Laboratory modeling of nonlinear trapping of Langmuir waves inside a small-scale magnetoplasma irregularity

Laboratory studies modeling the small-scale plasma filamentation under the conditions relevant to the ionospheric heating experiments are presented. Filamentation is caused by nonlinear interaction of the short-wavelength quasi-electrostatic waves of the Z-mode with the plasma. This interaction occurs due to thermal plasma nonlinearity, i.e. due to local plasma heating and consequent thermodiffusion, which results in the formation of a narrow magnetic-field-aligned density depletion. The quasi-electrostatic plasma waves, in their turn, are trapped inside the depletion due to their specific dispersion properties. Such nonlinear wave trapping have been observed only at the critical plasma density (ω = ωp). The trapped eigenmode has been associated with magnetized Langmuir waves, whose dispersion properties are analyzed using the kinetically modified plasma dispersion relation. Threshold of the nonlinear wave trapping exhibits significant growth in the vicinity of harmonics of the electron gyrofrequency.