A Concentrically Arranged Joint-Less HTS Coil System for Persistent Current Mode Operation

We have shown that a persistent current mode operation was possible in various types of HTS coils wound by the joint-less winding technique with 2G REBCO tape. However, in a previous test, a solenoid type of the joint-less HTS coil showed very poor magnetic field quality which was caused by the inevitable gap located at the very center part of the solenoid coil. In this paper, to improve the homogeneity of the magnetic field of the solenoid joint-less HTS coil, we proposed a joint-less HTS coil which had two separable parts of the solenoid coil arranged concentrically, just like a conventional high field magnet. By this arrangement, we could improve the homogeneity of the center magnetic field remarkably. A prototype coil was made and operated at the temperature of 77.3 K by liquid nitrogen cooling and charged up with a persistent current switch that was also a part of the perfect superconducting closed loop in the joint-less HTS coil.