Grain orientation and temperature dependences of bubbles at tungsten surfaces upon helium plasma exposure

Abstract

The impact of grain orientation and surface temperature on helium bubble growth at tungsten surfaces exposed to low-pressure helium plasmas was investigated by analyzing the nanoholes formed at the surface. Polycrystalline tungsten samples were exposed to a 2 Pa RF plasma at 400 W and 79 eV positive ion bombardment energy. Through detailed SEM imaging before and after plasma exposure and a developed image analysis protocol, we assessed quantitatively the size and density of helium bubbles that have burst on the surface upon plasma exposure. The results demonstrate a clear temperature dependence, with surface bubble density and size increasing at higher temperatures, and a dependence on grain orientation, with the (111) orientation giving slightly larger and denser surfaces of burst bubbles.