SRF2023 - Classification: Fundamental SRF research and development / New materials beyond niobium

Paper	Title	Page
MOPMB005	Muon Spin Rotation Studies of Bilayer Superconductors and Low Temperature Baked Niobium	62
SUSPB002	use link to see paper's listing under its alternate paper code
	M. Asaduzzaman, R.E. Laxdal, R.M.L. McFadden, E. Thoeng TRIUMF, Vancouver, Canada M. Asaduzzaman, T. Junginger, R.M.L. McFadden UVIC, Victoria, Canada E. Thoeng UBC & TRIUMF, Vancouver, British Columbia, Canada
	Funding: Financial support was provided by an Natural Sciences and Engineering Research Council of Canada (NSERC) Muon spin rotation (muSR) results have shown that vortex penetration into Nb can be delayed up to the superheating field Hsh by a single layer of a material with larger London penetration depth. For low temperature baked (LTB) Nb an increase in the vortex penetration field Hvp has also been observed. While clearly exceeding the lower critical field Hc1, Hvp was found to remain significantly below Hsh for LTB niobium (Superconductor Science and Technology 30 (12), 125012). Further, magnetometry experiments suggested that there is no interface barrier in LTB Nb and that the apparent Hvp increase as observed by muSR was due to surface pinning (Scientific Reports 12 (1), 5522). By varying the implantation depth of ~4.1 MeV muons using moderating foils, new muSR measurements confirm that the apparent Hvp increase in LTB Nb is indeed due to surface pinning, while for a Nb₃Sn/Nb bilayer we find an interface barrier for flux penetration. These results confirm the potential of using superconducting bilayers to achieve a flux free Meissner state up to the superheating field of the substrate.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB005
About •	Received ※ 17 June 2023 — Revised ※ 21 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 21 July 2023
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MOPMB011	Deposition and Characterisation of V₃Si films for SRF Applications	84
	C. Benjamin, J.A. Conlon, O.B. Malyshev, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, O.B. Malyshev, D.J. Seal, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom G. Burt, D.J. Seal Lancaster University, Lancaster, United Kingdom N.L. Leicester, H.S. Marks Cockcroft Institute, Lancaster University, Lancaster, United Kingdom L.G.P. Smith STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. A15 superconducting materials, like V₃Si and Nb₃Sn, are potential alternatives to Nb for next generation thin film SRF cavities when operated at 4 K. Their relatively high Tc and superconducting properties could allow for higher accelerating gradients and elevated operating temperatures. We present work on the deposition of V₃Si thin films on planar Cu substrates and an open structure 6 GHz cavity, using physical vapour deposition (PVD) and a V₃Si single target. The surface structure, composition and DC superconducting properties of two planar samples were characterised via secondary electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and in a magnetic field penetration facility. Furthermore, the first deposition using PVD of a V₃Si film on a 6 GHz split cavity and the RF performance is presented.
	Poster MOPMB011 [7.496 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB011
About •	Received ※ 16 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 19 July 2023
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MOPMB013	Influence of the Coating Parameters on the Tc of Nb₃Sn Thin Films on Copper Deposited via DC Magnetron Sputtering	92
SUSPB007	use link to see paper's listing under its alternate paper code
	D. Fonnesu, O. Azzolini, R. Caforio, E. Chyhyrynets, D. Ford, V.A. Garcia, G. Keppel, C. Pira, A. Salmaso, F. Stivanello INFN/LNL, Legnaro (PD), Italy G. Marconato Università degli Studi di Padova, Padova, Italy
	Funding: The I.FAST project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Work supported by the INFN CSNV experiment SAMARA. The I.FAST collaboration aims at pushing the performance of particle accelerators by developing sustainable innovative technologies. Among its goals, the development of thin film-coated copper elliptical accelerating cavities covers both the optimization of the manufacturing of seamless substrates and the development of functional coatings able to conform to the 3D cavity geometry while delivering the needed performance. For the latter, the optimization of the deposition recipe is central to a successful outcome. The work presented here focuses on the deposition of Nb₃Sn films on flat, small copper samples. The films are deposited via DCMS from a planar stoichiometric Nb₃Sn commercial target. The results of the film characterization are presented here. The observed dependencies between the film properties and, in particular, Tc(90%-10%) = (17.9±0.1)K is reported for Nb₃Sn on sapphire and Tc(90%-10%) = (16.9±0.2)K for Nb₃Sn on copper with a 30 micron thick niobium buffer layer.
	Poster MOPMB013 [1.749 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB013
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 02 July 2023
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MOPMB015	Development of a Plasma-Enhanced Chemical Vapor Deposition System for High-Performance SRF Cavities	100
SUSPB009	use link to see paper's listing under its alternate paper code
	G. Gaitan, A.T. Holic, W.I. Howes, G. Kulina, P. Quigley, J. Sears, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Liepe Cornell University, Ithaca, New York, USA B.W. Wendland University of Minnesota, Minnesota, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, or other compound superconductors are essential for reaching enhanced RF performance levels in SRF cavities. However, optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a high-vacuum, gas, and precursor delivery system, and uses plasma to significantly reduce the required processing temperature and promote precursor decomposition. Here we present an update on the development of this system, including final system design, safety considerations, assembly, and commissioning.
	Poster MOPMB015 [1.951 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB015
About •	Received ※ 16 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 16 July 2023
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MOPMB047	Commissioning of Dedicated Furnace for Nb₃Sn Coatings of 2.6 GHz Single Cell Cavities	216
SUSPB018	use link to see paper's listing under its alternate paper code
	P.A. Kulyavtsev, G.V. Eremeev, S. Posen, B. Tennis Fermilab, Batavia, Illinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. We present the results of commissioning a dedicated furnace for Nb₃Sn coatings of 2.6GHz single cell cavities. Nb₃Sn is a desired coating due to its high critical temperature and smaller surface resistance compared to bulk Nb. Usage of Nb₃Sn coated cavities will greatly reduce operating costs due to its higher operating temperature providing decreased cooling costs. Tin is deposited in the bulk Nb cavity by use of a tin chloride nucleation agent and tin vapor diffusion. Analysis of the resultant coating was performed using SEM/EDS to verify successful formation of desired Nb:Sn phase. Witness samples located in line of sight of the source were analyzed in order to understand the coating efficacy. The cavity’s performance was assessed in the Vertical Test Stand (VTS) at Fermilab.
