Parametric Coupling of Two Langmuir Waves in an Inhomogeneous Plasma, II. Stabilizing Effects Due to the Pondermotive Force Created by an Intense Pump Field

Abstract

Spatial behaviors of two electron Langmuir waves parametrically coupled because of the combined action of a density gradient and a high-frequency pump electric field which is uniform outside the plasma are investigated. It is shown that the effective density gradient decreases due to the electron ponderomotive force created by the space-dependent intense pump whose space-dependence is produced by the density gradient, leading to stabilizing effects on the convective-type instability treated in I, 7) because it is excited more strongly, the greater is the density gradient. In a non-magnetized plasma with a monotonously varying density profile, any effective trapping of the instability is shown not to be expected under usual practical conditions. The scale size of the region in which the instability may spread, however, increases with the pump intensity from “smaller than the Airy characteristic length l ” to “much larger than l .”