Acceleration of the normal zone propagation velocity (NZPV) in high temperature superconducting tapes

by Prof. Frédéric Sirois (Polytechnique Montreal, Canada)

Tuesday 8 Dec 2015, 14:00 → 15:00 Europe/Zurich

30/7-010 (CERN)

Commercial second generation (2G) high temperature superconductor (HTS) coated conductors (CCs) possess a low normal zone propagation velocity (NZPV) in comparison with low temperature superconductor wires. One consequence of a low NZPV is that 2G HTS CCs must be over-stabilized in order to prevent the appearance of hot spots, which reduces their engineering critical current and their resistance per unit length. Recently, a tape architecture called “current flow diverter (CFD)” was proposed to enhance by orders of magnitude the NZPV of 2G HTS CCs [1]. In the CFD concept, the interfacial resistance between the HTS and silver layers is strongly increased at the center of the tape but kept low at the tape edges. The current flow is then diverted towards the tape edges when it transfers from the HTS layer to the stabilizer, which results in an important increase of the current transfer length and the NZPV, with only a minor impact on tape stability, characterized by the minimum quench energy (MQE). In this work, we developed an electro-thermal model using the finite element method to investigate the effects of various parameters, such as the temperature, critical current, stabilizer thickness, applied current, etc., on the performance of the CFD architecture in comparison with commercial 2G HTS CCs. Our results show that the CFD architecture increases the NZPV for the whole range of operating temperature considered (4 – 90 K). Also, we found out that the benefits of the CFD architecture, in terms of NZPV, are higher when the stabilizer is thinner and the critical current gets higher. An enhancement of the NZPV of more than two orders of magnitude is predicted for specific tape configurations. Finally, we compared our numerical results with experimental ones and discuss the possible improvements to the model in order to fully reproduce the experimental behavior of CFD tapes. The results are directly applicable to the design of more robust fault current limiters and magnet quench protection systems. [1] C. Lacroix and F. Sirois, "Concept of current flow diverter for accelerating the normal propagation velocity area in 2G HTS coated conductors" (2014) Supercond. Sci. Technol., V27, p035003.