An 18 T cryocooled superconducting magnet (18T-CSM) with a 52-mm room temperature bore has been successfully constructed. The magnet consists of an outer NbTi coil, which generates 6.2 T, four Nb3Sn coils, which generate 9.3 T and a Bi2223 high-Tc insert coil, which generates 2.5 T. The magnet system is cooled by a GM/JT cryocooler and two single-stage GM cryocoolers. The initial cool down takes 11.5 days. The ramp time up to 18 T is 60 minutes. The innermost layer of the Nb3Sn coils employs an internal-tin processed Nb3Sn wire due to its high critical current density in high magnetic fields. High mechanical strength is required for other three layers because of the large hoop stress of 234 MPa at 18 T. With this view, bronze-processed high-strength Nb3Sn wires reinforced with Cu-NbTi lntermetallic compound are employed. The Bi2223 high-Tc insert coil is composed of 25 double pancake coils using Ag-alloy sheathed Bi2223 superconducting tape with stainless steel tape reinforcement. The reinforcement co-winding reduces the hoop stress down to 48 MPa, which is sufficiently applicable to the Bi2223 tape. The magnet is successfully operated up to 18.1 T.
- High magnetic field
- Super-conducting magnet