	Poster MOPMB047 [4.858 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB047
About •	Received ※ 26 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 08 July 2023
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MOPMB053	Theoretical Study of Thin Noble-Metal Films on the Niobium Surface	230
SUSPB021	use link to see paper's listing under its alternate paper code
	C.A. Méndez, T. Arias, M. Liepe, N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: The Center for Bright Beams, Supported by National Science Foundation award No. PHY-1549132 Recent experiments suggest that noble-metal deposition on niobium metal surfaces can remove the surface oxide and ultimately improve superconducting radio-frequency (SRF) cavities performance. In this preliminary study, we use density-functional theory to investigate the potential for noble-metal passivation of realistic, polycrystalline niobium surfaces for SRF. Specifically, we investigate the stability of gold and palladium monolayers on niobium surfaces with different crystal orientations and evaluate the impact of these impurities on superconducting properties. In particular, our results suggest that gold can grow in thin layers on the niobium surface, whereas palladium rather tends to dissolve into the niobium cavity. These results will help inform ongoing experimental efforts to passivate niobium surfaces of SRF cavities.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB053
About •	Received ※ 22 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023
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MOPMB093	Optimizing Growth of Niobium-3 Tin Through Pre-nucleation Chemical Treatments	337
SUSPB026	use link to see paper's listing under its alternate paper code
	S.G. Arnold, G. Gaitan, M. Liepe, L. Shpani, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Arias, N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams. Nb₃Sn is a promising alternative material for SRF cavities that is close to reaching practical applications. To date, one of the most effective growth methods for this material is vapor diffusion, yet further improvement is needed for Nb₃Sn to reach its full potential. The major issues faced by vapor diffusion are tin depleted regions and surface roughness, both of which lead to impaired performance. Literature has shown that the niobium surface oxide plays an important role in the binding of tin to niobium. In this study, we performed various chemical treatments on niobium samples pre-nucleation to enhance tin nucleation. We quantify the effect that these various treatments had through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). These methods reveal information on tin nucleation density and uniformity, and a thin tin film present on most samples, even in the absence of nucleation sites. We present our findings from these surface characterization methods and introduce a framework for quantitatively comparing the samples. We plan to apply the most effective treatment to a cavity and conduct an RF test soon.
	Poster MOPMB093 [1.118 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB093
About •	Received ※ 21 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 July 2023
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TUPTB001	Demonstration of Niobium Tin in 218 MHz Low-Beta Quarter Wave Accelerator Cavity	388
	T.B. Petersen, G. Chen, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, T. Reid ANL, Lemont, Illinois, USA G.V. Eremeev, S. Posen, B. Tennis Fermilab, Batavia, Illinois, USA
	A 218 MHz quarter wave niobium cavity has been fabricated for the purpose of demonstrating Nb₃Sn technology on a low-beta accelerator cavity. Niobium-tin has been established as a promising next generation SRF material, but development has focused primarily in high-beta elliptical cell cavities. This material has a significantly higher TC than niobium, allowing for design of higher frequency quarter wave cavities (that are subsequently smaller) as well as for significantly lowered cooling requirements (possibly leading to cryocooler based de-signs). The fabrication, initial cold testing, and Nb₃Sn coating are discussed as well as test plans and details of future applications.
	Poster TUPTB001 [0.653 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB001
About •	Received ※ 16 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 08 July 2023
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TUPTB004	Progress on Zirconium-Doped Niobium Surfaces	398
	N. Sitaraman, T. Arias, Z. Baraissov, D.A. Muller Cornell University, Ithaca, New York, USA G. Gaitan, M. Liepe, T.E. Oseroff, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the NSF under Award PHY-1549132, the Center for Bright Beams, and in part by CNF (NSF Grant NNCI-2025233), and in part by CCMR (DMR-1719875). The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB004
About •	Received ※ 30 June 2023 — Revised ※ 26 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 22 August 2023
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TUPTB006	Materials Design for Superconducting RF Cavities: Electroplating Sn, Zr, and Au onto Nb and and Chemical Vapor Deposition	401
	Z. Sun, M. Liepe, T.E. Oseroff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Z. Baraissov, D.A. Muller, M.O. Thompson Cornell University, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Materials scientists seek to contribute to the development of next-generation superconducting radio-frequency (SRF) accelerating cavities. Here, we summarize our achievements and learnings in designing advanced SRF materials and surfaces, including Nb₃Sn [1¿3], ZrNb(CO) [4, 5], and Au/Nb surface design [6,7]. Our efforts involve electrochemical synthesis, phase transformation, and surface chemistry, which are closely coupled with superconducting properties, SRF performance, and engineering considerations. We develop electrochemical processes for Sn, Zr, and Au on the Nb surface, an essential step in our investigation for producing high-quality Nb₃Sn, ZrNb(CO), and Au/Nb structures. Additionally, we design a custom chemical vapor deposition system to offer additional growth options. Notably, we find the second-phase NbC formation in ZrNb(CO) and in ultra-high-vacuum baked or nitrogen-processed Nb. We also identify low-dielectric-loss ZrO2 on Nb and NbZr(CO) surfaces. These advancements provide materials science approaches dealing with fundamental and technical challenges to build high-performance, multi-scale, robust SRF cavities for particle accelerators and quantum applications.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB006
About •	Received ※ 30 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
