Fabrication and characteristics of the joint properties in (Bi, Pb) ₂Sr₂Ca₂Cu₃O_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)₂Sr₂Ca₂Cu₃O_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 × 10 ^-9 Ω to 12.6 × 10^-9 Ω. 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.