Continuum-Kinetic Studies Modelling the Impact of Secondary Electron Emission on Sheath Structure and Dynamics

Plasma sheath studies are of great importance to fusion and propulsion applications involving the flow of plasma through a material channel. Emission of secondary electrons from the material wall is capable of altering the fundamental sheath structure and behavior. At very low energies, the emission spectrum is dominated by the elastic backscattering of particles, while at higher energies cold secondary electrons account for the bulk of the emission. Models for these mechanisms are applied at the boundary of continuum-kinetic plasma sheath simulations for a variety of material parameters. Simulations are performed where emission leads to formation of a space-charge limited sheath, as well as for high-emission cases where the ratio of emitted to impacting particles exceeds unity. Results are presented which examine the relationship between wall materials, emission mechanisms, the plasma regime, and resulting sheath structure.