Abstract
Hollow cathodes with various diameters and interelectrode lengths were tested to evaluate their effects on the performance of a magnetoplasmadynamic (MPD) thruster. The thruster was operated in a quasisteady mode in the specific impulse (Isp) range of 1000-2000 s. The arc chamber was designed so that its wall formed a divergent nozzle and the hollow cathode constituted a part of the flow tube. The entire propellant was injected through the hollow cathode and forced to be heated in the arc column so as to enhance the aerodynamic acceleration. An appropriate combination of cathode interior diameter and interelectrode length resulted in the maximum thrust power ratio of 25 mN/kW for hydrogen and a lower cathode erosion rate than occurs with a solid cathode. However, a similar configuration was not effective for ammonia propellant because the mass flow was interrupted by excessively high pressure due to induced electromagnetic pinch force in the hollow cathode interior. Consequently, the hollow cathode exhibited inferior thrust performance but superior erosion characteristics compared to the solid cathode.
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