Localized Fields and Density Perturbations Due to Self-Focusing of Nonlinear Lower-Hybrid Waves

Large-amplitude lower-hybrid wave bursts at ${\omega }_0>{\omega }_{\mathrm{LH}}$ are excited from a grid and propagate into a density gradient perpendicular to ${\overrightarrow{\mathrm{B}}}_0$. The evolution of the internal rf fields and the plasma parameters is investigated. Above threshold localized field maxima appear ($E_{\mathrm{int}}\gg E_{\mathrm{appl}}$) and, simultaneously, strong density perturbations are formed. The nonlinear phenomena are interpreted by ponderomotive-force and space-charge separation effects.