Rayleigh–Taylor instability: Comparison of hybrid and nonideal magnetohydrodynamic simulations

The evolution of the Rayleigh–Taylor instability in a low β, two-dimensional plasma is studied using a hybrid code and a nonideal magnetohydrodynamic (MHD) code. The Rayleigh–Taylor instability was chosen as a test case because it is an important mixing process at boundary layers, and because it exhibits different behaviors in the conventional and nonideal limits. The nonideal MHD effects considered are the Hall term and finite Larmor radius (FLR) corrections. Three cases are considered in detail: conventional MHD, weak nonideal effects, and strong nonideal effects. In the conventional MHD regime the usual “bubble and spike” behavior of the Rayleigh–Taylor instability is observed. In the weak nonideal MHD regime long wavelength modes, reminiscent of the Kelvin–Helmholtz instability, dominate nonlinearly but very short wavelength filaments develop at the boundary interface. In the strong nonideal MHD regime, small-scale structures dominate and the boundary layer relaxes via a diffusion-like process rather than a large-scale nonlinear mixing process. In general, the hybrid and fluid simulations are in good agreement. The differences, both physical and numerical, are discussed.