Electromagnetic Design and Fabrication of LPF2: A 12-T Hybrid Common-Coil Dipole Magnet With Inserted IBS Coil

High field dipole magnets with common-coil configuration are under development at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences) for key technology pre-study of high energy colliders. A model magnet named LPF1 has been fabricated and tested in 2018, which was made up of four flat racetrack NbTi coils and two flat racetrack Nb3Sn coils, and a main dipole field of 10.2 T has been reached in the two apertures at 4.2 K. A new model magnet LPF2 is being designed and fabricated in 2019, with four new Nb 3 Sn coils included comparing with LPF1, and the magnet is expected to reach a much higher field. To reduce the field enhancement at the coil ends, the newly fabricated Nb 3 Sn coils are designed with different straight lengths and bending radii. This hybrid dipole magnet is designed to provide a 12-T main field in the two apertures with an operating current of 5300 A, corresponding to a load line ratio of 78% at 4.2 K. A single-pancake racetrack IBS (Iron-based superconducting) coil wound with a 100-m IBS tape would be inserted into the middle of the magnet (between the inner-most two Nb 3 Sn coils). This magnet is also used to test the IBS coil performance under high field and high stress. The main design parameters, fabrication process of the magnet will be presented.