| Paper | Title | Page |
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| SUPCAV003 | Dynamic Temperature Mapping of Nb3Sn Cavities | 6 |
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| Niobium-3 Tin (Nb3Sn) is the most promising alternative material to niobium for SRF accelerator cavities. The material promises nearly twice the potential accelerating gradients (~100 MV/m in TESLA elliptical cavities), increased quality factors, and 4.2 K operation. Current state of the art Nb3Sn cavities reach quality factors of 2 x 1010 at 4.2 K and have reached 24 MV/m. Determining the cause of the premature field limitation is the topic of ongoing research. Cornell University has recently developed a high-speed temperature mapping system that can examine cavity quench mechanisms in never before achieved ways. Here we present high-speed temperature map results of Nb3Sn cavities and examine the quench mechanism and dynamic heating. We show an initial multipacting quench and sudden temperature jumps at multiple locations on the cavity. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPCAV003 | |
| About • | Received ※ 09 July 2021 — Accepted ※ 12 August 2021 — Issue date ※ 31 August 2021 | |
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| SUPTEV008 | CW Operation of Conduction-Cooled Nb3Sn SRF Cavity | 133 |
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| Significant progress in the performance of SRF cavities coated with Nb3Sn films during the last few years has provided an energy efficient alternative to traditional Nb cavities, thereby initiating a fundamental shift in SRF technology. These Nb3Sn cavities can operate at significantly higher temperatures than Nb cavities while simultaneously requiring less cooling power. This allows for the use of new cryogenic cooling schemes based on conduction cooling with robust, commercialized turn-key style cryocoolers. Cornell University has developed and tested a 2.6 GHz Nb3Sn cavity assembly which utilizes such cooling methods. These tests have demonstrated stable RF operation at 10 MV/m with measured thermal dynamics which match numerical simulations. These results also serve as a foundation for designing a new standalone SRF cryomodule which will use a pair of cryocoolers to cool a 1.3 GHz Nb3Sn cavity with an input coupler capable of supporting high beam current operation. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPTEV008 | |
| About • | Received ※ 22 June 2021 — Accepted ※ 13 August 2021 — Issue date ※ 08 November 2021 | |
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| TUOFDV05 | Dynamics of RF Dissipation Probed via High-Speed Temperature Mapping | 349 |
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| Recently, Cornell University has developed a new high-speed, high-resolution temperature mapping system that can resolve the time dynamics of RF dissipation, i.e., provide high-speed videos of the surface heating across the entire surface of the cavity. This new powerful tool allows to observe rapid changes in the local RF dissipation, as well as to resolve the dynamics of quenches, field emission processing, and other cavity events, giving new insights into these. This contribution presents the development of this new high-speed temperature mapping system, discusses its commissioning and extensive performance testing (e.g., demonstrating micro-Kelvin resolution), as well as show intriguing high-speed temperature mapping results from multiple Nb3Sn cavities. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUOFDV05 | |
| About • | Received ※ 01 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 06 February 2022 | |
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| TUPFDV010 | New Recipes to Optimize the Niobium Oxide Surface From First-Principles Calculations | 426 |
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Funding: This work was supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams The properties of niobium oxide are of critical importance for a wide range of topics, from the behavior of nitrogen during infusion treatments, to the nucleation of Nb3Sn, to the superconducting properties of the surface. However, the modeling of the oxide is often much simplified, ignoring the variety of niobium oxide phases and the extremely different properties of these phases in the presence of impurities and defects. We use density functional theory (DFT) to investigate how electrochemical treatments and gas infusion procedures change the properties of niobium oxide, and to investigate how these properties could be optimized for Nb3Sn nucleation and for niobium SRF performance. |
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| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUPFDV010 | |
| About • | Received ※ 01 July 2021 — Accepted ※ 18 November 2021 — Issue date ※ 22 February 2022 | |
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| WEOTEV03 | Toward Stoichiometric and Low-Surface-Roughness Nb3Sn Thin Films via Direct Electrochemical Deposition | 710 |
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| Reducing surface roughness and attaining stoichiometry of Nb3Sn superconducting films are required to push their superheating field to the theoretical limit in SRF cavities. As such, we explore direct electrochemical processes that minimize involving foreign elements to deposit high-quality Sn, Nb, and NbxSn films on Nb and Cu surfaces. These films are then thermally annealed to Nb3Sn. We find that smooth Sn pre-depositions via electroplating on Nb surfaces significantly reduce the average roughness of resultant Nb3Sn to 65 nm, with a dramatic reduction in power intensity at medium special frequencies. Structural and superconducting properties demonstrate a Nb3Sn A15 phase with a stoichiometry of 25 at% Sn. This process is being scaled-up to a 3.9 GHz cavity. Moreover, preliminary results on electroplating on Cu surface show that Nb plating undergoes a slow growth rate while subsequent Sn plating on the plated Nb surface can be controlled with varied thickness. The Nb plating process is currently being optimized. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEOTEV03 | |
| About • | Received ※ 09 July 2021 — Revised ※ 09 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 16 January 2022 | |
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| THPTEV004 | Surface Oxides on Nb and Nb3Sn Surfaces: Toward a Deeper Understanding | 836 |
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| Surface oxides on Nb and Nb3Sn SRF cavities, as a thin ’dirty’ layer, could be critical to their performance as suggested by recent theory. Although these oxides have been studied in the past, we intend here to provide a deeper understanding based on a systematic study on coupon samples that have been processed under the different conditions currently used in SRF cavity treatments. Our aim is to obtain a more complete picture of the oxide evolution. This then might help to explain the observed cavity performance variation, and might allow designing a process to achieve a designed, optimized surface with controlled oxides types and thickness. We find that the surface oxides are in amorphous phase that exhibits normal conducting behaviors, while the pentoxide further degrades with time. Also, we observed a thin hydroxide layer on the outermost surface and possibly Nb(OH)x motifs in the bulk. Moreover, distinctive oxide structures were found in Nb3Sn samples from vapor diffusion, electroplating, and sputtering. The semiconducting SnOx appeared through the oxide depth in vapor diffused Nb3Sn, while a ~1 nm SnOx layer merely exists at the outermost surface of electroplated Nb3Sn. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-THPTEV004 | |
| About • | Received ※ 09 July 2021 — Revised ※ 11 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 04 November 2021 | |
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