SATURATION OF RADIATION-INDUCED PARAMETRIC-INSTABILITIES BY EXCITATION OF LANGMUIR TURBULENCE

Progress made in the last few pars in the calculation of the saturatio n spectra of parametric instabilities which involve Langmuir daughter waves will be reviewed. These instabilities include the ion acoustic d ecay instability, the two plasmon decay instability (TPDI), and stimul ated Raman scattering (SRS). In particular we will emphasize spectral signatures which can be directly compared with experiment. The calcula tions are based on reduced models of driven Langmuir turbulence. Thoms on scattering from hf-induced Langmuir turbulence in the unpreconditio ned ionosphere has resulted in detailed agreement between theory and e xperiment at early times. Strong turbulence signatures dominate in thi s regime where the weak turbulence approximation fails completely. Rec ent experimental studies of the TPDI have measured the Fourier spectra of Langmuir waves as well as the angular and frequency spectra of lig ht emitted near 3/2 of the pump frequency again permitting some detail ed comparisons with theory. Thomson scattering measurements of the Lan gmuir wave spectra from SRS are consistent with the saturation by seco ndary and tertiary decay of the primary SRS Langmuir waves. Scaling la ws derived from a local model of SRS saturation are compared with full simulations and recent Nova experiments.