Resistive Insert Magnet Designs for the Series-Connected Hybrids Developed at the NHMFL

The National High Magnetic Field Laboratory (NHMFL) has developed series-connected hybrids (SCHs) each comprising of a superconducting outsert built with Nb3Sn cable-in-conduit conductor and a resistive insert using Florida Bitter technology. The first SCH, to be operated at the Helmholtz Center Berlin, has been tested successfully generating a central field above 25 T in a horizontal conical warm bore with a 30° opening angle suitable for neutron scattering experiments. The resistive insert contributing 13 T includes two coils electrically in series with a total power consumption of 4.4 MW. The second SCH, to be installed and operated at the NHMFL, has a target to provide 1-ppm maximum field inhomogeneity in a 36-T 40-mm bore for medium-resolution nuclear magnetic resonance science. The resistive insert contributes 23 T and includes four coils electrically in series with a total power consumption of 14 MW. The innermost two resistive coils include axial current grading targeting unshimmed field uniformity below 100 ppm over a 10-mm-diameter spherical volume. The design of the resistive insert for the second SCH was completed in mid-2014, and this project is currently in the final construction phase.