Speaker
Description
Superconducting radio-frequency (SRF) cavity surface treatment with nitrogen-doping (N-doping) was a breakthrough in cavity processing which was found capable of increasing the cavity quality factor (Q0) by more than a factor of 2 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 been extensively studied in 1.3 GHz cavities; however, a similarly significant increase in performance had not yet been observed in sub-GHz cavities. In this study, field-dependent BCS and residual resistances were measured in 644 MHz cavities for the FRIB energy upgrade with various surface treatments. The frequency dependence of the Q-slope was investigated by measuring BCS and residual resistances in the 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 performance, including achievements of Q0 as high as 4.9x10^10 at 17.5 MV/m 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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