FABRICATION OF SUPERCONDUCTING JOINTS FOR Bi-2212 PANCAKE COILS

To evaluate the possibility of persistent current operation for NMR/MRI using a Bi-2212 oxide superconductor at 4.2K, the temperature dependence of magnetic relaxation for the Bi-2212 single crystal have been measured. It was found that the operating current must be one-fourth of Jc at 4.2K in order to satisfy the stability condition for NMR/MRI operation (Delta J/J less than 0.005 ppm/hour). In order to establish the fabrication process of long wire, fabrication of superconducting coil made of a Bi-2212 silver sheathed wire was carried out by means of partial melt growth process. We have succeeded in generating 1.60T an the external magnetic field of 0T at 4.2K. This coil employed silver-sheathed Bi-2212 tape which was 100 mu m thick, 10mm wide and 150m long. We also have attempted to fabricate superconducting jointed pancake coils, the critical current reaching 80A in the external magnetic field of 1.0T at 4.2K.