Measurements of channel erosion of Hall thrusters by laser-induced fluorescence

The ion velocities within the discharge channel of the 600 W magnetically shielded and unshielded Hall thrusters are measured by the laser-induced fluorescence technique to quantitatively evaluate the erosion of the channel walls. Visual inspection of the magnetically shielded Hall thruster has qualitatively indicated that the discharge channel has been successfully shielded from the bombarding of the plasma, while the erosion occurs in the unshielded counterpart. In addition, the ion velocities along the thruster centerline indicate that the voltage utilization efficiency of MSHT-600 is higher than that of USHT-600 and comparable to the state-of-the-art BHT-600 thruster. Furthermore, measurements performed inside the discharge channel show that the ions deep inside the channel impact the channel walls backward in the shielded thruster, while forward in the unshielded one. Moreover, the plasma potential along the channel walls remains as high as the anode potential in the shielded thruster, while it dramatically decreases in the unshielded one. When accounting for the sheath potential acceleration, the maximum erosion rate of the inner and outer walls of USHT-600 is 1.3 and 3.1 μm/h, respectively, based on the plasma parameters of SPT-100, while the maximum value of the weighted average erosion rate of MSHT-600 is 0.08 and 0.04 μm/h, respectively, for two cases of the ion number density. Compared to the erosion rate of SPT-100, it is qualitatively and quantitatively confirmed that strong shielding of the discharge channel is realized and high performance is maintained in the designed thruster with a magnetically shielded configuration.