Division of accelerators, cryogenics and magnetism

In agreement with the CERN’s advertised will for the implementation of a super-collider, FCC type, high field superconducting electromagnets, based on Nb3Sn, are being developed. In the framework of the HFM (High Field Magnets) European collaboration, the LEAS at CEA Paris-Saclay is designing, manufacturing, and testing superconducting magnet demonstrators generating up to 16 T. Nb3Sn conductors require a heat treatment at 650 °C. During this heat treatment, several physico-chemical phenomena lead to the formation of the Nb3Sn superconducting phase. These phenomena induce a mechanical state impacting the superconducting properties of the material. A study of the different phenomena inducing dimensional changes inside the conductors would allow estimating the stresses inside the Nb3Sn superconducting phase following the heat treatment. The goal of this thesis is to study, using modeling and experiments, the thermomechanical state of the conductors during the heat treatment in order to estimate the internal stresses and their impact on the superconducting performances. The results will allow the improvement of the Nb3Sn superconducting properties in view of the production of high field magnets for future accelerators.