Nonlinear effects on the mode conversion of upper-hybrid waves

A simple model is presented which is capable of describing the nonlinear field across the upper-hybrid resonance layer, its time evolution and mode conversion. In the electrostatic approximation, when the density gradient scale length is small compared with the incident wave wavelength, the fields are governed by a driven nonlinear Schrödinger equation. It is found that the nonlinearity due to the ponderomotive force produces an enhancement and a spreading of the Bernstein wave accompanied by a flattening of the density profile. Mode conversion efficiencies as high as 200% of those of the linear regime are reached. The model shows the importance of nonlinearity in the analysis of mode conversion in ionospheric and laboratory, as well as fusion plasmas.