Effects of Neutral Density on Electron Temperature and Mobility in a Cross-field Trap

Abstract

An electron trapping apparatus was constructed to emulate the electric and magnetic fields found in a Hall-effect thruster in order to investigate cross-field electron mobility. Anomalous mobility was previously observed in this device that is orders of magnitude higher than classical. The focus of this manuscript is to investigate the effect of neutral density on the electron temperature and cross-field mobility in the electron trap. It was found that electron temperature decreases with increasing neutral density. When electron temperature is taken into account in the calculation of classical mobility, trends are observed in this device that resemble classical scaling with neutral density; however, the magnitude of the observed mobility is 100 to 1,000 times higher than classically predicted. On further investigation of the electron temperature, it is determined that in some cases the electron temperature is much higher than would be possible if collisions were responsible for transport, as inelastic collisions, which prevail at higher electron energies, would cause electron cooling that is not seen here. Furthermore, an examination of the probe I-V characteristic reveals that the electron distribution function is highly non-Maxwellian in these cases, supporting a collisionless anomalous mobility.