The University of Michigan
Department of Aerospace Engineering
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Plasma Diagnostics

Flush-mounted Wall Probe

A series of planar Langmuir probes mounted flush with the thruster walls for the experimental characterization of the near-wall region in Hall thrusters and its implications on performance and lifetime.


Above: A first generation near-wall (on channel exit) Langmuir probe (from ref. 1).

Specifically intended for non-intrusive, near-wall measurements, flush-mounted Langmuir probes are currently being used to interrogate the plasma adjacent to the channel walls within a Hall thruster. These probes are run in a similar manner to other Langmuir probes, and can be used to measure plasma number density, electron temperature, incident ion flux, floating and plasma potentials, even electron energy distribution functions, all of which are critical to understanding how the plasma interacts with the channel walls. Due to the nature of mounting the probes, it allows for a relatively non-intrusive method of interrogating a region which is otherwise inaccessible for other physical probes. The planar geometry of the probe allows for (1) a well-characterized sheath expansion and correction using Sheridan's model, which can then be used to determine a high-accuracy incident ion current density; as well as (2) the ability to detect ion beams. These features make flush-mounted Langmuir probes an excellent diagnostic for near-wall studies.


Above: Photographs of second generation flush-mounted Langmuir probes; six probes at differing azimuthal and axial locations line both the inner and outer thruster channel walls.

 

Selected Relevant Publications

  1. R. Shastry, A. Gallimore, R. Hofer, "Near-Wall Plasma Properties and EEDF Measurements of a 6-kW Hall Thruster," AIAA-2009-5356, 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Denver, Colorado, Aug. 2-5, 2009.
  2. R. Shastry, A. Gallimore, R. Hofer, "Interpretation of Wall-mounted Probe Characteristics in Hall Thrusters," AIAA-2008-4723, 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Hartford, CT, July 21-23, 2008.
  3. R. Shastry, A. D. Gallimore, and R. R. Hofer, "Erosion Characterization via Ion Power Deposition Measurements in a 6-kW Hall Thruster," 57th JANNAF Propulsion Meeting 7th Modeling and Simulation 5th Liquid Propulsion 4th Spacecraft Propulsion Joint Subcommittee Meeting, Cheyenne Mountain Resort, Colorado Springs, CO, 3-7 May, 2010.
  4. R. Shastry, A. D. Gallimore, and R. R. Hofer, "Near-Wall Plasma Characterization of a 6-kW Hall Thruster," IEPC-2009-133, 31st International Electric Propulsion Conference, University of Michigan, Ann Arbor, Michigan, USA September 20-24, 2009.
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