Investigation of advanced divertor magnetic configurations and coil arrangements for demo tokamak reactor

Asakura, Nobuyuki; Shinya, Kichiro*; Hoshino, Kazuo; Tobita, Kenji; Shimizu, Katsuhiro; Uto, Hiroyasu; Someya, Yoji; Nakamura, Makoto; Sakamoto, Yoshiteru

Design study of poloidal field coil (PFC) locations and current distribution for the advanced divertor in the Demo tokamak reactor was presented. Concept of the super-X divertor (SXD) for Demo reactor has an extra magnetic null in the outer divertor leg in order to increase both the target wetted area and connection length to the outer target (). Equilibrium calculation code, TOSCA, was developed by introducing two parameters, i.e. super-X null location (, ) and a ratio of the poloidal flux at the super-X null to that at the separatrix (). SXD magnetic configurations with minimal number of PFCs located inside and outside toroidal field coil (TFC) were demonstrated. Locations of the divertor target were also investigated. It was found that SXD has an advantage to increase by 40-60% with , while increase in the flux expansion on the target is small (less than 40%). On the other hand, large currents for the divertor PFCs were required for the case of outside TFC, thus inter-TFC design is a practical solution. Magnetic configurations and arrangement of the divertor PFCs for a snowflake divertor were also demonstrated.