Suppression of discharge current oscillations in a hall thruster

Results of controlling a discharge current oscillation in Hall thrusters at a frequency range of 10-100 kHz are presented. To understand the discharge current oscillation mechanism, the plasma behavior in the acceleration channel was observed with a high-speed camera using a 1-kW class, anode layer type Hall thruster. The emission intensity oscillates equably in the acceleration channel at the same period of the discharge current oscillation; the number density of excited xenon ions oscillates at the same oscillation period and is proportional to the discharge current. These results indicate that the discharge current oscillation is caused by the ionization instability and the number density of plasma oscillates equably in the acceleration channel. Furthermore, the oscillation amplitude was sensitive to the applied magnetic flux density, indicating that this oscillation is affected by electron mobility. The proposed oscillation model based on the experimental results demonstrated that the momentum transfer corresponding to a plasma fluctuation is crucial to achieving stability. Thus, the oscillation amplitude for various acceleration channel configurations - parallel and convergent - was measured, because channel configuration could affect the momentum transfer. The oscillation was successfully suppressed by adopting the convergent configuration, as shown by this model.