Nanoscale analysis of Nb3Sn superconducting wires for Fusion and Future Colliders

一些最先进的超导材料正在开发中，用于大型国际机器（加速器）、物理研究（欧洲核子研究中心）和聚变示范（ITER）的磁体和电力电缆。在现有的超导材料中，Nb3Sn已被选择用于ITER的大型强子对撞机升级。为这些大型应用而开发的最新一代Nb3Sn导体具有极其复杂的微结构，可以在大磁场中携带非常高的电流，并且在纳米尺度上控制元素分布是制造过程的重要组成部分。表征这些复杂结构目前主要使用电子显微镜技术，但是一些微量元素的规模和稀释浓度使得提取信息非常具有挑战性，这些信息可以帮助线材开发人员了解Zr， Ti， Hf和Ta等添加剂如何影响超导性能。原子探针层析成像（APT）是纳米尺度上研究这些材料的理想技术，但在该领域的应用很少。详细的原子组成数据将有助于理解这些添加物对形成超导相的固态相变动力学和纳米级通量钉钉景观（晶界和人工钉钉中心）的影响。这个项目的新颖之处主要在于将APT应用于我们在佛罗里达州立大学和塔拉哈西国家强磁场实验室的合作者研究最先进的Nb3Sn多丝导体。在项目的第一部分，学生将需要开发可靠的技术，从复杂的微观结构中提取特定地点的APT针，然后为相同体积的脆性材料的结构和化学相关性建立平行TKD和APT分析的条件。第二阶段将比较不同热处理和不同活性金属添加（和组合）的样品，具体目的是研究反应Nb3Sn超导层的晶界化学。在项目结束时，我们将从维也纳的合作者那里获得中子辐照的Nb3Sn样品，以便研究ITER中磁体绕组在服务中会经历的损伤机制。这项工作的一个具体重点将是了解原子尺度的化学变化作为辐射损伤的结果。该项目属于EPSRC能源主题和聚变子主题

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