FLR–Landau fluids for collisionless plasmas

Fluid descriptions of collisionless magnetized plasma are reviewed, with a special focus on Landau fluid models. Simpler than gyrofluids derived from the gyrokinetic equation, these models were first introduced as extensions of anisotropic MHD retaining linear Landau damping, and have recently been generalized by including finite Larmor radius effects in order to describe transverse scales significantly smaller than the ion gyroradius. Such FLR–Landau fluids satisfactorily compare with the hot plasma theory of linear kinetic Alfvén waves, and also accurately reproduce the mirror instability of anisotropic plasmas, including its quenching at small scales. They should provide an efficient tool to simulate phenomena involving a broad range of scales, in regimes where nonlinear kinetic effects such as wave particle trapping can be neglected.