Investigation of stabilized resonant cavity microwave plasmas for propulsion

Abstract

Results are presented for the performance of a microwave electrothermal thruster utilizing bluff-body and swirling flow stabilized plasmas with helium and nitrogen propellent. Stabilized plasmas have been produced in the TM011 electromagnetic cavity mode with coupling efficiencies approaching 100% and specific powers up to 27.3 MJ/kg. Fluid dynamic measurements indicate specific impulses of up to 543 s, efficiencies of 44-69%, and thrusts of 0.27—0.40 N with helium propellant. Spectroscopic results indicate plasma core electron temperatures of 11,840-12,170 K with extremely flat radial profiles. Nomenclature A = orifice area, m c = speed of light, m/s cp = specific heat, J/kg K g = gravitational acceleration, m/s2 7sp = specific impulse, s k = Boltzmann's constant, J/K m = particle mass, kg m = mass flow rate, kg/s P,- = incident power, W Po = chamber pressure, Pa Pr = reflected power, W R = gas constant, J/kg K 7} = thrust, N T(k, = stagnation temperature (cold), K Tl}l, = stagnation temperature (hot), K ue = exhaust velocity, m/s y = ratio of specific heats 77 = efficiency j]c = coupling efficiency A = wavelength, A