Conceptual design of an evaporation-cooled liquid metal divertor for fusion power plants

In fusion power plant divertors a significant portion of the total fusion power is absorbed. In order to achieve a high thermal plant efficiency this power has to be removed at high temperature levels. This calls for innovative designs which differ from those proposed for experimental fusion machines. In this study, evaporation cooling of liquid metals is considered evaluating: (i) a concept based on pool boiling; and (ii) a concept based on the transport of liquid through a capillary layer and evaporation at the surface of this layer. The latter concept employs characteristic features of high heat flux liquid metal heat pipes. Both concepts are characterised by the operation at high temperatures (between 750 and 1200 °C, depending on the choice of the liquid metal) but small stresses due to small temperature differences and operating pressures. The second concept is assessed to have the potential of significantly higher heat loads (in space craft applications heat loads of much larger than 10 MW/m2 were reached). A conceptional design description is presented; divertor relevant performance limits are estimated and open issues and the required R&D work are briefly addressed.