2020 Volume 55 Issue 4 Pages 268-274
The superconducting joint is a key technology to achieve persistent current operation for MRI and NMR magnets, thereby enabling to obtain higher resolution and sensitivity. A persistent current system including a superconducting joint, a persistent current switch and a double pancake coil fabricated with a REBCO tape was prepared by Furukawa Electric Co., Ltd. The magnetic-field decay behaviors during persistent current operation were observed in external fields of 0 and 1 T at 20 K. In a self-field, the decay rate of the persistent current excited up to 170 A reached 1.2 ppm/h after operating for five days, corresponding to a resistance of 5.1×10-13 Ω. From the current–voltage characteristics obtained from the magnetic field decay, it was found that the decay behavior of the persistent current is dominated by joint resistance in the case of high-load operation, but dominated by the shielding current in the case of low-load region of the operating current.
