Development of the K-DEMO divertor concept

Based on the legal framework of the Fusion Energy Development Promotion Law (FEDPL) enacted in 2007, a pre-conceptual design study for the Korean fusion demonstration tokamak reactor (K-DEMO) has been started in 2012. K-DEMO is characterized with its uniqueness of high magnetic field (a magnetic field of 7.4 T at the plasma center), major and minor radii of 6.8 m and 2.1 m, and steady-state operation [1,2]. The results of the preliminary concept study on K-DEMO divertor are summarized in this paper. Up-down symmetric double-null (DN) configuration is selected for K-DEMO as a primary choice for study with high elongation of 2 and triangularity of 0.625. For vertical maintenance of K-DEMO in-vessel components, upper and lower divertors are subdivided into 32 toroidal modules, respectively. With maintaining its functionality, the poloidal coverage of divertor is restricted to maximize the breeding area of blanket. The power loss scheme in the core and edge plasma and the fusion neutron wall loading onto the first walls of the in-vessel components were calculated. The divertor targets are tilted at ~10° against separatrix field line to handle the conceived engineering limit of steady 10 MW/m2 of peak heat flux with ~50% core plasma radiation, ~85% of divertor radiation. Divertor adopts tungsten monoblock targets, steel-based structures carrying water coolant. The developed concept on the target and structure is supported by preliminary thermohydraulic analyses using ANSYS, which shows the temperatures of the divertor structure materials are within their allowables.