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

摘要

We investigate electromagnetic buoyancy instabilities of the electron-ionplasma with the heat flux based on not the magnetohydrodynamic (MHD) equations,but using the multicomponent plasma approach when the momentum equations aresolved for each species. We consider a geometry in which the backgroundmagnetic field, gravity, and stratification are directed along one axis. Thenonzero background electron thermal flux is taken into account. Collisionsbetween electrons and ions are included in the momentum equations. Nosimplifications usual for the one-fluid MHD-approach in studying theseinstabilities are used. We derive a simple dispersion relation, which showsthat the thermal flux perturbation generally stabilizes an instability for thegeometry under consideration. This result contradicts to conclusion obtained inthe MHD-approach. We show that the reason of this contradiction is thesimplified assumptions used in the MHD analysis of buoyancy instabilities andthe role of the longitudinal electric field perturbation which is not capturedby the ideal MHD equations. Our dispersion relation also shows that the mediumwith the electron thermal flux can be unstable, if the temperature gradients ofions and electrons have the opposite signs. The results obtained can be appliedto the weakly collisional magnetized plasma objects in laboratory andastrophysics.