High accuracy plasma density measurement using hybrid Langmuir probe and microwave interferometer method

High spatial resolution plasma density measurements have been taken as part of an investigation into magnetic nozzle physics at the NASA/MSFC Propulsion Research Center. These measurements utilized a Langmuir triple probe scanned across the measurement chord of either of two stationary rf interferom...

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Bibliographic Details
Published in:Review of scientific instruments 2007-11, Vol.78 (11), p.113504-113504-7
Main Authors: Deline, C., Gilchrist, B. E., Dobson, C., Jones, J. E., Chavers, D. G.
Format: Article
Language:English
Subjects:
ACCURACY
COMPARATIVE EVALUATIONS
DENSITY
ELECTRIC POTENTIAL
ELECTROSTATIC PROBES
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
INTERFEROMETERS
LANGMUIR PROBE
MICROWAVE RADIATION
NASA
NOZZLES
PLASMA
PLASMA DENSITY
PROPULSION
SHAPE
SPATIAL RESOLUTION
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Summary:High spatial resolution plasma density measurements have been taken as part of an investigation into magnetic nozzle physics at the NASA/MSFC Propulsion Research Center. These measurements utilized a Langmuir triple probe scanned across the measurement chord of either of two stationary rf interferometers. By normalizing the scanned profile to the microwave interferometer line-integrated density measurement for each electrostatic probe measurement, the effect of shot-to-shot variation of the line-integrated density can be removed. In addition, by summing the voltage readings at each radial position in a transverse scan, the line density can be reconstituted, allowing the absolute density to be determined, assuming that the shape of the profile is constant from shot to shot. The spatial and temporal resolutions of this measurement technique depend on the resolutions of the scanned electrostatic probe and the interferometer. The measurement accuracy is 9%–15%, which is on the order of the accuracy of the rf interferometer. The measurement technique was compared directly with both scanning rf interferometer and standard Langmuir probe theory. The hybrid technique compares favorably with the scanning rf interferometer, and appears more accurate than probe theory alone. Additionally, our measurement technique is generally applicable even for nonaxisymmetric plasmas.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.2813885