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. How-ever, 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 vari-ous 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 substi-tutional 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 10 (20) -10 (24) m(-2)s(-1). At 10 0 0 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 contin-uous irradiation in W. This study provides new insights into the growth of the He bubble in W in the fusion environment. (C) 2022 Elsevier B.V. All rights reserved.