Nonlinear wave interaction and stationary fluctuation spectrum in a nonequilibrium plasma

The spectrum of electromagnetic fluctuations in a nonequilibrium steady-state plasma is investigated. It is shown that nonlinear wave interaction produces additional maxima in spectral distributions, which correspond to the combination frequencies. The amplification of fluctuational oscillations on intensive excitation of waves in the plasma by external sources is considered. Allowance for the nonlinear wave interaction eliminates the divergence in spectral distributions, which takes place in the case of linear approximation. The saturation of the critical-fluctuation level is the direct result of the nonlinear shift of eigen frequencies. It is shown that in a nonequilibrium plasma a stationary turbulent state is possible, in which the level of electromagnetic fluctuations can greatly exceed the thermal level