THEORY OF MODULATIONAL INTERACTIONS IN COLLISIONAL PLASMAS

The modulational instability development of Langmuir and electromagnet ic waves is reviewed in highly collisional plasmas where the character istic frequency OMEGA of the modulated perturbations is much less than nu(eff), the effective electron collision frequency. All calculations are based on Braginskii's system of hydrodynamic equations in collisi on-dominated plasmas and use a simple and universal formalism includin g new methods developed for description of the modulational effects in arbitrary media. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effe cts (differential Joule heating nonlinearity), in contrast to the well known modulational instability in collisionless plasmas (where pondero motive force nonlinearity dominates). Rates and thresholds of the inst abilities are found in various limits. Coupled nonlinear Langmuir and sound waves are presented. Theory taking into account combined effect of the differential Joule heating, ponderomotive force and relativisti c electron mass variation on the instability of electromagnetic waves is presented. Effects of magnetic fields are briefly discussed.