Erosion Dynamics Of Tungsten Fuzz During Elm-Like Heat Loading

Transient heat loading and high-flux particle loading on plasma facing components in fusion reactors can lead to surface melting and possible erosion. Helium-induced fuzz formation is expected to exacerbate thermal excursions, due to a significant drop in thermal conductivity. The effect of heating in edge-localized modes (ELMs) on the degradation and erosion of a tungsten (W) fuzz surface was examined experimentally in the Ultra High Flux Irradiation-II facility at the Center for Materials Under Extreme Environment. W foils were first exposed to low-energy He+ ion irradiation at a fluence of 2.6 X 10(24) ions m(-2) and a steady-state temperature of 1223 K. Then, samples were exposed to 1000 pulses of ELM-like heat loading, at power densities between 0.38 and 1.51GWm(-2) and at a steady-state temperature of 1223 K. Comprehensive erosion analysis measured clear material loss of the fuzz nanostructure above 0.76GWm(-2) due to melting and splashing of the exposed surface. Imaging of the surface via scanning electron microscopy revealed that sufficient heating at 0.76GWm(-2) and above caused fibers to form tendrils to conglomerate and form droplets. Repetitive thermal loading on molten surfaces then led to eventual splashing. In situ erosion measurements taken using a witness plate and a quartz crystal microbalance showed an exponential increase in mass loss with energy density. Compositional analysis of the witness plates revealed an increase in the W 4f signal with increasing energy density above 0.76GWm(-2). The reduced thermal stability of the fuzz nanostructure puts current erosion predictions into question and strengthens the importance of mitigation techniques. Published by AIP Publishing.