Multicomponent theory of buoyancy instabilities in magnetized plasmas: The case of magnetic field parallel to gravity

TL;DR

This paper develops a multicomponent plasma theory to analyze buoyancy instabilities with magnetic fields parallel to gravity, revealing that thermal flux generally stabilizes the plasma, contrasting with previous MHD-based conclusions.

Contribution

It introduces a multicomponent approach for buoyancy instabilities, accounting for electron thermal flux and collisions, and challenges MHD assumptions by highlighting the importance of electric field perturbations.

Findings

Thermal flux stabilizes buoyancy instabilities in the considered geometry.

Opposite temperature gradients of ions and electrons can lead to instability.

The multicomponent approach contradicts MHD results by including electric field effects.

Abstract

We investigate electromagnetic buoyancy instabilities of the electron-ion plasma with the heat flux based on not the magnetohydrodynamic (MHD) equations, but using the multicomponent plasma approach when the momentum equations are solved for each species. We consider a geometry in which the background magnetic field, gravity, and stratification are directed along one axis. The nonzero background electron thermal flux is taken into account. Collisions between electrons and ions are included in the momentum equations. No simplifications usual for the one-fluid MHD-approach in studying these instabilities are used. We derive a simple dispersion relation, which shows that the thermal flux perturbation generally stabilizes an instability for the geometry under consideration. This result contradicts to conclusion obtained in the MHD-approach. We show that the reason of this contradiction is the simplified assumptions used in the MHD analysis of buoyancy instabilities and the role of the longitudinal electric field perturbation which is not captured by the ideal MHD equations. Our dispersion relation also shows that the medium with the electron thermal flux can be unstable, if the temperature gradients of ions and electrons have the opposite signs. The results obtained can be applied to the weakly collisional magnetized plasma objects in laboratory and astrophysics.