Experimental evidence for melt layer convection during disruption simulation experiments

The simulation of disruptions in tokamak devices by electron beams has become a frequently used technique. Some of the physical phenomena which occur in these experiments have been studied on specimens of stainless steel AISI 316L by optical microscopy, scanning electron microscopy (SEM) and electron microprobe analysis (EMPA).The distribution of helium bubbles, volatile alloying elements and the coating material after disruptions, indicate that substantial convection takes place in the melt layer formed during the heat discharge. This convection likely originates from the momentum transfer from the electron beam to the liquid. For high energy densities the formation and percolation of metal vapour bubbles may also contribute to the process. The convection changes the heat transfer mechanism in the melt, and therefore influences melt depth and evaporation.