2D krypton density maps in a SPT-70 Hall effect thruster by two-photon absorption laser induced fluorescence (TALIF)

There is a growing recognition of the importance of neutral density fields to the physics, and particularly facility related effects, of Hall-effect thrusters (HETs). This work presents the first high-resolution (mm scale) spatial maps of neutral density in the near-field plume of a HET using two-photon absorption laser-induced fluorescence (TALIF). We employ a 212.6 nm TALIF excitation scheme, based on a pulsed nanosecond dye laser, to map absolute krypton neutral densities in the plume of a SPT-70 HET. Absolute densities are determined via a ratio-based approach using cold-flow measurements. The diagnostic system incorporates active wavelength stabilization via a feedback-controlled dye laser with drift correction algorithms to maintain measurement accuracy through extended mapping campaigns. Neutral density maps are acquired under cold-flow conditions and four plasma-operating states (540 and 720 W at varying background pressures), highlighting the effects of power level and background pressure on the near-field neutral particle profile. These results provide important experimental benchmarks for validating computational models and advancing physical understanding of neutral behavior and electric propulsion facility effects.