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TUPTB010	Preservation of the High Quality Factor and Accelerating Gradient of Nb₃Sn-Coated Cavity During Pair Assembly	405
	G.V. Eremeev, S. Cheban, S. Posen, B. Tennis Fermilab, Batavia, Illinois, USA J.F. Fischer, D. Forehand, U. Pudasaini, A.V. Reilly, R.A. Rimmer JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. Two CEBAF 5-cell accelerator cavities have been coated with Nb₃Sn film using the vapor diffusion technique. One cavity was coated in the Jefferson Lab Nb₃Sn cavity coating system, and the other in the Fermilab Nb₃Sn coating system. Both cavities were measured at 4 K and 2 K in the vertical dewar test in each lab and then assembled into a cavity pair at Jefferson Lab. Previous attempts to assemble Nb₃Sn cavities into a cavity pair degraded the superconducting properties of Nb₃Sn-coated cavities. This contribution discusses the efforts to identify and mitigate the pair assembly challenges and will present the results of the vertical tests before and after pair assembly. Notably, one of the cavities reached the highest gradient above 80 mT in the vertical test after the pair assembly.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB010
About •	Received ※ 23 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 02 July 2023 — Issue date ※ 09 July 2023
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TUPTB013	Commissioning of a New Sample Test Cavity for Rapid RF Characterization of SRF Materials	410
	S. Keckert, J. Knobloch, F. Kramer, O. Kugeler HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany
	RaSTA, the Rapid Superconductor Test Apparatus, is a new sample test cavity that is currently being commissioned at HZB. It uses the established QPR sample geometry but with a much smaller cylindrical cavity operating in the TM020 mode at 4.8 GHz. Its compact design allows for smaller cryogenic test stands and reduced turnaround time, enabling iterative measurement campaigns for thin film R&D. Using the same calorimetric measurement technique as known from the QPR allows direct measurements of the residual resistance. We report first prototype results obtained from a niobium sample that demonstrate the capabilities of the system.
	Poster TUPTB013 [0.464 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB013
About •	Received ※ 16 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023
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TUPTB014	Development of Nb₃Sn Coating System and RF Measurement Results at KEK	414
	H. Ito, H. Sakai, K. Umemori, T. Yamada KEK, Ibaraki, Japan K. Takahashi Sokendai, Ibaraki, Japan
	We have constructed an Nb₃Sn cavity coating system based on the Sn vapor diffusion method. After the construction, improvement of our coating system and environment has been conducted through sample and cavity coating research. Our cavity achieves a Q-value above 1E10 at 4 K after improvement. We will report on the detail of improvement on our coating system and RF measurement results of single-cell Nb₃Sn cavity.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB014
About •	Received ※ 18 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023
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TUPTB018	MgB₂ Coating Parameter Optimization Using a 1.3-GHz 1-Cell Cavity	425
	T. Tajima, T.P. Grumstrup, J.D. Thompson LANL, Los Alamos, New Mexico, USA H. Ito, E. Kako, T. Okada, H. Sakai, K. Umemori KEK, Ibaraki, Japan
	Funding: DOE Office of Science, Office of High Energy Physics We have started parameter optimization for the coating of MgB₂ using a 1-cell 1.3-GHz elliptical cavity with holes for small samples. Our coating method is based on a 2-step technique, i.e., coat a B layer by flowing diborane gas in the first step and react it with Mg vapor in the 2nd step. Three 6 mm x 6 mm B-coated flat samples are attached at inlet, outlet beam pipes, and at a cell equator and reacted with Mg vapor with different parameters and conditions. We started to see the superconducting transitions on samples but Tc is still lower than our goal of >35 K. We will present our current status of B-Mg reaction tests and construction of B coating system.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB018
About •	Received ※ 06 July 2023 — Revised ※ 26 July 2023 — Accepted ※ 02 September 2023 — Issue date ※ 03 September 2023
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TUPTB019	First Results from Nb₃Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System	429
SUSPB047	use link to see paper's listing under its alternate paper code
	M.S. Shakel, H. Elsayed-Ali ODU, Norfolk, Virginia, USA G.V. Eremeev Fermilab, Batavia, Illinois, USA U. Pudasaini, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Supported by DOE, Office of Accelerator R&D and Production, Contact No. DE-SC0022284, with partial support by DOE, Office of Nuclear Physics DE-AC05-06OR23177, Early Career Award to G. Eremeev. A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb₃Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb₃Sn phase and Nb (substrate). No peaks from any Nb-Sn compound other than Nb₃Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 µm thick Nb₃Sn. The first Nb₃Sn coated cavity reached close to E_acc = 8 MV/m, demonstrating a quality factor Q₀ of 3.2 × 10⁸ at Tbath = 4.4 K and E_acc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q₀ was close to 1.1 × 10⁹, dominated by the residual resistance, at 2 K and E_acc = 5 MV/m. The Nb₃Sn coated cavities demonstrated Tc in the range of 17.9 ¿ 18 K. Here we present the commissioning experience, system optimization, and the first results from the Nb₃Sn fabrication on flat samples and SRF cavities.
	Poster TUPTB019 [1.216 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB019
About •	Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 10 July 2023
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TUPTB020	Surface Properties and RF Performance of Vapor Diffused Nb₃Sn on Nb after Sequential Anneals below 1000 °C	433
	J.K. Tiskumara, J.R. Delayen ODU, Norfolk, Virginia, USA G.V. Eremeev Fermilab, Batavia, Illinois, USA U. Pudasaini JLab, Newport News, Virginia, USA
	Nb₃Sn is a next-generation superconducting material that can be used for future superconducting radiofrequency (SRF) accelerator cavities, promising better performance, cost reduction, and higher operating temperature than Nb. The Sn vapor diffusion method is currently the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Among post-coating treatments to optimize the coating quality, higher temperature annealing without Sn is known to degrade Nb₃Sn because of Sn loss. We have investigated Nb₃Sn/Nb samples briefly annealed at 800-1000 °C, for 10 and 20 minutes to potentially improve the surface to enhance the performance of Nb₃Sn-coated cavities. Following the sample studies, a coated single-cell cavity was sequentially annealed at 900 °C and tested its performance each time, improving the cavity’s quality factor relatively. This paper summarizes the sample studies and discusses the RF test results from sequentially annealed SRF Nb₃Sn/Nb cavity.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB020
