Paper |
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MOPA67 |
Examining the Effects of Oxygen Doping on SRF Cavity Performance |
cavity, SRF, niobium, ECR |
196 |
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- H. Hu, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
- D. Bafia
Fermilab, Batavia, Illinois, USA
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Superconducting radiofrequency (SRF) cavities are resonators with extremely low surface resistance that enable accelerating cavities to have extremely high quality factors (Q0). High (Q0) decreases the capital required to keep accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first 100 nm of the cavity surface. Impurities such as oxygen and nitrogen have been observed to yield high Q0, but their precise roles are still being studied. Here, we compare the performance of cavities doped with nitrogen and oxygen in terms of fundamental material properties to understand how these impurities affect performance. This enables us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q0 performance.
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DOI • |
reference for this paper
※ doi:10.18429/JACoW-NAPAC2022-MOPA67
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About • |
Received ※ 02 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 03 October 2022 |
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WEZE5 |
Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium |
cavity, SRF, niobium, ECR |
611 |
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- B.D. Khanal
ODU, Norfolk, Virginia, USA
- S. Balachandran, P.J. Lee
NHMFL, Tallahassee, Florida, USA
- S. Chetri
ASC, Tallahassee, Florida, USA
- P. Dhakal
JLab, Newport News, Virginia, USA
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Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.
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Slides WEZE5 [2.029 MB]
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DOI • |
reference for this paper
※ doi:10.18429/JACoW-NAPAC2022-WEZE5
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About • |
Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022 |
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WEPA27 |
Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities |
cavity, niobium, SRF, accelerating-gradient |
683 |
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- B.D. Khanal
ODU, Norfolk, Virginia, USA
- P. Dhakal
JLab, Newport News, Virginia, USA
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Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.
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DOI • |
reference for this paper
※ doi:10.18429/JACoW-NAPAC2022-WEPA27
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About • |
Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022 |
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THYE5 |
Analysis of Low RRR SRF Cavities |
cavity, SRF, niobium, accelerating-gradient |
877 |
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- K. Howard, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
- D. Bafia, A. Grassellino
Fermilab, Batavia, Illinois, USA
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Recent findings in the superconducting radio-frequency (SRF) community have shown that introducing certain impurities into high-purity niobium can improve quality factors and accelerating gradients. Success has been found in nitrogen-doping, diffusion of the native oxide into the niobium surface, and thin films of alternate superconductors atop a niobium bulk cavity. We question why some impurities improve RF performance while others hinder it. The purpose of this study is to characterize the impurity profile of niobium with a low residual resistance ratio (RRR) and correlate these impurities with the RF performance of low RRR cavities so that the mechanism of recent impurity-based improvements can be better understood and improved upon. Additionally, we performed surface treatments, low temperature baking and nitrogen-doping, on low RRR cavities to evaluate how the intentional addition of more impurities to the RF layer affects performance. We have found that low RRR cavities experience low temperature-dependent BCS resistance behavior more prominently than their high RRR counterparts. The results of this study have the potential to unlock a new understanding on SRF materials.
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Slides THYE5 [5.013 MB]
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DOI • |
reference for this paper
※ doi:10.18429/JACoW-NAPAC2022-THYE5
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About • |
Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 01 October 2022 |
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THYE6 |
First Demonstration of a ZrNb Alloyed Surface for Superconducting Radio-Frequency Cavities |
cavity, SRF, electron, superconductivity |
881 |
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- Z. Sun, M. Liepe, T.E. Oseroff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
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Surface design of the RF surface is a promising path to next-generation SRF cavities. Here, we report a new strategy based on ZrNb surface alloying. Material development via an electrochemical process will be detailed. RF performance evaluated in the Cornell sample host cavity will be discussed. Cornell demonstrates that ZrNb alloying is a viable new technology to improve the performance of SRF cavities.
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Slides THYE6 [1.459 MB]
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DOI • |
reference for this paper
※ doi:10.18429/JACoW-NAPAC2022-THYE6
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About • |
Received ※ 22 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 20 August 2022 |
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