Surface modification and helium release of tungsten irradiated by 40 keV helium ions

The effects of grain boundaries and surface roughness on tungsten irradiated by 40 keV He ions with a flux of 1.6 × 10¹⁷ He⁺/(m²s) to a fluence of 6.6 × 10²¹ He m⁻² at room temperature were investigated. It was found that rough surfaces can suppress the surface blistering on tungsten. This may be due to the grooves appeared on rough tungsten limiting crack growth, resulting in the release of helium. However, the influence of grain boundaries on denseness of blistering was not obvious except the difference in blistering cap. The number of blister with detached cap on large grain tungsten samples (LGW, with the grain size of ∼50 μm) is more than that on small grain tungsten samples (SGW, with the grain size of ∼5 μm). In addition, the effect of grain boundaries on helium retention in tungsten cannot be ignored. The total He release from SGW was 2.56 × 10²¹ He m⁻², which was smaller than the value (4.10 × 10²¹ He m⁻²) of LGW.