Influence of cathode position on the performance of a low-power planar Hall thruster

The planar Hall thruster (PHT) is a novel Hall thruster with an exposed ionization region, enhancing coupling between cathode and anode, though the enhanced coupling in PHT is insufficiently studied. This study experimentally investigates the effects of the coupling relationship—regulated primarily through cathode positioning—on the propulsion performance and oscillations of the PHT. The net magnetic region traversed by electrons initially expands and then contracts with increasing cathode radial position (r_c), resulting in performance that first declines before slightly recovering or stabilizing. Increasing the cathode axial position (z_c) reduces the net magnetic region, thereby optimizing the coupling relationship, lowering the coupling voltage (V_c) and ultimately improving performance. By appropriately adjusting r_c and z_c, thrust can be increased by up to 38.4% (from 3.65 to 5.05 mN) and 40.55% (from 3.97 to 5.58 mN) respectively. Increasing z_c can compress the beam half-angle, which decreases from 70.95° to 65.71°. The performance is also significantly affected by the cathode flow. The more active participation of cathode flow in discharge at smaller r_c leads to a deviation between the r_c for peak performance and that for V_c. Within the cathode flow range of 1~4 sccm (anode flow fixed at 5 sccm), the variation in total efficiency with cathode flow rate exhibits a strong dependence on cathode position. Cathode position also influences discharge oscillation. At z_c < 30 mm, discharge oscillation is enhanced by the cathode flow, while for z_c > 56 mm, oscillation decreases with increasing r_c because of reduced electron energy. By optimizing the cathode position, the discharge oscillation can be reduced by up to 56.3%. Adjusting r_c and z_c at a fixed cathode flow can reduce the beam divergence and discharge oscillation while maintaining relatively high performance. This work provides valuable insights for optimizing cathode parameters in PHTs.