Comment on higher-order nonlinearities and coupling saturation of parametric decay instabilities

The effect of higher-order nonlinearities on the coupling-saturation mechanism for parametric decay instabilities is analyzed. In particular it is shown that cubic nonlinearities in the Poisson equation describing the unstable electrostatic fields play an important role. In the case of the 2ω/sub p//sub e/ decay instability these effects increase the importance of coupling saturation for T/sub e/very-much-greater-thanT/sub i/ and reduce the saturated wave energy by a factor of T/sub i//T/sub e/