Wave breaking and electron heating of perpendicularly propagating x-mode waves in magnetized plasmas.

Abstract

This study uses three-dimensional particle-in-cell simulations to investigate the nonlinear evolution of electromagnetic waves propagating perpendicular to an external magnetic field in a magnetized plasma, with an emphasis on wave breaking and electron energization. In the weakly nonlinear regime (small nonlinearity parameter), the response exhibits two prominent frequency components that produce a beating signal, whose relative spectral weights vary with the magnetization parameter. As the nonlinearity parameter increases, nonlinear steepening and waveform distortion develop, accompanied by spectral broadening in wave-number space, and wave breaking eventually occurs. During the breaking regime, energy is irreversibly transferred from the electromagnetic fields to electrons, leading to a rapid increase of electron kinetic energy. We characterize the process using the breaking time, the saturated field energy, and an electron heating measure defined from the kinetic-energy gain. Over the scanned parameter range, this electron heating measure follows power-law scalings with the nonlinearity parameter and the magnetization parameter, with fitted exponents of approximately 3.15 and 0.28, respectively. These results are consistent with wave breaking providing an efficient dissipation pathway in the strongly driven regime considered here and constrain the scaling of electron energization with wave amplitude and the magnetization parameter.