Bi2212 HTS Conical Tubes Prepared by the Diffusion Process for Current Lead Application

Bi2212 HTS conical tubular 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. The HTS diffusion layers about 150 micrometer in thickness are formed around both outside and inside of the conical tubes 37/29 mm in outside/inside diameter at the larger end, 27/19 mm in outside/inside diameter at the smaller end, and 200 mm in length. The Ag added to the coating enhances the diffusion reaction, and precipitates on the surface of the specimen decreasing its contact resistance. The transport current of the specimen exceeds 7,000 A at 4.2 K and self-field, which corresponds to the current density of 32,000 A/cm
²
for the Bi2212 layer. The transport current decreases with increasing temperature at the warm end of the conical specimen, and is about 4,600 A at 30 K, 3,200 A at 40 K or 2,000 A at 50 K. The total heat loads composed of heat leakage conducted through the conical tube and Joule heating at the joint are estimated to be about 320 mW at 3,000 A between the warm end of 42 K and the cold end of 4.2 K, and is 400 mW at 2,000 A between 50 K and 4.2 K, respectively. Present Pb-free Bi2212 conical tubes seem to be promising as large transport current leads with small heat loads for superconducting magnets