Distributions of deposits and hydrogen on the upper and lower TDUs3 target elements of Wendelstein 7-X

Abstract

Distributions of deposits and hydrogen (H) on the graphite divertor target elements TM4h4 and TM3v5 in the test divertor units 3 (TDUs3) of Wendelstein 7-X (W7-X) are studied. The TM4h4 and TM3v5 are located at the magnetically symmetric positions in the upper and lower divertor. The microstructure of the deposition layer is characterized by a transmission electron microscope (TEM) combined with a focused ion beam (FIB). Metallic deposits such as iron (Fe), molybdenum (Mo), chromium (Cr) are detected in the deposition layer by energy-dispersive X-ray spectroscopy (EDS). The depth-resolved distribution patterns of boron (B) and metallic deposits on upper and lower horizontal (h) divertor target elements TM4h4 as well as upper and lower vertical (v) divertor target elements TM3v5 are clarified by glow discharge optical emission spectrometry (GDOES). Results for both TM4h4 and TM3v5 show that the B deposition regions exhibit higher H retention due to the co-deposition with deposits. On the other hand, up-down asymmetries in B deposition caused by particle drift exist on both TM4h4 and TM3v5. The B deposition amount on upper TM4h4 is 40% smaller than that on lower TM4h4. While for the vertical target elements, the B deposition amount on upper TM3v5 is 35% larger than that on lower TM3v5. Meanwhile, a shift of around 3 cm in B deposition peaks is observed on upper and lower TM4h4 and TM3v5. Results of numerical simulation of carbon deposition/erosion profiles on the target elements using ERO2.0 code and power flux measured by infrared cameras are shown and compared with the above mentioned B profiles.

Carbon erosion/deposition on the divertor of W7-X during the operational period OP 1.2b

“…Marker layers for erosion/deposition measurements were only available in target modules TM1v and TM2v. Some data about material deposition in target module TM3v can be found in [42].…”