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.