Design of a 15 T hybrid superconducting magnet

Abstract In the framework of the program to fabricate a high-field superconducting magnet of the order of 19 T @4.2 K with a 150 mm free bore, a 15 T hybrid solenoidal superconducting magnet with a 78 mm bore was developed and preliminary tested. The purpose of the program is to upgrade the material test facilities in the Institute of Plasma Physics Chinese Academy of Science (ASIPP) and further extend their measurement functionality. This paper presents the design of the 15 T hybrid magnet and its preliminary test results. The magnet comprises two high-performance Nb3Sn coils, one ITER Nb3Sn coil and one NbTi coil respectively for the high-, medium- and low field section. The axial length of the homogeneity within a 99 % magnetic field region is designed to more than 40 mm, and the ratio between the peak and central magnetic field is expected to be less than 1.025. The Nb3Sn coils were reacted separately, after which all coils including the NbTi coil were impregnated with CTD-101 K individually. Then, the impregnated sub-coils were assembled into a concentric-coaxial configuration and electrically connected in series. The hybrid magnet was inserted to a liquid helium bath for the excitation test, it finally reaches 97.8 % of the design current with a 14.84 T central magnetic field.