SRF2023 - Classification: Fundamental SRF research and development / Film coated copper cavities; multi-layer films

Paper	Title	Page
MOPMB001	Development and Testing of Split 6 GHz Cavities With Niobium Coatings	51
	N.L. Leicester, G. Burt, H.S. Marks Cockcroft Institute, Lancaster University, Lancaster, United Kingdom E. Chyhyrynets, C. Pira INFN/LNL, Legnaro (PD), Italy J.A. Conlon, O.B. Malyshev, B.S. Sian, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom D.J. Seal Lancaster University, Lancaster, United Kingdom
	Superconducting thin-films on a copper substrate are used in accelerator RF cavities as an alternative to bulk Nb due to the high thermal conductivity of copper and the lower production costs. Although thin-film coated RF cavities can match, or even exceed the performance of bulk Nb, there are some challenges around the deposition. The RF cavities are often produced as two half-cells with a weld across the centre where the RF surface current is highest, which could reduce cavity performance. To avoid this, a cavity can be produced in 2 longitudinally split halves, with the join parallel to the surface current. As the current doesn’t cross the join a simpler weld can be performed far from the fields, simplifying the manufacturing process, and potentially improving the cavities performance. This additionally allows for different deposition techniques and coating materials to be used, as well as easier post-deposition quality control. This paper discusses the development and testing of 6 GHz cavities that have been designed and coated at the Cockcroft Institute, using low temperature RF techniques to characterise cavities with different substrate preparations and coating techniques.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB001
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 July 2023
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MOPMB003	Flux Expulsion Lens: Concept and Measurements	56
	D.A. Turner European Organization for Nuclear Research (CERN), Geneva, Switzerland A. Gallifa Terricabras, T. Koettig, A. Macpherson, G.J. Rosaz, N. Stapley CERN, Meyrin, Switzerland I. González Díaz-Palacio University of Hamburg, Hamburg, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany M. Wenskat DESY, Hamburg, Germany
	A magnetic flux expulsion lens (MFEL) has been designed and built at CERN. This device uses closed topology conduction cooling of samples to quantify magnetic flux expulsion of superconductors, and allows for systematic measurements of the cooling dynamics and the magnetic response during the superconducting transition. Measurements for bulk Nb, cold worked Nb, sputtered Nb on Cu, and SIS multilayer structures are given. Preliminary results for both sample characterization of expulsion dynamics, and observation of an enhanced flux expulsion in SIS samples are also reported.
	Poster MOPMB003 [2.459 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB003
About •	Received ※ 27 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 14 July 2023
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MOPMB012	Investigation, Using Nb Foils to Characterise the Optimal Dimensions of Samples Measured by the Magnetic Field Penetration Facility	88
	L.G.P. Smith, D.A. Turner STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, O.B. Malyshev, D.A. Turner Cockcroft Institute, Warrington, Cheshire, United Kingdom G. Burt Lancaster University, Lancaster, United Kingdom T. Junginger TRIUMF, Vancouver, Canada T. Junginger UVIC, Victoria, Canada O.B. Malyshev STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	SRF cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, E_acc, where E_acc is limited by the maximum magnetic field, Bmax, that can be applied on the surface of the accelerating cavity wall. To increase E_acc, Bmax, which can be applied to the surface, must also be increased. The A15 materials or multilayer structures are the potential solution to increase Bmax. Since coating and RF testing of full size RF cavities is both expensive and time consuming, one need to evaluate new ideas in superconducting thin films quickly and at low cost. A magnetic field penetration experiment has been designed and built at Daresbury Laboratory to test small superconducting samples. The facility produces a parallel DC magnetic field, which applied from one side of the sample to the other similar to that in an RF cavity. The facility applies an increasing magnetic field at a set temperature to determine the field of full flux penetration which can give an insight into the quality and structure of the superconducting structure. The facility has been characterised using both type I and II superconductors and is now producing results from novel materials.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB012
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 17 July 2023
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MOPMB014	NbTi Thin Film SRF Cavities for Dark Matter Search	96
SUSPB008	use link to see paper's listing under its alternate paper code
	G. Marconato Università degli Studi di Padova, Padova, Italy D. Alesini, A. D’Elia, D. Di Gioacchino, C. Gatti, C. Ligi, G. Maccarrone, A. Rettaroli, S. Tocci LNF-INFN, Frascati, Italy O. Azzolini, R. Caforio, E. Chyhyrynets, D. Fonnesu, D. Ford, V.A. Garcia, G. Keppel, C. Pira, A. Salmaso, F. Stivanello INFN/LNL, Legnaro (PD), Italy C. Braggio Univ. degli Studi di Padova, Padova, Italy D. D’Agostino, U. Gambardella INFN-Salerno, Baronissi, Salerno, Italy S. Posen Fermilab, Batavia, Illinois, USA
	Funding: Resources from U.S. DOE, Ofce of Science, NQISRC, SQMS contract No DE-AC02-07CH11359. Also from EU’s Horizon 2020 Research and Innovation programme, Grant Agreement No 101004730; INFN CSNV exp. SAMARA The search for dark matter is now looking at ALPs (axion-like particles) as a very promising candidate to understand our universe. Within this framework, we explore the possibility to use NbTi thin film coatings on Cu resonating cavities to investigate the presence of axions in the range of 35-45 µeV mass by coupling the axion to a very strong magnetic field inside the cavity, causing its conversion to a photon which is subsequently detected. In this work the chemical treatments and DC magnetron sputtering details of the preparation of 9 GHz, 7 GHz, and 3.9 GHz resonant cavities and their quality factor measurements at different applied magnetic fields are presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB014
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 July 2023
