An Experimental Study of the Ferromagnetic Loss in 2G YBCO Tapes

Most second-generation high-temperature superconductor tapes are prepared on ferromagnetic substrates. It is known that the presence of this substrate increases the tape´s ac losses. Thus, it is important to determine the contribution of the ferromagnetic loss to adequately evaluate the ac loss and achieve good designs of superconducting power devices based on YBCO-coated conductors. We here describe the design and testing of an experimental method to determine the ferromagnetic loss in the substrate. The setup consists of two coils wound around a core made of a YBCO tape. One of the coils is a feed coil used to create an alternating magnetic field in the core. The other is a pickup coil used to measure the electromotive force (emf) due to the magnetic field. The core consists of three turns of RABiTS-processed YBCO-coated conductor with nickel alloy substrate and stainless steel stabilization. The values of B and H to obtain the hysteresis cycle were obtained as follows: H was obtained from the current in the feed coil, and B was obtained by integration of the emf measured in the pickup coil. The ferromagnetic loss was measured with different currents, as well as frequencies in the range of 50-100 Hz.