Influence of Flake Properties and Dropping Position on Hall Thruster Spark Discharge

Abnormal spark discharge can seriously compromise the on-orbit reliability of Hall thrusters. Ground-based experiments show that its instantaneous discharge parameters vary considerably, but the cause of this diversity remains unclear. The size, material, and dropping position of exfoliated wall-deposit flakes are likely key factors. To test this hypothesis, controlled flakes of graphite and boron nitride were released from specified positions into the discharge channel to actively trigger abnormal spark discharges. Four flake sizes were tested: [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. The total averaged peak-to-steady-state current [Formula: see text] for [Formula: see text] flakes was approximately 40% higher than that for [Formula: see text] flakes, and the value at 50% [Formula: see text] was approximately 54% higher than that at 10% [Formula: see text]. Compared with graphite, boron nitride produced approximately 15 and 4% higher total averaged [Formula: see text] for the [Formula: see text] and [Formula: see text] flakes, respectively. Furthermore, Pearson correlation coefficient analysis reveals that spark brightness and thruster body-to-ground potential are positively correlated with the discharge current pulse.