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MOPMB016	Successful Al₂O₃ Coating of Superconducting Niobium Cavities by Thermal ALD	104
	G.K. Deyu, W. Hillert, M. Wenskat University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany R.H. Blick, I. González Díaz-Palacio, R. Zierold University of Hamburg, Hamburg, Germany
	Funding: This work is supported by the BMBF under the research Grant 05K19GUB. Al₂O₃ is one of the potential insulator materials in the superconductor-insulator-superconductor (SIS) multilayer coatings of superconducting radio-frequency (SRF) cavities for pushing their performance limits. We report on the successful coating of two 1.3 GHz Tesla-shaped SRF cavities with 18 nm and 36 nm layers of Al₂O₃ deposited by thermal atomic layer deposition (ALD). The coating recipe was developed by thermal atomic layer deposition (ALD). The coating recipe was optimized with respect to different the applied process parameters such as exposure and purge times, substrate temperature and flow rates. After a proof-of-principle Al₂O₃ coating of a cavity, second the cavity maintained its maximum achievable accelerating field of more than 40 MV/m and no deterioration was observed [1]. On the contrary, an improvement of the surface resistance above 10 MV/m has been observed, which is now further under investigation. [1].Wenskat, Marc, et al. "Successful Al₂O₃ coating of superconducting niobium cavities with thermal ALD." Superconductor Science and Technology 36.1 (2022): 015010.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB016
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023
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MOPMB017	Development of a Thermal Conductance Instrument for Niobium at Cryogenic Temperatures	109
	C. Saribal, C. Martens University of Hamburg, Hamburg, Germany W. Hillert, M. Wenskat University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: University of Hamburg Particle accelerators form an important tool in a variety of research fields. In an effort to reduce operation costs while maintaining high energies, their accelerating structures are steadily improved towards higher accelerating fields and lower RF losses. Stable operation of such a cavity generally requires Joule-heating, generated in its walls, to be conducted to an outer helium bath. Therefore, it is of interest to experimentally evaluate how present and future cavity treatments affect thermal characteristics. We present an instrument for measuring the thermal performance of SRF cavity materials at cryogenic temperatures. Pairs of niobium disks are placed inside of a liquid helium bath and a temperature gradient is generated across them to obtain total thermal resistance for temperatures below 2 Kelvin. To get an idea of the instruments sensitivity and how standard cavity treatments influence thermal resistance, samples are tested post fabrication, polishing and 800 °C baking. The first tests show the commissioning of our newly set up system and if it is feasible to observe relevant changes and evaluate new and promising cavity treatments such as SIS structures.
	Poster MOPMB017 [3.217 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB017
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 July 2023
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MOPMB019	Numerical Calculations of Superheating Field in Superconductors with Nanostructured Surfaces	114
	M.R.P. Walive Pathiranage VMI, Lexington, USA A.V. Gurevich ODU, Norfolk, Virginia, USA
	Funding: This work was supported by DOE under Grant DE-SC 100387-020 and by Virginia Military Institute (VMI) under Jackson-Hope Grant for faculty travel and for New Directions in Teaching and Research Grants. We report calculations of a dc superheating field Hs in superconductors with nanostructured surfaces. Particularly, we performed numerical simulations of the Ginzburg-Landau (GL) equations for a superconductor with an inhomogeneous profile of impurity concentration, a thin superconducting layer on top of another superconductor, and S-I-S multilayers. The superheating field was calculated taking into account the instability of the Meissner state at a finite wavelength along the surface depending on the value of the GL parameter. Simulations were done for the materials parameters of Nb and Nb₃Sn at different values of the GL parameter and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of superconducting layers in S-I-S structures can be optimized to reach the maximum Hs, which exceeds the bulk superheating fields of both Nb and Nb₃Sn. For example, a S-I-S structure with 90 nm thick Nb₃Sn layer on Nb can boost the superheating field up to ~ 500 mT, while protecting the SRF cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.
	Poster MOPMB019 [1.214 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB019
About •	Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 16 July 2023
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MOPMB062	Optimisation of Niobium Thin Film Deposition Parameters for SRF Cavities	253
SUSPB023	use link to see paper's listing under its alternate paper code
	D.J. Seal, O.B. Malyshev, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom J.A. Conlon, O.B. Malyshev, K.T. Morrow, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	In order to accelerate the progression of thin film (TF) development for future SRF cavities, it is desirable to optimise material properties on small flat samples. Most importantly, this requires the ability to measure their superconducting properties. At Daresbury Laboratory, it has been possible for many years to characterise these films under DC conditions; however, it is not yet fully understood whether this correlates with RF measurements. Recently, a high-throughput RF facility was commissioned that uses a novel 7.8 GHz choke cavity. The facility is able to evaluate the RF performance of planar-coated TF samples at low peak magnetic fields with a high throughput rate of 2-3 samples per week. Using this facility, an optimisation study of the deposition parameters of TF Nb samples deposited by HiPIMS has begun. The ultimate aim is to optimise TF Nb as a base layer for multilayer studies and replicate planar magnetron depositions on split 6 GHz cavities. The initial focus of this study was to investigate the effect of substrate temperature during deposition. A review of the RF facility used and results of this study will be presented.
	Poster MOPMB062 [2.395 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB062
