Nonlinear Wave Interactions as Emission Process of Type II Radio Bursts

TL;DR

This paper uses particle-in-cell simulations to study how nonlinear wave interactions in a CME foreshock produce type II radio bursts, confirming the quadratic dependence of emission on beam strength.

Contribution

It demonstrates, through simulations, the self-consistent excitation of wave modes leading to fundamental and harmonic emissions in type II radio bursts, highlighting the nonlinear interaction process.

Findings

Electromagnetic emission depends quadratically on electron beam strength.

Simulation confirms self-consistent excitation of beam-driven wave modes.

Both fundamental and harmonic emissions are produced via three-wave interactions.

Abstract

The emission of fundamental and harmonic frequency radio waves of type II radio bursts are assumed to be products of three-wave interaction processes of beam-excited Langmuir waves. Using a particle-in-cell code, we have performed simulations of the assumed emission region, a CME foreshock with two counterstreaming electron beams. Analysis of wavemodes within the simulation shows self-consistent excitation of beam driven modes, which yield interaction products at both fundamental and harmonic emission frequencies. Through variation of the beam strength, we have investigated the dependence of energy transfer into electrostatic and electromagnetic modes, confirming the quadratic dependence of electromagnetic emission on electron beam strength.