Design of a cryocooler-cooled large bore superconducting magnet for a 30 T hybrid magnet

We are now developing a 30 T hybrid magnet utilizing a cryocooler-cooled superconducting magnet wound with highly strengthened (Nb, Ti)₃Sn. Diameter of the room temperature bore of the superconducting magnet is 360 mm and it generates 11.1 T. Water cooled resistive insert magnet generates 18.9 T, thus the hybrid magnet generates a central field of 30.0 T. The (Nb, Ti) ₃Sn multifilamentary wires are strengthened by Cu/NbTi composite which volume ratio in conductor is about 35 %. The reinforcing CuTNbTi composite changes to CuTi intermetallic compounds during heat treatment for reaction of (Nb, Ti)₃Sn phase formation. The Nb₃Sn coil with inner diameter of 400 mm will be fabricated by wind and react method with Cu/NbTi reinforced (Nb, Ti)₃Sn wires. The innermost section of Nb ₃Sn coil is wound with a wire which diameter is 1.85 mm and next second section is wound with a wire diameter of 1.8 mm. The Nb₃Sn coil is operated at 303 A and generates 5.8 T. The NbTi coil is wound with NbTi wires of 2.0 mm and 1.6 mm diameters. The NbTi coil generates 5.3 T at an operating current of 350 A. The maximum hoop stress is under 220 MPa for Nb ₃Sn coil and 200 MPa for NbTi coil.