Effects of the cathode electron emission and background gas pressure on transient phenomena in magnetized thruster discharge

Large-amplitude, low-frequency, discharge current oscillations invariably occur in the Hall thruster discharge. This discharges are characterized by magnetized electrons and unmagnetized ions. The oscillations are thought to result from various ionization mechanisms. A rotating potential perturbation, called a spoke, is observed to propagate in the ExJB direction for certain magnetic field topologies of the thruster discharge, including both cylindrical and annular configurations. We show that increasing the cathode electron emission or increasing the background pressure curiously suppresses both the rotating spoke and the low frequency oscillations. These effects correlate with the reduction of the electron cross-field transport in the thruster discharge. Possible physical mechanisms responsible for these effects are discussed.