Investigation of European tungsten materials exposed to high heat flux H/He neutral beams

Tungsten is being considered as a potential plasma-facing material for future fusion devices, primarily due to its low erosion rate and high heat resistance. The intrinsic problem of this material, the brittleness even at elevated temperatures, requires the development and assessment of new tungsten materials. In the frame of the European material development programme for future fusion power plants W containing 5 wt.% Ta as well as uniaxially forged ultra-high purity W and powder injection moulded W were assessed in a neutral beam high heat flux test facility at IPP Garching. The investigation of the morphology modification of tungsten, occurring during heat loading using H and He particles, which simulates the expected divertor operation conditions, is indispensable in order to develop reliable plasma-facing materials. The effects seen, erosion, gas retention and cavity formation, depend on both the loading conditions and the operating temperature. This contribution presents a comparative study of the surface morphology changes of different W materials under hydrogen and helium beam loading to surface temperatures between 1500 °C (1773 K) and 2000 °C (2273 K), using actively cooled mock-ups. Loading is performed with pure H and mixed 94% H/6% He beams (ϕ = 4 × 1021 m−2 s−1), resulting in 10 MW m−2 thermal load. Pulse durations of 30 s are applied to achieve fluences up to 3 × 1025 m−2 under stationary temperature conditions