Carbon Nanotube Field Emission Cold Cathode
The use of carbon nanotubes (CNTs) for field emission (FE) cathodes is of interest for use as a general electron emitter, especially in the area of electric propulsion (EP). There is a need for an efficient electron source to neutralize the exhaust plume in low-power EP devices (1). Most thrusters operate in conjunction with thermionic hollow cathodes, which require a gas flow in order to emit electrons. For a hollow cathode in use with a 200-W Hall effect thruster (HET) the propellant flow rate through the cathode is typically an additional 10% of the flow through the thruster itself. In addition, hollow cathodes are relatively complex in that they require a heater element, which is an additional load on the spacecraft power system. Since most low-power EP systems have limited power capacity, any expenditure in power that does not directly generate thrust is a source of inefficiency. Rather than use a hollow cathode, it is suggested that CNT cathodes be used for plume neutralization. Recent work demonstrates the potential of FE cathodes not only in the areas of low power EP, but also in the areas of propellant-less propulsion such as space tethers, and spacecraft charge control. 1,2
1) Mueller, J., Marrese, C., Wirz, R., Tajmar, M., Schein, J., Reinicke, R., Hruby, V., “JPL Micro-thrust Propulsion Activities,” 2002.
2) Gilchrist, B. E., Jensen, K. L., Gallimore, A. D., Severns, J. G., “Space Based Applications for FEA Cathodes (FEAC),” MateriaslResearch Society Symposium Proceedings, Vol. 621, 2000