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.