Investigation of Operation and Characteristics of Small SPT With Discharge Chamber Walls Made of Different Ceramics

This study characterizes the SPT-25 model with discharge chamber walls made of different materials, including the Russian BN-SiO2-type (BGP) ceramics and the AIN-BN-type and BN-type ceramics produced in France and in the United States, respectively. The first ceramic is used in modern SPT-70 and SPT-100 flight designs and the others are prospective materials for SPT discharge chamber manufacturing. These materials have good thermal resistance and, according to published data, they have different secondary electron emissions. Characterization of thrusters with discharge chamber walls made of these materials could give some indication of secondary electron emission influence on thruster operation and performance. The SPT-25 model has an external accelerating channel diameter of 25 millimeters and an acceptable performance level under discharge powers (100-200)W. To characterize its operation with discharge chamber walls made of different ceramics the authors determined the voltage-current characteristics of this model under different magnetic fields inside the accelerating channel and different mass flow rates through the channel. They also determined thrust values and other output parameters such as thrust efficiency and specific impulse, accelerated ion flow divergence, plume plasma parameters measured by cylindrical electrostatic probe, discharge voltage, and current oscillation characteristics. The results confirm a high performance level by the SPT-25 model with BGP ceramics. Total thrust efficiency was 0,25 and specific impulse 885s under power 100W, and total thrust efficiency was 0,32 and specific impulse 1300s under power 200W. Also, there were notable differences in voltage-current characteristics and thrust values for different ceramics under low mass flow rates and magnetic fields. Moreover, thrust and thrust efficiency were different with different materials even under similar discharge voltages and currents obtained under comparable conditions.7 Presented at the AIAA Joint Propulsion Conference held in Huntsville, AL, on 20-23 Jul 2003. Prepared in collaboration with the Russian Scientific Center, Kurchatov Institute, Moscow, Russia, and the University of Washington, Seattle, WA.