Experimental Study of a Hundred-Kilowatt-Class Applied-Field Magnetoplasmadynamic Thruster

An experimental investigation of a pulsed, quasi-steady, 100-kW-class applied-field magnetoplasmadynamic thruster is discussed. Measurements were obtained with argon propellant for a variety of currents, mass flow rates, and magnetic field strengths in a power range between 20 and 250 kW. Tests were carried out in Alta's IV-10 vacuum facility. With a volume of about 200 m(3), IV-10 allowed for a current-pulse duration up to 1 s as well as for minimization of the environmental interaction with the plume. Although the shot duration was still too short to achieve steady-state thermal conditions, it allows for direct, time-resolved thrust measurements. To this purpose, a new single-axis thrust stand was designed to improve the frequency response of the existing thrust stands commonly employed in high-power devices. A maximum thrust efficiency of 28% was obtained at about 200 kW for an applied magnetic field of 120 mT and a mass flow rate of 60 mg/s. At 100 kW, for the same mass flow rate and magnetic field, a thrust efficiency of 22% and a specific impulse of about 2500 s were achieved. Moreover, during the arc ignition phase, the cathode current attachment was found to be distributed mainly at the external surface of the electrode while a transition from diffuse to hollow cathode behavior was observed after approximately 400 ms from the breakdown.