He-cooled divertor for DEMO: Status of development and HHF tests

A modular He-cooled divertor concept for DEMO has been pursued at Karlsruhe Institute of Technology (KIT) in cooperation with Efremov with the goal of reaching a DEMO-relevant heat flux of 10 MW/m2 and 1000 load cycles. The reference design is based on the use of small cooling finger modules made of tungsten and tungsten alloy and on impingement cooling with helium. For the purpose of experimental verification of the design, a combined helium loop and electron beam facility was built at Efremov. Technological studies on fabrication of tungsten divertor mock-ups were carried out. Results of the first HHF test series 2006 confirmed already the divertor performance of 10 MW/m2. After some improvements of mock-ups the results of the following second and third test series in 2007–2008 showed noticeable enhancement in performance and resistance against thermal cyclic loadings. The fourth test series was continued in early 2010 after an upgrade of the EB facility. Six surviving mock-ups from the last test series were further tested. They survived differently between 180 and 1100 cycles in total under the maximum heat load of at least 10 MW/m2 before failure. Thus the first breakthrough is reached.