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

Alice Moros,Stefan Loffler,Anastasiia Tsapleva,Victor Pantsyrny,Michael Eisterer,Simon C Hopkins,Maxim Alekseev,Mattia Ortino,Michael Stoger-Pollach,Pavel Lukyanov,Ildar M Abdyukhanov,Johannes Bernardi

doi:10.1109/tasc.2021.3066541

Abstract

In the challenging project concerning the realization of the CERN Future Circular Collider (FCC), Nb 3 Sn represents the best candidate material for the construction of high-field superconducting dipole magnets, since it is able to satisfy the requirements of J c (non-Cu) = 1.5 kA/mm 2 at 16 T and 4.2 K. In that context, a cluster layout of prototype internal tin Nb 3 Sn 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 sub-element into clusters is reducing the effective sub-element size (d eff ). 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.

Highlights

THE European Organization for Nuclear Research (CERN) recently published a conceptual design study for a future hadron collider (FCC-hh)
By comparing the three-cluster wire T3 to the standard one T4 (Fig. 5a), the Sn concentration gradient was found to be smaller for the T3 (Fig. 5b): in both standard and cluster cases, the slope of the Sn gradient is slightly ascending towards the core at the limit of the measurement accuracy, but it is more pronounced in the case of the T4
As a first step to have a feel for the three-cluster layout transport performance, the T3 local properties were evaluated by scanning Hall probe microscopy (SHPM) remanent-field scans at Atominstitut, Technische Universität Wien (TU Wien)

Summary

Introduction

THE European Organization for Nuclear Research (CERN) recently published a conceptual design study for a future hadron collider (FCC-hh). This study aims at building a 100. This work is part of the Marie Skłodowska-Curie Action EASITrain (European Advanced Superconductivity Innovation and Training), funded by the European Union’s H2020 Framework Programme under grant agreement no. The development of wires by the Bochvar Institute (addenda KE2968 and KE4037) and their characterisation at TU Wien (addendum KE3194) was supported by CERN in the context of the FCC Study. Eisterer are with the TU Wien, ATOMINSTITUT, Stadionallee 2, 1020 Vienna, Austria

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