Transport Performance and Structures of Bi2212 Oxide Superconductors Prepared by Diffusion Process

Abstract

Bi2212 HTS conical tubular conductors have been prepared by diffusion process for current lead. 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 mm in thickness are formed around both outside and inside of the conical tubes 34/29 mm in outside/inside diameter at the larger end, 24/19 mm in outside/inside diameter at the smaller end, and 100 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 properties were evaluated by measuring system using two cryocoolers at Railway Technical Research Institute. The critical temperature of transport current of 1000 A at 0.5 T for the specimen is 57.4 K, which corresponds to the current density of 33 A/mm 2 for the Bi2212 layer. The transport current decreases with increasing temperature at the warm end of the conical specimen, and is about 800 A at 60.2 K and 600 A at 62.5 K. The joint voltage of 20 mV at cold end was generated at 50 K and 0.5 T with transport current of 1000 A, which corresponds to the small heat load of 20 mW resulted from the Joule heating. Present Bi2212 conical tubes seem to be promising as current leads with small heat loads for superconducting magnets.