Mechanical Design of FECD1 at IHEP: A 12-T Hybrid Common-Coil Dipole Magnet

A 12-T Nb3Sn/NbTi common-coil dipole magnet with the outer diameter of 720 mm is under development as the first R&D step towards the final 20-T accelerator dipole magnet which is required in the Super proton-proton Collider. This Flat End Common-coil Dipole magnet is based on the shell support structure with the bladder & key technology. The designed peak field is 12-T in the Nb3Sn inner coil at the operating current of 3,970 A, with a margin of 18.4% at 4.2 K. The coil structure is optimized to enhance the transfer efficiency of horizontal preload and the central magnetic field. The aluminum alloy tie rod is used to apply axial preload to the coils. The stress in the whole dipole magnet is below an acceptable level when the shell thickness is 60 mm and the friction coefficient is 0.2. The coil displacement after excitation is below 8 μm. Further analysis indicates that a larger shell thickness may increase the cold shrinking force and a larger friction coefficient value can lead to the rise of peak coil stress.