Continuum-kinetic studies modeling the impact of secondary electron emission on sheath structure and dynamics

Plasma-material interactions, such as those which occur in fusion and propulsion applications involving the flow of plasma through a channel, drive the emission of secondary electrons from the material wall. Such emission can alter the fundamental sheath structure and behavior, understanding of which is vital to support the success of multiple fusion and propulsion concepts. The emission spectrum is characterized by two regions, a peak of elastically backscattered primary electrons, and cold secondary electrons inelastically emitted directly from the material. Novel implementation of semi-empirical models allows the full range of emission to be captured at the boundary of continuum-kinetic simulations. Simulations are performed using the Gkeyll code examining the dependence of the emission on model and plasma parameters. Results are shown of high and low emission cases in the classical and space-charge limited sheath modes, with particular attention given to the regime where the yield ratio of emitted to impacting particles exceeds unity and theory predicts transition to an inverse sheath. We discuss the relationship between emission mechanisms and how they drive the overall trend in yield, as well as the resulting sheath structure.