Effects of microstructure on deuterium retention in tungsten under high-flux plasma in Magnum-PSI

During tokamak operation, plasma-facing materials in the divertor are exposed to high-flux hydrogen isotope (HI) plasma, with fluxes reaching up to ∼1024 m-2 s-1. The microstructure of tungsten (W), particularly the grain elongation direction, can significantly influence HI retention. However, under such high-flux plasma conditions, the effects of grain boundary orientation relative to the surface on HI retention have rarely been investigated. To address this issue, rolled W and ITER-like W were exposed to high-flux deuterium (D) plasma at 500+-10 K in this work, with fluxes of ∼1024 m-2 s-1 and fluences up to ∼1028 m-2. The results showed that surface blistering and subsurface crack depths increased with increasing fluence in both materials, with deeper cracks observed in ITER-like W. Thermal desorption spectroscopy (TDS) measurements revealed that D retention increased markedly with increasing fluence in both materials, with ITER-like W exhibiting higher D retention and a stronger increase. Simulations of TDS indicated that plasma-induced defect concentration increased rapidly with increasing fluence in both materials, particularly in ITER-like W. In addition, the maximum D trapping depth was greater in ITER-like W, suggesting that grain boundaries oriented perpendicular to the surface may act as fast diffusion pathways and facilitate deeper D diffusion. This is consistent with the deeper subsurface cracks observed in ITER-like W by FIB. Therefore, the higher D retention in ITER-like W is attributed to the combined effects of more plasma-induced defect concentration and accelerated D diffusion along grain boundaries perpendicular to the surface. This work provides valuable insights for understanding the effects of grain elongation direction on HI retention in W under high-flux, high-fluence plasma conditions in future fusion devices.