Nb₃Sn Wires for the Future Circular Collider at CERN: Microstructural Investigation of Different Wire Layouts

Abstract

In the challenging project concerning the realization of the CERN Future Circular Collider (FCC), Nb3Sn represents the best candidate material for the construction of high-field superconducting dipole magnets, since it is able to satisfy the requirements of Jc (non-Cu) = 1.5 kA/mm 2 at 16 T and 4.2 K. In that context, a cluster layout of prototype internal tin Nb3Sn wires, developed by TVEL and the Bochvar Institute (Russia), was analyzed and compared to a standard layout produced by the same manufacturer. The main reason for dividing the subelement into clusters is reducing the effective sub-element size (deff). The microstructural characterization of such a wire layout can provide fundamental contributions to steer the manufacturing processes towards higher performing wires. In particular, since the homogeneity in Sn concentration influences the superconducting properties, the effect of cluster and standard layouts on the Sn concentration gradient over the wire cross-section was evaluated. For this purpose, energy dispersive X-ray (EDX) spectroscopy was employed with both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Finally, scanning Hall probe microscopy (SHPM) measurements were performed to understand how these cluster wire sub-elements, with their specific geometry, influence the local currents flowing through the wire cross-section on a microscopic scale. The comprehension of the correlation between the microstructural characteristics and superconducting performance is crucial for obtaining wires meeting the requirements of FCC dipole magnets.

Development of an Alternative Manufacturing Technology for Niobium Components

“…Niobiumbased superconducting materials are used in particle accelerators, including the Large Hadron Collider (LHC) and will be used in the next generation of accelerators (Future Circular Collider, LCC). These materials provide a critical current density of up to 3500 A/mm 2 in a magnetic field of 12 T and at a temperature of 4.2 K. They are characterized by low residual resistivity and good mechanical properties [10,11]. Niobium is also used in the nuclear power industry due to its small effective neutron absorption cross-section (1.15 × 10 −28 m 2 ) and good tensile strength.…”