Effects of neutron radiation on the local Jc in YBCO on RABiTS templates

Abstract

HTS based coated conductors appear to be the go-to materials for future fusion magnet designs. Since they will be exposed to high neutron fluences, an understanding of the radiation effects on the coated conductors is of utmost importance. The current transport at low fields is restrained by the inter-granular current density (Jc,GB) flowing across grain boundaries, however at high fields, the critical current density within the grains (Jc,G) limits the current transport. Exposing the coated conductor to neutron radiation results in an initial increase of Jc,G, whereas Jc,GB continually degrades. The introduction of additional pinning centers in the material explains the increase of Jc,G, but the reason for the decrease of Jc,GB is yet to be fully understood and directly addressed in this study. YBCO films were grown on RABiTS templates and MgO single crystals via pulsed laser deposition. These materials were chosen, since they enable an in-depth analysis of the radiation effects on the local current density within grains and across grain boundaries. Local current maps were obtained by means of Scanning Hall Probe Microscopy and subsequent inversion of the Biot-Savart law. The density function of the Jc distribution was derived from these maps and provides insights into the magnetic granularity of the sample. Alterations in the current flow pattern in conjunction with shifts in the Jc distribution clarify the radiation effects and the underlying changes in Jc,G and Jc,GB of the coated conductor.