Usage of Bi-HTS in high field magnets

At present, superconducting high field magnets built up of metallic low temperature superconductors (LTS) like NbTi and ternary/quaternary Nb₃Sn is near to the upper limit of achievable field strength. Fields above approx. 23 T seem to be only reachable with LTS-HTS hybrid configurations consisting of an outer LTS section and a high temperature superconductor (HTS) insert. Commercially available Bi-HTS wires were investigated for their application in high field facilities like the HOMER II system with the goal of 25 T and in new generations of NMR magnets of 1000 MHz and above. Therefore the superconducting properties of the HTS wires were examined at 4.2 K in magnetic fields up to 10 T. The voltage-current relation was examined resistively using a high resolution four-point measurement technique. The dependence of the critical current and the n-value on the winding diameter, on the field alteration (increasing/decreasing), and on the field orientation to the wire is presented and discussed.