High-flux He⁺ irradiation effects on surface damages of tungsten under ITER relevant conditions

A large-power inductively coupled plasma source was designed to perform the continuous helium ions (He⁺) irradiations of polycrystalline tungsten (W) under International Thermonuclear Experimental Reactor (ITER) relevant conditions. He⁺ irradiations were performed at He⁺ fluxes of 2.3 × 10²¹–1.6 × 10²²/m² s and He⁺ energies of 12–220 eV. Surface damages and microstructures of irradiated W were observed by scanning electron microscopy. This study showed the growth of nano-fuzzes with their lengths of 1.3–2.0 μm at He⁺ energies of >70 eV or He⁺ fluxes of >1.3 × 10²²/m² s. Nanometer-sized defects or columnar microstructures were formed in W surface layer due to low-energy He⁺ irradiations at an elevated temperature (>1300 K). The diffusion and coalescence of He atoms in W surface layers led to the growth and structures of nano-fuzzes. This study indicated that a reduction of He⁺ energy below 12–30 eV may greatly decrease the surface damage of tungsten diverter in the fusion reactor.