Spectral-line structures of saturated parametric instabilities.

The nonlinear saturation spectrum of parametric instabilities is shown to be restricted to discrete values of the propagation vector if spontaneous emission is neglected and a one-dimensional analysis is used. The purely growing instability is not excited for equal ion and electron temperatures if the power is less than 3.5 times the threshold power. The inadequacy of the present one-dimensional treatment is pointed out, and it is shown that waves with propagation vectors that are not parallel to the pump field must be present even if spontaneous emission is neglected.