Effects of plasma flow velocity on melt-layer splashing and erosion

It is recognized both experimentally and computationally that the main damage of divertor in fusion devices such as ITER could be due to melting of metallic plasma facing components such as tungsten developed during plasma instabilities. Macroscopic melt motion and splashing with ejection of molten droplets into plasma are major concern. The computational modelling of uncoupled/coupled plasma–melt flows is carried out using the developed VoF-MHD model. The goal of this research is to study the effect of viscous plasma flowing with a velocity of 0–5 km s−1 on the melt stability. Development of running waves with large wavelengths is observed on the melt surface in the absence of plasma impact. The magnetic field of 5 T that is parallel to the direction of melt motion completely damps these surface waves. When the magnetic field is perpendicular to the direction of melt motion, the small-amplitude standing waves are formed. The viscous plasma streaming with ∼0.1–5 km s−1 over the melt surface develops waves that are not damped by the magnetic field which is either parallel or normal to the direction of melt motion. It is observed that the surface waves are generated much faster at higher plasma speeds and their wavelength decreases accordingly. The high-speed viscous plasma flowing with ∼5 km s−1 produces small melt ripples that break up into droplets carried away by the plasma wind. This is a major concern for magnetic fusion as a reliable source of energy production.