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The development of high-field accelerator magnets capable of providing 16-T dipolar fields is an indispensable technological breakthrough needed for the 100-TeV energy frontier targeted by the Future Circular Collider (FCC). Such a field level is about twice that of the Nb-Ti magnets installed in the Large Hadron Collider (LHC) at CERN, which represent the end-of-the-line in terms of performance of accelerator magnets based on this material.  Nb3Sn is the superconducting material poised to take the place of Nb-Ti as the next step in accelerator magnet technology, but the performance of state-of-the-art industrial wires is not sufficient in view of the projected target of a minimum critical current density, Jc, of more than 1’500 A/mm2 at 16 T and 4.2 K.

The WireDev project at UNIGE is motivated by the need to push Nb3Sn technology towards its ultimate performance in view of achieving and exceeding the requirements of the FCC study. The in-field critical current capabilities for any type-II superconductor rely on its ability to impede vortex motion, i.e. to pin the vortex lines into the material. This ability is given by the presence of the so-called pinning centers, features in the material that interact attractively with individual vortices. Grain boundaries represent the primary pinning centers in Nb3Sn: higher current densities are thus obtained in materials that have finer grains. The Group of Applied Superconductivity at UNIGE is working in close collaboration with CERN to the development of methods for refining the grain size of Nb3Sn in multifilamentary wires with processes scalable to the industrial production.

This research activity is part of the CHART initiative and is supported by the Swiss National Science Foundation (Grant No. 200021_184940) and by the European Organization for Nuclear Research (CERN), Memorandum of Understanding for the FCC Study, Addendum FCC-GOV-CC-0175 (KE 4663/ATS).

Since 2015, CHART, which stands for “Swiss Accelerator Research & Technology”, has been bringing together the Swiss leading forces in the R&D of superconductor technology for accelerators under the auspices of the State Secretariat for Education, Research and Innovation (SERI). This interdisciplinary collaboration includes researchers from the Paul Scherrer Institute (PSI), the two Federal Institutes of Technology in Zurich and Lausanne, the University of Geneva and, of course, CERN, and one of its main goals is the design, construction and test of a 16 T dipole prototype.