About •	Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 07 July 2023
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WEIAA03	Surface Roughness Reduction and Performance of Vapor-Diffusion Coating of Nb₃Sn Film for SRF Application	593
	U. Pudasaini, M.J. Kelley, E.M. Lechner, C.E. Reece, O. Trofimova, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	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 E_acc) 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.
	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
	L. Shpani, S.G. Arnold, G. Gaitan, M. Liepe, T.E. Oseroff, R.D. Porter, N.A. Stilin, Z. Sun, N.M. Verboncoeur Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA N. Sitaraman Cornell University, Ithaca, New York, USA
	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.
	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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WEIBA01	Surface Engineering by ALD for Superconducting RF Cavities	615
	Y. Kalboussi, C.Z. Antoine, M. Baudrier, Q. Bertrand, C. Boulch, B. Delatte, G. Jullien, L. Maurice, Th. Proslier, P. Sahuquet, T.V. Vacher CEA-IRFU, Gif-sur-Yvette, France M. Asaduzzaman, T. Junginger UVIC, Victoria, Canada M. Asaduzzaman TRIUMF, Vancouver, Canada D. Dragoe ICMMO, Orsay, France F. Éozénou CEA-DRF-IRFU, France N. Lochet CEA, DES, Université Paris-Saclay, Gif-sur-Yvette, France D. Longuevergne, T. Pépin-Donat Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France F. Miserque CEA, LECA, Université Paris-Saclay, Gif-sur-Yvette, France
	Atomic Layer Deposition is a synthesis method that enable a unique control of thin films chemical composition and thickness over complex shape objects such as SRF cavities. This level of control opens the way to new surface treatments and to study their effect on RF cavity performances. We will present coupon and, in some cases, preliminary cavity results, from various surface engineering routes based on the deposition of thin oxides and nitrides films combined with post annealing treatments and study their interactions with the niobium. Three main research directions will be presented: 1/ replacing the niobium oxides by other surface layers (Al₂O₃, Y2O3, MgO) and probe their effect on the low and high field performances, 2/ doping with N and combine approaches 1/ and 2/ and finally 3/ optimize the superconducting properties of NbTiN multilayers on Nb and Sapphire.
	Slides WEIBA01 [13.613 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIBA01
About •	Received ※ 06 July 2023 — Revised ※ 12 August 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023
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WEIXA01	Experimental Evidence for Current Suppression in Superconducting Hetero Structures
	M. Asaduzzaman, T. Junginger, R.M.L. McFadden UVIC, Victoria, Canada D.R. Beverstock, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA T. Junginger, R.M.L. McFadden TRIUMF, Vancouver, Canada T. Prokscha, Z. Salman, A. Suter PSI, Villigen PSI, Switzerland
	Coating Nb with thin layers of superconductors of higher penetration depth, than Nb have been proposed as a means of obtaining accelerating gradients (E_acc) of beyond Nb’s fundamental limit. Such heterostructures (which can also contain insulating layers between the superconductors) can potentially sustain their Meissner state above the superheating field, Bsh (of all the layers) due to the suppression of the Meissner screening current in the surface layer(s) induced by a counter-current in the substrate layer. We report evidence for counter-current flow in superconductor- superconductor (SS) Nb-Ti-N/Nb samples from depth-resolved measurements of their Meissner screening profiles at applied fields below or equal to 25 mT using the low energy muon spin rotation (LE-muSR) technique. Fits to the London model with appropriate boundary and continuity conditions determine the penetration depth of the Nb-Ti-N layers to be 182.5(31) nm in good agreement with literature values. Our results suggest that due to the strong suppression of the Meissner currents in the surface layer, multilayered structures of several superconducting and insulating layers are necessary to reach highest E_acc. An electronic pre-print is available at https://arxiv.org/abs/2304.09360
	Slides WEIXA01 [0.623 MB]
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WEPWB043	Nb₃Sn Vapor Diffusion Coating System at SARI: Design, Construction, and Commissioning	655
SUSPB038	use link to see paper's listing under its alternate paper code
	Q.X. Chen, Y. Zong SINAP, Shanghai, People’s Republic of China J.F. Chen, S. Xing SARI-CAS, Pudong, Shanghai, People’s Republic of China J. Rong SSRF, Shanghai, People’s Republic of China
	This paper describes the design of a coating system for the preparation of a superconducting radio-frequency cavity with Nb₃Sn thin films. The device consists of a coating chamber made of pure niobium, a vacuum furnace for heating the coating chamber, a superconducting cavity bracket and two crucible heaters. The chamber is vacuum isolated from the furnace body to protect the superconducting cavity from contamination during the coating process. The device has been built and commissioned, which could be used for Nb₃Sn coating of a 1.3 GHz single-cell superconducting cavity in future.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB043
About •	Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 08 July 2023
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WEPWB108	Update on Cornell High Pulsed Power Sample Host Cavity	841
SUSPB029	use link to see paper's listing under its alternate paper code
	N.M. Verboncoeur, A.T. Holic, M. Liepe, T.E. Oseroff, R.D. Porter, J. Sears, L. Shpani Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA R.D. Porter SLAC, Menlo Park, California, USA
	The Cornell High Pulsed Power Sample Host Cavity (CHPPSHC) is designed to measure the temperature-dependent superheating fields of future SRF materials and thereby gain insights into the ultimate limits of their performance. Theoretical estimation of the superheating fields of SRF materials is challenging and mostly has been done for temperatures near the critical temperature or in the infinite kappa limit. Experimental data currently available is incomplete, and often impacted by material defects and their resulting thermal heating, preventing finding the fundamental limits of theses materials. The CHPPSHC system allows reaching RF fields in excess of half a Tesla within microseconds on material samples by utilizing high pulsed power, thereby outrunning thermal effects. We are principally interested in the superheating field of Nb₃Sn, a material of interest for the SRF community, and present here the current fabrication and assembly status of the CHPPSHC as well as early results.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB108
About •	Received ※ 27 June 2023 — Revised ※ 20 July 2023 — Accepted ※ 20 August 2023 — Issue date ※ 22 August 2023
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Paper

