Emission of electromagnetic waves by proton beams in solar plasmas

Abstract

Aims. We investigate the emission process of electromagnetic waves from proton beams propagating to a low-density region from a high-density region. Methods. A two-dimensional, electromagnetic, relativistic Particle-In-Cell (PIC) code is used. Results. It is found that the proton beams propagating to the low-density region are forced to move, together with the background electrons, to keep charge neutrality, resulting in the excitation of electrostatic waves: proton beam modes and Langmuir waves. In the early stage of electrostatic wave excitation, both R and L modes near the fundamental plasma frequency can be generated along a uniform magnetic field. It is also found that, in the late stage, the second harmonics of electromagnetic waves can be excited through the interaction of three waves. During these emission processes, proton beams can move along the magnetic field almost without losing their kinetic energy. The wave emission process by the proton beams may be applied to both the solar type III and type II radio bursts.