Optimization and control of the field quality, the mechanical structure and the quench protection of superconducting dipoles for future accelerators

Future particle accelerators will require future magnets, this work addresses most of the problems involved in designing and building state-of-the-art superconducting magnets for particle accelerators. These issues are field quality control, mechanical design, and quench protection. This thesis includes, for each of these three topics, a general introduction, a case study, and the specific solutions implemented for it. In particular, in the case of field quality and quench protection analysis the case study is the MBRD separation/recombination dipole (Main Bending Recombination Dipole, or D2 for short) for the high luminosity upgrade of the LHC, while for the optimization of the mechanical design it is the FalconD magnet (Future Accelerator post-LHC Cos-theta Optimized Nb3Sn Dipole), which is a prototype that represents an intermediate step between the high-field magnets obtainable with today's technology and the magnets that will be required for the Future Circular Collider (FCC), a 100 TeV hadron accelerator. As regards the analysis of the quality of the field, it was possible to define the stability of the magnetic design of D2 the magnet by evaluating the sensitivity of the harmonic content of the field generated as the tolerances of the components involved in the coils varied. In addition, the optimal shimming strategy needed to finalize production of the D2 prototype and another one to meet the field quality acceptance criteria for the series magnets was found. For what concerns the studies on quench protection, one of the most recent computational tools specialized in the simulation of quench phenomena (LEDET) was used, calibrated, and validated both by using another older software (ROXIE) and by the measurements carried out on the short model of the D2 magnet. Thanks to this simulation campaign it was possible to set up the tests that will be performed on the D2 prototype and to update the quench protection strategy, since these simulations demonstrated that the previous one did not comply with the safety limits imposed on the project. The forthcoming measurements on the D2 prototype will validate both the quality of the construction process, the simulation models used and the design choices that have been made. Finally, the mechanical optimization work (performed with the f.e.m. software ANSYS) consists of the design of both the 2D and 3D mechanical structure of the Falcon Dipole, which is both a high field magnet (12 T of bore field) and a brittle superconductor (Nb3Sn). For these reasons, the success of the project strongly depends on the optimal management of the high Lorentz forces generated in the coils.