Lawrence Berkeley National Laboratory

Multifilamentary Bi₂Sr₂CaCu₂O_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 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/mm² and J _C (4.2 K, 30 T) = 4670 A/mm², which correspond to engineering critical current densities J _E (4.2 K, 15 T) = 1320 A/mm² and J _E (4.2 K, 30 T) = 930 A/mm².