SIMPLE-MODEL FOR ABLATIVE STABILIZATION

We present a simple analytic model for ablative stablization of the Rayleigh-Taylor instability. In this model the effect of ablation is to move the peak of the perturbations to the location of peak pressure. This mechanism enhances the density-gradient stabilization, which is effective at short wavelengths, and it also enhances the stabilization of long-wavelength perturbations due to finite shell thickness. We consider the following density profile: exponential blowoff plasma with a density gradient beta, followed by a constant-density shell of thickness deltat. For perturbations of arbitrary wave number k, we present an explicit expression for the growth rate gamma as a function of k,beta, and deltat. We find that "thick" shells defined by betadeltat greater-than-or-equal-to 1 have gamma2 greater-than-or-equal-to 0 for any k, while "thin" shells defined by betadeltat < 1 can have gamma2 < 0 for small k, reflecting stability by proximity to the back side of the shell. We also present LASNEX simulations that are in good agreement with our analytic formulas.