AC loss in ReBCO pancake coils and stacks of them: modelling and measurement

• Published in: Superconductor science & technology 2012-03, Vol.25 (3), p.035003-1-16
• Main Authors: Pardo, E, Šouc, J, Ková, J
• Format: Article
• Language: English
• Subjects: Alternating current; Applied sciences; Coiling; Computer simulation; Conductors; Electrical engineering. Electrical power engineering; Electromagnets; Exact sciences and technology; Optimization; Pancake coils; Stacks; Superconducting tapes; Various equipment and components
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/25/3/035003

Many applications of ReBCO-coated conductors contain stacks of pancake coils. In order to reduce their high AC loss, it is necessary to understand the loss mechanisms. In this paper, we measure and simulate the AC loss and the critical current, Ic, in stacks of pancake coils ('pancakes'). We construct stacks of up to four pancakes and we measure them by electrical means. We also obtain the anisotropic field dependence of Jc from Ic measurements of the tape. This Jc is the only input to the simulations, together with the coil dimensions. After validating our computations with the measurements, we simulate stacks of many pancakes, up to 32. We found that the AC loss in a stack of (four) pancakes is very high, two orders of magnitude larger than for a single tape. A double pancake behaves as a single one with double the width but a stack of more pancakes is very different. Finally, we found that a two-strand Roebel cable reduces the AC loss in a stack of pancakes but not in a single pancake. In conclusion, our simulations are useful to predict the AC loss of stacks of coated conductor pancake coils and to reduce the AC loss by optimizing the coil design.