Evaluation of the low power operation of ferroelectric emission cathodes for electric propulsion

Summary form only given, as follows. Expellantless neutralizers can improve the propellant utilization of very low-power colloid thrusters, field emission electric propulsion (FEEP) devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. In addition, spacecraft plasma contactors and electrodynamic tether systems could reap expellant mass reduction benefits from electron emitters that require very low gas flow rates or no gas flow to perform their functions. Ferroelectric emission (FEE) cathodes operating at minimized power are currently being studied as zero expellant flow rate cathode sources. Typical cathode operation requires 0.4 to 1 kV to be rapidly pulsed across a ferroelectric ceramic, triggering electron emission through a gridded electrode on the ceramic surface. Ceramics with painted-on Ag electrodes have produced peak current densities of 10s of mA/cm/sup 2/ with pulse voltages near current emission threshold (approximately 400 to 600 V). Additionally, thin film electrode grids have been deposited on two PZT ceramics with relative dielectric constants of 1000 and 4100. The thin film grids are composed of molybdenum and are 10 and 100 nm thick, 1 mm wide, and separated into strips by 1 mm. A parametric study of these FEE cathodes examines the effects of ferroelectric dielectric constant, grid thickness, and pulse geometry for low power operation. Additionally, cathode surface modification due to operation is studied.