Electromagnetic Ion-Ion Instabilities in Space Plasmas: Effects of Suprathermal Populations

TL;DR

This paper investigates how suprathermal ion populations and anisotropic electrons influence ion-ion instabilities in space plasmas, revealing their significant effects on instability characteristics and explaining observed low-frequency fluctuations.

Contribution

It extends previous models by incorporating suprathermal populations and electron anisotropy, providing a more comprehensive understanding of ion-ion instability behavior in space plasmas.

Findings

Suprathermal populations significantly alter instability dispersion and growth rates.

Electron anisotropy impacts the stability and wave properties of ion-ion instabilities.

Results explain the origin of low-frequency fluctuations observed in space plasmas.

Abstract

In collision-poor plasmas from space, three distinct ion-ion instabilities can be driven by the proton beams streaming along the background magnetic field: left-hand resonant, non-resonant, and right-hand resonant instabilities. These instabilities are in general investigated considering only idealized proton beams with Maxwellian velocity distributions, and ignoring the implications of suprathermal populations, usually reproduced by the Kappa power-laws. Moreover, the existing theories minimize the kinetic effects of electrons, assuming them isotropic and Maxwellian distributed. In an attempt to overcome these limitations, in the present paper we present the results of an extended investigation of ion-ion instabilities, which show that their dispersion and stability properties (e.g. growth rates, wave frequencies, and the unstable wave numbers) are highly sensitive to the influence of suprathermal populations and anisotropic electrons. These results offer valuable explanations for the origin of the enhanced low-frequency fluctuations, frequently observed in space plasmas and associated with proton beams.