Division of accelerators, cryogenics and magnetism

In the continuity of the Large Hadron Collider (LHC) large-scale projects are under development, such as the HiLumi - LHC and the Future Circular Collider (FCC), in order to produce particle collisions at higher luminosities and energies. The achievement of these projects strongly relies on the development of high field Nb₃Sn magnets. The Nb₃Sn intermetallic superconducting phase is produced through diffusion and phase transformations during a heat treatment at about 650 °C.

The study is focused on Rod Restacked Process (RRP) conductors. The heat treatment is composed of several dwells, activating different diffusion mechanisms and phase transformations. These mechanisms, located into the filament area of each strand, naturally lead to variations of the crystalline structure thus. In order to predict the mechanical state and therefore the stress conditions of Nb₃Sn conductors at a higher scale – cables and coils – it is primordial to first study the thermo-mechanical at the level of the strands.

Thus, a study of phase kinetic in strands is proposed, taking into account the chemical phenomena occurring during the heat treatment in the filament area. Chemical properties are here determined experimentally using Energy Dispersive X-ray Spectroscopy and microscope analysis on strand cross sections.

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