Performance Improvement of a Bi-2223 Solenoid Coil With Optimal Ferromagnetic Disks

Solenoid-type superconducting magnetic energy storage (SMES) coils wound by Bi-2223 tapes have strong anisotropic magnetic field dependence due to the fundamental anisotropic property inherited from Bi-2223 materials. The maximum perpendicular field components appearing around the turns located at the two coil ends degrade the critical current and energy storage capacity of the whole coil, and even cause significant AC loss and possible hot-spots during practical SMES operations. To enhance the critical current and reduce the ac loss of the turns located at the two coil ends, this paper investigates a novel ferromagnetic raised-edge disk structure for adjusting the magnetic field orientation to be as close as possible to a parallel angle. Finite element simulations and performance comparisons with a test 0.2-H Bi-2223 solenoid coil without any ferromagnetic disk, with a conventional flat disk, and with the proposed raised-edge disk are presented. The results obtained show that the proposed raised-edge disk has much better effects towards critical current improvement and AC loss reduction compared to a conventional flat disk, especially for the terminal coil turns near the inner wall of the whole coil.