Near RealTime Hall Thruster Erosion Diagnostics

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Near Real-Time Hall Thruster Erosion Diagnostics
Prof. Alec Gallimore and Dr. Timothy
Smith Plasmadynamics and Electric Propulsion
Laboratory The University of Michigan
In Collaboration with Prof. Azer Yalin, Colorado
State University
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HET Erosion Diagnostics
Background and Motivation

• HET lifetime generally limited by sputter
  erosion of the BN channel.
• Sputtered particles can coat spacecraft
  surfaces, posing risk to mission.
• Effect of varying thruster operating parameters
  on lifetime not well understood.
• Lack of understanding makes qualifying new HETs
  challenging and expensive.Life Tests, which
• are expensive, and labor and facility intensive
  
• allow only post-facto bulk analysis
• do not allow real-time erosion sensitivity
  measurements
• are inflexible and dependent on prescribed
  mission profiles and
• typically provide little information about
  spacecraft deposition/erosion rates

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HET Erosion Diagnostics
Objective of Research
Need method for measuring thruster erosion rates
non-intrusively in real-time. Such a technique
would allow one to evaluate HET design and
operating condition changes for performance and
life simultaneously. Cavity Ring-Down
Spectroscopy (CRDS) measurement of thruster
erosion rates non-intrusively and in real-time.
CRDS combined with wear testing would
enable monitoring of thruster performance and
erosion rates simultaneously, in real time.
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Cavity Ring-down Spectroscopy (CRDS)
Technical Approach

• CRDS method
• UV diode laser beam absorbed by BN erosion
  product (neutral, ground-state B)
• number density directly proportional to change in
  cavity ring-down time ?
• narrow linewidth permits high SNR (100)
• CSU (initial development by Prof. Azer Yalin)
• ion gun rig for BN sputtering
• initial pulsed laser (lower SNR) tests complete
• proof-of-concept CW testing underway
• PEPL (deployment in HET plume)
• UV diode laser installed
• optical cavity will sweep across HET exit plane
• line-integrated B number density from ?
• Abel inversion yields radial distribution

BN sputtering data from CRDS (CSU)

• Payoff
• Improves thruster wear testing for faster and
  cheaper Hall thruster development and
  qualification cycles
• HETs with enhanced lifetimes - Higher Total
  Impulse

Planned CRDS setup (PEPL)
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HET Erosion Diagnostics
Anticipated Results
Ultra-Sensitive CRDS Detection CRDS using
frequency-quadrupled UV external cavity
diode laser 300K investment (Air Force DURIP)
identical lasers installed at Michigan and
CSU. Integration with Large Vacuum Test
Facility CRDS system undergoing testing at CSU -
excellent results CRDS system integration with
LVTF at Michigan (6 x 9 m) Proof of Concept
Testing at Michigan CRDS measurements in HET
plume in LVTF Implementation Plan to Continue
Technique Development Incorporation of
MS Deposition measurements LIF