High Field Magnets With HTS Conductors

Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires is being pursued. Two specific projects are underway. The first is a user magnet with a 17 T YBCO coil set which, inside an LTS outsert, will generate a combined field of 32 T. The second is a 7 T Bi2212 demonstration coil set to be operated in a large bore resistive magnet to generate a combined magnetic field of 25 T. Owing to the substantial technological differences of the two conductor types, each project faces different conductor and magnet technology challenges. Two small coils have been tested in a 38-mm cold bore cryostat inserted in a 31 T resistive magnet: a Bi2212 round-wire layer-wound insert coil that generated 1.1 T for a total of 32.1 T and a YBCO double-pancake insert that generated 2.8 T for a total central field of 33.8 T. Four larger layer-wound coils have been manufactured and tested in a 20 T, 186-mm cold bore resistive magnet: a sizeable Bi-2212 coil and three thin large-diameter YBCO coils. The test results are discussed. The current densities and stress levels that these coils tolerate underpin our conviction that >30 T all-superconducting magnets are viable.