Kinematics of four-wave decay of high-frequency plasma oscillations into upper hybrid and electron-cyclotron plasma waves under multiple electron gyroresonance conditions

Abstract

We consider the conditions for four-wave decay of two primary plasmons with wave vector$\vec k_{_0 }$ and frequency ω₀ close to the multiple gyroresonance frequency nω_Be into two secondary plasmons with frequencies ω₁ > ω₀ and ω₂ < ω₀. The secondary plasmons belong to the upper hybrid and the electron cyclotron branches. It is shown that the main features of the broad upshifted maximum (BUM) in the SEE spectrum can be explained in the context of the proposed process. The BUM feature appears in the region of frequencies having a positive shift from the high-power radio wave frequency. In particular the broad band nature of the BUM can be a result of the broad spectrum of wave number k₀ of the primary plasma waves. In this case the observed cut-off frequency Δf_cutoff limiting the BUM spectrum on the lower side can result from the lower bound of k₀ (the increase in ω₁ corresponds to decay of shorter wave plasmons). In our approach we assume that the generation of primary plasma oscillations by the high-power radio wave and the conversion of secondary plasma waves into the electromagnetic waves is due to coherent scattering of corresponding waves by small-scale magnetic-field-aligned artificial irregularities or to another nonlinear processes.