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 24 July 2023
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MOPMB083	Investigation of the Multilayer Shielding Effect through NbTiN-AlN Coated Bulk Niobium	311
SUSPB025	use link to see paper's listing under its alternate paper code
	I.H. Senevirathne, J.R. Delayen, A.V. Gurevich ODU, Norfolk, Virginia, USA D.R. Beverstock, J.R. Delayen, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA D.R. Beverstock The College of William and Mary, Williamsburg, Virginia, USA
	We report measurements of the dc field onset B_p of magnetic flux penetration through NbTiN-AlN coating on bulk niobium using the Hall probe experimental setup. The measurements of Bp reveal the multilayer shielding effect on bulk niobium under high magnetic fields at cryogenic temperatures. We observed a significant enhancement in Bp for the NbTiN-AlN coated Nb samples as compared to bare Nb samples. The observed dependence of B_p on the coating thickness is consistent with theoretical predictions.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB083
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 12 August 2023
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TUIXA05	Energy Barrier at Superconductor-Superconductor Interfaces
	T. Junginger UVIC, Victoria, Canada
	Funding: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through grants SAPPJ-2020-00030 and SAPIN-2021-00032. In SUST 30 (12), 125012, we reported that coating a superconductor with a larger penetration depth on niobium can increase the field of first vortex penetration Hvp from niobium¿s lower critical field Hc1 to its superheating field Hsh. This was interpreted as an energy barrier at the superconductor-superconductor interface, analogous to the Bean-Livingston barrier at vacuum-superconductor interfaces. A smaller but significant increase in Hvp was observed for low-temperature baked (LTB) niobium. Results from muon spin rotation with variable implantation depth in the micrometer range and vibrating sample magnetometry (Scientific Reports 12 (1), 5522) suggest that the apparent Hvp increase in LTB niobium was due to surface pinning and not an actual Hvp increase. Low-energy muon spin rotation results further support that interpretation as a distinct bipartite magnetic screening profile is observed for actual bilayers (arXiv:2304.09360) but not for LTB niobium (PR Applied 19 (4), 044018 and arXiv:2305.02129). This suggests that the reason why some LTB niobium SRF cavities reach surface magnetic fields beyond Hc1 is specific to RF effects, such as the nucleation time.
	Slides TUIXA05 [0.997 MB]
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TUCXA02	RF Vortex Nucleation in Superconductors within Time-Dependent Ginzburg-Landau Theory: Role of Surface Defects
	S.M. Anlage, C.Y. Wang UMD, College Park, Maryland, USA
	Funding: This work is funded by US Department of Energy / High Energy Physics through grant # DE-SC0017931 and the Maryland Quantum Materials Center. We use time-dependent Ginzburg-Landau (TDGL) numerical simulations to study the nucleation of RF vortices in Nb in the presence of surface defects when the material is subjected to an intense RF magnetic field in the GHz regime. In this work, we solve the TDGL equations, and Maxwell¿s equations, for a spatially nonuniform RF magnetic field created by a point RF magnetic dipole above the Nb surface. Here surface defects are notionally modeled as grain boundaries filled with a low-Tc impurity, such as oxidized Nb. The dynamics of RF currents induced in the resulting proximity-coupled superconductor are studied, and it is observed that RF vortex semi-loops penetrate the surface through the grain boundaries. Besides the RF vortex dynamics, the resulting third harmonic nonlinear response of the superconductor is calculated, and is shown to be closely related to RF vortex nucleation. The simulations show that RF vortex nucleation by surface defects can be studied by analyzing the third harmonic response of the superconductor. We make connections between these numerical studies and the results of our scanned near-field microwave microscopy efforts on a variety of SRF materials.
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WECAA01	Progress in European Thin Film Activities	607
	C. Pira, O. Azzolini, R. Caforio, E. Chyhyrynets, D. Fonnesu, D. Ford, V.A. Garcia, G. Keppel, G. Marconato, A. Salmaso, F. Stivanello INFN/LNL, Legnaro (PD), Italy C.Z. Antoine, Y. Kalboussi, Th. Proslier CEA-IRFU, Gif-sur-Yvette, France C. Benjamin, O.B. Malyshev, N. Marks, B.S. Sian, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C. Benjamin, J.W. Bradley, G. Burt, O.B. Malyshev, N. Marks, D.J. Seal, B.S. Sian, S. Simon, D.A. Turner, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom S. Berry CEA-DRF-IRFU, France R. Berton, D. Piccoli, F. Piccoli, G. Squizzato, F. Telatin Piccoli, Noale (VE), Italy M. Bertucci, R. Paparella INFN/LASA, Segrate (MI), Italy M. Bonesso, S. Candela, V. Candela, R. Dima, G. Favero, A. Pepato, P. Rebesan, M. Romanato INFN- Sez. di Padova, Padova, Italy J.W. Bradley, S. Simon The University of Liverpool, Liverpool, United Kingdom G. Burt, D.J. Seal, D.A. Turner Lancaster University, Lancaster, United Kingdom O. Hryhorenko, D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France X. Jiang, T. Staedler, A.O. Zubtsovskii University Siegen, Siegen, Germany S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany N.L. Leicester Cockcroft Institute, Lancaster University, Lancaster, United Kingdom A. Medvids, A. Mychko, P. Onufrijevs Riga Technical University, Riga, Latvia S. Prucnal, S. Zhou HZDR, Dresden, Germany R. Ries Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic E. Seiler IEE, Bratislava, Slovak Republic L.G.P. Smith STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: This project has received funding from the European Union s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Thin-film cavities with higher Tc superconductors (SC) than Nb promise to move the operating temperature from 2 to 4.5 K with savings 3 orders of magnitude in cryogenic power consumption. Several European labs are coordinating their efforts to obtain a first 1.3 GHz cavity prototype through the I.FAST collaboration and other informal collaborations with CERN and DESY. R&D covers the entire production chain. In particular, new production techniques of seamless Copper and Niobium elliptical cavities via additive manufacturing are studied and evaluated. New acid-free polishing techniques to reduce surface roughness in a more sustainable way such as plasma electropolishing and metallographic polishing have been tested. Optimization of coating parameters of higher Tc SC than Nb (Nb₃Sn, V₃Si, NbTiN) via PVD and multilayer via ALD are on the way. Finally, rapid heat treatments such as Flash Lamp Annealing and Laser Annealing are used to avoid or reduce Cu diffusion in the SC film. The development and characterization of SC coatings is done on planar samples, 6 GHz cavities, choke cavities, QPR and 1.3 GHz cavities. This work presents the progress status of these coordinated efforts.
