Efficient helium cooling methods for nuclear fusion devices: Status and prospects

Helium-cooled reactors offer several important advantages as the helium is an inert and neutron transparent gas, compatible with high outlet temperatures and all structural and functional materials considered for plasma facing components. On the other hand, during the power plant studies performed up to now it became evident, that the helium pumping power could become very high if standard cooling methods based on hydraulically smooth cooling channels would be applied and that a very high heat flux in the divertor can only be achieved when using sophisticated gas cooling methods. In relation to this the main focus in this paper is on advanced gas cooling technology applications developed at Forschungszentrum Karlsruhe (FZK) for the main in-vessel components blanket/first wall and divertor of future fusion power reactors. Among a large number of considered cooling technologies the V-rib-based surface roughness approach for the first wall and the multiple jet impingement cooling technique for the divertor were identified as suitable and advantageous methods. The paper presents the main parameters to be considered and an evaluation of the achievable cooling performance in both cases.