Electron transport in multiple orifice hollow cathodes

The effect of keeper geometry on the transport of electrons is investigated experimentally using electrostatic probes in the plume of a hollow cathode. Three keeper configurations-one single orifice and two multiple orifices-were studied. The multiple orifice cases were chosen to examine the influence of the hole-pattern radius while the total exit area and the number of holes remained constant. Two-dimensional maps of the plasma parameters and wave properties were inferred from the probe measurements and were used to evaluate a generalized Ohm's law for the electron flow field. The contributions of pressure, fields, and drag on the transport of electrons were analyzed. The results indicate that increasing the hole-pattern spread reduces the electric field in the plume and increases the pressure contribution to the transport. A further analysis of turbulent wave energy conservation indicates that the multiple orifice keepers increase ion-neutral collisional damping, similar to auxillary flow injection. The implications of these findings on cathode plume modeling and keeper design are discussed.