Design of DEMO PF Coils Based on Cable-in-Conduit Conductor

The poloidal field (PF) coils are designed based on the requirements defined by the EUROfusion 2015 DEMO baseline. The conductors are forced flow, NbTi cable-in-conduit. The design addresses the dimensioning of the winding pack, the electromagnetic field calculation and mechanical load. The cross sections of the cable, i.e., superconductor, copper and helium are allocated to fulfill the design criteria for the temperature margin and pressure drop in the operation. The conductors have rectangular cross section and are layer wound, multiple-in-hand, to minimize the hydraulic length (1 single turn can be as long as 100 m). The orientation of the wide side parallel to the main field component minimizes the ac loss. The larger radius compared to international thermonuclear experimental reactor (ITER) PF coils calls for larger electromagnetic load and hence much larger cross section for the structural support, which must be added on top of the conductor conduit to avoid unmanageable thick conduit walls. For PF1 and PF6 coils, a design option with Nb3Sn conductor may need to be considered due to the effective magnetic field in excess of 6.2 T.