Cavity Ring-Down Spectroscopy Sensor for Real Time In Situ Measurement of Sputter Erosion in Anode Layer Type Hall Thrusters

Abstract

A Sputter monitoring system using continuous-wave cavity ring-down spectroscopy (cw-CRDS) was built for both lifetime assessment and contamination effects in Hall thrusters. First, we have performed proof of measurements of sputtered manganese atoms from manganese-iron alloy plate. The measurement strategy is based upon detection of manganese atoms via an absorption line from ground state at a wavelength of 403.076 nm. The hyperfine structure of the manganese spectrum can be observed owing to honeycomb structure mount as a velocity-filter. The number density estimated by CRDS is reasonable as comparison with simple estimates. These results validate the estimation of the erosion rate by CRDS. Next, we apply this system for erosion atoms from the acceleration channel wall (stainless steel 316) in an anode layer type Hall thruster. The path-integrated number density is 8.2  1.5 1012 m-2 at discharge voltage of 150 V and argon mass flow rate of 70 sccm. The number density is proportional to the discharge voltage, as expected. The number density and mass-loss have a relatively linear dependence. These results show the validity of the erosion sensor for Hall thruster lifetime estimation.