Operation of Spindt-Type, Carbon Nanotube Cold Cathodes in a Hall Effect Thruster Environment

Electric propulsion devices for space applications greatly reduce the propellant mass requirements on a spacecraft in comparison to chemical rockets. To date, gridded ion engines and Hall effect thrusters (HETs) rely on thermionic hollow cathodes to supply electrons for propellant ionization and ion beam neutralization. Hollow cathodes consume up to 10% of the total propellant used in low-power HET propulsion systems; however, such propellant usage does not contribute to thrust generation. An array of Spindt-type, carbon nanotube cold cathodes that emit electrons through field emission can potentially neutralize the ion beam without consuming any propellant. This work examines the effects that the plasma environment near an operating 200-W BHT-200 HET has on carbon nanotube cold cathodes placed around the circumference of the thruster at the exit plane. For this work, the thruster was operated at the 200 V, 1.05 A operating condition with a facility operating condition of 1.1 x 10 Torr-Xe. The physical structures that enable field emission appear largely unaffected by placement in the plasma as well as operation in the plasma. This indicates that a refined design of this carbon nanotube cold cathode could be an alternative to the thermionic cathode used on contemporary low-power HETs.