Sixteen-moment approximation for a collisionless space plasma: Waves and instabilities

Abstract

A study is carried out of waves and instabilities in an anisotropic collisionless plasma. In a strongly magnetized plasma, the velocity distributions along and across the magnetic field lines are different, which results in anisotropy of the total pressure and gives rise to an anisotropic heat flux. The fluid description of the plasma is based on the 16-moment integral transport equations, which are integral equations obtained from the Boltzmann-Vlasov kinetic equation. For small incompressible perturbations in a homogeneous plasma, the general dispersion relation implies that there are not only firehose modes, but also three additional modes, and that all four wave modes interact with each other if a heat flux is present. Heat fluxes do not change the properties of conventional firehose modes. The conditions for the onset of instabilities are investigated as functions of the parameters of the problems. Qualitative estimates for conditions typical of the solar corona are presented.