MODULATIONAL INSTABILITY OF LANGMUIR-WAVES IN DENSE-PLASMAS

The modulational instability development of Langmuir waves is investig ated in highly collisional plasmas where the characteristic frequency OMEGA of the modulated perturbations is much less than nu(eff), the ef fective electron collision frequency. It is demonstrated that the modu lational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the well-known modulational instability in collisionless p lasmas (where ponderomotive force nonlinearity dominates). Rates and t hresholds of the instability are found in various limits. The modulati onal instability is most effective when the angles between a pump wave vector and wave vectors of the modulational perturbations are of orde r unity.