Measurements of Velocity and Temperature Profiles of a Resistojet Exhaust Plume Using Two-Photon Absorption Laser Induced Fluorescence

Environmental effects during thruster testing result in discrepancies between laboratory performance and actual performance in space. Specifically, the buildup of ambient neutrals in test chambers affects measurements of thruster performance. To accurately and reliably assess thruster performance, measurements of ambient neutral distributions in space and time are essential. Non-invasive, spatially localized neutral diagnostics for thruster test chambers are rare. Here, we use planar two-photon absorption laser-induced fluorescence (TALIF) to excite neutral ground-state krypton non-intrusively. The thruster is operated in a pressure-controlled neutral argon background and the krypton exhaust is interrogated using a Quantel Q-Scan laser generating 212 nm light at a repetition rate of 10 Hz. Spatially resolved fluorescence intensity is measured using an Andor fast-gate iCCD camera. Custom nozzles of varying throat diameters are used to probe krypton dynamics for a range of operating pressures. The spatially resolved neutral number density, velocity, and temperature profiles in the exhaust plume of a krypton-fueled resistojet thruster and throughout the test chamber are presented. The effect of ambient pressure on thruster performance is investigated in both choked and unchoked flow regimes and compared with simulation.