Direct observation of mass oscillations due to ablative Richtmyer–Meshkov instability and feedout in planar plastic targets

Abstract

Perturbations that seed Rayleigh-Taylor (RT) instability in laser-driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite direction. During this time interval, areal mass perturbations caused by all sources of nonuniformity (laser imprint, surface ripple) are expected to oscillate. The first direct experimental observations of the areal mass oscillations due to ablative Richtmyer-Meshkov (RM) instability and feedout followed by the RT growth of areal mass modulation are discussed. The experiments were made with 40 to 99 µm thick planar plastic targets rippled either on the front or on the rear with a sine wave ripple with either Report Documentation Page Form Approved OMB No. 0704-0188 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.

Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

“…This trend is illustrated in Fig. 1(b [6][7][8]19 on the foam side of the target. For this target, the classical RM growth continues for only 0.6 ns after the incident shock wave hits the foam-plastic interface.…”

“…Solid plastic is less compressible by the transmitted shock wavecompression ratio of no more than 3 -and therefore a larger value of is appropriate; 10,18 we take here Side-on measurements of the interfacial modulation amplitude x in laser-driven solid targets are difficult, but the total mass modulation amplitude m is directly measurable by the face-on radiographic diagnostics. [6][7][8][9]13 Time history of m is plotted in Transition to an accelerated target provides additional complications. After the target starts to accelerate, the classical RM interfacial growth must evolve into RT.…”

“…[6][7][8] Our experiments were performed with the Nike KrF laser, 19 248 L nm. The 4 ns long laser pulse, with or without a ~5%, 3 ns foot was focused to a spot 750 m in diameter, producing intensity up to 50 TW/cm 2 .…”

LLE Review 98 (January-March 2004)

“…98. 41. This indicates that most of the background is coming from either Comptonscattered primary x rays or x-ray fluorescence in the structures around the CCD.…”

“…30,31,[39][40][41] To quantify imprinted modulation levels, imprint efficiency measurements 10,14,26 have used the acceleration-phase RT growth to magnify the ablation-front modulations in order to separate them from the shock-front modulations. Figure 98.26 (from Ref.…”