Mode Transition in a Low-current LaB6 Hollow Cathode for Electric Propulsion Systems for Small Satellites

Hollow cathodes are critical components of many space solar electric propulsion systems drastically influencing the performance and lifetime of the overall system. The PSAC LaB6 laboratory model cathode was systematically tested with Krypton in diode and triode configuration with an external disc anode and keeper electrode while mode transitions were observed over a wide range of discharge current (0.1 to 1 A), keeper current (0 to 0.2 A) and mass flow rate (0.1 to 0.25 mg s-Kr). The influence of the keeper current as well as the mass flow rate on mode transition was analyzed leading to a comprehensive results matrix which allows for the proper control of the cathode in the most efficient discharge mode, i.e. spot mode. Moreover, the thermal aspect of the model cathode was investigated, and the results were compared with thermal simulations in order to support the future improvements of the thermal management of the cathode. The results suggested the need for an improved thermal shielding and the reduction of thermal conduction from the emitter region to the cathode base to achieve lower start-up power requirements as well as auto-thermal (selfsustained) functioning.