Dependence of the Energetic Ion Distribution on Propellant Composition in Hollow Cathodes

Abstract

of the cathode axis pointing immediately downstream of the cathode orifice for pure xenon and pure krypton propellants. Consistent with previous studies with xenon, ions with energies much greater than the potential dierence between the anode and the cathode were detected. At the same discharge current, flow rate, and magnetic field, scans obtained with krypton had a substantially greater high-energy content. The eects of flow rate, discharge current, discharge voltage and strength of the applied magnetic field were examined. The high-energy content increases as flow rate decreases. Discharge current, discharge voltage, and the strength of the applied magnetic field influenced the high-energy content; however, the character of the variation depends on other flow conditions. The data were examined in light of proposed mechanisms for high-energy ion acceleration. The radial high-energy content and the apparent dependence on propellant mass suggest a wave acceleration mechanism. Additional massresolved energy distribution measurements using a mixture of xenon with trace amounts of krypton are proposed to determine if the greater high-energy ion content for krypton can be attributed to the mass dierence or to a dierence in the discharge operation with pure krypton.