Nanoscale analysis of Nb3Sn superconducting wires for Fusion and Future Colliders

一些最先进的超导材料正在被开发用于大型国际机器(加速器)、物理研究(CERN)和聚变演示器(ITER)的磁铁和电力电缆。在现有的超导材料中，Nb3Sn已被选为ITER大型强子对撞机的升级材料。为这些大型应用开发的最新一代Nb3Sn导体具有极其复杂的微结构，该结构针对在大磁场中传输非常高的电流进行了优化，而在纳米级控制元素分布是制造过程的关键部分。目前，表征这些复杂结构的方法主要是使用电子显微镜技术，但一些微量元素的规模和稀薄浓度都使提取信息变得非常困难，这些信息有助于线材开发人员了解添加的Zr、Ti、Hf和Ta是如何影响超导性能的。原子探针层析成像(APT)是在纳米尺度上研究这些材料的理想技术，但在这一领域的应用还很少。详细的原子组成数据将有助于理解这些添加对形成超导相的固态相变动力学和纳米尺度的磁通钉扎图景(晶界和人工钉扎中心)的影响。该项目的创新之处主要在于将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对Nb3Sn多丝导体的最新研究中。在项目的第一部分，学生将需要开发可靠的技术，从复杂的微结构中特定地点提取APT针，然后建立条件，对相同体积的脆性材料进行并行TKD和APT分析，以进行结构和化学关联。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超导层中的晶界化学。在项目接近尾声时，我们将获得我们在维也纳的合作者提供的经中子辐照的Nb3Sn样品，因此，研究在热核实验堆中使用的磁体绕组将经历的损坏机制。这项工作的一个具体焦点将是了解由于辐射破坏而导致的化学中原子尺度的变化。本项目属于EPSRC的能源主题和聚变的副主题

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