Review of the high heat flux testing as an integrated part of W7-X divertor development

The subject of the development of the WENDELSTEIN 7-X divertor is the manufacturing of approximately 900 plasma facing components (PFCs) that meet all requirements for reliable long pulse and long-term plasma operation. The actively cooled PFCs are made of CFC NB31 as plasma facing material bonded by Active Metal Casting® (AMC) copper interlayer onto CuCrZr cooling structure. The pre-series activities integrated extensive high heat flux (HHF) testing to assess the industrial manufacturing. Tests were performed in the GLADIS facility under load conditions similar to those expected during operation of W7-X. The investigations focused on the improvement of fatigue resistance of the CFC/Cu bonding. The results of the last HHF test campaign demonstrated a significant enhancement of the CFC bonding quality due to the introduction of the AMC/Cu bi-layer technology. The results of the micro-chemical analyses (using EDX, AES, XPS and SIMS) of the CFC/Cu interface performed after 5000 cycles at 10 MW/m2 confirmed its chemical stability. Far beyond the current available data about the expected lifetime of CFC-armoured PFCs, 10,000 cycles at 10 MW/m2 were applied without any damages at the interface. The present design and manufacturing process of the tested PFCs fulfil all requirements for W7-X operation.