Beaming electromagnetic (or heat-flux) instabilities from the interplay with the electron temperature anisotropies

Abstract

In space plasmas, kinetic instabilities are driven by the beaming (drifting) components and/or the temperature anisotropy of charged particles. The heat-flux instabilities are known in the literature as electromagnetic modes destabilized by the electron beams (or strahls) aligned to the interplanetary magnetic field. A new kinetic approach is proposed here in order to provide a realistic characterization of heat-flux instabilities under the influence of electrons with temperature anisotropy. Numerical analysis is based on the kinetic Vlasov-Maxwell theory for two electron counter-streaming (core and beam) populations with temperature anisotropies and stationary, isotropic protons. The main properties of electromagnetic heat-flux instabilities are found to be markedly changed by the temperature anisotropy of the electron beam _{A b} = _{T ⊥} / _{T ∥} ≠ 1 , leading to stimulation of either the whistler branch if _{A b} > 1 or the firehose branch for _{A b} < 1 . For a high temperature anisotropy, whistlers switch from heat-flux to a standard regime, when their instability is inhibited by the beam.