SRF2023 - Table of Session: WEIXA (Fundamental R&D V)

Paper	Title	Page
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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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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEIXA03	Optimizing the Manufacture of High-Purity Niobium SRF Cavities Using the Forming Limit Diagram: A Case Study of the HL-LHC Crab Cavities RFD Pole	627
	A. Gallifa Terricabras, I. Aviles Santillana, S. Barrière, M. Garlasché, L. Prever-Loiri, J.S. Swieszek CERN, Meyrin, Switzerland E. Cano-Pleite UC3M, Leganes, Spain M. Narduzzi Fermilab, Batavia, Illinois, USA S. Pfeiffer European Organization for Nuclear Research (CERN), Geneva, Switzerland
	Funding: CERN HL-LHC The Crab Cavities are key components of the High Luminosity Large Hadron Collider (HL-LHC) project at CERN, which aims to increase the integrated luminosity of the LHC, the world’s largest particle accelerator, by a factor of ten. This paper explores the application of the Forming Limit Diagram (FLD) to enhance the manufacturing process of complex-shape Nb-based cavities, with a focus on the formability challenges experienced with the pole of the Radio Frequency Dipole (RFD) Crab Cavities. The study includes the material characterization of ultra-high-purity niobium (Nb RRR300) sheets, namely mechanical tests and microstructural analysis; it also contains large-deformation Finite Element simulations of the pole deep drawing process, and the translation of the resulting strains in a FLD diagram, together with several suggestions on how to improve the manufacturing process of such deep drawn parts. The results of this study can provide valuable insights into improving the design and fabrication of complex-shaped superconducting radio-frequency cavities made by large-deformation metal-sheet forming processes.
	Slides WEIXA03 [15.991 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA03
About •	Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 27 June 2023
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WEIXA04	Development of the Directly-Sliced Niobium Material for High Performance SRF Cavities	634
	A. Kumar, H. Araki, T. Dohmae, H. Ito, T. Saeki, K. Umemori, A. Yamamoto, M. Yamanaka KEK, Ibaraki, Japan A. Yamamoto CERN, Meyrin, Switzerland
	For the purpose of cost reduction for the ILC, KEK has been conducting R&D on direct sliced Nb materials such as large grain and medium grain Nb. Single-cell, 3-cell, and 9-cell cavities have been manufactured, and each has demonstrated a high-performance accelerating gradient exceeding 35 MV/m. The results of applying high-Q/high-G recipes, such as two-step baking and furnace baking to these cavities are also shown. Moreover, mechanical tests have been carried out for the beforementioned materials to evaluate their strength for application to the High-Pressure Gas Safety Law. The status of development of these large grain and Medium grain Nb will be presented.
	Slides WEIXA04 [3.773 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA04
About •	Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 12 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEIXA05	Electropolishing Study on Nitrogen-Doped Niobium Surface	641
	V. Chouhan, T.J. Ring, G. Wu Fermilab, Batavia, Illinois, USA E.A.S. Viklund NU, Evanston, Illinois, USA
	The nitrogen doping (N-doping) process is applied to niobium (Nb) superconducting cavities to enhance their quality factors. The N-doping is followed by an electropolishing process that provides the final surface of the cavities. A controlled EP process is necessary to get the benefit of N-doping and achieve a high accelerating gradient. We have performed electropolishing of N-doped Nb surface under various conditions to understand their impact on the surface. A modified EP process was developed to obtain a smooth pit-free surface.
	Slides WEIXA05 [17.622 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA05
About •	Received ※ 19 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEIXA06	Recent Advances in Metallographic Polishing for SRF Application	646
	O. Hryhorenko JLab, Newport News, Virginia, USA C.Z. Antoine, F. Éozénou, Th. Proslier Université Paris-Saclay, CEA, Gif-sur-Yvette, France T. Dohmae KEK, Ibaraki, Japan S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
	Funding: ENSAR-2 under grant agreement N° 654002. IFAST under Grant Agreement No 101004730. The U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. This talk is an overview of the metallographic polishing R&D program covering Niobium and Copper substrates treatment for thin film coating as an alternative fabrication pathway for 1.3 GHz elliptical cavities. The presented research is the result of a collaborative effort between IJCLab, CEA/Irfu, HZB, and KEK in order to develop innovative surface processing and cavity fabrication protocols capable of meeting stringent requirements for SRF surfaces, including the reduction of safety risks and ecological footprint, enhancing reliability, improving the surface roughness, and potentially allowing cost reduction. The research findings will be disclosed.
	Slides WEIXA06 [7.469 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA06
About •	Received ※ 16 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 14 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEIXA07	Review of Thermal Treatments: Effects, Reliability, and Open Questions
	S. Posen Fermilab, Batavia, Illinois, USA
	Over years of research and development, a variety of thermal treatments have been developed for bulk niobium cavities, providing different high performance capabilities for SRF resonators depending on the application. Key considerations include maximum field, quality factor at a desired field, sensitivity to trapped flux, and reproducibility of performance. In this talk, we overview the last decade of development of heat treatments, as well as what is reliability achieved at different laboratories, and open questions.
	Slides WEIXA07 [6.423 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

