OPERATING CHARACTERISTICS OF A HOLLOW-CATHODE NEUTRALIZER FOR 5- AND 8-CENTIMETER-DIAMETER ELECTRON-BOMBARDMENT MERCURY ION THRUSTERS

摘要

Thin-tip 0. 3-cm-outside-diameter hollow-cathode neutralizers were used to investigate causes of neutralizer tip erosion experienced in thruster endurance tests. Bell-jar tests indicated that neutralizers with new rolled tantalum foil inserts coated with an emissive mixture eroded very little over the neutral flow rates investigated (3 to 10 mA) for sim¬ulated 5- and 8-cm-diameter thruster neutralizer conditions. Tip erosion rates of neu¬tralizers operated with no insert or emissive mixture increased by two orders of mag¬nitude for both configurations as the neutral flow rate decreased. Spectroscopic analysis of the discharge plasma from neutralizers operated with inserts coated with the emissive mixture detected tungsten at all neutral flow rates for both thruster neutralizer conditions. The only source of tungsten was the tip. Therefore, detection of tungsten indicated neu¬tralizer tip erosion. Barium, an element of the emissive mixture, was detected at low neutral flow rates for the 5-cm-diameter thruster neutralizer operating condition only.