2019 EPFL doctorate Award - Finalist – Nikolay Bykovskiy

State-of-the-art magnets of fusion devices, which are based on low temperature superconductors (LTS), have almost reached their technological limits. Further progress can be made using novel high temperature superconductors (HTS). While LTS conductors can be manufactured in a favorable geometry of round wires, the most promising HTS materials are only available as thin tapes. Thus, new cabling concepts suitable to arrange hundreds of thin tapes should be identified and developed. An intermediate cabling ’solution’ – the strand – where a stack of ten to forty tapes is encased between two semicircular copper profiles, twisted and soldered together, has been investigated in details for its mechanical, electromagnetic and thermal properties. Thanks to its round geometry, the HTS strand can be used in conventional cabling methods such as the Rutherford-like cable design. As a result of full-scale R&D activity at the Swiss Plasma Center, 60 kA-class HTS cable prototypes have been manufactured and successfully tested at high background magnetic fields, up to 12 T. Results and implications of these measurements constitute the backbone of this thesis and demonstrate that the use of HTS cables can open access to fields above 15 T in fusion magnets, which has potential to reduce the overall dimensions and cost of fusion devices.