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 to170 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.