Iodine compatible hollow cathode
Date
2019
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Abstract
Most electric propulsion (EP) systems utilize xenon gas as a propellant, which is expensive and must be stored in heavy high-pressure tanks, within which the storage density is still lower than desired. The halogen iodine (I2) has risen as a leading alternative propellant with the potential to overcome these drawbacks with its lower cost, higher storage density, and significantly reduced tank pressure. Hall-effect thrusters have been operated with iodine propellant in the range of a hundreds of watts to greater than ten kilowatts [1], [2], with performance comparable to that of devices operated on xenon; however, due to the reactive nature of iodine, the hollow cathode electron sources used with these thrusters, have been operated on xenon. Without being able to operate cathodes on iodine, the consideration of iodine propellant for many space missions is not possible. This research aims to develop and examine hollow cathode assemblies capable of operating on iodine propellant. We propose that a cathode can be constructed with iodine resistant materials and with an insert capable of participating in a tungsten-iodine life cycle that is utilized in halogen lamps to increase filament lifetime. Results from this work demonstrate that a cathode with a graphite tube and a tungsten-based ceramic-metal composite insert is capable of being operated on iodine for longer than any currently published operation time. This type of cathode has the potential to be operated on iodine for over 3,000 hours, a lifetime approaching the minimum requirement of EP systems currently being used.