PARAMETRIC-INSTABILITIES OF TRAPPED UPPER-HYBRID OSCILLATIONS

Parametric instabilities of upper-hybrid oscillations trapped in a pla sma density depletion across an ambient magnetic field are investigate d. Approximate dispersion relations are derived, which lead to the ide ntification of two parametric instabilities of the localized upper-hyb rid bounded wave structure. Both are related to trapped upper-hybrid o scillation resonances. The first is a decay to a frequency of a trappe d ware resonance, downshifted from the applied frequency, where the do wnshift must be slightly larger than the lower-hybrid frequency. The s econd instability can exist when the applied frequency is slightly bel ow the arithmetic mean of the frequencies of two trapped oscillation r esonances; then the antiStokes component of one is in resonance with t he Stokes component of the other. Both slab and two-dimensional geomet ries are considered.