Mirror instability including finite Larmor radius effects

We present a fully kinetic theory of the magnetic mirror instability accounting for finite ion Larmor radius (FLR) effects. Including FLR effects leads to a substantial modification of both the instability growth rate and the instability threshold. For wavelengths the order of the ion Larmor radius the effective elasticity of the magnetic field lines increases substantially. The latter results in an increase of the mirror instability threshold. A compact analytical expression is obtained for the growth rate of the fastest growing mode in the fully kinetic regime. In the presence of FLR effects, a non-coplanar component of the magnetic field perturbation is generated which is occasionally observed in satellite data.