Nonlinear theory of the ablative Rayleigh–Taylor instability

Abstract

Here, a model for the nonlinear Rayleigh-Taylor instability (RTI) of a steady ablation front based on a sharp boundary approximation is presented. The model includes the effect of mass ablation and represents a basic tool for investigating many aspects of the nonlinear ablative RTI relevant to inertial confinement fusion. The single mode analysis shows the development of a nonlinear exponential instability for wave numbers close to the linear cutoff. Such a nonlinear instability grows at a rate faster than the linear growth rate and leads to saturation amplitudes significantly larger than the classical value 0.1λ. We also found that linearly stable perturbations with wave numbers larger than the linear cutoff become unstable when their initial amplitudes exceed a threshold value. The shedding of long wavelength modes via mode coupling is much greater than predicted by the classical RTI theory. The effects of ablation on the evolution of a front of bubbles is also investigated and the front acceleration is computed.

Three-dimensional single-mode nonlinear ablative Rayleigh-Taylor instability

“…7 While ablation is stabilizing in the linear regime, the growth of the RTI in the deeply nonlinear regime is accelerated as a result of mass ablation off the fluid interface. An anomalous nonlinear growth, faster than exponential, was observed in the numerical solution of the nonlinear model of Sanz et al 11 The nonlinear theory of Ref. 11 treats the vortex flow in the ablated plasma as a small correction to the ablative flow.…”

Nonlinear excitation of the ablative Rayleigh-Taylor instability for all wave numbers

“…The nonlinear theory [21] based on a sharp boundary approximation and the ordering of an ablative potential flow much greater than the rotational flow suggested that the ARTI beyond the linear cutoff can be excited by a finite amplitude perturbation. It was speculated that only high wave number modes with terminal bubble velocity smaller than the ablation velocity are absolutely stable for any initial amplitude.…”

Simulations of laser imprint reduction using underdense foams and its consequences on the hydrodynamic instability growth

“…Comparing these two figures, we observe more merging of perturbations at different wavelengths and the development of multimode bubblespike structures. Thus, in the case of ablative RT, for a given wavelength λ, the nonlinear evolution begins for the amplitudes smaller than the standard criterion for the classical RT instability, a ∼ 0.1 λ as shown in [39].…”