Continuum kinetic investigation of the impact of bias potentials in the current saturation regime on sheath formation

TL;DR

This study uses kinetic simulations to analyze how bias potentials influence sheath formation and current saturation in plasma-wall interactions relevant to pulsed power fusion, revealing asymmetries and saturation behaviors.

Contribution

It provides the first detailed kinetic analysis of sheath behavior under bias potentials in the current saturation regime, highlighting effects on current, density, and heat flux.

Findings

Sheath near high potential wall remains similar to classical sheath.

Sheath near low potential wall becomes more prominent with larger bias.

Current density saturates with increasing bias potential.

Abstract

In this work, we examine sheath formation in the presence of bias potentials in the current saturation regime for pulsed power fusion experiments. It is important to understand how the particle and heat fluxes at the wall may impact the wall material and affect electrode degradation. Simulations are performed using the 1X-1V Boltzmann-Poisson system for a proton-electron plasma in the presence of bias potentials ranging from 0 to 10 kV. The results indicate that the sheath near the high potential wall remains generally the same as that of a classical sheath without the presence of a bias potential. However, the sheath near the low potential wall becomes more prominent with a larger potential drop, a significant decrease of electron density, and larger sheath lengths. The spatially constant current density increases to a saturation value with increasing bias potential. The current is dominated by the ions at the low potential wall and by the electrons at the high potential wall. The heat flux increases to a saturation value at the high potential wall and tends to zero at the low potential wall with increasing bias potential. The results trend with theory with differences attributed to the simplified assumptions in the theory and the kinetic effects considered in the simulations. Due to the significant computational cost of a well resolved 1X-2V simulation, only one such simulation is performed for the 5 kV case showing higher current.