Comparison of Medium Power Hall Effect Thruster Ion Acceleration for Krypton and Xenon Propellants
AFRL/RQRS Edwards AFB United States
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There is interest within the electric propulsion community in the use of krypton as a propellant for electrostatic thrusters. It is a lower cost replacement for xenon, may optimize to similar or potentially higher performance, and is enabling for very large solar electric transfer vehicles that would strain world-wide xenon production. This work compares the internal propellant acceleration of krypton ions within a laboratory medium power Hall effect thruster to xenon ion velocity data for the same thruster. One case matched in propellant particle flux, applied magnetic field, and accelerating potential is presented. The measurements consist of laser-induced fluorescence velocimetry extending from near the anode to 10 mm outside the thruster into plume along the center of the coaxial acceleration channel. This measurement region captures the majority of the propellant axial acceleration within the characterized 600 W medium power Hall effect thruster. The measurements show that krypton acceleration rate is lower and produces a lower effective electric field. As a result, energy conversion is lower than xenon for this flow matched case. In addition, there is clear evidence of krypton ionization throughout the acceleration channel, far downstream of where the majority of xenon acceleration occurs. This latent krypton ionization is consistent with the lower performance for krypton at this set of operating conditions due to low propellant utilization.