Boiling induced macroscopic erosion of plasma facing components in fusion devices

During plasma instabilities in tokamak devices, metallic plasma facing components (PFC) can undergo surface melting and vaporization. Macroscopic losses of melt layers developed during these instabilities are of a serious concern to the lifetime of PFC, the damage of nearby components, and potential core plasma contamination. Due to the presence of impurities and dissolved gas, boiling occurs in the superheated melt layer. The growing bubbles burst at the melt layer surface and induce the ejection of jet-droplets, therefore, contributing significantly to the erosion of PFC. In the present work, the boiling mechanism is investigated using a one-dimensional moving boundary model accounting for heating, melting, vaporization, and re-solidification. The collapse of a single bubble cavity and the jet formation, investigated numerically using computational fluid dynamics simulations, shows the amount of ejected jet-droplet is about ∼1% of the initial bubble volume for liquid tungsten and aluminum. The intensity of boiling decreases with the pressure in the melt layer and increases with the incident heat flux. Simulations and experiments show similar results on the boiling characteristics of tungsten and aluminum. The simple and realistic model of the boiling induced erosion, presented here, allows better understanding of the mechanisms threatening the lifetime of the metallic PFC.