Numerical Simulation of Melt Metal Layer Movement under Conditions Relevant to ITER Transient Regimes

Armor materials of the ITER divertor and the first wall will be subjected to intense plasma-thermal impact during reactor operation. One of the prevalent types of metal protective coating erosion is due to displacement of the molten surface layer. In order to obtain solid interpretations of physical processes, development and verification of numerical models are required. The aim of this paper is to outline initial development of the numerical model, which describes the motion of a metal molten layer under the impact of an intense plasma stream. Numerical calculations are based on experimental data obtained at the quasi-stationary high current plasma accelerator QSPA-T. The motion of the molten metal is described by a system of coupled heat transfer and Navier–Stokes equations. In the case of consideration of an external magnetic field, Maxwell’s equations are included in the system. It is assumed that a metal target is exposed to a pulsed plasma stream with specified temporal and spatial distributions of power and pressure. Plasma exposure causes melting and subsequent motion of the surface layer of the material. Thermophysical properties of the metal are considered temperature dependent. Material evaporation from the exposed surface is taken into account in the model. The metal layer displacement was obtained for various values of the plasma stream incident to the surface. It is shown that the melt motion observed in the experiment cannot be explained by the action of the plasma pressure stream gradient alone. The friction force between the near-surface plasma and the molten metal was implemented in the numerical model, whereby a quantitative agreement between the calculation results and experimental data was achieved. In addition, magnetic field conditions were applied in the model. The influence of both the stagnation pressure and power dynamics on the resulting profile of the target surface was studied.