Ion beam diagnostic for the assessment of miniaturized electric propulsion systems

An automated plume diagnostic system is presented for two-dimensional mapping of the ion beam produced by using miniaturized electric propulsion devices. The instrument is designed to operate with noble and reactive gases and consists of a semi-circular probe array with a unique angular distribution following a Gaussian shape for improved beam profile resolution. To demonstrate the operation of the diagnostic system, a series of experiments are conducted with a low-power gridded ion thruster using xenon and iodine propellants. The two-dimensional current density maps generated are used to calculate important beam properties for performance estimates, including the total ion current and the effective divergence angle, and we show how the measurements can be used to assess and optimize the design of ion optics for gridded ion thrusters. All current density measurements with the new instrument are corrected for secondary electron emission (SEE) due to ion bombardment, and using a separate, specially designed, electrostatic probe, we present the first measurements of the SEE yield for iodine ions impacting molybdenum and SAE 304 stainless steel surfaces.