The Langmuir probe system in the Wendelstein 7-X test divertor

The design and evaluation of the Langmuir probe system used in the first divertor operation phase of Wendelstein 7-X is described. The probes are integrated into the target plates and have individually facetted surfaces to keep the angle of incidence of the magnetic field within an appropriate range...

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Bibliographic Details
Published in:Review of scientific instruments 2020-06, Vol.91 (6), p.063505-063505
Main Authors: Rudischhauser, L., Endler, M., Höfel, U., Hammond, K. C., Kallmeyer, J. P., Blackwell, B. D.
Format: Article
Language:English
Subjects:
Bayesian inference
Current voltage characteristics
I-V characteristics
Incidence angle
Magnetic fields
Mathematical models
OTHER INSTRUMENTATION
Parameter uncertainty
Parametric inference
Plasma diagnostics
Plasma material interactions
Plasma properties and parameters
Scientific apparatus & instruments
Stellarators
Tokamaks
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Summary:The design and evaluation of the Langmuir probe system used in the first divertor operation phase of Wendelstein 7-X is described. The probes are integrated into the target plates and have individually facetted surfaces to keep the angle of incidence of the magnetic field within an appropriate range for different magnetic configurations. Multiple models for the derivation of plasma parameters from current–voltage characteristics are introduced. These are analyzed with regard to their assumptions and limitations, generalized, and adapted to our use case. A detailed comparison is made to determine the most suitable model. It is found that the choice of model has a large impact, for example, resulting in a change in the inferred temperatures of up to a factor two. This evaluation is implemented in a Bayesian modeling framework and automated to allow for joint analysis with other diagnostics and a replacement of ad hoc assumptions. We rigorously treat parameter uncertainties, revealing strong correlations between them. General and flexible model formulations permit an expansion to additional effects.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.5143013