	Slides WECAA01 [15.846 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WECAA01
About •	Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023
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WECBA01	Successful SIS Multilayer Activities on Cavities and Samples Using ALD
	I. González Díaz-Palacio, R.H. Blick, C. Saribal, R. Zierold University of Hamburg, Hamburg, Germany G.K. Deyu, W. Hillert, M. Wenskat University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Theoretically SIS multilayers predict to delay vortex penetration allowing for operation gradients more than the double of bulk Nb cavities and Q-values two orders of magnitude above. The University of Hamburg focuses on Atomic Layer Deposition (ALD) as most promising coating technique. In a proof-of principle experiment thermal ALD of Al₂O₃ was successfully applied to two 1.3GHz single-cell cavities achieving gradients above 40MV/m without any deterioration in Q-value [1]. Studies using plasma-enhanced ALD (PEALD) on planar samples focus on AlN and NbTiN as dielectric and superconductor material, respectively. The deposition process and post-deposition treatments have been optimized by studying the superconducting properties in magneto-transport and in vibrating sample magnetometry of the films. Different compositions, thicknesses, and thermal annealing treatments have been investigated with respect to their resistance, magnetization, flux trapping efficiency, thermal conductance, elemental composition, and crystallinity. Within this presentation, the aggregated results of all those measurements will be presented and discussed in detail. [1] Marc Wenskat et al 2023 Supercond. Sci. Technol. 36 015010
	Slides WECBA01 [4.209 MB]
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WEIXA02	Results of the R&D RF Testing Campaign of 1.3 GHz Nb/Cu Cavities	621
	L. Vega Cid, S. Atieh, G. Bellini, A. Bianchi, L.M.A. Ferreira, C. Pereira Carlos, G.J. Rosaz, W. Venturini Delsolaro CERN, Meyrin, Switzerland S.B. Leith European Organization for Nuclear Research (CERN), Geneva, Switzerland
	In the context of the R&D program on Nb/Cu carried out at CERN, a total of 25 tests have been performed since 2021. This talk will present these results. Three different manufacturing techniques have been used to produce the copper substrates, in order to investigate which is the most suitable in terms of quality and economy of scale. On one hand, the focus has been on optimizing the surface resistance at 4.2K, as this will be the operating temperature of FCC. The results at this temperature are encouraging, showing repeatable and optimized RF performance. On the other hand, RF tests have been done at 1.85 K too aiming at deepening the knowledge of the mechanisms behind the Q slope. This is key to work on the mitigation of this phenomenon and ultimately to extend the application of this technology to high energy, high gradient accelerators. The influence of the thermal cycles has been thoroughly investigated. A systematic improvement has been observed of both the Q slope and the residual resistance with slow thermal cycles.
	Slides WEIXA02 [5.385 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA02
About •	Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 02 July 2023
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WEPWB118	Study and Improvements of Liquid Tin Diffusion Process to Synthesize Nb₃Sn Cylindrical Targets	868
SUSPB033	use link to see paper's listing under its alternate paper code
	D. Ford, E. Chyhyrynets, D. Fonnesu, G. Keppel, G. Marconato, C. Pira, A. Salmaso INFN/LNL, Legnaro (PD), Italy
	Funding: This 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. Nb₃Sn thin films on bulk Nb cavities exhibit comparable performance to bulk Nb at lower temperatures, and using Cu as a substrate material can further improve performance and reduce costs. However, coating substrates with curved geometries like elliptical cavities can be challenging due to the brittleness of Nb₃Sn targets produced by a classical sintering technique. This work explores the use of the Liquid Tin Diffusion (LTD) technique to produce sputtering targets for 6 GHz elliptical cavities, which allows for the deposition of thick and uniform coatings on Nb substrate, even for complex geometries. The study includes improvements in the LTD process and the production of a single-use LTD target, as well as the characterization of Nb₃Sn films coated by DC magnetron sputtering using these innovative targets.
	Poster WEPWB118 [5.462 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB118
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 August 2023
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FRIXA02	SRF Thin Films: Not just for Cavities
	A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Recent years have seen renewed interest and activities in developing SRF cavity materials based on thin film technologies. In this framework, considerable progress has been achieved in the development of high quality films and layered structures along with associated deposition techniques such as ECR, HiPIMS, and ALD. Beyond cavity applications, the developments in SRF thin film technologies find a variety of applications in the fields of superconducting metamaterials, electronics, sensors and quantum devices. High quality Nb films with high RRR open the way for enhanced coherence times for quantum qbits. Other SRF thin films such as NbTiN are developed for superconducting backend processes for future generations of computing hardware and radiation-hard sensors for nuclear and high-energy physics. The unifying theme across these technologies is that the same physics and material properties such as extreme low loss, stability, and manufacturability are required. This talk will present an overview of the emerging applications of SRF films and structures beyond accelerator cavities.
	Slides FRIXA02 [6.385 MB]
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Paper

