A 26 T 35 mm winding diameter all-GdBa2Cu3O (GdBCO) magnet was designed by the MIT Francis Bitter Magnet Laboratory, and constructed and tested by the SuNAM Co., Ltd. With the multi-width (MW) no-insulation (NI) high temperature superconductor (HTS) winding technique incorporated, the magnet is highly compact; its overall diameter and height are 172 and 327 mm, respectively. It consists of a stack of 26 NI double pancake coils wound with MW GdBCO tapes in five different widths ranged 4.1–8.1 mm. In a bath of liquid nitrogen at 77 K, the magnet had a charging time constant of 16 min due to the intrinsic NI characteristics. In liquid helium at 4.2 K, the magnet generated a 26.4 T field at the center, a record high in magnetic fields from all-HTS magnets. The results demonstrate a strong potential of MW-NI GdBCO magnets for direct current high-field applications.

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A conduction-cooled 3 T 100 mm winding bore multi-width and no-insulation (NI) all-REBCO magnet was designed, constructed and tested at 13 K. The magnet consists of a stack of double pancake (DP) coils wound with, for the first time, REBCO tapes having a 1 μm thick layer of stainless steel, named ‘metallic cladding’, that surrounds the tapes in a hermetic way to substantially reduce the NI charging delay. After construction, the magnet was cooled down to the target operating temperature of 13 K using a two-stage pulse-tube cryo-cooler. During charging–discharging tests up to 200 A, magnetic center field, voltage of each DP coil, power supply current, and magnet temperature were monitored. The charging time constant of the magnet was measured to be about 10.1 s, 13 times smaller than that of its NI counterpart. The magnet experienced, due to an unexpected power supply trip, a sudden discharge at a peak coil current density of 353 A mm2, yet it survived without any degradation. The results demonstrated strong potential of the metallic cladding NI-REBCO magnet for significant charging-delay reduction and self-protecting operation.

We present a design of a 400-MHz/60-mm all-REBCO nuclear magnetic resonance (NMR) magnet (H400) that consists of a stack of 56 double-pancake (DP) coils. With the multiwidth no-insulation technique incorporated, DP coils were wound with REBCO tapes of five different widths, i.e., 4.1, 5.1, 6.1, 7.1, and 8.1 mm; DP coils placed at and near the magnet midplane were wound with the narrowest (4.1 mm wide) REBCO tapes, whereas those with progressively wider tapes were placed toward the top and bottom of the magnet, where the "perpendicular field B ⊥ " is at its peak within the magnet. The magnet was designed to be operated under a conduction cooling environment at 20 K. Once successfully completed, the magnet will be installed as an NMR user facility in the Korea Basic Science Institute. Basic magnet performances and major technical challenges were discussed.

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In order to improve the poor efficiency of the conventional induction heater using copper coil, a high temperature superconducting (HTS) DC induction heater is considered. In this study, we designed and built an HTS DC induction heater prototype with an iron core, and tested the insulated and noinsulation (NI) double pancake coils (DPCs). The results show that the critical currents of the DPCs with the iron core somewhat decrease than those without the iron core. The V-I curve of the insulated coil is a standard one of the superconductor, but a linear voltage appears in the NI coil due to the contact resistance between neighboring wires. For the insulated coil, the magnetic flux density of the air core is proportional to the coil current. However, a charging delay is found in the NI coil: the increment of the magnetic flux density for the NI coil is negligible when the current is increasing at first. Then the magnetic flux density increases and finally saturates even if the current is stable. The inductance of the coil with the iron core is about six times of that without the iron core.  Index Terms-charging delay, critical current, double pancake coil, HTS DC induction heater, iron core.

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