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
Comparison of different joint configurations between two parallel SS-laminated BSCCO/Ag tapes
Stainless steel laminated BSCCO/Ag tapes are commercially available for HTS pancake magnet development. The joint between pancakes could be achieved in several configurations like straight lap joint, cross-bridge joint and combination of both. Each type of joint shows different characteristic. We have experimentally studied the characteristic of three types of joint configuration between two pancakes made of SS-laminated BSCCO/Ag tape at 77 K. We have developed two types of cross-bridge joint and one with combination of both straight lap joint and cross-bridge joint. The joint resistance for all three configurations has been compared. The rise in temperature at each joint has been estimated. The joint configuration with the combination of both straight lap joint and cross-bridge joint has given lowest joint resistance which is 0.25 μΩ at 77 K but this configuration has more locally heated zones.
A superconducting joint between Bi?Pb?Sr?Ca?Cu?O multifilamentary tapes
We evaluated the effects of the joining process on the electrical properties of Bi–Pb–Sr–Ca–Cu–O (BSCCO) multifilamentary jointed tapes. In the process, a 37-filament BSCCO tape was fabricated by the powder-in-tube technique and the tapes were joined by a superconducting-joint method. To improve the filament connectivity between the tapes, the contacting surface of each tape was modified to a stepped shape, and the joined region was uniaxially pressed at 1000–2500 MPa. The critical current ratio (CCR) and n-value of the jointed tape were evaluated as a function of uniaxial pressure and number of steps in the contacting region. It was observed that those properties were dependent on the number of steps, but were almost independent of uniaxial pressure. The highest CCR and n-value for the jointed tape were 61.9% and 5.1, respectively, obtained by optimizing the number of steps and the pressure. It is believed that the highest values for the jointed tape resulted because the contacting area (the 'window') increased and more tape filaments were connected to each other in the joined region. The microstructural evolution was also evaluated and correlated to the resultant properties of the jointed tape.