Saturation of parametric instabilities by the nonlinear decay of electrostatic daughter wave

The nonlinear decay of the electrostatic daughter wave is shown to provide an efficient saturation mechanism for stimulated Brillouin and Raman scattering. The saturated steady-state reflectivity due to SBS depends on the plasma density. In the range n<0.1 n cr the reflection coefficient remains small approximately (n/n cr ) 2 . A large reflectivity due to SBS is predicted for n>or approximately=0.25 n cr . In the stimulated Raman scattering the saturation effect due to the Langmuir decay is even stronger. SRS saturates to the value of the order of (v e /c) 4 depending on the plasma temperature only. The effect of the ES daughter wave decay on the parametric decay instability is studied briefly. According to a rough analysis it seems likely that the secondary decay processes have only a small influence on the anomalous absorption near the critical density.