An alternative form of the fundamental plasma emission through the coalescence of Z-mode waves with whistlers

TL;DR

This paper proposes an alternative mechanism for fundamental plasma emission involving the resonant coupling of Z-mode and whistler waves, supported by theoretical analysis and PIC simulations, expanding understanding of plasma radiation processes.

Contribution

It introduces a new fundamental plasma emission process via Z-mode and whistler wave coupling, supported by theoretical and simulation evidence.

Findings

Resonant interaction condition (Z+W → O) can be satisfied over wide parameters.

The process can efficiently convert energy from Z and W modes to the fundamental O mode.

The mechanism may be relevant in astrophysical and laboratory plasma scenarios.

Abstract

Plasma emission (PE), i.e., electromagnetic radiation at the plasma frequency and its second harmonic, is a general process occurring in both astrophysical and laboratory plasmas. The prevailing theory presents a multi-stage process attributed to the resonant coupling of beam-excited Langmuir waves with ion-acoustic waves. Here we examine another possibility of the fundamental PE induced by the resonant coupling of Z-mode and whistler (W) waves. Earlier studies have been controversial in the plausibility and significance of such process in plasmas. In this study we show that the matching condition of three wave resonant interaction (Z+W ! O) can be satisfied over a wide regime of parameters based on the magnetoionic theory, demonstrate the occurrence of such process and further evaluate the rate of energy conversion from the pumped Z or W mode to the fundamental O mode with particle-in-cell (PIC) simulations of wave pumping. The study presents an alternative form of the fundamental PE, which could possibly play a role in various astrophysical and laboratory scenarios with both Z and W modes readily excited through the electron cyclotron maser instability.