Superconducting layer thickness dependence of magnetic relaxation property in CVD processed YGdBCO coated conductors

One of the most important properties of coated conductors for Superconducting Magnetic Energy Storage (SMES) is the relaxation property of persistent superconducting current. This property can be quantitatively characterized by the apparent pinning potential U-0(center dot). In this paper, the dependence of U-0(center dot) on the thickness of superconducting layer d is investigated in the range of 0.33-1.43 pm at the temperature range of 20-30 K and in magnetic fields up to 6.5 T for Y0.7Gd0.3Ba2Cu3O7-delta coated conductors. It was found that the value of critical current density did not appreciably depend on d at 20 K. This indicates that no structural deterioration of superconducting layer occurs during the process of increasing thickness. U-0(center dot) increases and then tends to decrease with an increasing magnetic field. The magnetic field at which U-0(center dot) starts to decrease increases with increasing thickness. This property was analyzed using the flux creep-flow model. Application of scaling law is examined for the dependence of U-0(center dot) on magnetic field and temperature. It was found that the dependence could be expressed using scaling parameters (B-peak,U-0 peak(center dot)) in the temperature range 20-30 K. (C) 2011 Published by Elsevier B.V.