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

Abstract

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 U0∗. In this paper, the dependence of U0∗ on the thickness of superconducting layer d is investigated in the range of 0.33–1.43μm at the temperature range of 20–30K and in magnetic fields up to 6.5 T for Y0.7Gd0.3Ba2Cu3O7−δ coated conductors. It was found that the value of critical current density did not appreciably depend on d at 20K. This indicates that no structural deterioration of superconducting layer occurs during the process of increasing thickness. U0∗ increases and then tends to decrease with an increasing magnetic field. The magnetic field at which U0∗ 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 U0∗ on magnetic field and temperature. It was found that the dependence could be expressed using scaling parameters Bpeak,U0peak∗ in the temperature range 20–30K.