Evaluation of Layer Thickness Dependence of Critical Current Density using Longitudinal Magnetic Field Effect in Superconducting Coated Conductors

When the critical current density J(c) for a superconductor is constant, the critical current I-c increases in proportion to the superconducting cross-sectional area. However, in the case of a superconducting coated conductor, when the thickness of the superconducting layer exceeds about 2 mu m, there is no further increase in I-c. This is because J(c) decreases due to the structural degradation of the superconducting layer. In this study, J(c) for samples with superconducting layers of different thicknesses was measured using the longitudinal magnetic field effect in order to investigate the optimum layer thickness for maximizing I-c. Differences in the J(c) characteristics due to the layer thickness appeared more clearly under a longitudinal magnetic field than a transverse magnetic field. This was particularly true at low temperatures, and the optimum layer thickness was found to be approximately 1 mu m.