Krypton-fluoride (KrF) lasers are of interest to laser fusion because they have both the large bandwidth capability (≳THz) desired for rapid beam smoothing and the short laser wavelength (1/4 μm) needed for good laser–target coupling. Nike is a recently completed 56-beam KrF laser and target facility at the Naval Research Laboratory. Because of its bandwidth of 1 THz FWHM (full width at half-maximum), Nike produces more uniform focal distributions than any other high-energy ultraviolet laser. Nike was designed to study the hydrodynamic instability of ablatively accelerated planar targets. First results show that Nike has spatially uniform ablation pressures (Δp/p<2%). Targets have been accelerated for distances sufficient to study hydrodynamic instability while maintaining good planarity. In this review we present the performance of the Nike laser in producing uniform illumination, and its performance in correspondingly uniform acceleration of targets.

New laser-driven shock experiments have been used to study the equation-of-state (EOS) properties of liquid deuterium. Reflected shocks are utilized to increase the shock pressure and to enhance the sensitivity to differences in compressibility. The results of these experiments differ substantially from the predictions of the Sesame EOS. EOS models showing large dissociation effects with much greater compressibility (up to a factor of 2) agree with the data. By use of independent techniques, this experiment offers the first confirmation of an earlier observation of enhanced compressibility in liquid deuterium.

We present experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic Report Documentation PageForm Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. We present experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. We observe large reductions in hydrodynamic instability seeded by laser imprint when certain minimum thickness gold or palladium layers are applied to the laser-illuminated surface of the targets. The experiment indicates that the reduction in imprint is at least as large as that obtained by a 6 times improvement in the laser uniformity. We present simulations supported by experiments showing that during the low intensity foot the laser light can be nearly completely absorbed by the high-Z layer. X-rays originating from the high-Z layer heat the underlying lower-Z plastic target material and cause large buffering plasma to form between the layer and the accelerated target. This long-scale plasma apparently isolates the target from laser nonuniformity and accounts for the observed large reduction in laser imprint. With onset of the higher intensity main pulse, the high-Z layer expands and the laser light is transmitted. This technique will be useful in reducing laser imprint in pellet implosions and thereby allow the design of more robust targets for high-gain laser fusion. Prescribed by ANSI Std Z39-18 2 shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. We observe large reductions in hydrodynamic instability seeded by laser...

The uniform and smooth focal profile of the Nike KrF laser [S. Obenschain, et. al., Phys. Plasmas 3, 1996 (2098] was used to ablatively accelerate 40 µm thick polystyrene planar targets with pulse shaping to minimize shock heating of the compressed material. The foils had imposed small amplitude sinusoidal wave perturbations of 60, 30, 20, and 12.5 µm wavelength. The shortest wavelength is near the ablative stabilization cutoff for Rayleigh-Taylor growth. Modification of saturated wave structure due to random laser imprint was observed. Excellent agreement was found between the two dimensional simulations and experimental data for most cases where laser imprint was not dominant. Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

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