Hybrid Magnet Design Consisting of a 20 T Superconducting Outsert and a 15 MW Resistive Insert

Internally reinforced Nb₃Sn strands with CuNb-reinforcing stabilizer have been developed for realizing a compact high-field superconducting magnet. The Rutherford flat cables composed of sixteen strands were made with a 0.8 mm diameter CuNb/Nb₃Sn strand. The designed critical current of the CuNb/Nb₃Sn Rutherford flat cable is I_c = 1890 A at 13 T and 4.2 K in case of an ordinary heat-treatment at 670 for 96 h, which is two times higher than an operation current desired for safety margin. In addition, mechanical characteristics for CVD-processed YBa₂Cu₃O₇ (YBCO) coated-conductor tapes were measured at 4.2 K in fields up to 18 T. It was found that YBCO tape exhibits the irreversible strain 0.5% and the irreversible stress 1140 MPa for the critical current at 4.2 K and 18 T for B//c. The cabling-and-react+prebending-processed CuNb/Nb₃Sn Rutherford flat cables and CVD-processed YBCO tapes will be used as a react-and-wind method for the development of a 20 T superconducting magnet with a wide room temperature bore. We design a 20 T-440 mm warm-bore superconducting magnet consisting of YBCO inner coils, middle coils, and NbTi outer coils, which has the coil parameters of inner diameter 480 mm, outer diameter 1283 mm, and coil height 1302 mm. Since the coil inductance is estimated to be 232 H, the magnetic stored energy is 94 MJ at an operation current 900 A. An energy-saving 47 T hybrid magnet can be constructed in combination with a wide-bore 20 T superconducting outsert and a 15 MW-27 T water-cooled resistive insert.