Advantages of the distributed structure concept of the Westinghouse LCP coil design-II

The forced flow Nb3Sn magnet concept developed by Westinghouse in cooperation with the Oak Ridge National Laboratory offers the fusion program the option of a reactor size superconducting toroidal field coil which has the capability of achieving peak fields of 12 tesla. The Westinghouse LCP coil concept offers a number of advantages besides high field capability. The coil is fabricated by winding stainless-steel-jacketed conductors into machined slots in the structural plates. This configuration provides positive conductor support and prevents accumulation of magnetic loading on individual conductors. Another advantage of this concept is the distribution of the conductors which results in more uniform current density in the overall coil cross-section. This distributed winding approach also provides higher fields on the plasma axis for given peak fields on the conductor. The distributed structure uniformly distributes eddy current losses and has lower losses than lumped structure concepts when subjected to the pulsed poloidal fields. The higher current densities possible, due to more efficient utilization of space coupled with the use of materials with good radiation properties (materials used for the Westinghouse LCP coil), allows for reduction in reactor size, which can be a substantial cost advantage. The modular concept of the Westinghouse coil allows for parallel manufacturing operations. The maintainability and repairability aspects of the coil are also discussed.