# Spontaneous multi-keV electron generation from Fermi acceleration and magnetic moment non-adiabaticity

## TL;DR

This paper investigates how collisionless scattering and Fermi acceleration in magnetic mirror plasmas lead to the generation of multi-keV electrons, revealing a novel non-adiabatic process responsible for high-energy electron production.

## Contribution

It introduces a heuristic model demonstrating that mu non-conservation causes electrons to undergo Fermi-like acceleration, producing multi-keV electrons in low-temperature plasmas.

## Key findings

- Electrons reach energies above 30 keV.
- Collisionless scattering enables electrons to persist and energize.
- Fermi-acceleration-like mechanism explains high-energy electron generation.

## Abstract

X-ray emission shows the existence of multi-keV electrons in low-temperature, low-power, capacitively-coupled RF-heated magnetic-mirror plasmas that also contain a warm (300 eV) minority electron population. Though these warm electrons are initially passing particles, we suggest that collisionless scattering - mu non-conservation in the static vacuum field - is responsible for a minority of them to persist in the mirror cell for thousands of transits during which time a fraction are energized to a characteristic temperature of 3 keV, with some electrons reaching energies above 30 keV. A heuristic model of the heating by a Fermi-acceleration-like mechanism is presented, with mu non-conservation in the static vacuum field as an essential feature.