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Title: Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets

Abstract

A mode-coupling model is developed to treat the multimode evolution of the ablative Richtmyer-Meshkov (RM) and Landau-Darrieus (LD) instability in the laser imprint of planar targets. Using this mode coupling model, the multimode power spectrum of the RM and LD instability is computed. For the RM instability, mode-coupling effects lead to a broadening of the oscillatory minima found in linear RM theory. For the LD instability, mode-coupling effects generate an inverse power law spectrum.

Authors:
; ;  [1];  [2];  [2]
  1. Charged Particle Physics Branch, Naval Research Laboratory, Washington, D.C. 20375 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20860448
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 12; Other Information: DOI: 10.1063/1.2399460; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COUPLING; EVOLUTION; ICF DEVICES; INERTIAL CONFINEMENT; LASERS; LIGHT TRANSMISSION; NONLINEAR PROBLEMS; PLASMA; PLASMA INSTABILITY; PLASMA WAVES

Citation Formats

Keskinen, M. J., Velikovich, A. L., Schmitt, A., Radiation Hydrodynamics Branch, Naval Research Laboratory, Washington, D.C. 20375, and Laser Plasma Branch, Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375. Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets. United States: N. p., 2006. Web. doi:10.1063/1.2399460.
Keskinen, M. J., Velikovich, A. L., Schmitt, A., Radiation Hydrodynamics Branch, Naval Research Laboratory, Washington, D.C. 20375, & Laser Plasma Branch, Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375. Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets. United States. doi:10.1063/1.2399460.
Keskinen, M. J., Velikovich, A. L., Schmitt, A., Radiation Hydrodynamics Branch, Naval Research Laboratory, Washington, D.C. 20375, and Laser Plasma Branch, Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375. Fri . "Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets". United States. doi:10.1063/1.2399460.
@article{osti_20860448,
title = {Multimode evolution of the ablative Richtmyer-Meshkov and Landau-Darrieus instability in laser imprint of planar targets},
author = {Keskinen, M. J. and Velikovich, A. L. and Schmitt, A. and Radiation Hydrodynamics Branch, Naval Research Laboratory, Washington, D.C. 20375 and Laser Plasma Branch, Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375},
abstractNote = {A mode-coupling model is developed to treat the multimode evolution of the ablative Richtmyer-Meshkov (RM) and Landau-Darrieus (LD) instability in the laser imprint of planar targets. Using this mode coupling model, the multimode power spectrum of the RM and LD instability is computed. For the RM instability, mode-coupling effects lead to a broadening of the oscillatory minima found in linear RM theory. For the LD instability, mode-coupling effects generate an inverse power law spectrum.},
doi = {10.1063/1.2399460},
journal = {Physics of Plasmas},
number = 12,
volume = 13,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The first observations of the interaction of the Richtmyer-Meshkov (RM) instability with reflected shock and rarefaction waves in laser-driven targets are reported. The RM growth is started by a shock wave incident upon a rippled interface between low-density foam and solid plastic. The subsequent interaction of secondary rarefaction and/or shock waves arriving from the ablation front and the rear surface of the target with the RM-unstable interface stops the perturbation growth and reverses its direction. The ensuing exponential Rayleigh-Taylor growth thus can sometimes proceed with an inverted phase.
  • The Richtmyer-Meshkov instability (RMI) at the ablation front of laser-irradiated planar targets is investigated by two-dimensional numerical hydrodynamics simulations. The linear evolution of perturbations seeded either by surface roughness or target inhomogeneity is studied for perturbation wavelengths in the range 10{<=}{lambda}{<=}400 {mu}m and laser intensity 4x10{sup 12{<=}}I{<=}4x10{sup 14} W/cm{sup 2} (with laser wavelength {lambda}{sub laser}=0.35 {mu}m). Thin and thick cryogenic deuterium or deuterium-tritium (DT) planar targets are considered. For targets irradiated at constant intensity, it is found that perturbations with wavelength below a given threshold perform damped oscillations, while perturbations above such a threshold are unstable and oscillate with growingmore » amplitude. This is qualitatively in agreement with theoretical predictions by Goncharov et al. [Phys. Plasmas 13, 012702 (2006)], according to which ablation related processes stabilize perturbations with kD{sub c}>>1, where D{sub c} is the distance between the ablation front and critical density for laser propagation. For kD{sub c}<1 a weakly growing Landau-Darrieus instability (LDI) is instead excited. The stability threshold increases substantially with laser intensity, given the dependence of D{sub c} on laser intensity I (roughly D{sub c{proportional_to}}I, according to the present simulations). Direct-drive laser fusion targets are irradiated by time-shaped pulses, with a low intensity initial foot. In this case, perturbations with wavelengths below some threshold (about 10 {mu}m, for typical ignition-class all-DT targets) are damped after an initial growth. In a thin target, initial perturbations, either damped or amplified by RMI and LDI, seed the subsequent Rayleigh-Taylor instability. Finally, it is shown that RMI growth of fusion targets can be reduced by using laser pulses including an initial adiabat-shaping picket (originally proposed to reduce the growth of Rayleigh-Taylor instability).« less
  • Theory of the ablative Richtmyer-Meshkov instability is presented. It is shown that the main stabilizing mechanism of the ablation-front perturbations during the shock transit time is the dynamic overpressure that causes perturbation oscillations. The amplitude of the oscillation is proportional to c{sub s}/{radical}(V{sub a}V{sub bl}) and its frequency is {omega}=k{radical}(V{sub a}V{sub bl}) , where k is the wave number, and c{sub s} , V{sub a} , and V{sub bl} are sound speed, ablation, and blow-off plasma velocities, respectively. {copyright} {ital 1999} {ital The American Physical Society}