of the laser energy is absorbed in the dielectric tamper, not the ablator. Good agreement is found between simulated and measured pressure histories for materials irradiated with several tens of joules using a single-beam neodymium-glass laser at the Lawrence Livermore National Laboratory.

Hard x-ray (>100 keV) imager to measure hot electron preheat for indirectly driven capsule implosions on the NIFa) Rev. Sci. Instrum. 83, 10E508 (2012); K and Lshell xray spectroscopy of indirectly driven implosions (invited) Rev. Sci.The performance of indirectly driven fusion capsules has been improved by mid Z doping of the plastic capsule ablator. The doping increases x-ray preheat shielding leading to a more isentropic compression, higher convergence, and higher neutron yield. A 4ϫ increase in neutron yield is both calculated and observed as the Ge doping level is increased from 0% to 3% by atomic fraction. A predicted 40% decrease in x-ray image core size with increasing Ge content is confirmed.

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