Investigation of advanced divertor magnetic configuration for Demo tokamak reactor

Asakura, Nobuyuki; Shinya, Kichiro*; Tobita, Kenji; Hoshino, Kazuo; Shimizu, Katsuhiro; Uto, Hiroyasu; Someya, Yoji; Nakamura, Makoto; Ono, Noriyasu*; Kobayashi, Masahiro*; Tanaka, Hirohiko*

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 outer divertor leg longer than the conventional divertor, and it extends outboard 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 radius () and a ratio of the poloidal flux at the super-X null to that at the separatrix (). Some SXD magnetic configurations with minimal number of PFCs located outside toroidal field coil (TFC) were Demonstrated. Locations of the divertor target were also investigated. It was found that the flux expansion can be increased up to 4-10 depending on the target location and , and that SXD has an advantage to increase with . Thus, the divertor plasma temperature is expected to decrease at the same upstream plasma density. On the other hand, large currents for the divertor PFCs were necessary. Other arrangements of PFCs such as (1) larger and (2) inside TFC, can reduce the PFC currents.