Mirror Instability in Space Plasmas: Finite Ion Larmor Radius Effects

Abstract

A fully kinetic theory of the magnetic mirror instability accounting for the finite ion Larmor radius (FLR) effect is developed. It is shown that the FLR effect leads to a substantial modification of both the instability growth rate and the instability threshold. It is found that for wavelengths of the order of the ion Larmor radius the effective elasticity of the magnetic field lines increases substantially. The latter results in a subsequent increase of the mirror instability threshold. An analytical expression for the growth rate of the fastest growing mode in the fully kinetic regime is derived. Furthermore, it is shown that the presence of FLR effect leads to the generation of the non-coplanar components of the magnetic field perturbations occasionally observed in satellite data.