Development of metal-insulated iron-based superconducting coils and charging tests under high magnetic fields up to 32 T

To explore the potential of iron-based superconducting (IBS) tapes in high-field applications, IBS pancake coils were dry-wound using the uninsulated IBS tape, supplemented with cowound stainless steel tapes for reinforcement. We have successfully fabricated a double pancake coil (DP-1) and a series-connected coil consisting of six DP coils (DP-6). These coils underwent multiple charging tests in a 35 T resistive magnet and retesting in a 14 T superconducting magnet. After conducting multiple rounds of retesting in two different background field magnets, it was found that the IBS coils did not show any degradation in their current-carrying performance. The critical current (I c) value of the DP-1 at 4.2 K and 32 T reached 60 A. To systematically evaluate the I c performance of the six coils in the DP-6, we monitored the V-I curves between 26 voltage taps. The resistive voltage rise was observed at low charging currents, indicating that each coil has suffered different levels of damage. Nevertheless, the overcurrent tests demonstrated that the IBS coil can still carry a current far exceeding its I c without irreversible degradation. We concluded the possible reasons for these phenomena by analyzing the experimental details and test data. In addition, the coil's internal structure was observed to assess the quality of coil winding, joint soldering, and epoxy resin impregnation. This study will provide references for the electromagnetic and mechanical properties of IBS tapes under ultra-high magnetic fields and contribute to the future development of higher-performance practical IBS coils.