Speaker
Description
Superconducting radiofrequency (SRF) cavity surface treatment with nitrogen-doping (N-doping) was a breakthrough in cavity processing which was found capable of increasing cavity quality factor (Q0) by over a factor of two compared to standard electropolish (EP) surface treatments, as well as achieving a highly desirable anti-Q slope behavior, an increase of Q0 with increasing accelerating field, in 1.3 GHz superconducting niobium cavities. N-doping has since been extensively studied in 1.3 GHz cavities; however, due to the frequency dependence of these effects, a similarly significant increase in Q0 and anti-Q slope had not yet been realized in sub-GHz cavities. In this study, field-dependent BCS and residual resistances were measured in 644 MHz FRIB400 R&D cavities with various surface treatments. Frequency dependence of the Q-slopes was investigated by measuring BCS and residual resistances in the 644 MHz fundamental mode (FM) and 1.45 GHz higher-order mode (HOM) in the same cavity. We will report effects of various N-doping surface treatments on the FM and HOM Q-curves, including an observed anti-Q slope in the 644 MHz FM with 900 degrees C N-doping, a never-before-seen behavior in this class of SRF cavities.
Funding Agency
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC0023633.
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