Evaluation AC Losses in Large-Scale Conductors Consisting of Stacked REBCO Tapes

In this work, stacked model conductors consisting of dozens of YBCO tapes were fabricated and experimentally investigated to determine whether the hysteresis and coupling losses affect each other. When an oblique magnetic field is applied to the tape, hysteresis and coupling losses are expected to be generated simultaneously. A uniform AC transverse magnetic field was applied to the sample in liquid nitrogen, and the AC losses were measured via the pickup coil method. The measurements were carried with the magnetic field applied at various angles with respect to the tape wide surface. The measured AC losses were separated into hysteresis and coupling losses. The measured hysteresis losses well agreed with the theoretical values for a square cross-section superconductor. This indicates that hysteresis losses can be considered in terms of the magnetic field component perpendicular to the flat face of the YBCO tape. The coupling time constant was found to be independent of the applied magnetic field angle. This shows that coupling losses can be considered in terms of the magnetic field component parallel to the tape's wide surface, and the permeability in the conductor can be assumed to be the vacuum permeability.