Coulomb Bubbles: Over-stable Driving of Magnetoacoustic Waves Due to the Rapid and Anisotropic Diffusion of Energy

We perform a linear magnetohydrodynamic perturbation analysis for a stratified magnetized envelope where the diffusion of heat is mediated by charged particles that are confined to flow along magnetic field lines. We identify an instability, the ``coulomb bubble instability,'' which may be thought of as standard magnetosonic fast and slow waves, driven by the rapid diffusion of heat along the direction of the magnetic field. We calculate the growth rate and stability criteria for the coulomb bubble instability for various choices of equilibrium conditions. The coulomb bubble instability is most strongly driven for weakly magnetized atmospheres that are strongly convectively stable. We briefly discuss a possible application of astrophysical interest: diffusion of interstellar cosmic rays in the hot T ~ 10^6 K Galactic corona. We show that for commonly accepted values of the cosmic ray and gas pressure as well as its overall characteristic dimensions, the Galactic corona is in a marginal state of stability with respect to a cosmic ray coulomb bubble instability. The implication being that a cosmic ray coulomb bubble instability plays a role regulating both the pressure and transport properties of interstellar cosmic rays, while serving as a source of acoustic power above the galactic disk. (abridged)