The Anomalous Resonant Frequency Variation of Microwave Superconducting Niobium Cavities Near $T_c$

• URL: http://arxiv.org/abs/2103.10601v2
• Date: Mon, 4 Oct 2021 17:06:10 GMT
• Title: The Anomalous Resonant Frequency Variation of Microwave Superconducting Niobium Cavities Near $T_c$
• Authors: D. Bafia (1), A. Grassellino (1), M. Checchin (1), J. F. Zasadzinski (2), and A. Romanenko (1) ((1) Fermi National Accelerator Laboratory, (2) Illinois Institute of Technology)
• Abstract summary: We report a systematic effect in Nb cavities indicative of improved superconducting properties. The frequency dip magnitude correlates with cavity quality factor, near-surface impurity distribution, and $T_mathrmc$. A first demonstration of the coherence peak in the AC conductivity in Nb SRF cavities is also presented and found to correlate with a large frequency dip.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Superconducting radio-frequency (SRF) niobium cavities are the modern means of particle acceleration and an enabling technology for record coherence superconducting quantum systems and ultra-sensitive searches for new physics. Here, we report a systematic effect in Nb cavities indicative of improved superconducting properties - an anomalous decrease (dip) in the resonant frequency at temperatures just below the critical temperature $T_\mathrm{c}$. The frequency dip magnitude correlates with cavity quality factor, near-surface impurity distribution, and $T_\mathrm{c}$. It is also a precursor of the peculiar decrease in the BCS surface impedance with increasing RF current. A first demonstration of the coherence peak in the AC conductivity in Nb SRF cavities is also presented and found to correlate with a large frequency dip.

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