Two-dimensional simulations of nonlinear beam-plasma interaction in isotropic and magnetized plasmas

TL;DR

This study uses two-dimensional particle-in-cell simulations to explore how a low-density electron beam interacts nonlinearly with isotropic and magnetized plasmas, revealing the formation of phase space structures and the influence of magnetic fields on energy transfer.

Contribution

It provides new insights into the nonlinear evolution of beam-plasma interactions, especially how magnetic fields affect wave spectra and instability mechanisms.

Findings

Filamentation modes form due to two-stream and oblique instabilities.

Energy transfer depends on magnetic field strength, favoring upper-hybrid waves or whistlers.

Secondary instabilities can destroy BGK-type nonlinear waves.

Abstract

Nonlinear interaction of a low density electron beam with a uniform plasma is studied using two-dimensional particle-in-cell (PIC) simulations. We focus on formation of coherent phase space structures in the case, when a wide two-dimensional wave spectrum is driven unstable, and we also study how nonlinear evolution of these structures is affected by the external magnetic field. In the case of isotropic plasma, nonlinear buildup of filamentation modes due to the combined effects of two-stream and oblique instabilities is found to exist and growth mechanisms of secondary instabilities destroying the BGK--type nonlinear wave are identified. In the weak magnetic field, the energy of beam-excited plasma waves at the nonlinear stage of beam-plasma interaction goes predominantly to the short-wavelength upper-hybrid waves propagating parallel to the magnetic field, whereas in the strong magnetic field the spectral energy is transferred to the electrostatic whistlers with oblique propagation.