Diamond based, field emission cathode for small electrostatic thrusters

Low power electrostatic thrusters are greatly penalized by the lack of small efficient cathodes. Conventional hollow cathodes are relatively large and consume power and propellant at a rate approaching that required by the small thruster, thus greatly reducing the overall efficiency and Isp. An attractive alternative to the hollow cathodes (which are thermionic emitters) are field emission array (FEA) cathodes. These do not require propellant or a heater and operate at low power. Many FEA cathodes can be considered including the original metal based Spindt cathode, diamond like carbon (DLC) and diamond based cathodes. Most recently, CVD diamond film emitters have demonstrated promising performance. Therefore, the development of a diamond film cathode will be the focus of our effort.In Phase I we will deposit various nitrogen doped CVD diamond films on silicon substrates and characterize them using SEM and the Rutherford back-scattering technique to determine their morphology and nitrogen content. Selected samples will be incorporated into an electron emission test fixture and their voltage-current characteristic will be measured as a function of the vacuum tank environment (Ar, Xe) and pressure. The effort will be carried out in cooperation with ASTeX Inc. under subcontract to Busek. ASTeX has demonstrated expertise in CVD diamond deposition.In Phase II, diamond cathodes suitable for operation with electrostatic thrusters will be constructed and tested on an existing low power Hall thruster.