Molecular dynamics simulation of bubble growth under surface of tungsten under helium irradiation

Understanding the fuzz growth mechanism on tungsten (W) surface under the helium (He) particles irradiation is an important guide for structural design of the first wall materials. In this work, molecular dynamics simulation was used to explore the process of He bubble formation, growth and rupture under irradiation to understand the initial stage of fuzz nanostructure formation. It was found that He clusters had the most movable ability at the surface temperature around 800∼1800 K and thus big bubbles were favorable to be aggregated. We simulated the growth, rupture and merging of He bubbles to reproduce the process of protrusion's formation on the surface which induced the formation of fuzz nanostructure. It was found that the shallow bubble burst led to the pinhole in surface layer. The dislocation slip in the growth process of deep bubbles was the main factor for the configurations of protrusion on surface. It mainly pushes the W above He bubble along the <111> directions, while the different surfaces have different relation with the <111> directions. Thus, the different morphology of protrusion induced by the bubble appeared on different surfaces as observed in experiments.