Structure and performance of Bi-2212 hollow cylinders prepared by a new diffusion process

Abstract

Bi 2Sr 2CaCu 2O 8+ X (Bi-2212) high- T c superconductors (HTS) bulk conductors have been prepared by a new diffusion process for current lead application. The Bi-2212 HTS diffusion layer is synthesized through the reaction between a Sr–Ca–Cu oxide substrate and a Bi–Cu oxide coating with Ag addition. The HTS diffusion layers about 150 μm in thickness are formed around both outside and inside of the hollow cylinders. The Ag added to the coating enhances the diffusion reaction, and precipitates on the surface of the specimen decreasing the contact resistance between the HTS ceramic layer and the current terminal. The Bi-2212 HTS layer consists of thin plate-like grains grown in the diffusion direction. They are mainly composed of grains with a-axis orientation. The transport current is expected to pass longitudinally through the cylinders on the ab planes. The transport current of the hollow cylinder 27/19 mm in outside/inside diameter and 200 mm in length reaches 6000 A at 4.2 K and self-field, which corresponds to the current density of 28,000 A/cm 2. The total heat load, including the heat leakage conducted through the cylinder between 4 and 40 K, is estimated to be less than 400 mW at 5000 A. Present Bi-2212 HTS conductors seem to be promising as large transport current leads for superconducting magnets.