Microwave discharge Hall thrusters have been investigated as a double-stage Hall thruster. Our original microwave discharge Hall thruster, where 2.45-GHz microwaves were employed, needed voluminous waveguides for microwave transmission; therefore direct thrust measurements using a thrust stand were not achieved. Based on the background, by changing wave frequency from 2.45 GHz into 5.8 GHz and developing a new microwave discharge Hall thruster adequate for 5.8-GHz microwaves, the required volume of a waveguide has been decreased: thus a pendulum type thrust stand using a smaller waveguide as a pendulum arm has been built. The 5.8-GHz microwave discharge Hall thruster can be operated in two operating modes; the first one is “non-microwave injection mode” referred to as “single-stage” and the second one is “microwave injection mode” referred to as “double-stage”. The thruster channel length can be adjusted to 8 or 13 mm. To examine the influence on thrust performance of microwave, the thrust measurements have been conducted in both singleand double-stage operations for each channel length condition, at xenon flow rates of 1.36, 2.05 and 2.73 mg/s, and discharge voltages of 200, 250 and 300 V. As a result, thrust and specific impulse in double-stage operation have been higher than that in single-stage operation for the same channel length, flow rate, and discharge voltage. Moreover, higher thrust efficiencies in double-stage operation, as compared to single-stage operation, have been attained when the thruster operates at low flow rate such as 1.36 and 2.05 mg/s, and low discharge voltage such as 200 V. The paper also reports on the reduction in discharge current oscillations due to microwave injection. * Graduate Student, Department of Advanced Energy Engineering Science, E-mail: h-kuwano@hotmail.co.jp † Graduate Student, Department of Aeronautics and Astronautics, E-mail: ohno@ep.isas.jaxa.jp ‡ Professor, Department of Space Transportation Engineering, E-mail: kuninaka@isas.jaxa.jp § Professor, Department of Advanced Energy Engineering Science, E-mail: nakasima@aees.kyushu-u.ac.jp The 30 International Electric Propulsion Conference, Florence, Italy September 17-20, 2007 2 Nomenclature F = thrust g0 = standard acceleration of gravity Id = discharge current, or current flowing from an anode to a cathode Ii = ion beam current Isp = specific impulse L = channel length of a Hall thruster mdot = propellant mass flow rate Vd = discharge voltage, or voltage applied between an anode and a cathode Pmw = net input microwave power η t = thrust efficiency
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