Comparison of mechanical concepts for $Nb_3Sn$ high field accelerator magnets

Several magnets using Nb$_{3}$Sn as conductor are currently developed at CERN; these magnets are either slated for future updates of the LHC or for research purposes relating to future accelerators. The mechanical structure is one of the challenging aspects of superconducting high-field magnets. The main purpose of the mechanical structure is to keep the coils in compression till the emergence of the highest electromagnetic forces that are developed in the ultimate field of the magnet. Any loss of pre-compression during the magnet’s excitation would cause too large deformation of the coil and possibly a quench in the conductor owing to relative movements of strands in contact associated with excessive local heat release. However, too high pre-compression would overstrain the conductor and thereby limit the performance of the magnet. This thesis focuses on the mechanical behaviour of three of these magnets. All of them are based on different mechanical designs, “bladder and key” and “collar-based”, for the support of the coils. The magnets compared in this thesis are the DS11T and SMC dipole and the MQXF quadropole. Based on the experience of already built magnets, a matrix of parameters is defined to assess the performance of each structure. These parameters are: the maximal transversal and equivalent stress during the assembly and the powering of the magnet; the loss of pre-compression of the conductor during the powering; the overstraining of the conductor and by thus reducing the critical current