Critical current densities of AgCu-sheathed Bi-2212 multifilamentary roundwires in long length

Ag-Cu alloy sheathed Bi-2212 round wires have been fabricated by the powder -in-tube method. Short samples show critical current (I-c) values of more t han 150 A at 4.2 K and 10 T, while I-c, for a small coil with total length of 10 m reduces to about 30% of the values obtained for short samples. In o rder to clarify the factors to deteriorate I-c, for coils, superconducting properties and the microstructures have been examined. The difference in tr ansport I-c, between short samples and coils can be attributed not to the i ntrinsic properties of Bi-2212 grains but to the extrinsic limiting factors , such as voids that are formed by the released gases inside the wires with long length during heat treatment. (C) 2001 Elsevier Science B.V. All righ ts reserved.