The Experimental Study of Wave-Wave Coupling Processes in a Beam Plasma System

摘要

The wave-wave coupling processes in a cold-beam cold-plasma system have been investigated under conditions such that nonlinear wave-particle effects are negligible. In this experiment a low density monoenergetic beam in the energy range of 15 to 16 keV was premodulated at two frequencies, f(0) = 9.5 GHz and f(1) = 9.4 GHz and injected into the afterglow of a discharge in neon. The interaction between these two launched waves and their difference frequency, f(2), was investigated and at low wave amplitudes was found to be in general agreement with the theory of the three-wave decay instability. At larger wave amplitudes, a strong remixing of the three waves occurred which gave rise to satellite waves at frequencies f(0) plus or minus nf(2) and f(1) plus or minus nf(2) where n is an integer. Measurements of the spatial evolution of these satellite waves and their dependence on the modulation power and difference frequency are presented. The results are discussed in the light of the theory of coupling among spatially growing waves. (Author)