From Double-Pancake Coils to a Layer Wound 5 T REBCO-HTS High Field Insert Coil Design

The superconducting high field facility HOMER II of the Karlsruhe Institute of Technology (KIT) provides a magnetic field of 20 T in a large bore of 185 mm using solenoid magnet sections made of NbTi and (NbX)3Sn wires. One of the major goals of the high field laboratory at KIT is to upgrade this basic magnet configuration of HOMER II to achieve a total field of 25 T. Recently, a design for a 5 T insert has been proposed using REBCO-HTS. The envisaged layout consists of two series-connected nested stacks of double pancakes. Meanwhile, the increased long-length availability of REBCO-HTS makes a 5 T insert composed of layer wound solenoid sections an attractive option. In this paper, a design for such a layer wound 5 T insert for the HOMER II upgrade is presented. Furthermore, the manufacture and test of a prototype layer wound HTS section made of a 170 m length of RE BCO coated conductor tape is reported.