A ring beam mechanism for radio wave emission in the interplanetary medium

Radio wave emission sources in the interplanetary medium (IPM) include type II and type III radio bursts and emission from planetary bow shock regions. The presence of electron beams in a range of energies suggests the possibility of a ring beam‐plasma interaction as a mechanism for the generation of radio waves at both the fundamental and the second harmonic of the background electron plasma frequency. In this paper, ring beam‐plasma interactions are simulated for the conditions of the IPM, ω e /Ω e = 100 to 200. In these simulations, the ring beam‐plasma interaction couples the electrostatic Langmuir waves at the fundamental plasma frequency to electromagnetic waves; harmonic radiation is produced by an electrostatic trapped electron instability. Mode conversion processes permit the Z mode radiation generated through these instabilities to be converted to the X mode. Examination of both theory and observations suggests the ring beam‐plasma interaction as a candidate for many of the radio phenomena in the IPM.