High-Performance Bi-2212 Round Wires Made With Recent Powders

Multifilamentary Bi2Sr2CaCu2Ox (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).