Explosively Unstable Waves in an Ion Beam-Plasma System

Abstract

Explosively unstable waves in an ion beam-plasma system are experimentally studied by use of the pump field method. The generated waves of an ion acoustic (γ) and a fast(α)- and a slow(β)-modes of the ion beam satisfy the resonance conditions both for frequency f_β=f_α+f_γ and for wave number k_β=k_α+k_γ. They at first all grow rapidly and attain their respective maximum intensities which are several times of their initial ones. There is an optimum intensity of the pump field to excite these three waves at the same time. The behaviors of their temporal growths are well explained by a nonlinear theory of coherent three-wave interaction.