Title

Page

Development and Testing of Split 6 GHz Cavities With Niobium Coatings

51

N.L. Leicester, G. Burt, H.S. Marks
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
E. Chyhyrynets, C. Pira
INFN/LNL, Legnaro (PD), Italy
J.A. Conlon, O.B. Malyshev, B.S. Sian, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
D.J. Seal
Lancaster University, Lancaster, United Kingdom

Superconducting thin-films on a copper substrate are used in accelerator RF cavities as an alternative to bulk Nb due to the high thermal conductivity of copper and the lower production costs. Although thin-film coated RF cavities can match, or even exceed the performance of bulk Nb, there are some challenges around the deposition. The RF cavities are often produced as two half-cells with a weld across the centre where the RF surface current is highest, which could reduce cavity performance. To avoid this, a cavity can be produced in 2 longitudinally split halves, with the join parallel to the surface current. As the current doesn’t cross the join a simpler weld can be performed far from the fields, simplifying the manufacturing process, and potentially improving the cavities performance. This additionally allows for different deposition techniques and coating materials to be used, as well as easier post-deposition quality control. This paper discusses the development and testing of 6 GHz cavities that have been designed and coated at the Cockcroft Institute, using low temperature RF techniques to characterise cavities with different substrate preparations and coating techniques.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB001

About •

Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 July 2023

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB003

Flux Expulsion Lens: Concept and Measurements

56

D.A. Turner
European Organization for Nuclear Research (CERN), Geneva, Switzerland
A. Gallifa Terricabras, T. Koettig, A. Macpherson, G.J. Rosaz, N. Stapley
CERN, Meyrin, Switzerland
I. González Díaz-Palacio
University of Hamburg, Hamburg, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
M. Wenskat
DESY, Hamburg, Germany

A magnetic flux expulsion lens (MFEL) has been designed and built at CERN. This device uses closed topology conduction cooling of samples to quantify magnetic flux expulsion of superconductors, and allows for systematic measurements of the cooling dynamics and the magnetic response during the superconducting transition. Measurements for bulk Nb, cold worked Nb, sputtered Nb on Cu, and SIS multilayer structures are given. Preliminary results for both sample characterization of expulsion dynamics, and observation of an enhanced flux expulsion in SIS samples are also reported.

Poster MOPMB003 [2.459 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB003

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Received ※ 27 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 14 July 2023

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MOPMB012

Investigation, Using Nb Foils to Characterise the Optimal Dimensions of Samples Measured by the Magnetic Field Penetration Facility

88

L.G.P. Smith, D.A. Turner
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, O.B. Malyshev, D.A. Turner
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt
Lancaster University, Lancaster, United Kingdom
T. Junginger
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada
O.B. Malyshev
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

SRF cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, E_acc, where E_acc is limited by the maximum magnetic field, Bmax, that can be applied on the surface of the accelerating cavity wall. To increase E_acc, Bmax, which can be applied to the surface, must also be increased. The A15 materials or multilayer structures are the potential solution to increase Bmax. Since coating and RF testing of full size RF cavities is both expensive and time consuming, one need to evaluate new ideas in superconducting thin films quickly and at low cost. A magnetic field penetration experiment has been designed and built at Daresbury Laboratory to test small superconducting samples. The facility produces a parallel DC magnetic field, which applied from one side of the sample to the other similar to that in an RF cavity. The facility applies an increasing magnetic field at a set temperature to determine the field of full flux penetration which can give an insight into the quality and structure of the superconducting structure. The facility has been characterised using both type I and II superconductors and is now producing results from novel materials.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB012

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Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 17 July 2023

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MOPMB014

NbTi Thin Film SRF Cavities for Dark Matter Search

96

SUSPB008

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

G. Marconato
Università degli Studi di Padova, Padova, Italy
D. Alesini, A. D’Elia, D. Di Gioacchino, C. Gatti, C. Ligi, G. Maccarrone, A. Rettaroli, S. Tocci
LNF-INFN, Frascati, Italy
O. Azzolini, R. Caforio, E. Chyhyrynets, D. Fonnesu, D. Ford, V.A. Garcia, G. Keppel, C. Pira, A. Salmaso, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
C. Braggio
Univ. degli Studi di Padova, Padova, Italy
D. D’Agostino, U. Gambardella
INFN-Salerno, Baronissi, Salerno, Italy
S. Posen
Fermilab, Batavia, Illinois, USA

Funding: Resources from U.S. DOE, Ofce of Science, NQISRC, SQMS contract No DE-AC02-07CH11359. Also from EU’s Horizon 2020 Research and Innovation programme, Grant Agreement No 101004730; INFN CSNV exp. SAMARA
The search for dark matter is now looking at ALPs (axion-like particles) as a very promising candidate to understand our universe. Within this framework, we explore the possibility to use NbTi thin film coatings on Cu resonating cavities to investigate the presence of axions in the range of 35-45 µeV mass by coupling the axion to a very strong magnetic field inside the cavity, causing its conversion to a photon which is subsequently detected. In this work the chemical treatments and DC magnetron sputtering details of the preparation of 9 GHz, 7 GHz, and 3.9 GHz resonant cavities and their quality factor measurements at different applied magnetic fields are presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB014

