2D coherence imaging measurements of C2+ ion temperatures in the divertor of Wendelstein 7-X. (8th October 2021)

• Record Type: Journal Article
• Authors: Gradic, D.; Perseo, V.; Kriete, D.M.; Krychowiak, M.; König, R.; Feng, Y.; Otte, M.; Pedersen, T. Sunn; Gao, Y.; Jakubowski, M.; Schlisio, G.; Warmer, F.; W7-X Team, the
• Is Part Of: Nuclear fusion. Volume 61:Number 10(2021)
• Publication Date: 2021-10-08
• Subjects: coherence imaging spectroscopy -- SOL ion temperature -- Wendelstein 7-X -- Doppler line broadening -- Zeeman effect; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ac25bf
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: For the first time, 2D ion temperature values are derived from coherence imaging spectroscopy (CIS) fringe contrast measurements by taking Zeeman line broadening effects into account during the analysis procedure of a spatial-heterodyne CIS instrument. This allowed 2D images of C 2+ ion temperatures ( T i ) across the 3D-shaped island divertor of the Wendelstein 7-X stellarator. Ion temperatures ranging from 10 to 20 eV are observed for the C 2+ impurity species in the region above the divertor targets. During the transition from the attached to the detached plasma state, the C 2+ radiation zone moves from close to the divertor target towards the last closed flux surface. Within this radiation zone, C 2+ temperature does not decrease significantly. Experimentally, the coherence imaging measurements were cross-calibrated at one poloidal cross-section using a high resolution Echelle spectrometer, that shared its sightlines with the coherence imaging diagnostic. The spectra demonstrated that, apart from Doppler broadening, the Zeeman effect significantly contributes to the spectral line broadening and cannot be neglected when analyzing the CIS contrast data for T i extraction in the edge and scrape-off-layer of Wendelstein 7-X (W7-X), due to the relatively low temperatures ( T i < 100 eV) and high magnetic fields ( B ≈ 2.5 T).