Fabrication of Bi-2212 Wires and Solenoid Coils by Gas Pressure Melting(GPM) Method.

Void formation is a serious problem for Ag-sheathed Bi-2212 superconductor wires produced by a partial melt process. We established a gas pressure melting (GPM) method which utilizes a combination of -1.0atm oxygen partial pressures and ≤6atm of total gas pressure. The method has proved very effective for obtaining a homogeneous dispersion of small voids and good superconductivity. A solenoid coil fabricated under usual atmospheric pressure showed no zero-resistivity due to the presence of large 50-mm-long void agglomerates. On the other hand, the newly developed GPM method reduced agglomerate size to -10mm, and enabled solenoid coils fabricated using 9 and 5 pieces of 25-m-long round wire to generate a maximum magnetic field of 0.67T and 1.1T, respectively, at 4.2K.