A novel trapped field magnet enabled by a quasi-operational HTS coil

This study introduces a novel approach to realizing compact high-field superconducting magnets by enabling a closed-loop high temperature superconducting (HTS) coil through magnetization. A circular closed-loop HTS coil is fabricated with a low resistive joint for field cooling magnetization. The HTS coil achieved a trapped field with only a 0.0087% decay in central field over 30 minutes. More interestingly, the central trapped field of 4.59 T exceeds the initial applied field of 4.5 T, while a peak trapped field of 6 T near the inner edge of the HTS coil, is identified through further numerical investigation. This phenomenon differs from the trapped field distributions observed in HTS bulks and stacks, where the trapped cannot exceed the applied one. Unique distributions of current density and magnetic field are identified as the reason for the trapped field exceeding the applied field. This study offers a new way to develop compact HTS magnets for a range of high-field applications such as superconducting magnetic energy storage (SMES) systems, superconducting machines, Maglev and proposes a viable method for amplifying the field strength beyond that of existing magnetic field source devices.