Plume Investigation of a Modular Hollow Cathode for ground testing of Plasma Thrusters

Conventional hollow cathode neutralizers which provide seed electrons for plasma generation and compensate for charge imbalances in electrostatic electric propulsion systems suffer from lifetime issues due to gas impurity poisoning, structural degradation, and localised heating, making their development process expensive and time-consuming. Customisation to meet research laboratory needs is also challenging due to fixed off-the-shelf designs. A modular hollow cathode design is proposed to enable parametric studies, flexibility of adaptation to different test setups, and reduced replacement costs. This work describes a modular hollow cathode design and discusses its plume diagnostics and current-voltage characterisation for xenon and krypton.

The modular hollow cathode has novel mechanical features that allow for direct contact between the emitter and heating element, resulting in higher thermal efficiency and better thermionic emission. The design includes an annular ceramic plate that separates the orifice plate from the keeper electrode, creating a high neutral density and potentially increasing the plasma density due to higher ionisation rates. To investigate this conjecture, experiments were conducted using invasive and non-invasive techniques in diode and triode mode. The experiments measured electron temperature, electron number density, and the plasma potential for a fixed distance as a function of mass flow rate at the keeper-anode and keeper-orifice gaps.