Title

Page

MOPMB005

Muon Spin Rotation Studies of Bilayer Superconductors and Low Temperature Baked Niobium

62

SUSPB002

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M. Asaduzzaman, R.E. Laxdal, R.M.L. McFadden, E. Thoeng
TRIUMF, Vancouver, Canada
M. Asaduzzaman, T. Junginger, R.M.L. McFadden
UVIC, Victoria, Canada
E. Thoeng
UBC & TRIUMF, Vancouver, British Columbia, Canada

Funding: Financial support was provided by an Natural Sciences and Engineering Research Council of Canada (NSERC)
Muon spin rotation (muSR) results have shown that vortex penetration into Nb can be delayed up to the superheating field Hsh by a single layer of a material with larger London penetration depth. For low temperature baked (LTB) Nb an increase in the vortex penetration field Hvp has also been observed. While clearly exceeding the lower critical field Hc1, Hvp was found to remain significantly below Hsh for LTB niobium (Superconductor Science and Technology 30 (12), 125012). Further, magnetometry experiments suggested that there is no interface barrier in LTB Nb and that the apparent Hvp increase as observed by muSR was due to surface pinning (Scientific Reports 12 (1), 5522). By varying the implantation depth of ~4.1 MeV muons using moderating foils, new muSR measurements confirm that the apparent Hvp increase in LTB Nb is indeed due to surface pinning, while for a Nb₃Sn/Nb bilayer we find an interface barrier for flux penetration. These results confirm the potential of using superconducting bilayers to achieve a flux free Meissner state up to the superheating field of the substrate.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB005

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Received ※ 17 June 2023 — Revised ※ 21 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 21 July 2023

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MOPMB011

Deposition and Characterisation of V₃Si films for SRF Applications

84

C. Benjamin, J.A. Conlon, O.B. Malyshev, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, O.B. Malyshev, D.J. Seal, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt, D.J. Seal
Lancaster University, Lancaster, United Kingdom
N.L. Leicester, H.S. Marks
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
L.G.P. Smith
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730.
A15 superconducting materials, like V₃Si and Nb₃Sn, are potential alternatives to Nb for next generation thin film SRF cavities when operated at 4 K. Their relatively high Tc and superconducting properties could allow for higher accelerating gradients and elevated operating temperatures. We present work on the deposition of V₃Si thin films on planar Cu substrates and an open structure 6 GHz cavity, using physical vapour deposition (PVD) and a V₃Si single target. The surface structure, composition and DC superconducting properties of two planar samples were characterised via secondary electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and in a magnetic field penetration facility. Furthermore, the first deposition using PVD of a V₃Si film on a 6 GHz split cavity and the RF performance is presented.

Poster MOPMB011 [7.496 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB011

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Received ※ 16 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 19 July 2023

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MOPMB013

Influence of the Coating Parameters on the Tc of Nb₃Sn Thin Films on Copper Deposited via DC Magnetron Sputtering

92

SUSPB007

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D. Fonnesu, O. Azzolini, R. Caforio, E. Chyhyrynets, D. Ford, V.A. Garcia, G. Keppel, C. Pira, A. Salmaso, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
G. Marconato
Università degli Studi di Padova, Padova, Italy

Funding: The I.FAST project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Work supported by the INFN CSNV experiment SAMARA.
The I.FAST collaboration aims at pushing the performance of particle accelerators by developing sustainable innovative technologies. Among its goals, the development of thin film-coated copper elliptical accelerating cavities covers both the optimization of the manufacturing of seamless substrates and the development of functional coatings able to conform to the 3D cavity geometry while delivering the needed performance. For the latter, the optimization of the deposition recipe is central to a successful outcome. The work presented here focuses on the deposition of Nb₃Sn films on flat, small copper samples. The films are deposited via DCMS from a planar stoichiometric Nb₃Sn commercial target. The results of the film characterization are presented here. The observed dependencies between the film properties and, in particular, Tc(90%-10%) = (17.9±0.1)K is reported for Nb₃Sn on sapphire and Tc(90%-10%) = (16.9±0.2)K for Nb₃Sn on copper with a 30 micron thick niobium buffer layer.

Poster MOPMB013 [1.749 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB013

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Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 02 July 2023

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MOPMB015

Development of a Plasma-Enhanced Chemical Vapor Deposition System for High-Performance SRF Cavities

100

SUSPB009

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G. Gaitan, A.T. Holic, W.I. Howes, G. Kulina, P. Quigley, J. Sears, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Liepe
Cornell University, Ithaca, New York, USA
B.W. Wendland
University of Minnesota, Minnesota, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams
Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, or other compound superconductors are essential for reaching enhanced RF performance levels in SRF cavities. However, optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a high-vacuum, gas, and precursor delivery system, and uses plasma to significantly reduce the required processing temperature and promote precursor decomposition. Here we present an update on the development of this system, including final system design, safety considerations, assembly, and commissioning.

Poster MOPMB015 [1.951 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB015

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Received ※ 16 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 16 July 2023

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MOPMB047

Commissioning of Dedicated Furnace for Nb₃Sn Coatings of 2.6 GHz Single Cell Cavities

216

SUSPB018

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P.A. Kulyavtsev, G.V. Eremeev, S. Posen, B. Tennis
Fermilab, Batavia, Illinois, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
We present the results of commissioning a dedicated furnace for Nb₃Sn coatings of 2.6GHz single cell cavities. Nb₃Sn is a desired coating due to its high critical temperature and smaller surface resistance compared to bulk Nb. Usage of Nb₃Sn coated cavities will greatly reduce operating costs due to its higher operating temperature providing decreased cooling costs. Tin is deposited in the bulk Nb cavity by use of a tin chloride nucleation agent and tin vapor diffusion. Analysis of the resultant coating was performed using SEM/EDS to verify successful formation of desired Nb:Sn phase. Witness samples located in line of sight of the source were analyzed in order to understand the coating efficacy. The cavity’s performance was assessed in the Vertical Test Stand (VTS) at Fermilab.

