R and D on large grain niobium materials for SCRF-cavity applications

We present a study of superconducting properties and thermal conductivity in large grain (1 mm average grain size). Niobium-materials that have been used in the fabrication of high accelerating gradient superconducting radio frequency (SCRF) cavities. We found that the chemical polishing of these Niobium-materials caused a distinct reduction in the superconducting parameters like Tc and Hc1. However, the deteriorating effect of electropolishing (EP) on the superconducting properties of Niobium-materials is distinctly less than that of buffer chemical polishing (BCP). Correlations between the microscopic superconducting properties of Niobium-materials and the performance of Niobium-SCRF cavities are discussed especially the anomalous high field RF losses that have been reported in the literature. (author)