Bi2212 HTS bulk tubes prepared by the diffusion process for current lead application

Bi2212 HTS tubular bulk conductors have been prepared by the diffusion process for current lead application. The Bi2212 HTS layers are synthesized through the diffusion reaction between a Sr–Ca–Cu oxide substrate and a Bi–Cu oxide coating with Ag addition. Two different shaped substrates were prepared. The former substrates are formed into the cylindrical tubes 30 mm in outside diameter and 200 mm in length by cold isostatic pressing, and then sintered. The latter ones are the conical tubes with larger end of 30–40 mm and smaller end of 20 mm in diameter. The transport current of the specimen depends on the cross-sectional area of Bi2212 layers, and varies from 4000 to 8000 A at 4.2 K, which corresponds to the current density of about 2–3 × 104 A/cm2 for the Bi2212 layer. The transport current decreases with increasing temperature at the warm end of the specimen, which is, for example, about 3200 A at 40 K or 2000 A at 50 K. The total heat loads composed of heat leakage conducted through the tube between the warm joint and the cold joint at 4.2 K, and of Joule heating at the cold joint are estimated. Present Pb-free Bi2212 HTS bulk tubes seem to be promising for large transport current leads with small heat loads for superconducting magnets.