AC loss measurement of HTS coils with ferromagnetic disks

Manufacturing techniques for low AC loss high-T_c superconducting coils are necessary to realize high efficiency superconducting power equipments. High-T_c superconducting tape conductors have anisotropic magnetic field dependence on critical current and AC magnetization loss. A magnetic field component perpendicular to the tape surface degrades HTS coil performance. We numerically investigated a magnetic field adjusting method and AC loss reduction effects by attaching ferromagnetic materials to both ends of HTS coils. We also measured total AC loss of an HTS coil comprising 10 HTS double pancake coils by the boil-off method. Total AC loss of the coil was dominated by mechanical loss due to vibration and movement of conductors and pancake coils. In this paper, methods to reduce total AC loss of HTS coils are discussed.