Abstract
To enhance the critical current density (Jc) in magnetic fields, we performed heavy-ion irradiation to introduce artificial pinning centers into YBCO—coated conductors. It is well known that high-energy heavy-ion irradiation introduces amorphous tracks along ion trajectories. Since the morphology and the size of the defect depend on the electron stopping power, Se, we used three different irradiation conditions, namely, 400 MeV Kr-ions, 450 MeV Xe-ions, and 500 MeV Au-ions, to study its effect. All of them enhance the in-field Jc, though the largest enhancement was observed after irradiation with 450 MeV Xe-ions. We also studied the dependence of Jc enhancement to optimize irradiation fluence. In all cases, the reduction of Jc was observed when the irradiation fluence exceeded 1 x 1012 ions/cm2, which may be attributed to the reduction of superconducting volume as well as the depression of superconductivity. From the angular dependence of Jc measurement, the columnar defects act as unidirectional pinning sites, as expected, but with a very large trapping angle of approximately 45°.
