# Highly efficient electromagnetic emission during 100 keV electron beam relaxation in a thin magnetized plasma

## TL;DR

This study uses particle-in-cell simulations to explore highly efficient electromagnetic wave generation during 100 keV electron beam relaxation in a thin, magnetized plasma, relevant to laboratory experiments and plasma antenna mechanisms.

## Contribution

It demonstrates the effectiveness of the beam-driven plasma antenna mechanism in a realistic GOL-3 experimental setup with density gradients and beam angular spread.

## Key findings

- Electromagnetic emission near doubled plasma frequency can reach 1% of beam power.
- The plasma antenna mechanism effectively explains high-efficiency wave generation.
- Simulation results align with experimental observations at GOL-3.

## Abstract

In this paper, electromagnetic emissions produced by a beam-plasma system are investigated using particle-in-cell simulations for the particular case when the typical transverse size of both 100 keV electron beam and produced plasma channel is comparable to the radiation wavelength. The interest in this regime of beam-plasma interaction is associated with highly efficient generation of electromagnetic waves near the plasma frequency harmonics that has been recently observed in laboratory experiments on the GOL-3 mirror trap. It has been found that the radiation power only from the vicinity of the doubled plasma frequency in these experiments can reach 1% of the total beam power. Subsequent theoretical and simulation studies have shown that the most likely candidate for explaining such efficient generation of electromagnetic radiation is the mechanism of a beam-driven plasma antenna based on the conversion of the most unstable plasma oscillations on a longitudinal density modulation of plasma ions. In this paper, we investigate how effectively this mechanism can work in a real experiment at the GOL-3 facility, when a thin sub-relativistic electron beam gets a large angular spread due to compression by a magnetic field, and the gas into which it is injected has macroscopic density gradients.