Study of dislocation content near grain boundaries using electron channeling contrast imaging and its effect on the superconducting properties of niobium∗

Trapped micro-Tesla levels of magnetic flux degrade the performance of Nb superconducting radio frequency (SRF) accelerators. Recent studies have revisited the role of small deformation (dislocation substructure influence) on cavity performance. However, the link between microstructural defects and mechanisms leading to poor performance is still unresolved. To examine the mechanism of flux pinning by dislocations and grain boundaries, bi-crystal Nb tensile samples were designed with strategically chosen tensile axes to favor introduction of dislocation content near grain boundaries by a small tensile strain. Dislocation structures near the grain boundaries were characterized before and after 5% tensile deformation using electron channeling contrast imaging (ECCI), after which the magnetic flux behavior was observed using cryogenic magneto-optical (MO) imaging. The conditions which increase the tendency to trap flux in regions of high dislocation density of one Nb bi-crystal are discussed.