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Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 July 2023

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MOPMB016

Successful Al₂O₃ Coating of Superconducting Niobium Cavities by Thermal ALD

104

G.K. Deyu, W. Hillert, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
R.H. Blick, I. González Díaz-Palacio, R. Zierold
University of Hamburg, Hamburg, Germany

Funding: This work is supported by the BMBF under the research Grant 05K19GUB.
Al₂O₃ is one of the potential insulator materials in the superconductor-insulator-superconductor (SIS) multilayer coatings of superconducting radio-frequency (SRF) cavities for pushing their performance limits. We report on the successful coating of two 1.3 GHz Tesla-shaped SRF cavities with 18 nm and 36 nm layers of Al₂O₃ deposited by thermal atomic layer deposition (ALD). The coating recipe was developed by thermal atomic layer deposition (ALD). The coating recipe was optimized with respect to different the applied process parameters such as exposure and purge times, substrate temperature and flow rates. After a proof-of-principle Al₂O₃ coating of a cavity, second the cavity maintained its maximum achievable accelerating field of more than 40 MV/m and no deterioration was observed [1]. On the contrary, an improvement of the surface resistance above 10 MV/m has been observed, which is now further under investigation.
[1].Wenskat, Marc, et al. "Successful Al₂O₃ coating of superconducting niobium cavities with thermal ALD." Superconductor Science and Technology 36.1 (2022): 015010.

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB016

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023

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MOPMB017

Development of a Thermal Conductance Instrument for Niobium at Cryogenic Temperatures

109

C. Saribal, C. Martens
University of Hamburg, Hamburg, Germany
W. Hillert, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: University of Hamburg
Particle accelerators form an important tool in a variety of research fields. In an effort to reduce operation costs while maintaining high energies, their accelerating structures are steadily improved towards higher accelerating fields and lower RF losses. Stable operation of such a cavity generally requires Joule-heating, generated in its walls, to be conducted to an outer helium bath. Therefore, it is of interest to experimentally evaluate how present and future cavity treatments affect thermal characteristics. We present an instrument for measuring the thermal performance of SRF cavity materials at cryogenic temperatures. Pairs of niobium disks are placed inside of a liquid helium bath and a temperature gradient is generated across them to obtain total thermal resistance for temperatures below 2 Kelvin. To get an idea of the instruments sensitivity and how standard cavity treatments influence thermal resistance, samples are tested post fabrication, polishing and 800 °C baking. The first tests show the commissioning of our newly set up system and if it is feasible to observe relevant changes and evaluate new and promising cavity treatments such as SIS structures.

Poster MOPMB017 [3.217 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB017

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 July 2023

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MOPMB019

Numerical Calculations of Superheating Field in Superconductors with Nanostructured Surfaces

114

M.R.P. Walive Pathiranage
VMI, Lexington, USA
A.V. Gurevich
ODU, Norfolk, Virginia, USA

Funding: This work was supported by DOE under Grant DE-SC 100387-020 and by Virginia Military Institute (VMI) under Jackson-Hope Grant for faculty travel and for New Directions in Teaching and Research Grants.
We report calculations of a dc superheating field Hs in superconductors with nanostructured surfaces. Particularly, we performed numerical simulations of the Ginzburg-Landau (GL) equations for a superconductor with an inhomogeneous profile of impurity concentration, a thin superconducting layer on top of another superconductor, and S-I-S multilayers. The superheating field was calculated taking into account the instability of the Meissner state at a finite wavelength along the surface depending on the value of the GL parameter. Simulations were done for the materials parameters of Nb and Nb₃Sn at different values of the GL parameter and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of superconducting layers in S-I-S structures can be optimized to reach the maximum Hs, which exceeds the bulk superheating fields of both Nb and Nb₃Sn. For example, a S-I-S structure with 90 nm thick Nb₃Sn layer on Nb can boost the superheating field up to ~ 500 mT, while protecting the SRF cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.

Poster MOPMB019 [1.214 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB019

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Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 16 July 2023

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MOPMB062

Optimisation of Niobium Thin Film Deposition Parameters for SRF Cavities

253

SUSPB023

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

D.J. Seal, O.B. Malyshev, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
J.A. Conlon, O.B. Malyshev, K.T. Morrow, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

In order to accelerate the progression of thin film (TF) development for future SRF cavities, it is desirable to optimise material properties on small flat samples. Most importantly, this requires the ability to measure their superconducting properties. At Daresbury Laboratory, it has been possible for many years to characterise these films under DC conditions; however, it is not yet fully understood whether this correlates with RF measurements. Recently, a high-throughput RF facility was commissioned that uses a novel 7.8 GHz choke cavity. The facility is able to evaluate the RF performance of planar-coated TF samples at low peak magnetic fields with a high throughput rate of 2-3 samples per week. Using this facility, an optimisation study of the deposition parameters of TF Nb samples deposited by HiPIMS has begun. The ultimate aim is to optimise TF Nb as a base layer for multilayer studies and replicate planar magnetron depositions on split 6 GHz cavities. The initial focus of this study was to investigate the effect of substrate temperature during deposition. A review of the RF facility used and results of this study will be presented.

