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
Experimental investigations on the soldering performances of the joints for Bi-2223/Ag tapes
Abstract In this paper, we have fabricated Bi-2223/Ag jointed tapes and evaluated its joint resistance at liquid nitrogen temperature (77 K). The tapes were joined by the conventional resistive joint method using five kinds of solders with different melting points. The lower melting point Bi–Sn–Pb and high melting point Sn–Ag–Cu solders have lower joint resistances. In addition, two different joining processes were compared by joining the copper sheet. The joint resistances were measured at lower temperature and the resistance appears comparable to each other. It indicated that the direct-jointing is more effective method for high temperature superconductor (HTS) joining.
Superconducting Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ closed-loop coils carrying persistent current at temperatures above 77 K
We have succeeded in producing superconducting closed-loop coils from Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tape. These coils can be operated in a persistent current mode even at temperatures above the boiling point of liquid nitrogen. The persistent current density value has been deduced to be 600 A/cm/sup 2/ at 77 K and the current has been estimated to run for 10/sup 16/ years. The persistent critical current density in our coils was about one order of magnitude smaller than the critical current density value determined by a 1 /spl mu/V/cm criterion. The decay behaviour of the current in the coils was clearly separated in two regimes, an initial fast decay of the order of minutes followed by a slow logarithmic-like decay. In this paper, experimental results of the persistent current density as a function of temperature and applied magnetic field are also presented.