Design and Fabrication of a 13-T Twin-Aperture Superconducting Dipole Magnet With Graded Common-Coil Configuration

R&D of high field accelerator magnets is ongoing at the Institute of High Energy Physics, Chinese Academy of Sciences (IHEP, CAS) for pre-study of the next-generation high energy colliders like Super Proton-Proton Collider (SPPC), Future Circular Collider (FCC) and etc. A 12.47-T main field at 4.2 K has been attained in 2021 within two 14-mm apertures of LPF1-U, a superconducting model dipole magnet with Nb
₃
Sn & NbTi combined common-coil configuration. Based on the experiences mastered in the LPF1 series magnets, a 16-T high field dipole magnet named LPF3 has been designed, fabricated and is in the performance test process. LPF3 is also a combined magnet with six racetrack Nb
₃
Sn coils outside, expected to provide a 13-T main field within two 50-mm apertures, and with inserted HTS coils to enhance the field up to 16 T or even higher. The 13-T Nb
₃
Sn dipole magnet, named LPF3-LTS, incorporates a graded common-coil configuration to enhance superconductor efficiency. The optimization of coil layouts includes varying bending radii (BR) and lengths of straight sections (LSS) to mitigate field accumulation in the outer four coils near the central posts and coil ends, respectively. Several Rutherford cables over 200 meters were fabricated for the coils winding, and with the maximum strands count of 42. The support structure for LPF3-LTS has adopted a shell-based design, with an improved “Bladder & Key” technology. Dedicated hydraulic pistons were investigated and utilized to replace the traditional bladders. The main design characteristics, fabrication process and some preliminary test results of the magnet are presented in this paper.