Development of high-current compact radial field emission cathodes for space applications

Field emission cathodes are being developed as replacements for hollow cathodes, which are impractical for electrodynamic tether systems on small and microsatellites due to their size constraints. We have designed a novel radial electron emitter based on commercially available carbon nanotube fibres and yarns. To create a field emission array capable of delivering currents exceeding 10 mA over extended periods, we fabricated and tested miniaturised prototypes of varying sizes. This parameter study aimed to explore the complex interplay between the electric field, emitter design, and carbon nanotube degradation. Long-term testing of up to 350 hours for each configuration provided insights into the radial emitter’s performance and allowed for a reliable assessment of the long-term degradation of the carbon nanotube material. Using the best configuration, we achieved a power efficiency of 1.7 mA/W at 1.5 mA after 300 hours of operation. We have identified cathodes with a large emission surface and small electrode spacing as the best design for scaling to the application case. Additionally, we were able to successfully describe the degradation-induced voltage rise for the three very different cathodes in a mathematical model, which significantly simplifies the design of scaled versions.