Ultra low resistance joints for high temperature superconducting magnets

用于医疗保健和材料表征的下一代超高场磁体将需要我们利用高温超导(HTS)材料的特殊性能。这些磁体最具挑战性的设计特征之一是要求不同长度的超导导线之间的接头允许持续电流通过(电阻小于10-14欧姆！)在非常强的磁场中。这个与牛津仪器公司合作的EPSRC工业案例项目将专注于设计新的工艺来形成商业高温超导体之间的连接，并在实际工程条件下测量它们的性能。它将建立牛津仪器公司在高场超导磁体方面的世界领先专业知识，以及与牛津大学材料系成功的长期合作。实用的高场强超导磁体系统需要高温超导体(HTS)之间的低阻连接。此外，高温超导与低温超导(LTS)材料的连接将在高温超导/低温超导混合磁体中有实际应用。几种已开发的连接技术将根据它们的适用性进行选择，并应用于包含这种连接的示范超导磁体线圈的制造。然后将进行测试，以证明这些技术对真实研究仪器的适用性。到目前为止，牛津材料公司的工作已经产生了一种制造电流容量有限的超导接头的方法。对这个专业来说，一个新的研究挑战是开发临界电流与超导导线本身相当的接头。除了提供实验数据来阐明候选高温超导材料如Bi2Sr2CaCu2O8(Bi2212)和REBa2Cu3O7(REBCO)之间在低电阻下自连接的实用性外，该项目还将进一步包括确定将陶瓷高温超导材料连接到候选低温超导金属合金(LTS)的实际可能性的工作，这对材料提出了进一步的挑战，并在HTS/LTS混合超导磁体中具有实际应用。由于需要接头的重复性和坚固性，将超导接头集成到实际磁铁线圈中是一个进一步的挑战。一个实用的工程解决方案必须经受住反复的热循环和强磁场，这将出现在强场超导磁体系统中。学生将首先开发现有的管内粉末连接技术，应用于由牛津材料公司开发的Bi2212多丝导线。这项工作将包括实验，以澄清高温超导材料(如Bi2212和REBCO)以及高温超导材料和候选LTS材料之间在低电阻下自连接的实用性。将对接头的运输性能进行测量，作为接头质量的评估，并将使用扫描电子显微镜等技术来探索接头的微观结构。这项工作的最终结果将是制造包含超导连接首选方法的技术演示线圈。这些设备将在牛津仪器公司位于牛津郡塔布尼森林的现场在低温下设计、建造和测试，并得到OI人员的支持。在技术开发团队内进行以产品为重点的研究培训将完美地补充牛津大学材料组的学术重点。这种材料技术是未来产品的关键，无论是为了研究量子现象，还是为了提高固体和液体的核磁共振能力，特别是那些在高时间持久性下表征长链分子所需的能力。

The next generation of ultra-high field magnets for applications in healthcare and materials characterisation will need us to take advantage of the exceptional properties of high temperature superconducting (HTS) materials. One of the most challenging design features in these magnets is the requirement for joints between individual lengths of superconducting wire that allow the passage of persistent currents (resistances less than 10-14 Ohms!) in very high magnetic fields. This EPSRC Industrial CASE project with Oxford Instruments will focus on designing novel processes to form joints between commercial high temperature superconductors, and measuring their performance under real engineering conditions. It will build Oxford Instruments' world leading expertise in high field superconducting magnets and the successful long standing collaboration with the Department of Materials at the University of Oxford. Practical high field superconducting magnet systems with high temporal persistence will require low resistance joints between high temperature superconductors (HTS). Further to this, joints between HTS and low temperature superconductor (LTS) materials will have practical applications in HTS/LTS hybrid superconducting magnets. Several the developed jointing techniques will be selected based on their suitability and applied to the manufacture of demonstration superconducting magnet coils incorporating such a joint. Tests will then be carried out to demonstrate the applicability of the techniques to real research instruments. Work to date at Oxford Materials has resulted in a method of making superconducting joints that have limited current capacity. A novel research challenge for this studentship is the development of joints with comparable critical current to the superconducting wire itself.In addition to providing experimental data to clarify the practicalities of self-jointing at low resistance between candidate HTS materials such as Bi2Sr2CaCu2O8 (Bi-2212) and REBa2Cu3O7 (REBCO), the project will further encompass work to determine the practical possibilities of joining ceramic HTS materials to candidate low temperature superconducting metal alloys (LTS) which presents a further materials challenge and has practical applications in HTS/LTS hybrid superconducting magnets. Integration of superconducting joints into a practical magnet coil represents a further challenge due to the need for repeatability and robustness of the joint. A practical engineering solution must survive repeated thermal cycles and high magnetic fields that would be present in high field superconducting magnet systems. The student will begin by developing existing powder in tube jointing techniques applied to Bi-2212 multifilamentary wires, developed by Oxford Materials. The work will involve experiments to provide clarity on the practicalities of self-jointing at low resistance between HTS materials such as Bi-2212 and REBCO, and between HTS and candidate LTS materials. Measurement of the transport properties of the joints will be carried out as an assessment of joint quality, and techniques such as SEM will be used to explore the microstructure of joints. The work will culminate in manufacture of technology demonstration coils incorporating the preferred method of superconducting joint. These will be designed, built, and tested at cryogenic temperature at Oxford Instruments site at Tubney Woods in Oxfordshire, with support from OI personnel. Training on product focussed research within the technology development team would perfectly complement the academic focus in the materials group at Oxford University. This materials technology is key for future products both for the study of quantum phenomena and to enhance capabilities in NMR for solids and liquids, especially those required for long chain molecule characterisation at high temporal persistence.