Nonlinear thermocurrent beam instability of a weakly ionized plasma

The boundaries of the thermocurrent instability in the linear theory and its maximum development increment are determined. It is shown that the group velocity in this instability depends on the wave vector giving rise to the modulational instability. Then the theory of the thermocurrent instability is considered in the nonlinear regime. In the nonlinear regime, the one-dimensional theory of the thermocurrent instability shows that the instability is caused by negative diffusion in a dense quasineutral plasma under the condition of nonresonant Cerenkov radiation. In this case, plasma diffuses from the rarefied region to the dense region until density falls down so that the quasineutrality condition would be violated and thus diffusion again would become positive. In conclusion, a longitudinal periodic nonlinear structure with a specific parameter is formed in the plasma. (c) 2008 American Institute of Physics.