Stability and erosion of melt layers

Melting of metallic plasma facing components such as tungsten (W) divertor, macroscopic melt motion, and melt splashing due to edge localized modes and plasma disruptions is a major concern in fusion devices such as ITER. The viscous stability analysis and computational modelling of coupled W-melt-plasma flows are performed using the developed volume-of-fluid magnetohydrodynamic code. The effects of plasma velocity and magnetic field, whether parallel or perpendicular to the direction of W-melt flow, on melt motion and splashing from a melt pool are studied. The distributions of hydrodynamic and magnetic pressure as well as the vector fields of velocity and magnetic field are investigated. The development of waves with certain wavelengths on the W-melt surface and formation of W-melt blob on the pool’s edge are observed in the absence and presence of an external magnetic field. For the investigated speeds of viscous plasma, the parallel magnetic field of 5 T does not suppress W-melt motion and splashing from the pool, plasma-induced surface waves, and ejection of molten droplets. However, the Lorentz force induced by a perpendicular magnetic field accelerates the splashing of W-melt from a melt pool but only when the stream of viscous plasma becomes well coupled to the melt motion. Under the plasma impact with high velocity of ∼5000 m s−1, the W-melt does not undergo a significant motion disintegrating quickly into droplets dragged away by the plasma wind, independent of the presence or absence of a magnetic field. This magnitude of plasma velocity is found to be in good agreement with that predicted by the viscous stability analysis.