Segregation and coalescence behavior of helium bubbles in tungsten

We used molecular dynamics to study the segregation and coalescence of helium bubbles in tungsten. We found that, similar to the case of tungsten surface, small mobile helium clusters can segregate and be trapped by helium bubbles. However, the trapping behavior is different for different temperatures. At 700 K, the movement of mobile helium clusters placed near a bubble has a high probability to be confined in the periphery of the bubble, without merging with the bubble. At 1500 K, the mobile He clusters have a high probability to merge with the bubble, forming a single larger bubble. For two immobile helium clusters, it is usually difficult for them to coalesce. In some cases, a single layer of tungsten atoms, or even a single tungsten atom, can prevent two clusters from merging.