Processing issues of Bi-2212 wires

Long length (> 100 meters) Ag-sheathed high temperature superconducting (HTS) Bi₂Sr₂CaCu₂O₈ (Bi-2212) oxide conductors have been processed using conventional powder-in-tube (PIT) and partial-melt-growth (PMG) techniques. Results show that the critical current density (J_c) of long length tapes is significantly lower when compared with J_cs of shorter length conductors (< 1 meter). This decrease in J_c is attributed to: (a) processing temperature non-uniformities along the conductor length, and (b) J_c sensitivity to temperature variations. The non-uniformity and sensitivity issues are being addressed by new furnace designs and annealing methods (such as the isothermal melt process method which has the potential to reduce the J_c temperature sensitivity), respectively. Simultaneously, other defects that are incorporated into the conductor during processing, with detrimental effect to the J_c, need to be addressed. The issues relevant to processing of long length HTS Bi-2212 conductors with uniformly high J_c are discussed.