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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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