Ultra low resistance joints for high temperature superconducting magnets

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.