Deuterium retention in tungsten used in ASDEX Upgrade: Comparison of tokamak and laboratory studies

Deuterium (D) retention in tungsten (W) materials, i.e. two types of W coatings and solid bulk W, used as outer divertor target in ASDEX Upgrade (AUG), was investigated and compared with laboratory experiments. The D concentration in the W coatings was larger than in solid bulk W because W coatings generally have higher inherent defect density, which is consistent with laboratory data. No clear blistering was found on the solid bulk polycrystalline-W, which could be due to its technically-machined surface. The amount of D retained in the solid bulk W tile of AUG showed a nearly square-root dependence on the incident fluence, suggesting that a diffusion-limited trapping process plays a dominant role for the D accumulation. The overall retention behaviour in AUG W materials was reasonably within the range of the predictions based on laboratory studies.