Upgrade Design to a Cryogen-Free 20-T Superconducting Outsert for a 47-T Hybrid Magnet

A Rutherford flat cable composed of sixteen 0.8-mm-diameter Nb₃ Sn strands with CuNb-reinforced stabilizers (CuNb/Nb₃Sn) has been developed for use as an outsert for a 47-T hybrid magnet. To guarantee the safety of the magnet in the event of a quench, the low residual resistance ratio characteristic of arc-melted-in-situ CuNb composite had to be improved upon, and to obtain high electric conductivity, a new CuNb fabrication method using a Nb rod was attempted. The thermal runaway characteristics of chemical vapor deposition- YBa₂Cu₃O_7-δ (Y123) coated-conductor tapes with varying Cu stabilizer thicknesses were measured in magnetic fields of up to 10 T at temperatures ranging from 17 to 60 K. It was found that the ratio of the thermal runaway over-current to the critical current decreases as temperature decreases and that thermal runaway occurs just above the critical current level at 5 K. The properties of a cryogen-free, 20-T superconducting outsert for a 47-T hybrid magnet utilizing CuNb/Nb₃Sn Rutherford flat cables and Y123 tapes and having a room temperature bore of 400 mm were investigated.