Preliminary characterization of an iodine-compatible LaB₆ hollow cathode

Currently, iodine-compatible cathodes for iodine propulsion systems that can provide ampere-level electron currents with a reasonable power consumption are lacking. In this study, a conventional LaB₆ hollow cathode made with iodine-resistant materials was designed and tested in an iodine-compatible vacuum facility. The ignition characteristics, the V-I (Volt-Ampere characteristic) curve, and long steady-state discharge sequence of the iodine hollow cathode were analyzed and compared with those using a krypton propellant. After the experiment, the composition of the cathode emitter was studied by scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS). The results show that ignition takes > 10 s to reach a steady state, and the discharge voltage of the iodine was 25–95 V higher than that of krypton. According to the EDS results, this was mainly caused by emitter contamination with iron from the stainless-steel components of the cathode and oxygen from the iodine feed system. The iodine hollow cathode achieved a cumulative 12.5 h stable discharge, with the longest single discharge of 5 h and a 3% change in the inner diameter of the emitter.