Poster MOPMB047 [4.858 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB047

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Received ※ 26 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 08 July 2023

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MOPMB053

Theoretical Study of Thin Noble-Metal Films on the Niobium Surface

230

SUSPB021

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C.A. Méndez, T. Arias, M. Liepe, N. Sitaraman
Cornell University, Ithaca, New York, USA

Funding: The Center for Bright Beams, Supported by National Science Foundation award No. PHY-1549132
Recent experiments suggest that noble-metal deposition on niobium metal surfaces can remove the surface oxide and ultimately improve superconducting radio-frequency (SRF) cavities performance. In this preliminary study, we use density-functional theory to investigate the potential for noble-metal passivation of realistic, polycrystalline niobium surfaces for SRF. Specifically, we investigate the stability of gold and palladium monolayers on niobium surfaces with different crystal orientations and evaluate the impact of these impurities on superconducting properties. In particular, our results suggest that gold can grow in thin layers on the niobium surface, whereas palladium rather tends to dissolve into the niobium cavity. These results will help inform ongoing experimental efforts to passivate niobium surfaces of SRF cavities.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB053

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Received ※ 22 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023

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MOPMB093

Optimizing Growth of Niobium-3 Tin Through Pre-nucleation Chemical Treatments

337

SUSPB026

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S.G. Arnold, G. Gaitan, M. Liepe, L. Shpani, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Arias, N. Sitaraman
Cornell University, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
Nb₃Sn is a promising alternative material for SRF cavities that is close to reaching practical applications. To date, one of the most effective growth methods for this material is vapor diffusion, yet further improvement is needed for Nb₃Sn to reach its full potential. The major issues faced by vapor diffusion are tin depleted regions and surface roughness, both of which lead to impaired performance. Literature has shown that the niobium surface oxide plays an important role in the binding of tin to niobium. In this study, we performed various chemical treatments on niobium samples pre-nucleation to enhance tin nucleation. We quantify the effect that these various treatments had through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). These methods reveal information on tin nucleation density and uniformity, and a thin tin film present on most samples, even in the absence of nucleation sites. We present our findings from these surface characterization methods and introduce a framework for quantitatively comparing the samples. We plan to apply the most effective treatment to a cavity and conduct an RF test soon.

Poster MOPMB093 [1.118 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB093

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Received ※ 21 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 July 2023

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TUPTB001

Demonstration of Niobium Tin in 218 MHz Low-Beta Quarter Wave Accelerator Cavity

388

T.B. Petersen, G. Chen, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, T. Reid
ANL, Lemont, Illinois, USA
G.V. Eremeev, S. Posen, B. Tennis
Fermilab, Batavia, Illinois, USA

A 218 MHz quarter wave niobium cavity has been fabricated for the purpose of demonstrating Nb₃Sn technology on a low-beta accelerator cavity. Niobium-tin has been established as a promising next generation SRF material, but development has focused primarily in high-beta elliptical cell cavities. This material has a significantly higher TC than niobium, allowing for design of higher frequency quarter wave cavities (that are subsequently smaller) as well as for significantly lowered cooling requirements (possibly leading to cryocooler based de-signs). The fabrication, initial cold testing, and Nb₃Sn coating are discussed as well as test plans and details of future applications.

Poster TUPTB001 [0.653 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB001

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Received ※ 16 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 08 July 2023

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TUPTB004

Progress on Zirconium-Doped Niobium Surfaces

398

N. Sitaraman, T. Arias, Z. Baraissov, D.A. Muller
Cornell University, Ithaca, New York, USA
G. Gaitan, M. Liepe, T.E. Oseroff, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the NSF under Award PHY-1549132, the Center for Bright Beams, and in part by CNF (NSF Grant NNCI-2025233), and in part by CCMR (DMR-1719875).
The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB004

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Received ※ 30 June 2023 — Revised ※ 26 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 22 August 2023

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TUPTB006

Materials Design for Superconducting RF Cavities: Electroplating Sn, Zr, and Au onto Nb and and Chemical Vapor Deposition

401

Z. Sun, M. Liepe, T.E. Oseroff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Z. Baraissov, D.A. Muller, M.O. Thompson
Cornell University, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Materials scientists seek to contribute to the development of next-generation superconducting radio-frequency (SRF) accelerating cavities. Here, we summarize our achievements and learnings in designing advanced SRF materials and surfaces, including Nb₃Sn [1¿3], ZrNb(CO) [4, 5], and Au/Nb surface design [6,7]. Our efforts involve electrochemical synthesis, phase transformation, and surface chemistry, which are closely coupled with superconducting properties, SRF performance, and engineering considerations. We develop electrochemical processes for Sn, Zr, and Au on the Nb surface, an essential step in our investigation for producing high-quality Nb₃Sn, ZrNb(CO), and Au/Nb structures. Additionally, we design a custom chemical vapor deposition system to offer additional growth options. Notably, we find the second-phase NbC formation in ZrNb(CO) and in ultra-high-vacuum baked or nitrogen-processed Nb. We also identify low-dielectric-loss ZrO2 on Nb and NbZr(CO) surfaces. These advancements provide materials science approaches dealing with fundamental and technical challenges to build high-performance, multi-scale, robust SRF cavities for particle accelerators and quantum applications.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB006

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Received ※ 30 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023

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TUPTB010

Preservation of the High Quality Factor and Accelerating Gradient of Nb₃Sn-Coated Cavity During Pair Assembly

