Experimental Investigation of LaB₆ Hollow Cathode with Radiative Heater

Abstract

A lanthanum hexaboride (LaB₆) hollow cathode with radiative heater has been developed for high power Hall thruster neutralizer. The influences of orifice and keeper shapes on the performance of the hollow cathode and on its operating characteristics are investigated by measuring the discharge voltage and current. Six different orifice shapes are used in this study: straight, long tapered, and short tapered, each with an orifice diameter of 2 or 3 mm. The straight orifice with the 2-mm diameter has the widest range of spot-mode operation, although no effect of orifice shape is observed for the 3-mm diameter. This is because the high neutral-gas density around the orifice fosters transition to the spot mode from the plume mode with a straight Φ2-mm orifice. Regarding the effect of the keeper, having a large exit diameter and the shortest distance possible between the cathode tube and the keeper gives the widest range of spot-mode operation.