Transport performance of Bi-2212 current leads prepared by a diffusion process

Bi-2212 bulk cylinders have been prepared by the diffusion process for current lead application. The Bi-2212 oxide superconducting layer is synthesized through the reaction between a Sr-Ca-Cu oxide tubular substrate and a Bi-Cu oxide coating layer with Ag addition. The Bi-2212 diffusion layer about 150 μm in thickness with textured structure formed around a tube 20/16 mm in outside/inside diameter. The transport current of the tube specimen exceeds 6.250 A at 4.2 K under self-field, which corresponds to a transport current density of 35,000 A/cm² . The overall joint resistance is measured to be about 150 mΩ at both ends of the specimen, composed of Cu endcap, Sn-Pb solder and Ag contact on the specimen. The resistivity of the commercial Sn-Pb solders is About 2 nΩm at 4.2 K, and one order of the magnitude higher than that of Cu and Ag. Therefore, the soldering process is important in reducing the joint resistance and the resultant Joule heat. Present Bi-2212 bulk conductors with large transport current are promising as current leads for superconducting magnets