An Evaluation of Hollow Cathode Scaling to Very Low Power and Flow Rate

As Hall and ion thrusters are scaled to power levels below 300 W to operate on small- and micro-satellites, hollow cathodes must be designed to accommodate the new operating regimes with efficient use of power and propellant. The conclusions of previous cathode scaling efforts by other authors are reviewed, and the importance of heat transfer and orifice processes are emphasized. Performance data for 3.2 mm orificed hollow cathodes are presented. Spot mode operation was achieved on Xe at the same equivalent mass flow rate as the SERT II ion thruster neutralizer. An insert with a diameter on the order of the orifice size was tested and required ten times the mass flow of the SERT II neutralizers to generate enough ions within the cavity for charge neutralization. Design considerations ant discussed for improvement of the power and propellant consumption of the cathodes presented in this work. Nomenclature AR = orifice to insert area ratio d = orifice diameter D = insert diameter I = current, A JCI = equivalent flow rate, A 1 = orifice length L = orifice plate to keeper gap length W = atomic mass, amu 0 = cross-section, m2