Molten layer characteristics of W materials and film coated W by pulsed laser irradiation

Molten layer characteristics were investigated for four W materials; pure W, W-10wt%Re, W-2wt%Ta and W with Al coating. Specimens were irradiated by a Nd:YAG laser (wavelength 1064 nm) simulating transient heat loads such as ELMs and disruption. The power density of the heat loads were varied in the 2.3-6.6 GW/m2 range. Surface profiles were observed with a laser microscope. The central part of irradiated W-2wt%Ta became dented deeply in a wider range with increasing the power density in comparison with pure W and W-10wt%Re. This could be attributed to the release of Ta droplets by bumping (rapid boiling), closely related to microstructure and/or impurity concentration determined by the materials production processes. We also observed surface morphology changes of pure W with and without Al coating after irradiation in order to investigate the effect of the protective coatings. Melting of W with Al coating seems to be suppressed by a protective effect of Al film when compared with pure W.