Sensitivity Improvements to Laser Sensor for Boron Nitride Erosion in Hall Thrusters IEPC-2011-068

Sputter erosion of boron nitride (BN) is a critically important process in Hall thrusters from the point of view of both lifetime assessment and contamination effects. This contribution describes recent improvements to a laser sensor being developed for in situ monitoring of sputtered BN from Hall thrusters. The sensor employs the continuous-wave cavity ringdown spectroscopy (cw-CRDS) technique to probe an atomic absorption line of boron (250 nm). Recent improvements include piezo-electric cavity modulation, improved ring-down acquisition rate, and a custom AOM driver. We present demonstrative results illustrating these improvements and discuss their implications for Hall thruster diagnostics. A factor of ∼5 improvement in optical sensitivity is demonstrated compared to the previous sensor.

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