High-n Rydberg transition spectroscopy for heavy impurity transport studies in W7-X (invited)

Here, we present a novel spectroscopy approach to investigate impurity transport by analyzing line-radiation following high-n Rydberg transitions. While high-n Rydberg states of impurity ions are unlikely to be populated via impact excitation, they can be accessed by charge exchange (CX) reactions a...

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Bibliographic Details
Published in:Review of scientific instruments 2024-09, Vol.95 (9)
Main Authors: Swee, Colin, Geiger, Benedikt, Ford, Oliver, O’Mullane, Martin, Poloskei, Peter, Reimold, Felix, Romba, Thilo, Wegner, Thomas
Format: Article
Language:English
Subjects:
Charge exchange
Confidence intervals
Constraints
Emission analysis
Error analysis
High temperature plasmas
Impurities
Ion beams
Modelling
Neutral beams
Radiation
Rydberg states
Spectroscopic analysis
Spectrum analysis
Transport properties
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Summary:Here, we present a novel spectroscopy approach to investigate impurity transport by analyzing line-radiation following high-n Rydberg transitions. While high-n Rydberg states of impurity ions are unlikely to be populated via impact excitation, they can be accessed by charge exchange (CX) reactions along the neutral beams in high-temperature plasmas. Hence, localized radiation of highly ionized impurities, free of passive contributions, can be observed at multiple wavelengths in the visible range. For the analysis and modeling of the observed Rydberg transitions, a technique for calculating effective emission coefficients is presented that can well reproduce the energy dependence seen in datasets available on the OPEN-ADAS database. By using the rate coefficients and comparing modeling results with the new high-n Rydberg CX measurements, impurity transport coefficients are determined with well-documented 2σ confidence intervals for the first time. This demonstrates that high-n Rydberg spectroscopy provides important constraints on the determination of impurity transport coefficients. By additionally considering Bolometer measurements, which provide constraints on the overall impurity emissivity and, therefore, impurity densities, error bars can be reduced even further.
ISSN:0034-6748
1089-7623
1089-7623
DOI:10.1063/5.0219589