Electromagnetic design optimization of the 12 T Cos-theta dipole model for the FCC

The Falcon Dipole (Future Accelerator post-Lhc Costheta Optimized Nb3Sn Dipole) is a single aperture Nb3Sn cos-theta dipole short model in the framework of the Future Circular Collider (FCC) project. The Italian Institute of Nuclear Physics (INFN), in collaboration with CERN, is in charge of designing and constructing the magnet, which is supposed to be a crucial step towards the construction of high field Nb3Sn magnets suitable for a post LHC collider. The short model has a target bore field of 12T, but the design presented has a short sample field of 15.59 T at 1.9 K. The aperture diameter is 50 mm, and the field is generated by two layers of state-of-art Nb3Sn Rutherford cable in costheta configuration. The magnet is pre-loaded with the Bladder&Key technique to minimize the stress in the coils, which are prone to degradation because of the Nb3Sn cable strain sensitivity. In the thesis, the electromagnetic design is presented, focusing on field quality and performance. The 2D and 3D FEM are used to design the coil layout, compute the margins and analyse the field quality. A special focus is given to the superconductor magnetization which is due to persistent current arising during the ramp-up and down of the magnet operational current. This effect perturbs the field quality especially during the beam injection phase and is a source of dissipation because of its hysteretic behavior. In Nb3Sn-based magnets the level of the magnetization is almost one order of magnitude higher than in the NbTi-based magnets, therefore in this work some compensation methods are proposed as suitable solutions in view of the construction of high field magnets for the next generation accelerators.