Macroscopic quasilinear theory of parallel electron firehose instability associated with solar wind electrons

Abstract

A number of different microinstabilities are known to be responsible for regulating the upper bound of temperature anisotropies in solar wind protons, alpha particles, and electrons. In the present paper, quasilinear kinetic theory is employed to investigate the time variation in electron temperature anisotropies in response to the excitation of parallel electron firehose instability in homogeneous and non-collisional solar wind plasma under the condition of Tke > T?e. By assuming the bi-Maxwellian form of velocity distribution functions, various velocity moments of the particle kinetic equation are taken in order to reduce the theory to macroscopic model in which the wave-particle interaction is incorporated, hence, the macroscopic quasilinear theory. The threshold condition for the parallel elec tron firehose instability, empirically constructed as a curve in ðbke; T?e=TkeÞ phase space, is implicit in the present macroscopic quasilinear calculation. Even though the present calculation excludes the oblique firehose instability, which is known to possess a higher growth rate, the basic methodology may be further extended to include such a mode. Among the findings is that the parallel electron fire hose instability dynamically couples the electrons and protons, which implies that this instability may be important for overall solar wind dynamics. The present analysis shows that the macroscopic quasi linear approach may eventually be incorporated in global-kinetic models of the solar wind electrons and ions. Published by AIP Publishing