An Investigation of the Influence of Grain Boundaries on Flux Penetration in High Purity Large Grain Niobium for Particle Accelerators

To measure inter and intra-Jb we applied transport current as a function of perpendicular magnetic field on chemically polished single and bi-crystals on as-received, high-purity (RRR>250), large-grain niobium sheet [1]. After measurement, we were able to use magneto-optical imaging to observe preferential flux penetration at some Nb grain boundaries, and finally we observed the microstructure of the GB in the same sample by scanning transmission electron microscopy (STEM), using EELS (Electron Energy Loss Spectroscopy) for oxygen analysis. The TEM sample was prepared using a FIB (Focused Ion Beam) tool, which can create cross sectional TEM lamellae and preserve the topmost layer of the sample. The STEM and EELS study was accomplished at ORNL as part of a SHaRE collaboration [2].