Vlasov Simulation of Emissive Plasma Sheath with Energy-Dependent Secondary Emission Coefficient and Improved Modeling for Dielectric Charging Effects

TL;DR

This study uses Vlasov simulations to explore plasma sheaths with energy-dependent secondary electron emission and dielectric charging, revealing nonlinear sheath behavior and saturation effects at high electron temperatures.

Contribution

It introduces an improved SEE model accounting for wall charging and energy dependence, enhancing the accuracy of plasma sheath simulations.

Findings

SEE coefficient increases with wall charge

Sheath potential becomes nonlinear with electron temperature

Space charge limited sheath forms at high temperatures

Abstract

A one dimensional Vlasov Poisson simulation code is employed to investigate the plasma sheath considering electron induced secondary electron emission (SEE) and backscattering. The SEE coefficient is commonly treated as constant in a range of plasma simulations, here improved SEE model of a charged dielectric wall is constructed which includes the wall charging effect on SEE coefficient and the energy dependency of SEE coefficient. Pertinent algorithms to implement above SEE model in plasma simulation are studied in detail. It is found that the SEE coefficient increases with the amount of negative wall charges, which in turn reduces the emissive sheath potential. With energy dependent SEE coefficient, the sheath potential is a nonlinear function of the plasma electron temperature, as opposed to the linear relation predicted by classic emissive sheath theory. Simulation combining both wall charging effect and SEE coefficient energy dependency suggests that the space charged limited sheath is formed at high plasma electron temperature levels, where both sheath potential and surface charging saturate. Additionally, different algorithms to implement the backscattering in kinetic simulation are tested and compared. Converting backscattered electron to secondary electron via an effective SEE coefficient barely affects the sheath properties. The simulation results are shown to be commensurate with the upgraded sheath theory predictions.