405

G.V. Eremeev, S. Cheban, S. Posen, B. Tennis
Fermilab, Batavia, Illinois, USA
J.F. Fischer, D. Forehand, U. Pudasaini, A.V. Reilly, R.A. Rimmer
JLab, Newport News, Virginia, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Two CEBAF 5-cell accelerator cavities have been coated with Nb₃Sn film using the vapor diffusion technique. One cavity was coated in the Jefferson Lab Nb₃Sn cavity coating system, and the other in the Fermilab Nb₃Sn coating system. Both cavities were measured at 4 K and 2 K in the vertical dewar test in each lab and then assembled into a cavity pair at Jefferson Lab. Previous attempts to assemble Nb₃Sn cavities into a cavity pair degraded the superconducting properties of Nb₃Sn-coated cavities. This contribution discusses the efforts to identify and mitigate the pair assembly challenges and will present the results of the vertical tests before and after pair assembly. Notably, one of the cavities reached the highest gradient above 80 mT in the vertical test after the pair assembly.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB010

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Received ※ 23 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 02 July 2023 — Issue date ※ 09 July 2023

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TUPTB013

Commissioning of a New Sample Test Cavity for Rapid RF Characterization of SRF Materials

410

S. Keckert, J. Knobloch, F. Kramer, O. Kugeler
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany

RaSTA, the Rapid Superconductor Test Apparatus, is a new sample test cavity that is currently being commissioned at HZB. It uses the established QPR sample geometry but with a much smaller cylindrical cavity operating in the TM020 mode at 4.8 GHz. Its compact design allows for smaller cryogenic test stands and reduced turnaround time, enabling iterative measurement campaigns for thin film R&D. Using the same calorimetric measurement technique as known from the QPR allows direct measurements of the residual resistance. We report first prototype results obtained from a niobium sample that demonstrate the capabilities of the system.

Poster TUPTB013 [0.464 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB013

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Received ※ 16 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023

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TUPTB014

Development of Nb₃Sn Coating System and RF Measurement Results at KEK

414

H. Ito, H. Sakai, K. Umemori, T. Yamada
KEK, Ibaraki, Japan
K. Takahashi
Sokendai, Ibaraki, Japan

We have constructed an Nb₃Sn cavity coating system based on the Sn vapor diffusion method. After the construction, improvement of our coating system and environment has been conducted through sample and cavity coating research. Our cavity achieves a Q-value above 1E10 at 4 K after improvement. We will report on the detail of improvement on our coating system and RF measurement results of single-cell Nb₃Sn cavity.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB014

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Received ※ 18 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023

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TUPTB018

MgB₂ Coating Parameter Optimization Using a 1.3-GHz 1-Cell Cavity

425

T. Tajima, T.P. Grumstrup, J.D. Thompson
LANL, Los Alamos, New Mexico, USA
H. Ito, E. Kako, T. Okada, H. Sakai, K. Umemori
KEK, Ibaraki, Japan

Funding: DOE Office of Science, Office of High Energy Physics
We have started parameter optimization for the coating of MgB₂ using a 1-cell 1.3-GHz elliptical cavity with holes for small samples. Our coating method is based on a 2-step technique, i.e., coat a B layer by flowing diborane gas in the first step and react it with Mg vapor in the 2nd step. Three 6 mm x 6 mm B-coated flat samples are attached at inlet, outlet beam pipes, and at a cell equator and reacted with Mg vapor with different parameters and conditions. We started to see the superconducting transitions on samples but Tc is still lower than our goal of >35 K. We will present our current status of B-Mg reaction tests and construction of B coating system.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB018

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Received ※ 06 July 2023 — Revised ※ 26 July 2023 — Accepted ※ 02 September 2023 — Issue date ※ 03 September 2023

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TUPTB019

First Results from Nb₃Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System

429

SUSPB047

use link to see paper's listing under its alternate paper code

M.S. Shakel, H. Elsayed-Ali
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Supported by DOE, Office of Accelerator R&D and Production, Contact No. DE-SC0022284, with partial support by DOE, Office of Nuclear Physics DE-AC05-06OR23177, Early Career Award to G. Eremeev.
A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb₃Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb₃Sn phase and Nb (substrate). No peaks from any Nb-Sn compound other than Nb₃Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 µm thick Nb₃Sn. The first Nb₃Sn coated cavity reached close to E_acc = 8 MV/m, demonstrating a quality factor Q₀ of 3.2 × 10⁸ at Tbath = 4.4 K and E_acc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q₀ was close to 1.1 × 10⁹, dominated by the residual resistance, at 2 K and E_acc = 5 MV/m. The Nb₃Sn coated cavities demonstrated Tc in the range of 17.9 ¿ 18 K. Here we present the commissioning experience, system optimization, and the first results from the Nb₃Sn fabrication on flat samples and SRF cavities.

Poster TUPTB019 [1.216 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB019

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Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 10 July 2023

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TUPTB020

Surface Properties and RF Performance of Vapor Diffused Nb₃Sn on Nb after Sequential Anneals below 1000 °C

433

J.K. Tiskumara, J.R. Delayen
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini
JLab, Newport News, Virginia, USA

Nb₃Sn is a next-generation superconducting material that can be used for future superconducting radiofrequency (SRF) accelerator cavities, promising better performance, cost reduction, and higher operating temperature than Nb. The Sn vapor diffusion method is currently the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Among post-coating treatments to optimize the coating quality, higher temperature annealing without Sn is known to degrade Nb₃Sn because of Sn loss. We have investigated Nb₃Sn/Nb samples briefly annealed at 800-1000 °C, for 10 and 20 minutes to potentially improve the surface to enhance the performance of Nb₃Sn-coated cavities. Following the sample studies, a coated single-cell cavity was sequentially annealed at 900 °C and tested its performance each time, improving the cavity’s quality factor relatively. This paper summarizes the sample studies and discusses the RF test results from sequentially annealed SRF Nb₃Sn/Nb cavity.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB020

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Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 07 July 2023

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WEIAA03

Surface Roughness Reduction and Performance of Vapor-Diffusion Coating of Nb₃Sn Film for SRF Application

593

U. Pudasaini, M.J. Kelley, E.M. Lechner, C.E. Reece, O. Trofimova, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

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 E_acc) 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.

