Fluid simulations of non-resonant anisotropic ion heating

Abstract

The finite Larmor radius (FLR)-Landau fluid model, which extends the usual anisotropic magnetohydrodynamics to magnetized collisionless plasmas by retaining linear Landau damping and finite Larmor radius corrections down to the sub-ionic scales in the quasi-transverse directions, is used to study the non-resonant heating of the plasma by randomly driven Alfvén waves. One-dimensional numerical simulations, free from any artificial dissipation, are used to analyze the influence on the thermal dynamics, of the beta parameter and of the separation between the driving and the ion scales. While the gyrotropic heat fluxes play a dominant role when the plasma is driven at large scales, leading to a parallel heating of the ions by Landau damping, a different regime develops when the driving acts at scales comparable to the ion Larmor radius. Perpendicular heating and parallel cooling of the ions are then observed, an effect that is mostly due to the work of the non-gyrotropic pressure force and that can be viewed as the fluid signature of the so-called stochastic heating. A partial characterization of the plasma by global quantities (such as the magnetic compressibility and the density-magnetic field correlations that provide information on the dominant type of waves) is also presented. The enhancement of the parallel electron heating by a higher level of fast magnetosonic waves is in particular pointed out.