Linear modes in the partially ionized heliosphere plasma

TL;DR

This paper develops a one-dimensional linear theory to analyze instabilities in the partially ionized heliosphere plasma, revealing that charge exchange coupling influences certain wave modes but not Alfvén waves.

Contribution

It introduces a self-consistent linear model coupling MHD and hydrodynamics to study wave instabilities in partially ionized plasma systems.

Findings

Charge exchange coupling is more effective at larger scales.

Alfvén waves remain unaffected by charge exchange.

Fast and slow waves are linearly unstable.

Abstract

The heliosphere is predominantly a partially ionized plasma that consists of electrons, ions and significant neutral atoms. Nonlinear interactions amongst these species take place through direct collision or charge exchange processes. These interactions modify linear and non linear properties of the plasma. In this work, we develop a one dimensional linear theory to investigate linear instabilities in such system. In our model, the electrons and ions are described by a single fluid compressible magnetohydrodynamic (MHD) model and are coupled self-consistently to the neutral fluid via compressible hydrodynamic equations. The coupling is mediated by the charge exchange process. Based on our self-consistent analysis, we find that the charge exchange coupling is more effective at larger length scales, and Alfv\'en waves are not affected by the charge exchange coupling. By contrast, the fast and slow waves are driven linearly unstable.