A review of field emission cathode technologies for electric propulsion systems and instruments

Cold field emission (FE) cathodes are being considered as the electron sources for propellant ionization and ion beam neutralization in electric propulsion systems. Compatible field emission cathodes will enable the development of microscale electric propulsion systems. The hostile environments of propulsion systems are very demanding on the cathode performance. Advanced cold FE cathode technologies are reviewed in this article. Field emission array cathode materials and configurations were optimized using theoretical and experimental results to meet the demands of electric propulsion applications. It was determined that the FE cathode configurations and materials which are required for electric propulsion systems have not yet been fabricated. It is recommended that Mo FEA cathodes are fabricated with VECTL architectures and CLAIR structures and coated with carbide or carbon films to achieve performance and lifetime compatible with microscale electric propulsion systems. Instrument systems are much less demanding on the cathode performance; therefore the advantages of the recommended cathode configuration will also be realized for instrument systems.