Discharge mode transition in a Krypton-fed 1 A-class LaB6 cathode for low-power Hall thrusters for small satellites

Abstract

Thermionic cathodes are essential for the operation of various electrostatic propulsion devices. They strongly influence the performance and lifetime of the propulsion system. In this study, a 1 A-class LaB 6 laboratory model hollow cathode has been tested with krypton in diode and triode configurations in order to assess the cathode discharge mode transition behavior. Measurements have been performed over a range of krypton mass flow rates (0.1, 0.15, and 0.21 mg/s, or 1.6, 2.4, and 3.4 sccm), keeper (0.1, 0.15, and 0.2 A), and anode currents (0.1-1 A) at a fixed cathode-to-anode distance. Seven criteria were used to distinguish between the spot and plume mode operations. The results show that the mode transition in low-current cathodes may be a nonlinear phenomenon, and only some of the existing mode transition criteria can be used to accurately predict the spot/plume discharge regions at low emission currents.