Plasma emission induced by ring-distributed energetic electrons in overdense plasmas

TL;DR

This study uses particle-in-cell simulations to reveal a new mechanism for plasma emission driven by ring-distributed energetic electrons, involving electron cyclotron maser and thermal anisotropic instabilities, differing from the standard bump-on-tail scenario.

Contribution

It introduces an alternative plasma emission mechanism in overdense plasmas involving ring-distributed electrons and specific wave instabilities, expanding current understanding.

Findings

Efficient fundamental and harmonic emissions observed.

Emission mechanisms differ from standard bump-on-tail scenario.

Electron cyclotron maser and thermal anisotropic instabilities are key.

Abstract

According to the standard scenario of plasma emission, escaping radiations are generated by the nonlinear development of the kinetic bump-on-tail instability driven by a single beam of energetic electrons interacting with plasmas. Here we conduct fully-kinetic electromagnetic particle-in-cell simulations to investigate plasma emission induced by the ring-distributed energetic electrons interacting with overdense plasmas. Efficient excitations of the fundamental (F) and harmonic (H) emissions are revealed with radiation mechanism(s) different from the standard scenario: (1) The primary modes accounting for the radiations are generated through the electron cyclotron maser instability (for the upper-hybrid (UH) and Z modes) and the thermal anisotropic instability (for the whistler (W) mode); the F emission is generated by the nonlinear coupling of the Z and W modes and the H emission by the nonlinear coupling of the UH modes. This presents an alternative mechanism of coherent radiation in overdense plasmas.