Performance of an HTS persistent current system for REBCO pancake coil

A superconducting joint and a persistent current switch are the key technologies in persistent current operation for MRI and NMR magnets to obtain higher resolution and sensitivity. We prepared a persistent current system including a superconducting joint, a persistent current switch, and a double pancake coil, which were fabricated with a REBCO tape. The magnetic field decay behavior in persistent current operation were observed in a self-field and the external magnetic field of 1 T at 20 K. In the self-field, the decay rate of persistent current excited up to 170 A reached to 1.7 ppm/h after five days operation. This means that the practical persistent current operation has been achieved successfully using the REBCO superconducting joint. From the voltage–current characteristics estimated from the magnetic field decay, it was found that the decay behavior of persistent current is dominated by the joint resistance in 1 T, but by the shielding current in the self-field.