Electric Field Breakdown Characteristics of Molybdenum and Carbon-Based Electrodes under Conditions Where Ions are being Extracted

Measurements of the enhanced electric field at breakdown for perforated flat plates fabricated from carbon-carbon composite, Poco graphite, pyrolytic graphite, and molybdenum are presented. The perforated flat plates represent electrodes used in ion sources and ion thrusters and measurements are made with and without ion beamlet extraction through the perforations. A ranking of the materials is presented of their suitability in ion source applications. The electrical breakdown characteristics of candidate materials for ion optics systems used in satellite propulsion systems are of importance for several reasons, including (1) the necessity to specify the maximum applied electric field to reduce the probability of arcing and/or frequency of arcing, (2) the need to specify the maximum tolerable charge transfer level to avoid damage to the grids that would reduce their voltage standoff capability, (3) the avoidance of incessant arcing between the grids that would result in unacceptable electromagnetic interference levels, and (4) the impact that incessant arcing would have on the power production, power processing, and power distribution system