Fatigue tests of YBCO coated conductors

Abstract

In this paper, we report the fatigue characteristics of IBAD/PLD YBCO coated conductors. A YBCO coated conductor used in the superconducting coil of a SMES system is repeatedly subjected to mechanical tensile or compressive strain due to the Lorentz force during electrical charging or discharging. The superconducting characteristic of this conductor may deteriorate because of this cyclic strain. Therefore, it is necessary to investigate the effect of cyclic strain on the superconducting characteristics of YBCO coated conductors that have a laminated structure. We developed an experimental apparatus with a U-shaped sample holder in order to apply cyclic strain to the sample tape. This apparatus was used to perform the fatigue tests on YBCO coated conductors in liquid nitrogen in the absence of an external magnetic field. The strain cycles with the maximum strain ϵmax (zero external strain → ϵmax → zero external strain) were applied and repeated up to 5000 times, and the Ic measurements were performed at ϵmax. Therefore, the application of cyclic strain with ϵmax ranging from 0.3% to 0.5% did not result in any significant deterioration of the superconducting characteristics of the conductor.