AC Loss Properties of YBCO Superconducting Tapes Exposed to External Ac Magnetic Field

We investigated the ac loss properties of YBCO superconducting tapes fabricated by IBAD-PLD technique. The thickness of a YBCO superconducting layer was 0.5 and 1 /spl mu/m. Sample tapes of 60 mm in length and 10 mm in width were stacked into multilayers and inserted into a saddle-shaped pickup coil. The ac loss was measured at 64 K and 77 K by applying external ac magnetic field. The magnetic field angle was changed by rotating the sample stack around its longitudinal axis. The ac loss for the smaller amplitude than the effective penetration field strongly depended on the number of stacked tapes owing to the demagnetization effect. On the other hand, the ac loss for the much larger amplitude than that was independent of the number of tapes. In addition the ac loss decreased monotonically with decreasing field angle against the wide surface for any amplitude. We proposed the theoretical expression to estimate the ac losses for any field angle by using the observed ac losses in perpendicular magnetic field and confirmed the applicability by good agreement between theory and experiment.