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Since 2001, when magnesium diboride (MgB2) was first reported to have a transition temperature of 39 K, conductor development has progressed to where MgB2 superconductor wire in kilometer‐long piece‐lengths has been demonstrated in coil form. Now that the wire is available commercially, work has started on demonstrating a MgB2 wire in superconducting devices. This article discusses the progress on MgB2 conductor and coil development, and the potential for MgB2 superconductors in a variety of commercial applications: magnetic resonance imaging, fault current limiters, transformers, motors, generators, adiabatic demagnetization refrigerators, magnetic separation, magnetic levitation, superconducting magnetic energy storage, and high‐energy physics applications.

Three solenoids have been wound and with MgB 2 strand and tested for transport properties. One of the coils was wound with Cu-sheathed monofilamentary strand and the other two with a seven filament strand with Nb-reaction barriers, Cu stabilization, and an outer monel sheath. The wires were first S-glass insulated, then wound onto an OFHC Cu former. The coils were then heat treated at 675°C/30 min (monofilamentary strand) and 700°C/20 min (multifilamentary strand). Smaller (1 m) segments of representative strand were also wound into barrel-form samples and HT along with the coils. After HT the coils were epoxy impregnated. Transport J c measurements were performed at various taps along the coil lengths. Measurements were made initially in liquid helium, and then as a function of temperature up to 30 K. Homogeneity of response along the coils was investigated and a comparison to the short sample results was made. Each coil contained more than 100 m of 0.84-1.01 mm OD strand. One of the 7 strand coils reached 222 A at 4.2 K, self field, with a J c of 300 kA/cm 2 in the SC and a winding pack J e of 23 kA/cm 2 .At 20 K these values were 175 kA/cm 2 and 13.4 kA/cm 2 . Magnet bore fields of 1.5 T and 0.87 T were achieved at 4.2 K and 20 K, respectively. The other multifilamentary coil gave similar results. Keywords Strand FabricationThe continuous tube forming/filling (CTFF) process was used to produce Table 1. For further details on these multifilamentary strands, see [24]. Coil Winding, Heat Treatment, Epoxy ImpregnationThe former was solenoidal and made from OFHC Cu. The strands for all three coils were insulated with S-glass insulation. The coils had from 364 to 538 turns of strand, see Table 2. Cu-1 was HT for 675°C/30 min, while NbCu-7A and B were HT for 700°C/20 min. The ramp up time was 2.5 h and the ramp-down time was approximately 5-6 h, and all HT were performed under flowing Ar. Coils Cu-1 and NbCu-7A were vacuum impregnated with mixed Stycast 1266 epoxy heated to 40°C. NbCu-7B was merely dipped into degassed epoxy (40°C). After removal from the epoxy bath the coil curing was performed in air (at room temperature). Total curing time was estimated at 6-12 h. Coil Measurement and ResultsTransport properties of the coils were measured in a LHe cryostat (Figure 1 shows Cu-1 mounted and ready for insertion). The 4.2 K measurements were performed in liquid He, while higher temperature measurements were made as the coil warmed up.Two Cernox temperature sensors were mounted on the coil, one on the top and one on the bottom. The temperature difference across the coil was never greater than 0.3 K. Voltage taps were placed an various places along the winding. The typical distance between successive taps was about 14-20 m. The field was measured with a cryogenic hall probe and a Bell gaussmeter calibrated to achieve a 2% or better accuracy. The probe was inserted in the center of the bore during measurement. from the strands with a Nb-chemical barrier (Table 2), as might be expected. Strand and coil J e val...

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Two types of Rutherford cables made of two strand layers of commercial MgB2 wires manufactured by Hyper Tech Research, Inc. have been made. Flat rectangular cables consisting of 12 single-core MgB2/Nb/Cu10Ni, or 6-filaments MgB2/Nb/Cu strands, both of diameter 390 mewm, were assembled using a back-twist cabling machine with transposition length of 20 mm. In order to analyze impact of the cable compaction on critical currents, cables were two-axially rolled, each by a single step reduction of 3.5%−29.7% to thickness range of 0.775−0.62 mm. It was found that by increasing the packing factor (PF) of cable above 0.79, the critical current begins to increase. It is improved nearly two times up to the PF limit 0.89. Compaction over the PF limit introduced cable degradation and decrease of critical current. Bending tests applied to cables showed that critical current degradation starts below the bending diameter 120 mm for 6-filaments Cu sheath and 70 mm for single-core Cu10Ni sheath cable. Tensile tests showed similar irreversible strain values for the both types of cables. Rutherford cables assembled of single-core strands are promising for low field (2.7−4 T) applications where low bending diameters are required.