Nanoscale analysis of Nb3Sn superconducting wires for Fusion and Future Colliders

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Some of the most advanced superconducting materials are being developed for applications in the magnets and power cables for large international machines (accelerators) for physics research (CERN) and for fusion demonstrators (ITER). Of the available superconducting materials, Nb3Sn has been chosen for ITER the LHC upgrade. The latest generation of Nb3Sn conductors developed for these large applications have extremely complex microstructures that are optimised for carrying very high currents in large magnetic fields, and controlling the elemental distributions at the nanoscale is a vital part of the manufacturing process. Characterising these complex structures is currently done using mostly electron microscopy techniques, but both the scale and the dilute concentrations of some of the trace elements makes it very challenging to extract the information that helps the wire developers understand how additions like Zr, Ti, Hf and Ta effect the superconducting properties. Atom Probe Tomography (APT) is the ideal technique to study these materials at the nanoscale, but has hardly been used in this field. Detailed atomistic composition data will help understand the influence of these additions on both the kinetics of the solid state phase transformation that forms the superconducting phase and the nanoscale flux pinning landscape (grain boundaries and artificial pinning centres). The novelty in this project lies primarily in the application of APT in the study of state of the art Nb3Sn multifilamentary conductors from our collaborators in Florida State University and the National High Magnetic Field Laboratory in Tallahassee. In the first part of the project, the student will need to develop reliable techniques for the site-specific extraction of APT needles from a complex microstructure, and then to establish conditions for parallel TKD and APT analysis of the same volume of a brittle material for structural and chemical correlation. A second stage will be to compare samples with different heat treatments and different reactive metal additions (and combinations), with a specific aim to study the grain boundary chemistry in the reacted Nb3Sn superconducting layers. Towards the end of the project we will have access to neutron irradiated Nb3Sn samples from our collaborators in Vienna so study the damage mechanisms that the magnet windings will experience in service in ITER. A specific focus of this work will be to understand atomic scale changes in chemistry as a result of the radiation damage.This project falls within the EPSRC Theme of Energy and sub-theme of Fusion