He-cooled Divertor for DEMO Status of Design and HHF Tests

A modular He-cooled divertor concept for DEMO has been developed at Forschungszentrum Karlsruhe in cooperation with the Efremov Institute. The work covers the areas of design, analyses, fabrication technology, and experimental design verification. The overall design goal is to reach a heat flux of 10 MW/m² at least. The selected reference design HEMJ (He-cooled modular divertor with multiple-jet cooling) employs small tiles made of tungsten, which are brazed to a finger-like thimble structure, which is made of tungsten alloy. The finger module is cooled by multiple jets of helium (10 MPa, 634degC) directly impinging onto the inner heated surface of the thimble. For the experimental verification of the design, a combined facility at Efremov, comprising a helium loop and an electron beam facility, was used. Technological studies focussed on the fabrication of tungsten divertor mock-ups, combined with an Eurofer steel structure. The first series of 1-finger mock-ups manufactured in this way were successfully HHF-tested in 2006. The test results confirmed the feasibility and the required performance of the design. The 2007 test series use mock-ups which have been improved in terms of thermal stress reduction and increasing manufacturing quality of tungsten parts (tile and thimble) and show a tendency of lifetime enhancement, i.e. surviving larger thermal cycles.