Exploration of RF-controlled high current density Hollow cathode concepts

Exploration of a novel RF-Controlled Hollow Cathode concept is presented using finite element analysis. Commercial software is used to model the extent of RF power absorption in one configuration of such a cathode in order to describe whether the RF power is localized as in a "stinger" concept or is projected downstream to lower the emission current density while maintaining a constant discharge current. Plasma conductivity along the major axis is calculated from a baseline high current density lanthanum hexaboride hollow cathode and is used in the modeling of RF power absorption by the internal plasma. It was found that within a maximum axial distance from the orifice, a direct coaxial-cathode mating can lead to high percentages (>96%) of localized microwave power absorption. The configuration analyzed acted more as a stinger, as approximately 62% of the RF power was absorbed within 2 mm of the inner coaxial conductor tip. Xenon gas breakdown using RF waves was explored and deemed practical for the cathode parameters studied. RF heating of the emitter prior to plasma ignition was also examined, but low RF power absorption (<5%) without a lossy plasma suggested poor feasibility of this potential function.