Effects of thin high-Z layers on the hydrodynamics of laser-accelerated plastic targets

Abstract

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...

Numerical simulations of the ablative Rayleigh-Taylor instability in planar inertial-confinement-fusion targets using the FastRad3D code

“…In such cases, additional methods of instability suppression may be needed. One such approach that has been proposed previously makes use of a thin "high Z" layer [76][77][78][79] on the outside of a spherical ICF target. The radiation from this layer could increase the stabilization of the ablation front by lowering the peak density there.…”

Classical and ablative Richtmyer–Meshkov instability and other ICF-relevant plasma flows diagnosed with monochromatic x-ray imaging

“…For this, the target is covered by a very thin (~1000 Å) layer of a high-Z material, like gold or palladium [63]. Laser radiation absorbed by the high-Z material is immediately converted into x- rays and re-radiated, ablating the target by x-ray drive until the high-Z layer expands and becomes transparent.…”

Laser requirements for a laser fusion energy power plant

“…The CH layer provides a base to deposit the Au/Pd coating, and it also seals in evaporating DT gas from the DT. The Au/Pd coating protects the target from preheating by the infrared radiation from the chamber wall, and it also helps reduce the imprinting of laser nonuniformities on to the target [10] . The use of the Au/Pd alloy rather than pure Au allows for relatively fast filling of the target with DT.…”