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 C2+ 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 C2+ impurity species in the region above the divertor targets. During the transition from the attached to the detached plasma state, the C2+ radiation zone moves from close to the divertor target towards the last closed flux surface. Within this radiation zone, C2+ 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).
Highlights
In the boundary of magnetic fusion experiments, the measurement of ion temperature, Ti, is less advanced than in the plasma core and rarely attempted
C2+ ion temperature images are derived with the coherence imaging spectroscopy (CIS) system that had a direct view onto one of the ten island divertors of Wendelstein 7-X (W7-X)
Both CIS and the spectrometer cover a large part of the horizontal target and the lower part of the vertical target plates, which are made of fine graphite
Summary
In the boundary of magnetic fusion experiments, the measurement of ion temperature, Ti, is less advanced than in the plasma core and rarely attempted. It is reported that Ti > Te in the scrape-off-layer (SOL) of many devices [2], which is related to the different transport mechanisms of electrons and ions along the open magnetic field lines. Many theories and models for the plasma SOL assume Ti = Te due to the lack of knowledge about Ti, solely relying on electron temperature (Te) measurements. In particular for future, larger plasma experiments such as ITER, accurate measurements and understanding on Ti could
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
