High-performance Bi-2212 round wires made with recent powders

Multifilamentary Bi ₂ Sr ₂ CaCu ₂ O _x (Bi-2212) wire made by the powder-in-tube technique is the only high-temperature superconductor made in the round shape preferred by magnet builders. The critical current density (J _C ) of Bi-2212 round wire was improved significantly by the development of overpressure heat treatment in the past few years. Bi-2212 wire is commercially available in multiple architectures and kilometer-long pieces and is a very promising conductor for very high-field NMR and accelerator magnets. We studied the effects of precursor powder and heat treatment conditions on the superconducting properties and microstructure of recent Bi-2212 wires. Short samples of recent wire with optimized overpressure processing showed J _C (4.2 K, 15 T) = 6640 A/mm ² and J _C (4.2 K, 30 T) = 4670 A/mm ² , which correspond to engineering critical current densities J _E (4.2 K, 15 T) = 1320 A/mm ² and J _E (4.2 K, 30 T) = 930 A/mm ² .