Assessment of the high heat flux performance of European DEMO divertor mock-ups

In the framework of the DEMO divertor project an extensive R&D programme has been carried out to develop advanced design concepts for hot water cooled divertor targets. These plasma-facing components are made of W monoblocks as plasma facing material bonded on CuCrZr cooling tubes. They are designed to allow a reliable DEMO operation of 2 h long pulses up to a 20 MW m(-2) maximum heat flux. Considering the current experiences of the qualification of ITER divertor components, the operation at significantly higher neutron fluence, the longer required lifetime, and the coolant temperature of 150 degrees C are challenges for design and manufacturing. The aim of the performed HHF tests is to support the identification of the most promising design concepts for further development. Eight different types of monoblock mock-ups were designed and manufactured by the involved research groups. These mock-ups were assessed by HHF examination in the test facility GLADIS at IPP Garching. The HHF tests were focused on 20 MW m(-2) loading with 500-1000 cycles using hot water cooling to simulate slow thermal transients in DEMO. In screening tests heat fluxes up to 32 MW m(-2) were applied to study the performance of the components against single thermal events exceeding the expected heat flux limits. This paper gives an overview of the main results obtained from the HHF tests of about 45 components. The microscopic examination after loading analyses recrystallization effects and investigates the W/Cu interfaces in more detail.