On the interactions of interstitial helium atom with helium bubble in tungsten: A molecular dynamics study

Tungsten (W) has been chosen as the primary plasma-facing material in nuclear fusion reactors. However, when helium (He) ions are continuously irradiated, enormous amounts of He atoms react with W generating He clusters and bubbles. The interactions of interstitial He atoms with He bubbles of various helium-to-vacancy ratios (RHe/V) in W were investigated using molecular dynamics simulation. Single He atoms were discovered to cause trap mutations in the periphery of He bubbles, particularly those with relatively low RHe/V. The processes of these trap mutations were analyzed, and the substitutional He atoms formed in these trap mutations were generally divided into two types: the T type and the S type. Afterward, the detrapping behaviors of the S-type He atoms were investigated using a linearly increasing temperature method, and their average lifetime was also calculated. The results suggest that these substitutional He atoms’ average lifetime depends on their neighboring W atoms and the RHe/V of He bubbles. Additionally, the average duration for a He atom colliding with He bubbles in the fusion environment was estimated using He atom distributions obtained using rate theory. At 500 K, most of the average lifetime of the S-type He atoms is longer than the colliding time for the fluxes of around 1020–1024 m−2s−1. At 1000 K, although the average lifetime decreases compared with 500 K, some S-type He atoms, especially the one trapped around the He bubble with RHe/V = 1, can be trapped longer than the colliding time. Our results demonstrate that it is likely to form satellite nanobubble around the He bubble during its continuous irradiation in W. This study provides new insights into the growth of the He bubble in W in the fusion environment.