Interaction between hydrogen and helium in tungsten successively exposed by helium and hydrogen plasma

The modification of surface, distribution of helium bubbles and the behavior of helium release are reported through a careful investigation on tungsten samples which were exposed to helium plasma and subsequent hydrogen plasma. For the tungsten samples exposed to helium plasma with a fluence of 3.8×1024 He/m2, no obvious change can be seen on the tungsten surface. Then the samples were exposed to subsequent hydrogen plasma for 1 h. Hydrogen blistering was significantly suppressed on the tungsten surface compared to a reference sample which was only irradiated by hydrogen plasma. However, as the exposure time of hydrogen plasma increased to about 16 h, a large number of hydrogen blisters appeared on the surface of tungsten pre-irradiated by helium plasma. Moreover, there was no significant difference in hydrogen blistering between the helium pre-exposure samples and the reference sample. The results indicate that most of the hydrogen atoms can diffuse into tungsten through the nano-helium bubble layer after 16 h of hydrogen plasma exposure. The results of transmission electron microscope show that the size of bubbles was increased with the increase of hydrogen exposure time. In contrast, the helium release peaks obtained through thermal desorption spectra are reduced with the increase of hydrogen exposure time.