Analysis of Low Purity Niobium SRF Cavities

Superconducting radio-frequency (SRF) cavities are resonant structures that generate the accelerating electric field inside many particle accelerators. Introducing certain impurities into high-purity niobium can improve quality factors and accelerating gradients, allowing for lower cryogenic costs which may enable the next generation of accelerators. Success has been found in nitrogen-doping, infusion of the native oxide into the niobium surface, and thin films upon a niobium bulk. We question why some impurities improve RF performance while others hinder it. The purpose of this study is to characterize the impurity profile of low purity niobium, and correlate these intrinsic impurities with the performance of cavities with low residual resistance ratio (RRR) so that the mechanism of these impurity-based improvements can be better understood and improved upon. We have found behavioral similarities between low RRR cavities and to high RRR cavities that are weakly nitrogen-doped. Additionally, we performed surface treatments such as low temperature baking and nitrogen-doping on low RRR cavities to evaluate how the intentional addition of more impurities to the RF layer affects performance. Our results have the potential to unlock a new understanding on SRF materials.