Melting and solidification of a metal surface subjected to a rapid high heat load

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A first wall of a thermonuclear fusion reactor is exposed to a high heat load in case of a plasma disruption ; then melting, evaporation and resolidification of the first wall surface are anticipated. This would cause a serious problem for estimation of the first wall life. The present study aims to investigate experimentally and numerically the melting behavior of a metal surface subjected to a rapid high heat load. Especially, a numerical method was developed to simulate the melting and the resultant thermocapillary flow. In a simulation experiment, a thin film of a low-melting-point metal was exposed to one-sided heating of an infrared lump. The melting and thermocapillary flow were observed, and the movement of the melt layer resulted in a wavy resolidified surface.Intensive heating experiments were performed by one of the present investigators using the hydrogen ion beam at Japan Atomic Research Institute. Two distinguished features were observed on the metal surface after the resolidification. One was the smooth surface with a surrounding ring hedge and the other was a rough surface with distributed wavy bumps.In the numerical analysis, thermocapillary flow of the melt layer was calculated with the surface deformation taken into consideration. The calculation was made using the boundary fit coordinate method. The deflection of the free surface was calculated successfully for various head inputs and depth-width ratios.The results indicated that the surface deformation was more prominent for the smaller depth-width ratio and the larger heat input. The effect of the sign of the surface tension temperature coefficient was investigated and found to have a considerable influence on the surface deformation.To perform an efficient numerical calculation, the parallel computation using a transputer array was attempted. The efficiency of the parallelism was examined and an high efficiency was attained by optimizing the communication order.