Multicomponent theory of buoyancy instabilities in magnetized
  astrophysical plasmas: MHD analysis revisited
  We develop a theory of buoyancy instabilities of the electron-ion plasma with
the heat flux based on not the MHD equations, but using the multicomponent
plasma approach. We investigate a geometry in which the background magnetic
field, gravity, and stratification are directed along one axis. No
simplifications usual for the MHD-approach in studying these instabilities are
used. The background electron thermal flux and collisions between electrons and
ions are included. We derive the simple dispersion relation, which shows that
the thermal flux perturbation generally stabilizes an instability. There is a
narrow region of the temperature gradient, where an instability is possible.
This result contradicts to a 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 MHD equations. Our
dispersion relation also shows that a medium with the electron thermal flux can
be unstable, if the temperature gradient of ions and electrons have the
opposite signs. The results obtained can be applied to ICM and clusters of
galaxies.
