Nonlinearly coupled upper-hybrid and magnetoacoustic waves in collisional magnetoplasmas

The nonlinear interaction between large amplitude electrostatic upper-hybrid (UH) waves and magnetoacoustic perturbations in a collisional magnetoplasma is considered. For this purpose, we present a nonlinear Schrödinger equation for the UH wave envelope in the presence of the electron density, electron temperature, and compressional magnetic field perturbations of the dispersive magnetoacoustic waves, and derive an equation for the latter taking into account the combined influence of the UH ponderomotive force and the differential electron Joule heating in the UH wave electric field. The coupled equations are employed to investigate modulational instabilities of a constant amplitude UH wave, and the density profile modifications due to the UH ponderomotive and thermal forces. It is found that the thermal instability has its maximum at a wavelength half the one of the UH wave, and a numerical solution of the coupled time-dependent system of equations reveals that localized density cavities are also created with a spacing approximately half the wavelength of the pump wave.