Poster MOPMB062 [2.395 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB062

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 24 July 2023

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MOPMB083

Investigation of the Multilayer Shielding Effect through NbTiN-AlN Coated Bulk Niobium

311

SUSPB025

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

I.H. Senevirathne, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
D.R. Beverstock, J.R. Delayen, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA
D.R. Beverstock
The College of William and Mary, Williamsburg, Virginia, USA

We report measurements of the dc field onset B_p of magnetic flux penetration through NbTiN-AlN coating on bulk niobium using the Hall probe experimental setup. The measurements of Bp reveal the multilayer shielding effect on bulk niobium under high magnetic fields at cryogenic temperatures. We observed a significant enhancement in Bp for the NbTiN-AlN coated Nb samples as compared to bare Nb samples. The observed dependence of B_p on the coating thickness is consistent with theoretical predictions.

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB083

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Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 12 August 2023

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TUIXA05

Energy Barrier at Superconductor-Superconductor Interfaces

T. Junginger
UVIC, Victoria, Canada

Funding: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through grants SAPPJ-2020-00030 and SAPIN-2021-00032.
In SUST 30 (12), 125012, we reported that coating a superconductor with a larger penetration depth on niobium can increase the field of first vortex penetration Hvp from niobium¿s lower critical field Hc1 to its superheating field Hsh. This was interpreted as an energy barrier at the superconductor-superconductor interface, analogous to the Bean-Livingston barrier at vacuum-superconductor interfaces. A smaller but significant increase in Hvp was observed for low-temperature baked (LTB) niobium. Results from muon spin rotation with variable implantation depth in the micrometer range and vibrating sample magnetometry (Scientific Reports 12 (1), 5522) suggest that the apparent Hvp increase in LTB niobium was due to surface pinning and not an actual Hvp increase. Low-energy muon spin rotation results further support that interpretation as a distinct bipartite magnetic screening profile is observed for actual bilayers (arXiv:2304.09360) but not for LTB niobium (PR Applied 19 (4), 044018 and arXiv:2305.02129). This suggests that the reason why some LTB niobium SRF cavities reach surface magnetic fields beyond Hc1 is specific to RF effects, such as the nucleation time.

Slides TUIXA05 [0.997 MB]

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TUCXA02

RF Vortex Nucleation in Superconductors within Time-Dependent Ginzburg-Landau Theory: Role of Surface Defects

S.M. Anlage, C.Y. Wang
UMD, College Park, Maryland, USA

Funding: This work is funded by US Department of Energy / High Energy Physics through grant # DE-SC0017931 and the Maryland Quantum Materials Center.
We use time-dependent Ginzburg-Landau (TDGL) numerical simulations to study the nucleation of RF vortices in Nb in the presence of surface defects when the material is subjected to an intense RF magnetic field in the GHz regime. In this work, we solve the TDGL equations, and Maxwell¿s equations, for a spatially nonuniform RF magnetic field created by a point RF magnetic dipole above the Nb surface. Here surface defects are notionally modeled as grain boundaries filled with a low-Tc impurity, such as oxidized Nb. The dynamics of RF currents induced in the resulting proximity-coupled superconductor are studied, and it is observed that RF vortex semi-loops penetrate the surface through the grain boundaries. Besides the RF vortex dynamics, the resulting third harmonic nonlinear response of the superconductor is calculated, and is shown to be closely related to RF vortex nucleation. The simulations show that RF vortex nucleation by surface defects can be studied by analyzing the third harmonic response of the superconductor. We make connections between these numerical studies and the results of our scanned near-field microwave microscopy efforts on a variety of SRF materials.

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WECAA01

Progress in European Thin Film Activities

607

C. Pira, O. Azzolini, R. Caforio, E. Chyhyrynets, D. Fonnesu, D. Ford, V.A. Garcia, G. Keppel, G. Marconato, A. Salmaso, F. Stivanello
INFN/LNL, Legnaro (PD), Italy
C.Z. Antoine, Y. Kalboussi, Th. Proslier
CEA-IRFU, Gif-sur-Yvette, France
C. Benjamin, O.B. Malyshev, N. Marks, B.S. Sian, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C. Benjamin, J.W. Bradley, G. Burt, O.B. Malyshev, N. Marks, D.J. Seal, B.S. Sian, S. Simon, D.A. Turner, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
S. Berry
CEA-DRF-IRFU, France
R. Berton, D. Piccoli, F. Piccoli, G. Squizzato, F. Telatin
Piccoli, Noale (VE), Italy
M. Bertucci, R. Paparella
INFN/LASA, Segrate (MI), Italy
M. Bonesso, S. Candela, V. Candela, R. Dima, G. Favero, A. Pepato, P. Rebesan, M. Romanato
INFN- Sez. di Padova, Padova, Italy
J.W. Bradley, S. Simon
The University of Liverpool, Liverpool, United Kingdom
G. Burt, D.J. Seal, D.A. Turner
Lancaster University, Lancaster, United Kingdom
O. Hryhorenko, D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
X. Jiang, T. Staedler, A.O. Zubtsovskii
University Siegen, Siegen, Germany
S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
N.L. Leicester
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
A. Medvids, A. Mychko, P. Onufrijevs
Riga Technical University, Riga, Latvia
S. Prucnal, S. Zhou
HZDR, Dresden, Germany
R. Ries
Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
E. Seiler
IEE, Bratislava, Slovak Republic
L.G.P. Smith
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: This project has received funding from the European Union s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730.
Thin-film cavities with higher Tc superconductors (SC) than Nb promise to move the operating temperature from 2 to 4.5 K with savings 3 orders of magnitude in cryogenic power consumption. Several European labs are coordinating their efforts to obtain a first 1.3 GHz cavity prototype through the I.FAST collaboration and other informal collaborations with CERN and DESY. R&D covers the entire production chain. In particular, new production techniques of seamless Copper and Niobium elliptical cavities via additive manufacturing are studied and evaluated. New acid-free polishing techniques to reduce surface roughness in a more sustainable way such as plasma electropolishing and metallographic polishing have been tested. Optimization of coating parameters of higher Tc SC than Nb (Nb₃Sn, V₃Si, NbTiN) via PVD and multilayer via ALD are on the way. Finally, rapid heat treatments such as Flash Lamp Annealing and Laser Annealing are used to avoid or reduce Cu diffusion in the SC film. The development and characterization of SC coatings is done on planar samples, 6 GHz cavities, choke cavities, QPR and 1.3 GHz cavities. This work presents the progress status of these coordinated efforts.

