A review of surface damage/microstructures and their effects on hydrogen/helium retention in tungsten

The change in surface damage/microstructures and its effects on the hydrogen (H) isotope/helium (He) dynamic behavior are the key factors for investigating issues of tungsten (W)-based plasma-facing materials (PFMs) in fusion such as surface erosion, H/He retention and tritium (T) inventory. Complex surface damage/microstructures are introduced in W by high-temperature plasma irradiation and new material design, typically including pre-damage and multi-ion co-deposition induced structures, solute elements and related composites, native defects like dislocations and interfaces, and nanostructures. Systematic experimental and theoretical researches were performed on H isotope/He retention in complex W-based materials in the past decades. In this review, we aim to provide an overview of typical surface damage/microstructures and their effects on H/He retention in W, both in the experiment and multiscale modeling. The distribution/state, dynamics evolution, and interaction with defects/microstructures of H/He are generally summarized at different scales. Finally, the current difficulties, challenges and future directions are also discussed about H/He retention in complex W-based PFMs.