Growth rates of the ablative Rayleigh–Taylor instability in inertial confinement fusion

Abstract

A simple procedure is developed to determine the Froude number Fr, the effective power index for thermal conduction , the ablation-front thickness L 0 , the ablation velocity V a , and the acceleration g of laser-accelerated ablation fronts. These parameters are determined by fitting the density and pressure profiles obtained from one-dimensional numerical simulations with the analytic isobaric profiles of Kull and Anisimov ͓Phys. Fluids 29, 2067 ͑1986͔͒. These quantities are then used to calculate the growth rate of the ablative Rayleigh-Taylor instability using the theory developed by Goncharov et al. ͓Phys. Plasmas 3, 4665 ͑1996͔͒. The complicated expression of the growth rate ͑valid for arbitrary Froude numbers͒ derived by Goncharov et al. is simplified by using reasonably accurate fitting formulas.

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

“…(2) for all of the planar examples considered herein, but with magnitudes that are generally smaller than those reported in Ref. 47. It is speculated that differences in the EOS and opacity models used in the two studies are largely responsible for this discrepancy.…”

“…In Sec. II, we preface the presentation of our results by first reviewing the work of Betti et al, 47 who previously studied the ablative RT instability in laser-accelerated planar foils and derived linear growth-rate formulae for specific target materials and laser intensities. Since experimental measurements over the full range of the RT dispersion spectrum are lacking, we chose to model in this study the same target and laser-pulse parameters that were considered in Ref.…”

“…Since experimental measurements over the full range of the RT dispersion spectrum are lacking, we chose to model in this study the same target and laser-pulse parameters that were considered in Ref. 47 in order to have a comparative framework with which to evaluate our growth-rate predictions. In Sec.…”

“…For target materials in which radiative effects are important, however, it is now understood that this last approximation leads to an overestimate of the ablative RT growth-rate because it overlooks the stabilizing effect of a finite density scale-length created by the radiation field. 47 Consequently, the Takabe-Bodner formula should only be applied to very sharp ablation fronts (or to large wavelength modes) and must be modified to describe RT growth in materials in which significant radiation transport exists.…”

A hybrid Rayleigh-Taylor-current-driven coupled instability in a magnetohydrodynamically collimated cylindrical plasma with lateral gravity

“…[6][7][8][9] In laser-based inertial confinement fusion and laser-produced plasma experiments, the RT instability happens when the ablation fronts are accelerated by laser irradiation. 10,11 The Parker instability or magnetic buoyancy instability can occur when a horizontal magnetic field increasing with depth supports heavier gas on top. [12][13][14][15] This instability shares the same physics as the MRT instability.…”