Performance comparison between standard and magnetically shielded 200 W Hall thrusters with BN-SiO2 and graphite channel walls

Magnetic shielding is a specific magnetic topology that can increase the lifespan of Hall thrusters by an order of magnitude. Magnetically shielded thrusters have similar performances as standard unshielded thrusters in the 5–15 kW power range. A comparison of the performances of two 200 W shielded (ISCT200-MS) and unshielded (ISCT200-US) Hall thrusters is presented here. The effects of replacing the usual BN-SiO2 walls with graphite are investigated on both thrusters. The ISCT200-US thruster has a peak anode efficiency of 39% and a specific impulse of 1400 s at 250 W with the ceramic discharge channel. However with graphite wall, the discharge current increases by 25% which reduces the efficiency down to 31% (1360 s specific impulse). The ISCT200-MS performances are significantly lower than the ISCT200-US at similar operating points. It only reaches 24% anode efficiency and 1020 s specific impulse at 250 W. The switch to graphite has little effects on its performances below 300 V. The lower performances are due to a low propellant utilization. We propose that this low propellant utilization is caused by lower ionization near the walls which as a large impact in small thrusters due to their higher surface to volume ratio.