Effects of mass diffusion on Rayleigh–Taylor instability under a large gravity

Abstract

Rayleigh–Taylor instabilities (RTI) play an important role in the evolution of inertial confinement fusion (ICF) processes, while analytical prediction of the RTI growth rate often fails to reach an agreement with the experimental and simulation results. Accurate analytical prediction of RTI growth is of great significance to the success of ICF schemes. In this paper, we study the effects of mass diffusion and exponential density distribution on RTI under a large gravity by solving the Rayleigh equation with a linear approximation to the density distribution of the mixing layer. The width of the mixing layer is assigned by evaluating the length scale of concentration diffusion and gravitational sedimentation. The latter term is missing in the former isobaric diffusion treatment and is supposed to change the structure of the mixing layer under the gravity. While both effects tend to dampen the instability growth, mass diffusion dominates the damping of perturbations of larger wavenumber and exponential density distribution dominates those of smaller wavenumber, resulting in a non-monotonicity of the density suppression factor of the instability growth rate over perturbation wavenumbers.