W-1% La2O3 submitted to a single laser pulse: Effect of particles on heat transfer and surface morphology

Abstract

W-1% La2O3 has been irradiated by a single laser pulse (λ = 1064 nm, pulse duration τ ≈ 15 ns, pulse energy Ep ≈ 4 J, spot size Φ = 200 µm, surface power density I = 8.5 × 1011 W·cm−2) to simulate the effects of transient thermal loads of high energy occurring in a tokamak under operative conditions. The samples have been then examined by scanning electron microscope (SEM) observations to investigate erosion effects and surface morphological features. A surface depression forms in the spot central area surrounded by a ridge due to the movement of molten metal. Owing to the burst of gas bubbles, hemispherical cavities of about 10 µm and deposited droplets are observed in the ridge while the zones surrounding the ridge thermal stresses arising from fast heating and successive cooling produce an extended network of micro-cracks that often follow grain boundaries. The results are discussed and compared to those obtained in a previous work on pure bulk W.