Two distinct discharge modes were observed in a 50 W-class micro-Hall thruster plasma under different operating conditions. A ball-shaped plasma with a broad plume (mode A) was observed at low mass flow rates (less than 0.37 mg s⁻¹) over the entire operational anode voltage range (160–280V). Raising the anode voltage beyond 200V with the mass flow rate fixed (larger than 0.37 mg s⁻¹) produced a narrow plume and stretched jet-like structure (mode B). In mode B, the thruster showed performance improvements in terms of thrust (3.8mN vs 3.3mN), specific impulse (913s vs 800s), and anode efficiency (28% vs 22%), with only a 2W difference in the anode power (61W in mode B and 59W in mode A). This suggests that operation is more advantageous in mode B than in mode A for the utilization of such low-power Hall thrusters. Unique plume properties were observed in the two modes and considerable differences were measured in the Xe II ion acceleration structure, beam angle, and ionization rate as the mode changes, which were not reported in previous studies. Mode A exhibits an axially extended ion acceleration structure outside the discharge channel, where 75% of the final ion velocity is achieved at approximately 40mm from the thruster exit, while most of the ion acceleration occurs within 10mm from the thruster exit in mode B. Measurements show that the full width at half maximum of the Xe II ion energy distribution function, electron temperature, and Xe II emission intensity decreased after the plasma transitioned from mode A to mode B. Based on the optical emission spectroscopy, the ionization rate in the plasma plume decreased by 30%–41% after the mode change, which is likely related to the reduction of the beam angle and electron current by 24% and 30%, respectively.

在不同操作条件下，在 50 W 级微霍尔推进器等离子体中观察到两种不同的放电模式。在整个操作阳极电压范围（160-280V）内，在低质量流速（小于 0.37 mg s ^-1）下观察到具有宽羽流（模式 A）的球形等离子体。在质量流量固定（大于 0.37 mg s ^-1) 产生了狭窄的羽流和拉伸的喷射状结构（模式 B）。在模式 B 中，推进器在推力（3.8mN 对 3.3mN）、比冲（913s 对 800s）和阳极效率（28% 对 22%）方面表现出性能改进，阳极功率仅相差 2W（模式 B 下为 61W，模式 A 下为 59W）。这表明在使用这种低功率霍尔推进器时，在模式 B 中的操作比在模式 A 中更有利。在两种模式中都观察到了独特的羽流特性，并且随着模式的变化，在 Xe II 离子加速结构、束角和电离率方面测量到了相当大的差异，这在以前的研究中没有报道。模式A在放电通道外呈现轴向延伸的离子加速结构，