Protection of superconducting wires and cables used in high power/high field applications

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Superconducting materials have the unique property of carrying lossless DC currents below a given critical current (Ic) and critical temperature (Tc). Superconductors considered in this proposal are called “High Temperature Superconductors” (HTS), because they exhibit superconductivity above liquid nitrogen temperature, i.e. 77 K (-196oC), a cheap coolant that is affordable in large-scale applications such as power devices. HTS wires come in the form of flat tapes and can carry amazingly high current densities, e.g. >2 MA/cm2 at 77 K. They are perfect for applications such as high field electromagnets, which allow reaching unprecedented field values, e.g. up to 50 T at 4 K. This could be a game changer in high-resolution magnetic resonance imaging (MRI), nuclear fusion, particle accelerators, etc. Also, since magnets typically require hundreds of kilometers of HTS tapes, they are expected to be the big market “driver” sought for scaling-up the production and reduce costs of HTS wires in a near future. The biggest challenge with superconducting devices is to protect them reliably against thermal instabilities that can destroy them rapidly. In this proposal, we propose to expand the application range of a concept discovered within my research group and that is called “current flow diverter” (CFD). This concept allows speed-up by an order of magnitude the propagation of a thermal instability when it occurs, which considerably simplifies the protection of HTS devices, in particular HTS magnets. It is seen as a potential breakthrough in the discipline, and therefore deserves serious consideration in the short term. The technology was awarded a U.S. patent in May 2015, and further I.P. could arise form short-term research, with potentially wide market if it penetrates the MRI market. Within this project, the following main objectives will be pursued: 1) Find an effective and economical approach to implement the current flow diverter (CFD) concept on long lengths of commercial HTS tapes 2) Understand the impact of a hot spot nucleation in high-current cables made of many HTS tapes (e.g. Roebel or TASC cables) under various experimental conditions 3) Evaluate the impact of using the CFD concept combined with state-of-the-art protection systems for HTS magnets These objectives are aligned with the ultimate goal of my research program, which is to “allow the emergence of a new generation of compact and efficient superconducting devices for improving security of supply in power systems and enable the emergence of high field HTS magnets”. Along the project, it is planned to train 3 Ph.D. students, 5 Master’s student, and 5 summer interns. Some parts of the project will be carried out with international partners in order to take advantage of existing infrastructures and speed-up the generation of research results.