Performance Improvement and Optimization of New High-Temperature Superconducting Coil Assembly

To practically use high-temperature superconducting (HTS) coils, it is necessary to reduce the total length of the HTS tape while maintaining a large amount of stored energy and small magnetic field leakage. In this paper, we propose a new HTS coil assembly, which is distinct from solenoid and toroid coils. Using the typical r- z axes of cylindrical coordinates, several small coils having rectangular cross sections are placed such that they form a circle in the r- z plane. Note that these small coils are coaxial along the z -axis. To form the solid structure, these cross sections are rotated about the z-axis. The analysis of the coil assembly allowed for performance improvements and optimization. The performance improvement resulted from the large modification of the magnetic field angles, which are achieved by the cancelation of Br magnetic field components from each element coil. The critical current of the optimized assembly is greater than that of a normal rectangular solenoid by 1.6 times. As a result, the optimized assembly results in 78% increase in stored energy and a large reduction in the magnetic field leakage, as compared with a normal rectangular solenoid coil with the same HTS tape length.