Enhanced isotropic pinning at 20K from columnar defects

Nov. 30 10:55-11:10

*Nicholas M Strickland1, Arya A Soman1, Stuart C Wimbush1, Nicholas J Long1, Patrick Kluth2, Christian Notthoff2, Martin W Rupich3, Ruth Knibbe4, Ming Li4
Victoria University of Wellington1
Australian National University2
American Superconductor Corporation3
University of Queensland4

Ion irradiation of REBCO thin films and coated conductors is well known to introduce extra pinning centers. These arise as damage tracks from the passage of the ions and can range from point-like defects to discontinuous columns to fully continuous columns depending on the energy-loss profile of the ion. We have explored irradiation with Ag ions with energies from 50 MeV to 150 MeV and have seen that in this range the defects transition from point-like defects at the low energy end to discontinuous columns at the high end. The columnar defects result in strong peaks appearing in the angular dependence of critical currents at temperatures above 40 K, with strong pinning enhancements for field applied parallel to the irradiation direction. Below 40 K there is a transition to the pinning enhancement becoming quite isotropic. We interpret this as arising from an interaction between the columnar pins, intrinsic pins and point pins. The result is an enhancement of up to a factor of 3 for the angular minimum critical current at 20 K.

Keywords: coated conductors, ion irradiation, columnar defects, critical current