On Cathode Position and Inclination Angle in Magnetically Shielded Hall Thrusters

This study systematically investigated the influence of the position and inclination angle of an externally mounted hollow cathode in 1.35 kW magnetically shielded Hall thrusters to establish the relationship between thruster performance, plume state, and cathode placement. For this purpose, a combined motor driver with a three-degree-of-freedom movement was designed to move the cathode over a wide range of positions and inclination angles. In an experiment performed on a thruster with outer magnetic columns, placing the cathode inside the magnetic separatrix resulted in a considerable amount of thrust. However, an extremely small distance between the cathode and thruster can cause a sharp increase in the discharge current; hence, the optimal cathode position should be determined. It was also found that a small inclination angle was favorable for obtaining high performance. In addition, a strong correlation was found between the plume image and thruster performance. Under improved performance conditions, the visible light region of the plume had a shorter axial length and a broader pink halo. Finally, a comparative experiment was conducted on a thruster with an outer magnetic shell. The thruster of this structure was observed to be insensitive to the cathode position; hence, to protect the cathode from ion sputtering, the distance between the cathode and thruster can be appropriately increased.