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

TL;DR

This paper introduces a kinetic approach to study heat-flux electromagnetic instabilities in space plasmas, revealing how electron temperature anisotropies influence the stability and nature of these instabilities.

Contribution

It provides a new kinetic model incorporating electron temperature anisotropies to analyze heat-flux instabilities in space plasmas.

Findings

Electron anisotropy significantly alters instability properties.

Whistler instabilities are stimulated when $A_b > 1$.

Firehose instabilities are enhanced when $A_b < 1$.

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 electron beam $A_b = T_\perp / T_\parallel \ne 1$, 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.