High-$Q_0$ Treatment of CEBAF 1.5 GHz SRF Cavities

Abstract

The Continuous Electron Beam Accelerator Facility (CEBAF) was the first large-scale accelerator to employ superconducting radiofrequency (SRF) cavities for continuous-wave operation. Ongoing research and development efforts continue to focus on increasing the intrinsic quality factor ($Q_0$) of these cavities in order to reduce cryogenic losses while maintaining operational gradients. In this work, we report on the application of high-$Q_0$ surface treatments to single-cell and multicell C100 and C75 style 1.5 GHz niobium cavities used in the CEBAF accelerator. Nitrogen infusion and oxygen alloying via medium-temperature baking were applied under heat-treatment constraints relevant to existing cavity hardware. Both processes yielded substantial improvements in $Q_0$ at moderate accelerating gradients, achieving values of approximately 2 $\times$ 10$^{10}$ at 2.07 K and 20 MV/m. The effectiveness of nitrogen infusion at reduced annealing temperatures and the successful extension of oxygen alloying to multicell cavities are demonstrated. These results establish viable pathways for implementing high-$Q_0$ treatments in CEBAF-compatible cavities and support future integration into cryomodules for reduced operational cryogenic load.