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Influence of Beam Diameter on Molten Depths in Tungsten During Simulated Plasma Disruptions

George Tsotridis

Fusion Science and Technology

Volume 32 / Number 1 / August 1997 / Pages 35-44


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Plasma-facing components in tokamak-type fusion reactors are subjected to intense heat loads during plasma disruptions, which causes melting and evaporation of the surface layer. The influence of the beam cross section of the incident energy on the depths of heat-affected zones on pure tungsten metal has been studied by using a two-dimensional transient computer model that solves the equations of motion and energy. Results are presented for relatively long disruption times for different beam cross sections and for a range of energy densities. It is demonstrated that there exists a critical value of cross-section area beyond which any further increase has no appreciable influence on the resulting depths of molten layers. It is also demonstrated that as the cross section increases, the convective flows caused by surface tension gradients resulting from variations of surface impurities are confined at regions close to the periphery of the molten zone, whereas at the center of the molten pool, heat is transported in the molten metal by conduction. It is demonstrated that by increasing the beam cross-section area, the resulting depths of molten layers increase. However, there exists a critical value of cross section beyond which the resulting molten layer depths are invariant to the beam cross section. It is further appreciated that there are other important phenomena taking part during plasma disruptions, such as electromagnetic forces, but at this stage, such influences on the molten layers will not be studied. Nevertheless, the influence of the beam cross-sectional area would be of similar importance.

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