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。这些磁体中最具挑战性的设计特征之一是要求在允许持续电流（电阻小于10-14欧姆！）通过的各个长度的超导导线之间的接头。在非常强的磁场中。这个EPSRC工业案例项目与牛津仪器将专注于设计新的工艺，以形成商业高温超导体之间的接头，并在真实的工程条件下测量其性能。它将建立牛津仪器在高场超导磁体领域的世界领先的专业知识，并与牛津大学材料系成功地长期合作。具有高时间持久性的实用高场超导磁体系统将要求高温超导体（HTS）之间的低电阻接头。此外，高温超导体和低温超导体（LTS）材料之间的连接将在高温超导/低温超导混合超导磁体中具有实际应用。几个开发的连接技术将选择其适用性的基础上，并应用于示范超导磁体线圈的制造，包括这样的联合。然后将进行测试，以证明这些技术对真实的研究仪器的适用性。迄今为止，牛津材料公司的工作已经产生了一种制造具有有限电流容量的超导接头的方法。该研究项目的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HTS材料（如Bi-2212和REBa 2Cu 3 O 7）之间低电阻自连接的实用性外，该项目还将进一步开展工作，确定将陶瓷高温超导材料与候选的低温超导金属合金（LTS）连接起来的实际可能性这提出了进一步的材料挑战，并在HTS/LTS混合超导磁体中具有实际应用。由于需要接头的可重复性和鲁棒性，将超导接头集成到实际的磁体线圈中代表了进一步的挑战。一个实用的工程解决方案必须经受住重复的热循环和高磁场，这将存在于高场超导磁体系统中。学生将开始通过开发现有的粉末在管焊接技术应用到Bi-2212多芯线，由牛津材料开发。这项工作将涉及实验，以提供在低电阻的自连接HTS材料，如Bi-2212和REBCO之间，以及HTS和候选LTS材料之间的实用性的清晰度。将对接头的传输特性进行测量，以评估接头质量，并使用SEM等技术探索接头的微观结构。这项工作将最终在制造技术示范线圈纳入超导接头的首选方法。这些将在牛津郡Tubney Woods的Oxford Instruments工厂的低温下设计、制造和测试，并得到OI人员的支持。在技术开发团队中对产品进行重点研究的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，无论是量子现象的研究，还是提高固体和液体的NMR能力，特别是那些需要在高时间持久性的长链分子表征。

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.