Electromagnetic behavior of HTS coils in persistent current operations

The current decay behaviors in high-temperature superconducting (HTS) coils using Bi-2223/Ag tapes are investigated. Generally, the resistance of a superconducting closed loop is determined by the joints and electric field versus current density relationship of the HTS tape. In this paper, we demonstrate that the resistance is enhanced due to the decay of the shielding current by the flux creep and flux flow in HTS tapes. Experiments with HTS coils with persistent current operations were carried out and the results are compared with numerical analysis using a finite element method. Furthermore, the improvement of the current decay behavior is also discussed by choosing an overshooting excitation technique.