Instability of velocity distributions of slightly ionized gases in electric fields

If a slightly ionized gas is subject to a constant electric field the (time- and space independent) distribution function for the electrons may be double-humped if the cross section for electron-molecule interactions is changing sufficiently rapidly with velocity. Accordingly 'inverse Landau-damping' can make the distribution function unstable with respect to longitudinal waves if the collisional damping is not too large. The results in the present paper indicate that the plasma can be unstable and parameters involved are estimated in order to get the conditions for instability. (author)