Investigation of advanced divertor magnetic configuration for demo tokamak reactor

Design study of the magnetic configuration and divertor geometry for the “advanced divertor” in a Demo tokamak reactor is summarized. Equilibrium calculation code, TOSCA, was developed for the super-X divertor (SXD) design by introducing two parameters, i.e. location of the super-X null and a ratio of the poloidal magnetic fluxes at the super-X null to that at the separatrix. SXD has an advantage to increase connection length from the divertor null point to the divertor target (L_// ^div), which is 1.6-1.8 times larger with increasing f_SX, compared to that in the conventional long-leg divertor. Whereas flux expansion near the super-X null was increased, increase in the target wet area (A_wet) was small. Snowflake divertor (SFD) magnetic configuration was produced by adjusting PFC locations and the current distribution. L_// ^div was largely increased near the SF null in the conventional divertor size. Key issues remain: control scenario for SF-null and high plasma shaping should be developed, and appropriate SFD design is necessary. For the advanced divertor design, divertor coils inside TFC are preferable due to the maximum current and size.