Repair processes of Wendelstein 7-X target modules

The highly loaded surface of the actively water-cooled divertor of Wendelstein 7-X (W7-X) is made of 100 individual target modules. In each target module, a set of target elements is water-cooled in parallel and fed by manifolds. A target element is made of a CuCr1Zr copper alloy heat sink, armored with CFC NB31 tiles. He leak testing under pressure in a vacuum oven was performed for each individual target element and module. One series target element of type 5S did not pass this test after high heat flux testing. The leakage was the result of the combination of a porosity concentration due to the overlap of CFC-CuCr1Zr welds in the centre part along the element and the reduced CuCr1Zr thickness at this location due to machined cut-out in the cooling channel. The repair process, which was successfully applied to all 307 target elements of type 5S, was sealing the slit between two CFC tiles by electron beam welding. Two target modules of type 7H did not pass the integral leak test. Leaks were localized by sniffing the weld seam between the target element connectors and manifold pipes. The one leak of the first module was successfully repaired by hand-welding. The positions of the two leaks in the other module did not allow such a repair process. Drilling apertures through the neighbouring manifolds allowed a direct access to the leaking seams from inside. The openings allowed a stable and precise installation of an inside orbital welding anode. The repaired target module successfully passed the He leak test in oven after HHF testing.