Development of demountable superconducting contacts for MRI magnet switches

商用磁共振成像（MRI）人体扫描仪中的静态背景场是由超导磁体在没有电源的情况下以持续模式运行而产生的。磁铁通常在不同长度的Nb-Ti多丝超导线之间包含超过10个接头，每个接头的电阻必须小于10-13 ω，以实现持久模式操作。为了在第一次给磁铁充电，需要一个特殊的接头来形成超导开关。在安装磁铁时，开关打开，使电流从电源进入磁铁，然后关闭，形成一个连续的超导电路，这样电源就可以移除。目前的开关制造技术是利用超导/正常转变，在充电过程中通过加热将一段特殊的超导开关线驱动到正常状态。西门子希望设计和测试一种替代开关概念，这将为其商业磁铁的设计提供更大的灵活性。目的和目标：该项目将开发和测试一种新的开关系统，该系统能够通过物理上可拆卸的超导触点而不是单独的开关电路来控制大电流超导电路。一个成功的工程解决方案需要更好地理解如何控制构成开关元件的接触面的结构和电（超导）特性。该项目旨在将该概念提升至技术准备程度4级——离线概念验证。它将包括调查和选择合适的接触材料，并探索在主要载流超导材料之间创建合适的界面或中间层的加工技术。研究方法的新颖性：众所周知，由于大多数可用材料的相干长度短以及暴露表面的污染和/或氧化过程，超导体-超导体界面很少允许简单的接触接头在超导状态下工作。在过去的十年中，超导小组建立了一套设计不同类别超导材料之间接头的方法，测试它们的性能，并将这种性能与接头的微观结构和纳米级化学分析联系起来，使用各种先进的显微镜技术。该项目的新颖之处在于将这些材料选择和分析技术应用于各种超导材料的表面和界面，以便设计和制造原型开关，这些开关可以在工业赞助商西门子医疗保健有限公司的高电流设施中进行测试。该项目得到了EPSRC工业科学与工程合作奖的支持，该奖的奖券编号为20000165，授予西门子医疗保健有限公司，属于EPSRC的研究主题工程、医疗保健技术和制造业的未来。Adrian Thomas博士和M'hamed Lakrimi将担任该项目的工业主管。

The static background field in commercial magnetic resonance imaging (MRI) body scanners is generated by superconducting magnets operating in persistent mode without a power supply. The magnets typically contain more than 10 joints between separate lengths of Nb-Ti multifilamentary superconducting wire, each of which must have a resistance <10-13 omega to enable persistent mode operation. In order to charge the magnet in the first instance, a special joint is needed to form a superconducting switch. On installation of the magnet, the switch is opened to allow current to be driven into the magnet from a power supply and then closed to form a continuous superconducting circuit so the power supply can be removed. Current technology to fabricate a switch exploits the superconducting/normal transition to drive a length of special superconducting switch wire into the normal state during the charging process by heating. Siemens wish to design and test an alternative switch concept which will offer greater flexibility in the design of their commercial magnets. Aims and objectives: This project will develop and test a new switch system capable of controlling a high current superconducting circuit through physically demountable superconducting contacts rather than a separate switching circuit. A successful engineering solution will require a much better understanding of how to control the structure and electrical (superconducting) properties of the contact surfaces that form the switching element. The project is intended to take the concept to Technology Readiness Level 4 - offline concept validation. It will involve investigating and selecting suitable contact materials and explore the processing techniques for creating suitable interfaces or intermediary layers between the main current carrying superconducting materials. Novelty of the research methodology: It is known that superconductor-to-superconductor interfaces rarely allow simple contact joints to operate in the superconducting state because of the short coherence lengths in most available materials and contamination and/or oxidation processes on exposed surfaces. The Superconductivity Group has over the past decade built up a methodology for the design of joints between different classes of superconducting materials, in testing their performance and in correlating this performance with the joint microstructure and nanoscale chemistry analysed using a wide variety of advanced microscopy techniques. The novelty of the project lies in applying these materials selection and analysis techniques to the surfaces and interfaces of a wide range of superconducting materials in order to design and fabricate prototype switches that can be tested using high current facilities in the industrial sponsor, Siemens Healthcare Limited. This project is supported by EPSRC Industrial Collaborative Award in Science and Engineering voucher number 20000165 awarded to Siemens Healthcare Limited, and falls within the EPSRC research themes Engineering, Healthcare Technologies and Manufacturing the Future. Dr Adrian Thomas and M'hamed Lakrimi will be the industrial supervisors of this project.