The rapid growth of He nanobubbles in vicinity of the axis of W nanofibers under fusion-relevant He ion irradiations

The He nanobubbles growth is one of the key factors in affecting surface microstructures of tungsten-based divertor targets. In this work, the growth of He bubbles in W nanofibers has been studied based on He diffusion and reaction rate model. Computational results show that the He bubbles tend to grow rapidly in vicinity of the axis of W nanofibers due to the diffusion and trapping of solute He atoms in W nanofibers while the nanobubbles in W bulk mainly grow in the near-surface layer. Decreasing the radius of W nanofibers and increasing He+ energy can significantly contribute to the growth of the He bubbles in vicinity of the axis of W nanofibers, which has been confirmed by our TEM measurements. The continuous growth of He bubbles in W nanofibers can not only lead to the tensile driven cracking but also the thinning of W nanofibers.