Influence of propellant oxygen concentration on LaB₆ hollow cathode for electric propulsion

To avoid cathode poisoning in electric propulsion systems, a stringent standard for propellant purity is often mandated, which can lead to significant hidden costs due to gas loss during the fueling process. To appropriately relax this standard, this study investigated the discharge performance of hollow cathodes under varying water-oxygen concentrations and different exposure accumulations, as well as their coupling performance with Hall thrusters. The results showed that after short-term exposure, both the discharge voltage and operating temperature of the cathode decreased. However, after long-term exposure (1.89 Pah), an increase in discharge voltage of 2–3V was observed. Coupling test results indicate that the impact of short-term exposure on thrust was within the measurement error range. After long-term exposure (0.97 Pah), the total thrust increased by 8.6 %. This change was primarily attributed to performance drift caused by the ceramic channel coating, while the 1.5 % variation due to coupling pressure drop was a secondary factor. Nonetheless, it was noted that short-term exposure had a significant effect on the amplitude and wavelength of the thruster's breathing mode oscillation. Therefore, the accumulation limit that the cathode could withstand might need to be analyzed in conjunction with the sensitivity of different thruster instabilities.