Positron Annihilation Lifetime Spectroscopy Study of Neutron Irradiated High Temperature Superconductors YBa_2Cu_3O_(7-δ) for Application in Fusion Facilities

摘要

This study focuses on the crystallographic defects introduced by neutron irradiation and the resulting changes of the superconducting properties in the high temperature superconductor YBa_2Cu_3O_(7-δ). This material is considered to be most promising for magnet systems in future fusion reactors. Two different bulk samples, pure non-doped YBa_2Cu_3O_(7-δ) (YBCO) and multi-seed YBa_2Cu_3O_(7-δ) doped by platinum (MS2F) were studied prior to and after irradiation in the TRIGA MARK II reactor in Vienna. Neutron irradiation is responsible for a significant enhancement of the critical current densities as well as for a reduction in critical temperature. The accumulation of small open volume defects (<0.5 nm) partially causes those changes. These defects were studied by positron annihilation lifetime spectroscopy at room temperature. A high concentration of Cu-O di-vacancies was found in both samples, which increased with neutron fluence. The defect concentration was significantly reduced after a heat treatment.