A Surface Composition Study of Niobium after BCP for SRF Cavity in Particle Accelerator

Abstract

Nitrogen contamination from post-processing significantly affects the performance of niobium superconducting radiofrequency (SRF) cavities. Therefore, several performance-boosting strategies, including nitrogen doping, infusion and chemical acid reactions, have been explored in various studies. Among these studies, some secondary ion mass spectrometry (SIMS) results showed that nitrogen contamination exists on the niobium surface after the buffered chemical polishing (BCP) process. However, the compositions of these nitrogen byproducts were hard to detect. In this work, we calculated the chemical reaction process by the density function theory (DFT), predicted the reaction product, and then analyzed the Nb sample surface after BCP with X-ray Photoelectron Spectroscopy (XPS) to determine the composition of these contaminations.