Electrostatic Wave Instability and Plasma Radiation from Coronal Loops

Abstract

Polarization properties of solar and stellar radio emission require, in some cases, emission below the third or fourth coronal electron gyro level, ω < 3,ω_c; 4, ω_c. In the context of plasma radiation, the source parameters should be such that the ‘intermediate magnetic field condition’ 1 < ω p 2 /ω c 2 < 3 is satisfied. Supposing this condition, we investigate the generation of electrostatic waves in a ‘warm’ background plasma with a high-energy component of magnetically trapped electrons. We invoke the conversion of upper-hybrid waves and Bernstein waves into electromagnetic radiation as being responsible for intense radio emission from a coronal magnetic loop. Moreover, ‘odd-half’ harmonic emissions in the solar radio spectrum as well as the o-mode polarization at the second harmonic of the plasma frequency are natural consequence of this proposed model.