Evaluation of Joint Resistance Between Bi-2223/Ag Superconducting Tapes
We fabricated Bi-2223/Ag jointed tape and evaluated its current carrying capacity and joint resistance at 77.3 K as a function of the contact length. The tapes were jointed by the conventional resistive joint method with 40Pb-60Sn solder as an insert material and their joint resistance was measured by two different techniques, i.e., the standard four-probe and field decay methods. It was observed that the current carrying capacity and joint resistance were significantly dependent on the contact length. As the contact length increased, the current carrying capacity improved and increased to the level of critical current in the unjoined tape at the contact length of 5 cm. On the other hand, the joint resistance linearly decreased as the contact length increased. In addition, the joint resistances measured by the two methods were similar to each other (7.3times10-9 Omega~8.0times10-9 Omega), indicating that the standard four-probe method maintained a moderate degree of accuracy at the level of resistance of 10-9 Omega
Fabrication and characteristics of the joint properties in (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ closed double pancake coil
We fabricated two superconducting closed coils and evaluated the joint resistance of the coils by a field decay technique at 77 K. In the process (Bi, Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x//Ag tape was wound in the form of double-pancake coils, and the ends of the tape were joined to each other by a resistive-joint method. Joint resistance of the coils was evaluated as a function of critical current of the coil, contact length, sweep time, and external magnetic flux density. Joint resistance was observed to be almost independent of critical current, sweep time, and external magnetic flux density, i.e., resistances were within the range of 7.8 /spl times/ 10/sup -9/ /spl Omega/ to 12.6 /spl times/ 10/sup -9/. On the other hand, the joint resistance was dependent on the contact length of the closed coil. The initially induced current/magnetic flux was observed to be dependent on critical current and contact resistance of the coil.
Superconducting joints formed between powder-in-tube Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub z//Ag tapes
Superconducting joints between Ag-clad, Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub z/ tapes have been obtained with approximately 1/2 the current capacity of the tapes themselves. The Ag sheath is removed from one side of each tape without significantly disturbing the superconducting core. The exposed superconducting core of the two tapes is brought into contact and pressed so as to again seal the superconductor in a Ag sheath. A reaction anneal is performed to join the two cores together and repair damage associated with the removal of Ag and the pressing. Transport measurements using multiple voltage taps have been found useful in characterizing the critical current variation across the joint.<<ETX>>