Development of demountable superconducting contacts for MRI magnet switches

商业磁共振成像(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。磁体通常在不同长度的Nb-Ti多丝超导导线之间包含10个以上的接头，每个接头必须具有10-13欧米伽的电阻才能实现持久模式操作。为了第一次给磁体充电，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，允许电流从电源进入磁铁，然后闭合形成连续的超导电路，从而可以移除电源。目前制造开关的技术利用超导/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，这将在其商业磁铁的设计中提供更大的灵活性。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来控制大电流超导电路，而不是单独的开关电路。一个成功的工程解决方案需要更好地了解如何控制构成开关元件的接触面的结构和电(超导)特性。该项目旨在将概念带到技术准备级别4-离线概念验证。它将涉及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较短，以及暴露表面上的污染和/或氧化过程，超导体到超导体的界面很少允许简单的接触接头在超导状态下运行。在过去的十年里，超导小组建立了一套方法，用于设计不同类别的超导材料之间的接头，测试它们的性能，并将这种性能与使用各种先进显微技术分析的接头微观结构和纳米级化学相关联。该项目的创新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，以设计和制造可使用工业赞助商西门子医疗有限公司的大电流设施进行测试的原型开关。该项目由西门子医疗有限公司获得EPSRC工业科学与工程合作奖支持，奖券编号为20000165，属于EPSRC的研究主题工程、医疗保健技术和制造未来。禤浩焯博士、托马斯博士和莫哈迈德·拉克里米博士将担任该项目的工业监督。

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.