Geometric Scaling of Applied-Field Magnetoplasmadynamic Thrusters

Eight magnetoplasmadynamic thruster configurations were tested with argon propellant at power levels between 20-130 kW to study the effects of geometry and applied magnetic field strength on thruster performance. The discharge voltage, thrust efficiency, and specific impulse increased monotonically with increasing applied-field strength for all geometries. The highest measured performance was 23 percent thrust efficiency at 2300-s specific impulse at a power of 113 kW. Both cathode and anode radii fundamentally influenced the efficiency-specific impulse relationship, whereas their lengths influenced only the magnitude of the applied magnetic field required to reach a given performance level. At a given specific impulse, large electrode radii resulted in lower efficiencies, although the rate at which efficiency increased with applied-field strength was higher with larger anode radii. Anode power deposition was the largest efficiency loss, and represented between 50-80 percent of the input power. The fraction of the input power deposited into the anode decreased with increasing applied-field strength and anode radius. (Author)