Surface morphology of tungsten exposed to helium plasma at temperatures below fuzz formation threshold 1073 K

Impact of crystal orientation on the surface morphology of the helium plasma exposed tungsten has been investigated on the linear device PSI-2. A nanoscale undulating surface structure having a periodic arrangement is formed for temperatures below 1073 K, in contrast to the fuzz nanostructure formation in a higher temperature range. The crests of undulation align with the $\langle 1\,0\,0\rangle $ direction. The interval of the undulation is narrowest at the crystal grain of {1 1 0} surface. The interval becomes wider as the crystal grain surface tilts away from the {1 1 0} surface, and the undulating surface structure is not formed near the {1 0 0} surface. The height of undulations is $\sim 8$ nm, independently of the interval of the undulations, and it corresponds to the depth of the layer heavily damaged due to helium plasma exposure