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Title: A cavity ring-down spectroscopy sensor for real-time Hall thruster erosion measurements

A continuous-wave cavity ring-down spectroscopy sensor for real-time measurements of sputtered boron from Hall thrusters has been developed. The sensor uses a continuous-wave frequency-quadrupled diode laser at 250 nm to probe ground state atomic boron sputtered from the boron nitride insulating channel. Validation results from a controlled setup using an ion beam and target showed good agreement with a simple finite-element model. Application of the sensor for measurements of two Hall thrusters, the H6 and SPT-70, is described. The H6 was tested at power levels ranging from 1.5 to 10 kW. Peak boron densities of 10 ± 2 × 10{sup 14} m{sup −3} were measured in the thruster plume, and the estimated eroded channel volume agreed within a factor of 2 of profilometry. The SPT-70 was tested at 600 and 660 W, yielding peak boron densities of 7.2 ± 1.1 × 10{sup 14} m{sup −3}, and the estimated erosion rate agreed within ∼20% of profilometry. Technical challenges associated with operating a high-finesse cavity in the presence of energetic plasma are also discussed.
Authors:
 [1] ;  [2] ; ; ;  [3] ;  [4]
  1. Physics Department, Colorado State University, Fort Collins, Colorado 80521 (United States)
  2. NASA Glenn Research Center, 2100 Brookpark Rd., Cleveland, Ohio 44135 (United States)
  3. Mechanical Engineering Department, Colorado State University, Fort Collins, Colorado 80521 (United States)
  4. Aerospace Engineering Department, University of Michigan, Ann Arbor, Michigan 48109 (United States)
Publication Date:
OSTI Identifier:
22308852
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 74 ATOMIC AND MOLECULAR PHYSICS; BORON; BORON NITRIDES; EROSION; FINITE ELEMENT METHOD; GROUND STATES; ION BEAMS; ION THRUSTERS; LASER CAVITIES; LASERS; PLASMA; SENSORS; SPECTROSCOPY; SPUTTERING; TIME MEASUREMENT