29th Symposium on Fusion Technology (SOFT 2016)

P2.124 Local copper coating of the connectors of the divertor target elements of Wendelstein 7-X

6 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 124

Poster F. Plasma Facing Components P2 Poster session

Speaker

Patrick Junghanns (Max-Planck-Institut für Plasmaphysik)

Description

The 890 target elements of the high heat flux divertor of Wendelstein 7-X (W7-X) are made of a CuCrZr copper alloy heat sink armored with carbon reinforced carbon (CFC) NB31 tiles. Connectors with an internal diameter of 10 mm are electron beam welded to heat sink for the water inlet and outlet. They are produced by electron beam welding thicker tubes of CuCrZr and stainless steel with a Nickel 270 transition, which are machined at the inside and outside to reach a final thickness of 1mm. The length of the Nickel transition is 5 mm. During the incoming inspection performed at IPP, some target elements did not pass the Helium leak test in oven. In addition one element developed a Helium leak after high heat flux testing. The level of leak was always very small in the range of 10^-4-4 - 10^-6-6 Pa l/s, and always located in the welding area between the steel and Ni-Adapter transition. The detailed analysis of the manufacturing process (material charges, production batches, inspection sheets of dye penetration and x-ray) and additional examinations (non-destructive such as x-ray, metallography) did not allow understanding the reason for the initiation of these leaks. Different options were examined, and the selected solution was the electrolytic copper coating of the transition area of the connectors. The development activities of this coating are presented. The selected copper grade CW0009A is compatible with the W7-X divertor operation. The nominal thickness and the length are 0.3 and 20 mm. After bending loads up to 2000 cycles reproducing expected operation conditions of the connectors, the metallography analyses of test pieces demonstrated a good adhesion of the coating to the connector. Based on these results, it was decided to coat the connectors of the already delivered target elements.