Experimental study on abnormal spark discharge characteristics of a Hall thruster

Abnormal spark discharge could cause a Hall thruster to malfunction, and numerous experiments have pinpointed the cause as exfoliation of channel wall deposits. Due to the high randomness and uncertainty of natural abnormal spark discharge, a device was designed to actively trigger abnormal spark discharge to imitate the process by which artificial flakes similar to the exfoliated deposit enter the discharge channel. Then, discharge experiments were conducted by releasing flakes made of graphite with a volume of 2 × 2 × 0.5 mm³ from the top of the discharge channel. During the experiment, the changes in discharge current, discharge voltage, shell-to-ground potential, ion current density, and cathode-to-ground potential were monitored, and transient spark images were captured at the moment of abnormal discharge. It was found that the current pulse peak has 2–3, 3–4, or 18–22 times the normal discharge current types, and the larger the current pulse peak, the shorter the pulse duration. It was also found that the brightness of the spark corresponds to the amplitude of the current disturbance. By comparing and analyzing both the monitored discharge parameter curves and captured spark images, it was concluded that natural abnormal spark discharge is the result of interaction between the exfoliated deposit and electrons rather than ions.