Particle-in-cell simulation of plasma emission in solar radio bursts

Abstract

Aims. The present study aims to shed light on our understanding of the radiation processes of solar radio bursts associated with nonthermal electron propagation in the corona and interplanetary space. Methods. We performed 2.5-dimensional particle-in-cell (PIC) simulations to investigate the plasma emission excited by a relativistic electron beam using different pitch angles in the magnetized plasma. Results. Langmuir waves at the fundamental and harmonic frequencies were excited via the energy dissipation of the electron beam. For the first time, the backward Langmuir waves up to the third harmonic frequencies were reproduced in the cases of large pitch angles, likely arising from the relecting and scattering of density fluctuations to the Langmuir waves during electrom beam-plasma interaction. Electromagnetic (EM) waves were generated via the mode conversion of electrostatic (ES) waves and the nonlinear wave coupling. Specifically, the harmonic EM emission comes from the coupling of forward and backward Langmuir waves, namely, L + L′ → 2H, while the higher harmonic EM emissions generally come from the coupling of the Langmuir wave and lower-order harmonic EM wave, namely, L + (n − 1)H → nH. When the electron beam exhibits a large pitch angle, another possible mechanism for the third harmonic EM emission might be the coalescence of three ES waves, namely, L + L′ + L″ → 3H.