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
.