Paper | Title | Page |
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WEIAA01 |
The Frequency Shift and Q of Disordered Superconducting RF Cavities | |
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Funding: U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract No. DE-AC02-07CH11359. Superconducting RF (SRF) cavity resonators with ultrahigh-Q, originally developed for particle accelerator technology, are a key technology platform for detectors of rare events, e.g. light by light scattering mediated by virtual electron-positron pairs, axions [1] and high-frequency gravitational waves [2]. The mechanism(s) leading to current limits in Q are not fully understood. We developed a numerical method to calculate Q and cavity resonant frequency shifts based on nonequilibrium theory of superconductivity, including the role of impurity disorder, combined with Slater’s method for solving Maxwell’s equations for the EM field confined in a cavity [3]. Our results for the frequency shift and Q are in excellent agreement with experimental data reported by the SRF group at Fermilab [4]. As a measure of the predictive capability of the theory we are able to quantitatively account for changes in the resonant frequency of order 10 Hz for GHz SRF cavities over temperature ranges of 0.001 Tc. This level of predictive theory is essential for further improvements in performance of superconducting resonators and devices for quantum sensing and quantum processors. [1] Z. Bogorad et al., Phys. Rev. Lett. 123, 021801 (2019). [2] A. Berlin et al., arXiv:2303.0151. [3] H. Ueki, M. Zarea, and J. A. Sauls, arXiv:2207.14236. [4] D. Bafia et al., arXiv:2103.10601. |
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Slides WEIAA01 [4.722 MB] | ||
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WEIAA02 |
Temperature Responses of Superconducting Niobium Properties in Experiment and Simulation | |
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Mild, medium, and high temperature baking has been researched to obtain high-Q₀ SRF niobium cavities in past decades. It suggests that niobium has different properties when treated at different temperatures. We conducted various experiments on SRF-cavity-class niobium samples, and the systematic measurements included not only impurity analysis via TOF-SIMS, in-situ XPS, in-situ ESEM, HRTEM, but also superconductor measurements via in-situ ARPES. We also performed quantitative atomic simulation of the impurities in niobium bulks at zero temperature, and found interstitial carbon had similar trapping effect on interstitial hydrogen as interstitial nitrogen and oxygen did. We found the mildly increased interstitial carbons and oxygens during medium temperature baking not only suppressed the hydrogen accumulation and hydride precipitation during cooling down, but also reduced the electron mean free path to the optimal range which yielded declined BCS resistance. Therefore, the surface resistances of the cavities were reduced and the Q₀ values were improved correspondingly. | ||
Slides WEIAA02 [15.615 MB] | ||
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WEIAA03 | Surface Roughness Reduction and Performance of Vapor-Diffusion Coating of Nb₃Sn Film for SRF Application | 593 |
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Funding: This work is authored by Jefferson Science Associates LLC under U.S. DOE Contract No. DE-AC05- 06OR23177. Nb₃Sn offers the prospect of better RF performance (Q and Eacc) than niobium at any given temperature because of its superior superconducting properties. Nb₃Sn-coated SRF cavities are routinely produced by growing a few microns thick Nb₃Sn film on Nb cavities via tin vapor diffusion. It has been observed that a clean and smooth surface can enhance the performance of the Nb₃Sn-coated cavity, typically, the attainable acceleration gradient. The reduction of surface roughness is often linked with a correlative reduction in average coating thickness and grain size. Besides Sn supply’s careful tuning, the temperature profiles were varied to reduce the surface roughness as low as ~40 nm in 20 µm × 20 µm AFM scans, one-third that of the typical coating. Samples were systematically coated inside a mock single-cell cavity and examined using different material characterization techniques. A few sets of coating parameters were used to coat 1.3 GHz single-cell cavities to understand the effects of roughness variation on the RF performance. This presentation will discuss ways to reduce surface roughness with results from a systematic analysis of the samples and Nb₃Sn-coated single-cell cavities. |
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Slides WEIAA03 [7.231 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA03 | |
About • | Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 21 August 2023 | |
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WEIAA04 | Development of High-performance Niobium-3 Tin Cavities at Cornell University | 600 |
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Funding: Work supported by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beam and U.S. DOE grant No. DE-SC0008431. Niobium-3 tin is a promising material for next-generation superconducting RF cavities due to its high critical temperature and high theoretical field limit. There is currently significant worldwide effort aiming to improve Nb₃Sn growth to push this material to its ultimate performance limits. This talk will present an overview of Nb₃Sn cavity development at Cornell University. One approach we are pursuing is to further advance the vapor diffusion process through optimized nucleation and film thickness. Additionally, we are exploring alternative Nb₃Sn growth methods, such as the development of a plasma-enhanced chemical vapor deposition (CVD) system, as well as Nb₃Sn growth via electrochemical synthesis. |
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Slides WEIAA04 [5.260 MB] | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA04 | |
About • | Received ※ 29 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 21 August 2023 — Issue date ※ 22 August 2023 | |
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