Potential Fluctuations of Emissive Sheaths in Collisional Boundary Layer Plasmas Using a Kinetic Approach

Abstract Emissive plasma sheaths are subject to various instabilities, including two-stream (TS) and self-spike (SS) oscillations, both of which play critical roles in the sheath dynamics. This study extends our previous work by examining the effects of these instabilities on potential field fluctuations and the electron velocity distribution functions (EVDFs) in boundary layer plasmas. Using a fully kinetic PIC-DSMC approach, we demonstrate that the TS instability induces strong oscillations in the sheath potential, exceeding the sheath potential by up to tenfold in large domains. In contrast, the SS instability produces sawtooth oscillations with instantaneous, non-amplifying disturbances. Additionally, the TS instability significantly alters the EVDFs, creating highly non-Maxwellian distributions, while the SS instability causes instantaneous shifts in the EVDF peaks during SS ejections.