[3N08-13] Plasma Facing Materials

[3N11] Impact of surface helium on hydrogen isotopes retention behavior in tungsten materials

*Fei Sun¹, T. Wada¹, S. Yamazaki¹, A. Koike¹, M. Zhao¹, S.E. Lee², M. Hara², Y. Oya¹ (1. Shizuoka Univ., 2. Univ. of Toyama)

Keywords:Hydrogen retention, Helium bubble, Diffusion barrier, Modelling and simulation, Fusion

Surface helium effect on hydrogen isotopes diffusion and trapping/detrapping behavior in tungsten materials was investigated by modeling and simulation approaches. Total hydrogen retention was reduced due to the existence of He bubbles on the surface, resulting from a synergetic impact on the diffusivity, solubility, reflection rate and recombination coefficient. The most significant influence was the diffusion barrier created by He bubbles, which can change hydrogen retention and the shape of TDS profile. Three desorption stages, namely surface desorption, major desorption and backside desorption, could characterize the TDS spectra with different mechanisms. In the simulation the barrier factor was introduced. It was found that when the barrier factor was higher than 0.4, the accumulation of hydrogen isotope beneath the He bubble layer was increased since hydrogen was occupied not only in trapping sites, but also in lattice sites.