Evaluation of a Planar Scandate Cathode for Hall Thruster Operation

Cathodes are often implemented as a component of electrostatic electric propulsion devices to enable plasma production and to minimize spacecraft charging. However, cathodes can be a limiting factor on the lifetime and operation of thrusters due to eventual degradation of the emitting surface. This study evaluated the operational characteristics and plasma plume properties of a planar scandate cathode to assess the feasibility of the cathode supporting operation of a Hall effect thruster. The cathode was operated in a pure xenon environment within a sealed vacuum tube. Two operational modes were studied: cup connected and cup disconnected. In each mode, the cathode was operated at a series of heater voltages and anode currents to investigate operational behavior. Analysis of the cup disconnected data produced plasma plume properties including the electron current, electron current density, electron density, plasma density, and electron temperature. The cathode produced a maximum electron current of 3 A, a maximum electron current density of 616 A cm² at the cup orifice, an average electron density and plasma density on the order of 10¹³ cm⁻³ , and an electron temperature ranging from 0.53 eV to 0.87 eV. These plasma properties are comparable to the plasma plume properties generated by hollow cathodes that have successfully operated with a Hall effect thruster. The planar scandate cathode has been shown to produce 3 A of electron current which suggests that it may operate any Hall thruster that requires a discharge current of up to 3 A. Since the planar scandate cathode produces plasma properties that are comparable to existing cathodes and sufficient electron current to operate a Hall thruster, it is reasonable to conclude that the cathode should be considered as a candidate for Hall thruster operation.