Simulation of instability growth rates on the front and back of laser accelerated planar targets

Abstract

The ability of an inertial confinement fusion target to achieve ignition and burn depends critically upon controlling the growth of hydrodynamic perturbations originating on the outer ablator surface and the inner deuterium–tritium (DT) ice. The MIMOZA-ND code [Sofronov et al., Voprosy Atomnoy Nauki i Tehniki 2, 3 (1990)] was used to model perturbation growth on both sides of carbon foils irradiated by 0.35 μm light at 1015 W/cm2. When an initial perturbation was applied to a laser irradiated surface, the computational instability growth rates agreed well with the existing theoretical estimates. Perturbations applied to the rear side of the target for wavelengths that are large compared to the thickness (d/Λ≪1) behave similarly to the perturbations at the ablation front. For d/Λ⩾1, the shorter the wave length is, the faster the decrease of the growth rate of the amplitudes at the interface (and the mass flows) as compared to the perturbations at the ablation front. This is due to the Richtmyer–Meshkov instability-induced transverse velocity component. The time of Rayleigh–Taylor instability transition to the nonlinear phase depends on the initial amplitude and is well modeled by an infinitely thin shell approximation. The transverse velocity generated by the Richtmyer–Meshkov instability causes the interaction of Λ=10 μm and Λ=2 μm wavelength modes to differ qualitatively when the perturbations are applied to the ablation front or to the rear side of target.