Results of the examinations of the W7-X pre-series target elements

The target elements of the WENDELSTEIN 7-X (W7-X) divertor are designed to sustain a stationary heat flux of 10 MW/m2 and to remove a maximum power of 100 kW. CFC Sepcarb® NB31 tiles are bonded to a water-cooled CuCrZr heat sink in two steps: active metal casting (AMC®) of an AMC®-copper interlayer to CFC tiles, electron beam welding (EBW) or hot isostatic pressing (HIP) of the AMC®-NB31 tiles to CuCrZr. The fabrication of the whole amount of CFC NB31 has been completed. The key target of the pre-series phase is the qualification of this bond based on a series of examinations. The introduction of silicon during the AMC® process significantly improved the strength of the joint between CFC and AMC®-copper. The strength of the bond is preserved after either EBW or HIP processes. High heat flux testing carried out in the ion beam facility GLADIS exhibited a too high percentage of defective tiles. Pre-series activities have been extended to reduce the stress concentration at the interface between tiles and heat sink by optimizing the design.