Quasiresonant mode coupling of electron plasma waves

Abstract

A finite amplitude ion fluctuations (wave number k_i) couples a primary electron plasma wave (wave number k₀) to a whole spectrum of plasma oscillations (wave numbers k₀±nk_i). Simple fluid equations are used to analyze the effect and computer simulation is used to verify the theory, and show the limits of the analysis. If the variation in plasma frequency Δω_p associated with the ion fluctuation exceeds the frequency mismatch between the primary wave and the nth mode, then a large fraction of the energy can be transferred to that mode, while if the mismatch in frequency is greater than Δω_p only a relatively small energy transfer occurs. Because the frequency of plasma oscillations varies only weakly with wavelength, very small ion fluctuations are sufficient to couple long-wavelength waves to short-wavelength waves which are Landau damped. This phenomenon may also account for some experimental observations of fluctuations in which the frequency and wave number do not appear to satisfy the normal plasma dispersion relation.