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Evaluation of Sub-Scale NEXIS Ion Optics and Strategies for Performing Accelerated Wear Testing

Sub-scale ion optics assemblies (gridlets) are used to investigate the operational limits of the NEXIS thruster on beamlet (or per hole) ion current. Gridlet data are presented over wide ranges of net and total voltage, grid-to-grid spacing, and accelerator hole diameter. A discussion of a technique that can be used for performing accelerated wear tests (at rates that are 50x higher than standard tests) is also presented that may be useful for quickly and inexpensively evaluating the life time of the NEXIS accelerator grid for missions requiring long (~100 khr) thruster firing times. The technique is based on exposing the accelerator grid surface (through a mask) to an ion beam that is capable of trenching pit and groove patterns on the downstream face and eroding side-wall and etching upstream surfaces of apertures. The status of this work is summarized, and beam current profiles and related facility details are presented. Data on a specially designed power supply with ultra-low stored energy features are also presented. Low stored energy power supplies are critical for high specific impulse ion thrusters that utilize carbon-based ion optics systems in order to avoid arc damage of the accelerator grid surface when the thruster is operated at high total accelerating voltages.