Systematic investigation of the formation behavior of helium bubbles in tungsten

The formation of He bubbles in tungsten under exposure to a He plasma was systematically investigated using low energy (∼50eV) He+ ions with a wide fluence range (∼1023 to 1026m−2) in the linear divertor plasma simulator PISCES-A at several temperatures (523–973K). TEM observations after thinning exposed W samples with FIB revealed that the layer thickness (>30nm) of He bubbles largely exceeds the ion implantation range of a few nm. The size of He bubbles was found to increase with an increase in the sample temperature: it was around 10nm at 973K, while only small He bubbles of 1–2nm were observed at