Background: In fusion reactors

W suffers from the displacement damage caused by high energy neutrons

and surface damage

such as blistering

erosion

and sputtering caused by low-energy (tens of eV to several keV) and high-flux (1020?1024 m?2?s?1) helium and hydrogen ions. Purpose: The understanding of the behavior of W materials in fusion environment is a major issue of the material-related stake of fusion reactors. Methods: W samples were irradiated with low-energy (100 eV) and high-flux (6×1020 ions?m?2?s?1) He+ at a sample temperature changing from room temperature to 800 °C to a fluence of 1×1025 ions?m?2. Microscopic evolution of these samples was carried out using scanning electron microscopy (SEM)

transmission electron microscopy (TEM)

conductive atomic force microscopy (CAFM) and X-ray diffraction (XRD). Results: Analysis indicates that the nanometer-sized fibre-form structure is formed in the surface of W. The spacing and the covering degree of the nanostructure increase with the irradiation temperature. Nanostructure layer may cause the damage of W surface

resulting in surface delocalized

but does not cause a change in the crystal phase of tungsten. Conclusion: Non-destructive conductive atomic force microscopy gives the direct evidence that the forming of the nanometer-sized fibre-form structure is related to the nano-sized He bubbles. This is important for understanding the microstructure formation process of tungsten material. Abstract