Particle-in-cell simulations of a current-free double layer

TL;DR

This paper combines theoretical modeling and particle-in-cell simulations to investigate current-free double layers in plasmas, focusing on how electron velocity distributions influence their formation and properties.

Contribution

It introduces a theoretical model explaining EVDF depletion and repletion mechanisms, predicting double layer formation conditions and potential drops, validated by simulations.

Findings

The model accurately predicts the pressure range for double layer formation.

Simulation results agree with theoretical predictions of potential drops.

Electron velocity distribution functions are key to understanding double layer dynamics.

Abstract

Current-free double layers of the type reported in plasmas in the presence of an expanding magnetic field [C. Charles and R. W. Boswell, Appl. Phys. Lett. 82, 1356 (2003)] are modeled theoretically and with particle-in-cell/Monte Carlo simulations. Emphasis is placed on determining what mechanisms affect the electron velocity distribution function (EVDF) and how the EVDF influences the double layer. A theoretical model is developed based on depletion of electrons in certain velocity intervals due to wall losses and repletion of these intervals due to ionization and elastic electron scattering. This model is used to predict the range of neutral pressures over which a double layer can form and the electrostatic potential drop of the double layer. These predictions are shown to compare well with simulation results.