TEM observation of the growth process of helium nanobubbles on tungsten: Nanostructure formation mechanism

In future fusion devices, helium irradiation to tungsten could lead to the formation of tungsten nanostructure, which has both pros and cons as a plasma facing component. Although the nanostructure may have considerable influences in fusion devices, there still exist open questions with regards to the formation mechanism and its characteristics. Here we show from a detailed TEM investigation the roles of helium nanobubbles on the formation of the nanostructured tungsten. The result also indicates that the growth of helium bubbles beneath the nanostructured layer could lead to the formation of tungsten dusts, which might have fatal influence to the tokamak operation, when the surface temperature is significantly high, say higher than 1800 K.