Kinetic Modeling of Emissive Sheaths in Flowing Plasma

Plasma sheaths control particle and energy transport between the plasma and surface [1]. They can be further complicated when the surface is electron emitting (i.e., thermionic emission). These emissive sheaths are seen in various engineering applications such as RF devices, dusty plasmas, divertors/scrape-off layers, and plasma probes. Recently, emissive sheaths have been hypothesized to promote surface cooling on hypersonic vehicles via thermionically emitted electrons in Hanquist et al. [2] , where a space-charge limiting (SCL) sheath assumption was used to predict the electron current exiting the sheath. However, excessive emission from a surface may lead to the formation of an inverse sheath [3] , which may further reduce the number of electrons escaping the surface. In recent experimental works by Kraus et al. [3] , thermionically emitting filaments (thoriated tungsten) were submersed in Xe plasma flow that produced a space-charge limited (SCL) sheath. We will present a 1D study on sheath formation for an emissive surface that may prevent the emitted electrons from reaching the bulk plasma using the Particle-in-Cell (PIC) method. Prediction of these sheaths is important as they may affect the heat loss and charge flux from the surface [1].