Slides WECAA01 [15.846 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WECAA01

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Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023

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WECBA01

Successful SIS Multilayer Activities on Cavities and Samples Using ALD

I. González Díaz-Palacio, R.H. Blick, C. Saribal, R. Zierold
University of Hamburg, Hamburg, Germany
G.K. Deyu, W. Hillert, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Theoretically SIS multilayers predict to delay vortex penetration allowing for operation gradients more than the double of bulk Nb cavities and Q-values two orders of magnitude above. The University of Hamburg focuses on Atomic Layer Deposition (ALD) as most promising coating technique. In a proof-of principle experiment thermal ALD of Al₂O₃ was successfully applied to two 1.3GHz single-cell cavities achieving gradients above 40MV/m without any deterioration in Q-value [1]. Studies using plasma-enhanced ALD (PEALD) on planar samples focus on AlN and NbTiN as dielectric and superconductor material, respectively. The deposition process and post-deposition treatments have been optimized by studying the superconducting properties in magneto-transport and in vibrating sample magnetometry of the films. Different compositions, thicknesses, and thermal annealing treatments have been investigated with respect to their resistance, magnetization, flux trapping efficiency, thermal conductance, elemental composition, and crystallinity. Within this presentation, the aggregated results of all those measurements will be presented and discussed in detail.
[1] Marc Wenskat et al 2023 Supercond. Sci. Technol. 36 015010

Slides WECBA01 [4.209 MB]

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WEIXA02

Results of the R&D RF Testing Campaign of 1.3 GHz Nb/Cu Cavities

621

L. Vega Cid, S. Atieh, G. Bellini, A. Bianchi, L.M.A. Ferreira, C. Pereira Carlos, G.J. Rosaz, W. Venturini Delsolaro
CERN, Meyrin, Switzerland
S.B. Leith
European Organization for Nuclear Research (CERN), Geneva, Switzerland

In the context of the R&D program on Nb/Cu carried out at CERN, a total of 25 tests have been performed since 2021. This talk will present these results. Three different manufacturing techniques have been used to produce the copper substrates, in order to investigate which is the most suitable in terms of quality and economy of scale. On one hand, the focus has been on optimizing the surface resistance at 4.2K, as this will be the operating temperature of FCC. The results at this temperature are encouraging, showing repeatable and optimized RF performance. On the other hand, RF tests have been done at 1.85 K too aiming at deepening the knowledge of the mechanisms behind the Q slope. This is key to work on the mitigation of this phenomenon and ultimately to extend the application of this technology to high energy, high gradient accelerators. The influence of the thermal cycles has been thoroughly investigated. A systematic improvement has been observed of both the Q slope and the residual resistance with slow thermal cycles.

Slides WEIXA02 [5.385 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA02

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Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 02 July 2023

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WEPWB118

Study and Improvements of Liquid Tin Diffusion Process to Synthesize Nb₃Sn Cylindrical Targets

868

SUSPB033

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D. Ford, E. Chyhyrynets, D. Fonnesu, G. Keppel, G. Marconato, C. Pira, A. Salmaso
INFN/LNL, Legnaro (PD), Italy

Funding: This 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.
Nb₃Sn thin films on bulk Nb cavities exhibit comparable performance to bulk Nb at lower temperatures, and using Cu as a substrate material can further improve performance and reduce costs. However, coating substrates with curved geometries like elliptical cavities can be challenging due to the brittleness of Nb₃Sn targets produced by a classical sintering technique. This work explores the use of the Liquid Tin Diffusion (LTD) technique to produce sputtering targets for 6 GHz elliptical cavities, which allows for the deposition of thick and uniform coatings on Nb substrate, even for complex geometries. The study includes improvements in the LTD process and the production of a single-use LTD target, as well as the characterization of Nb₃Sn films coated by DC magnetron sputtering using these innovative targets.

Poster WEPWB118 [5.462 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB118

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 August 2023

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FRIXA02

SRF Thin Films: Not just for Cavities

A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Recent years have seen renewed interest and activities in developing SRF cavity materials based on thin film technologies. In this framework, considerable progress has been achieved in the development of high quality films and layered structures along with associated deposition techniques such as ECR, HiPIMS, and ALD. Beyond cavity applications, the developments in SRF thin film technologies find a variety of applications in the fields of superconducting metamaterials, electronics, sensors and quantum devices. High quality Nb films with high RRR open the way for enhanced coherence times for quantum qbits. Other SRF thin films such as NbTiN are developed for superconducting backend processes for future generations of computing hardware and radiation-hard sensors for nuclear and high-energy physics. The unifying theme across these technologies is that the same physics and material properties such as extreme low loss, stability, and manufacturability are required. This talk will present an overview of the emerging applications of SRF films and structures beyond accelerator cavities.

Slides FRIXA02 [6.385 MB]

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