Analytical and simulation studies of nonlinear effects caused by upper-hybrid waves in plasmas

Abstract

Nonlinear interactions between large amplitude upper-hybrid waves and low-frequency electromagnetic waves in a magnetized plasma have been considered. Specifically, the decay of upper-hybrid waves into lower-hybrid and magnetosonic waves, as well as the modulational instabilities leading to the formation of density cavities which trap upper-hybrid wave envelopes, are investigated both theoretically and numerically. It is found that the three-wave process between two upper-hybrid waves and the lower-hybrid wave, which is the fastest growing instability of the system, is important for the generation of waves of small wave numbers, via the self-interaction of the generated decay products from the three-wave interaction. A comparison between the theory of the parametric decay, simulations of a generalized Zakharov system of equations modeling the interaction between upper-hybrid, lower-hybrid and magnetosonic (fast Alfvénic) waves is presented. Comparisons are made with a simulation of the fully electromagnetic Vlasov–Maxwell system for ions and electrons where a sudden onset of cavities and long wavelength magnetosonic wave emission could be seen, similar as in the simulation of the Zakharov-type system.