Hydrogen retention in ITER relevant mixed material layers

D retention in mixed layers of ITER first wall materials, i.e. Be2C (prepared by annealing C film on Be substrate sample at 773 K), Be12W (by annealing W film on Be substrate at 1073 K) and tungsten carbide (by annealing W film on graphite substrate annealed at 1373 K) was investigated under controlled laboratory conditions. D retention in Be2C and Be12W layers was similar to that of Be rather than that of graphite or W respectively, while D retention in tungsten carbide layers was similar to that of polycrystalline W rather than that of graphite. The fluence dependence of the retained D fraction in each mixed layer showed no clear saturation in the experimentally accessible implantation fluence range (<4.0 x 1023 D/m2), and increased with incident fluence as ∼Φ0.2 in Be2C, Be12W and ∼φ0.5 in tungsten carbide.