Particle-in-cell modeling of the heaterless hollow cathode operation: Keeper region

Recently, a two-dimensional (2D) self-consistent particle-in-cell Monte Carlo collision (PIC MCC) simulation code has been developed¹ to study operation of heaterless thermionic hollow cathode (HTHC) proposed to use in microsatellite propulsion systems. Unique design of the cathode and attractive performance characteristics were reported in Ref. 2. This study has been carried out as a part of continued development and validation of the HTHC simulation code WARP at the Plasma & Pulsed Power Lab in Technion. The focus of this study is modeling of the processes in the cathode keeper region where the plasma particles experience many collisions and cannot be described by fluid simulation modeling accurately. The potential of the keeper during the cathode DC operation is self-consistently adjusted to allow operation of the cathode in self-heating mode. Thus the understanding of the physical processes governing formation of the potential distribution between the emitter and keeper is of great importance for development of reliable and efficient cathode. For this the simulation code implements the phenomenon of thermionic emission, secondary electron emission, various particle collisions and non-uniform Xe gas distribution. The obtained behavior of the plasma density, potential distribution, and energy flux towards the emitter and keeper are presented and discussed. In addition, dependences of the cathode operational parameters on the Xe gas pressure, orifice size, and keeper voltage are presented. Finally, the results of simulations are compared with available experimental data.