Emission of electromagnetic waves by proton beams propagating in nonuniform solar plasmas

Laboratory for Plasma Astrophysics, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan e-mail: sakaijun@eng.u-toyama.ac.jp

Received: 20 December 2006
Accepted: 24 April 2007

Abstract

Aims.We investigate the dynamics of proton beams propagating along a uniform magnetic field, as well as across the magnetic field in nonuniform solar plasmas, paying attention to the emission process of electromagnetic waves. The aim is to understand a new solar-burst component emitting only in the terahertz range during the solar flare observed by Kaufmann et al. (2004, ApJ, 603, L121).

Methods.We used a 2D3V, fully relativistic, electromagnetic particle-in-cell (PIC) simulation.

Results.From the simulation where the proton beams propagate along a uniform magnetic field into the high-density region, we found that strong electromagnetic waves are generated behind the proton beams. When the proton beams propagate perpendicular to the magnetic field, we found that the extra-ordinary mode can be excited from two electron Bernstein waves through three-wave interactions. These simulation results could be applied to the electromagnetic wave emission from the solar photosphere during the solar flares.