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TWO-PHOTON ABSORPTION LASER INDUCED FLUORESCENCE (TALIF) OF NEUTRAL XENON IN A HALL EFFECT THRUSTER PLASMA This work presents measurements of ground state neutral xenon in the plume of a 1.5 kW Hall Effect thruster (HET) using two-photon absorption laser induced fluorescence (TALIF).Neutral xenon particles in the thruster plasma play an important role in ionization processes, overall energy conversion, and life-limiting interactions with surrounding wall materials in the thruster. Therefore, a detailed understanding of the neutral particle dynamics within the plume is desired. The TALIF diagnostic technique allows for laser induced excitation of xenon from its ground state using commercially available laser systems at accessible ultraviolet wavelengths (~222 nm). The signal collected from fluorescence of the excited atoms can be used to determine the local neutral density. We present a demonstration of TALIF first in a barium oxide (BaO) hollow cathode plume at varying radial positions, then in an HET plume at varying axial positions using fiber coupled collection optics with a spatial resolution of 3.14 mm 2 . The detection limit of the TALIF measurement system 2.1 cm downstream of the thruster face was estimated to be 8 x 10 17 m -3 as determined by comparison to a known reference signal. The ability to analyze ionization and thermal characteristics using these results is also discussed.

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We present a combined electrostatic and magnetostatic plasma diagnostic tool used to measure current fractions of ion species in a Hall-effect thruster plume. Hall thrusters produce thrust by accelerating singly and multiply charged ions to high velocity. Singly charged ions fall through potential differences from their point of creation to the location of measurement, which varies as a function of time and position resulting in a relatively wide distribution of energy. This process is further complicated by both direct and multi-step creation of multiply charged ions and by ion-neutral collisions. The result is that Wien velocity filter (ExB) spectra typically have overlapping peaks. Analysis of these spectra requires assumptions about the velocity distribution function (VDF) that are hard to verify and can result in the incorrect species current distribution used to calculate thruster performance efficiencies. We present how adding an energy filter in line with an ExB probe can result in a more accurate measurement of the species current fraction while also providing information about the ion energy distribution of each species. The combined diagnostic was used to measure the species current distribution in a 1.5 kW Hall thruster operating on krypton. The diagnostic setup and data analysis of the probe measurements are presented and compared against results utilizing established VDF-fit and integration techniques applied to standard spectra measured by a standalone ExB probe.