Surface modification of molten W exposed to high heat flux helium neutral beams

High heat flux tests with central heat flux of 10.5MW/m2 using helium neutral beams have been carried out on rolled tungsten. The energy of helium particles is 33keV and the particle flux is 2×1021m−2s−1. An 80×65×3mm3 rolled tungsten plate is firstly exposed to a 4.6s pulse resulting in partially molten surfaces. Thereafter the tungsten plate is irradiated by several helium pulses with fluences of 1.2–2.5×1022/m2 and peak temperatures from 1450 to 2590°C. The experiments show that: (1) helium-induced surface modification of the resolidified tungsten surface is very different from that of the non-molten surface; (2) the surface morphology of molten surface is closely related to the orientation of the resolidified grain; (3) the evolution of surface modifications, for both of the molten and non-molten tungsten surfaces, indicates a strong dependence on the surface temperature and local helium fluence.