Slides WEIAA03 [7.231 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA03

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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

L. Shpani, S.G. Arnold, G. Gaitan, M. Liepe, T.E. Oseroff, R.D. Porter, N.A. Stilin, Z. Sun, N.M. Verboncoeur
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
N. Sitaraman
Cornell University, Ithaca, New York, USA

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.

Slides WEIAA04 [5.260 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA04

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Received ※ 29 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 21 August 2023 — Issue date ※ 22 August 2023

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WEIBA01

Surface Engineering by ALD for Superconducting RF Cavities

615

Y. Kalboussi, C.Z. Antoine, M. Baudrier, Q. Bertrand, C. Boulch, B. Delatte, G. Jullien, L. Maurice, Th. Proslier, P. Sahuquet, T.V. Vacher
CEA-IRFU, Gif-sur-Yvette, France
M. Asaduzzaman, T. Junginger
UVIC, Victoria, Canada
M. Asaduzzaman
TRIUMF, Vancouver, Canada
D. Dragoe
ICMMO, Orsay, France
F. Éozénou
CEA-DRF-IRFU, France
N. Lochet
CEA, DES, Université Paris-Saclay, Gif-sur-Yvette, France
D. Longuevergne, T. Pépin-Donat
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
F. Miserque
CEA, LECA, Université Paris-Saclay, Gif-sur-Yvette, France

Atomic Layer Deposition is a synthesis method that enable a unique control of thin films chemical composition and thickness over complex shape objects such as SRF cavities. This level of control opens the way to new surface treatments and to study their effect on RF cavity performances. We will present coupon and, in some cases, preliminary cavity results, from various surface engineering routes based on the deposition of thin oxides and nitrides films combined with post annealing treatments and study their interactions with the niobium. Three main research directions will be presented: 1/ replacing the niobium oxides by other surface layers (Al₂O₃, Y2O3, MgO) and probe their effect on the low and high field performances, 2/ doping with N and combine approaches 1/ and 2/ and finally 3/ optimize the superconducting properties of NbTiN multilayers on Nb and Sapphire.

Slides WEIBA01 [13.613 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIBA01

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Received ※ 06 July 2023 — Revised ※ 12 August 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023

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WEIXA01

Experimental Evidence for Current Suppression in Superconducting Hetero Structures

M. Asaduzzaman, T. Junginger, R.M.L. McFadden
UVIC, Victoria, Canada
D.R. Beverstock, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA
T. Junginger, R.M.L. McFadden
TRIUMF, Vancouver, Canada
T. Prokscha, Z. Salman, A. Suter
PSI, Villigen PSI, Switzerland

Coating Nb with thin layers of superconductors of higher penetration depth, than Nb have been proposed as a means of obtaining accelerating gradients (E_acc) of beyond Nb’s fundamental limit. Such heterostructures (which can also contain insulating layers between the superconductors) can potentially sustain their Meissner state above the superheating field, Bsh (of all the layers) due to the suppression of the Meissner screening current in the surface layer(s) induced by a counter-current in the substrate layer. We report evidence for counter-current flow in superconductor- superconductor (SS) Nb-Ti-N/Nb samples from depth-resolved measurements of their Meissner screening profiles at applied fields below or equal to 25 mT using the low energy muon spin rotation (LE-muSR) technique. Fits to the London model with appropriate boundary and continuity conditions determine the penetration depth of the Nb-Ti-N layers to be 182.5(31) nm in good agreement with literature values. Our results suggest that due to the strong suppression of the Meissner currents in the surface layer, multilayered structures of several superconducting and insulating layers are necessary to reach highest E_acc.
An electronic pre-print is available at https://arxiv.org/abs/2304.09360

Slides WEIXA01 [0.623 MB]

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WEPWB043

Nb₃Sn Vapor Diffusion Coating System at SARI: Design, Construction, and Commissioning

655

SUSPB038

use link to see paper's listing under its alternate paper code

Q.X. Chen, Y. Zong
SINAP, Shanghai, People’s Republic of China
J.F. Chen, S. Xing
SARI-CAS, Pudong, Shanghai, People’s Republic of China
J. Rong
SSRF, Shanghai, People’s Republic of China

This paper describes the design of a coating system for the preparation of a superconducting radio-frequency cavity with Nb₃Sn thin films. The device consists of a coating chamber made of pure niobium, a vacuum furnace for heating the coating chamber, a superconducting cavity bracket and two crucible heaters. The chamber is vacuum isolated from the furnace body to protect the superconducting cavity from contamination during the coating process. The device has been built and commissioned, which could be used for Nb₃Sn coating of a 1.3 GHz single-cell superconducting cavity in future.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB043

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Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 08 July 2023

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WEPWB108

Update on Cornell High Pulsed Power Sample Host Cavity

841

SUSPB029

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N.M. Verboncoeur, A.T. Holic, M. Liepe, T.E. Oseroff, R.D. Porter, J. Sears, L. Shpani
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
R.D. Porter
SLAC, Menlo Park, California, USA

The Cornell High Pulsed Power Sample Host Cavity (CHPPSHC) is designed to measure the temperature-dependent superheating fields of future SRF materials and thereby gain insights into the ultimate limits of their performance. Theoretical estimation of the superheating fields of SRF materials is challenging and mostly has been done for temperatures near the critical temperature or in the infinite kappa limit. Experimental data currently available is incomplete, and often impacted by material defects and their resulting thermal heating, preventing finding the fundamental limits of theses materials. The CHPPSHC system allows reaching RF fields in excess of half a Tesla within microseconds on material samples by utilizing high pulsed power, thereby outrunning thermal effects. We are principally interested in the superheating field of Nb₃Sn, a material of interest for the SRF community, and present here the current fabrication and assembly status of the CHPPSHC as well as early results.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB108

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Received ※ 27 June 2023 — Revised ※ 20 July 2023 — Accepted ※ 20 August 2023 — Issue date ※ 22 August 2023

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