Divertor study on DEMO reactor

Huge power handling in the SOL/divertor region is one of the crucial issues for a tokamak fusion reactor. Divertor design study of a DEMO reactor with fusion power of 3 GW and ITER size plasma has progressed using the integrated divertor code SONIC. Recently, to improve conversion of the solution for the DEMO divertor plasma simulation, SONIC code has been improved. The calculation time is significantly reduced by (1) the backflow model for the simplified impurity exhaust process and (2) optimization on HELIOS at BA-IFERC. In the SONIC simulation, the partial detached divertor plasma was obtained by the Ar impurity seeding. Although the plasma heat load at the outer target was reduced by the partial detachment, the contribution of the impurity radiation and the surface recombination of the fuel ions to the target heat load became large. As a result, the peak of the total target heat load was estimated to be 16 MW/m². In order to reduce the total heat load, control of the impurity radiation profile by kind of seeding impurity species and the divertor geometry has been studied. They can decrease the target heat load, but the peak heat load is still larger than the heat removal capability of the present divertor target concept. Further design study including change of the machine specifications is necessary. (author)