Saturday, 3F-06, 9:20-9:30

Alternating Current Losses of Infinite Stacks of Superconductor/Ferromagnet Tapes

Yasunori Mawatari

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305–8568 Japan
Phone: +81-29-861-5737; Fax: +81-29-861-5726; E-mail: y.mawatari@aist.go.jp

Ferromagnetic materials (e.g., Ni-W alloys) are used as metal substrates for superconducting coated conductors, and such tapes have superconductor/ferromagnet (SC/FM) bilayer structures. The contributions of ferromagnetic hysteresis losses to the total losses of SC/FM tape are negligibly small, and the superconducting hysteresis losses are dominant especially in large current and/or magnetic field regions. Nevertheless, the superconducting hysteresis losses are affected by the ferromagnetic substrates, because the current/field (i.e., current density and magnetic field) distributions in superconducting layers are changed by the magnetic interaction between the superconductors and ferromagnets. By using the complex field approach and the ideal soft magnet model, we recently proposed an analytical model to investigate current/field distributions and ac losses of SC/FM tapes [1]. The ferromagnetic substrate is considered as an ideal soft magnet, which has an infinite permeability without magnetic saturation and has no ferromagnetic hysteresis. The critical state model with a constant jc is adopted for superconducting layers, and the thickness/width ratio of the SC/FM tapes is treated as an infinitesimal. This simplified model allows us to obtain analytical expressions of the current/field distributions and the ac losses of a single isolated SC/FM tape [1]. We have also theoretically investigated current/field distributions and ac losses of infinite stacks of SC/FM tapes, and we found that the effects of the ferromagnetic substrates on the ac losses of the stacks of SC/FM tapes are smaller than those of a single isolated SC/FM tape.
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[1] Y. Mawatari, Phys. Rev. B 77, 140545 (2008).

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