Nonlinear saturation of the absolute stimulated Raman scattering instability in a finite collisional plasma

Abstract

Using multiple time scale analysis, the nonlinear saturation of the absolute stimulated Raman scattering instability is examined in a finite homogeneous collisional plasma. The amplitude of the incident wave is assumed to exceed the absolute instability threshold by the fractional amount Δ(≪1). A single backscattered wave and a single plasma wave grow until time-asymptotic saturation occurs. The reflected light intensity is determined analytically and is proportional to Δ. The spatial variation of the saturated wave amplitudes is also obtained. The reflected intensity is compared to the values predicted for the convective instability, for incident intensities which are marginally less than the absolute threshold intensity. In ‘‘short’’ plasmas, i.e., ones which extend over only a few linear convective gain lengths, the reflected light intensity is found to be much higher when the absolute instability is excited.