LIFETIME EVALUATION OF PLASMA-FACING MATERIALS DURING A TOKAMAK DISRUPTION

Erosion losses of plasma-facing materials in a tokamak reactor during major disruptions, giant ELMs, and large power excursions are serious concerns that influence component survivability and overall lifetime. Two different mechanisms lead to material erosion during these events: surface vaporization and loss of the melt layer. Hydrodynamics and ra diation transport in the rapidly developed vapor-cloud region above th e exposed area are found to control and determine the net erosion thic kness from surface vaporization. A comprehensive self-consistent kinet ic model has been developed in which the time-dependent optical proper ties and the radiation field of the vapor cloud are calculated in orde r to correctly estimate the radiation flux at the divertor surface. Th e developed melt layer of metallic divertor materials will, however, b e free to move and can be eroded away due to various forces. Physical mechanisms that affect surface vaporization and cause melt layer erosi on are integrated in a comprehensive model. It is found that for metal lic components such as beryllium and tungsten, lifetime due to these a bnormal events will be controlled and dominated by the evolution and h ydrodynamics of the melt layer during the disruption. The dependence o f divertor plate lifetime on various aspects of plasma/material intera ction physics is discussed.