Measurement of joint properties of Bi(Pb)-Sr-Ca-Cu-O (2223) tapes by field decay technique

We joined 19-multifilamentary Bi-2223 superconductor tapes and fabricated double-pancake coils by using resistive- and superconducting-joint methods. The critical current ratio (CCR) of the jointed tape and the decay characteristics, joint resistance, and n-value of the pancake coils were evaluated. The joint resistance of the coils was characterized by the field decay technique. It was observed that the CCR was higher in the joined tape made by the resistive-joint method, compared to that by the superconducting-joint method. On the other hand, joint resistance was measured to be 4 orders of magnitude smaller in the superconducting-joint coil; approximately 40% of critical current was retained in the persistent current mode and the joint resistance was 0.18 n(Omega). Better and longer retention of the magnetic field in the superconducting-joint coil is believed to be due to the direct connection between the superconducting cores.