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]

Cite •

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

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

Cite •

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

WEIXA03

Optimizing the Manufacture of High-Purity Niobium SRF Cavities Using the Forming Limit Diagram: A Case Study of the HL-LHC Crab Cavities RFD Pole

627

A. Gallifa Terricabras, I. Aviles Santillana, S. Barrière, M. Garlasché, L. Prever-Loiri, J.S. Swieszek
CERN, Meyrin, Switzerland
E. Cano-Pleite
UC3M, Leganes, Spain
M. Narduzzi
Fermilab, Batavia, Illinois, USA
S. Pfeiffer
European Organization for Nuclear Research (CERN), Geneva, Switzerland

Funding: CERN HL-LHC
The Crab Cavities are key components of the High Luminosity Large Hadron Collider (HL-LHC) project at CERN, which aims to increase the integrated luminosity of the LHC, the world’s largest particle accelerator, by a factor of ten. This paper explores the application of the Forming Limit Diagram (FLD) to enhance the manufacturing process of complex-shape Nb-based cavities, with a focus on the formability challenges experienced with the pole of the Radio Frequency Dipole (RFD) Crab Cavities. The study includes the material characterization of ultra-high-purity niobium (Nb RRR300) sheets, namely mechanical tests and microstructural analysis; it also contains large-deformation Finite Element simulations of the pole deep drawing process, and the translation of the resulting strains in a FLD diagram, together with several suggestions on how to improve the manufacturing process of such deep drawn parts. The results of this study can provide valuable insights into improving the design and fabrication of complex-shaped superconducting radio-frequency cavities made by large-deformation metal-sheet forming processes.

Slides WEIXA03 [15.991 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA03

About •

Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 27 June 2023

Cite •

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

WEIXA04

Development of the Directly-Sliced Niobium Material for High Performance SRF Cavities

634

A. Kumar, H. Araki, T. Dohmae, H. Ito, T. Saeki, K. Umemori, A. Yamamoto, M. Yamanaka
KEK, Ibaraki, Japan
A. Yamamoto
CERN, Meyrin, Switzerland

For the purpose of cost reduction for the ILC, KEK has been conducting R&D on direct sliced Nb materials such as large grain and medium grain Nb. Single-cell, 3-cell, and 9-cell cavities have been manufactured, and each has demonstrated a high-performance accelerating gradient exceeding 35 MV/m. The results of applying high-Q/high-G recipes, such as two-step baking and furnace baking to these cavities are also shown. Moreover, mechanical tests have been carried out for the beforementioned materials to evaluate their strength for application to the High-Pressure Gas Safety Law. The status of development of these large grain and Medium grain Nb will be presented.

Slides WEIXA04 [3.773 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA04

About •

Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 12 July 2023

Cite •

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

WEIXA05

Electropolishing Study on Nitrogen-Doped Niobium Surface

641

V. Chouhan, T.J. Ring, G. Wu
Fermilab, Batavia, Illinois, USA
E.A.S. Viklund
NU, Evanston, Illinois, USA

The nitrogen doping (N-doping) process is applied to niobium (Nb) superconducting cavities to enhance their quality factors. The N-doping is followed by an electropolishing process that provides the final surface of the cavities. A controlled EP process is necessary to get the benefit of N-doping and achieve a high accelerating gradient. We have performed electropolishing of N-doped Nb surface under various conditions to understand their impact on the surface. A modified EP process was developed to obtain a smooth pit-free surface.

Slides WEIXA05 [17.622 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA05

About •

Received ※ 19 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023

Cite •

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

WEIXA06

Recent Advances in Metallographic Polishing for SRF Application

646

O. Hryhorenko
JLab, Newport News, Virginia, USA
C.Z. Antoine, F. Éozénou, Th. Proslier
Université Paris-Saclay, CEA, Gif-sur-Yvette, France
T. Dohmae
KEK, Ibaraki, Japan
S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

Funding: ENSAR-2 under grant agreement N° 654002. IFAST under Grant Agreement No 101004730. The U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
This talk is an overview of the metallographic polishing R&D program covering Niobium and Copper substrates treatment for thin film coating as an alternative fabrication pathway for 1.3 GHz elliptical cavities. The presented research is the result of a collaborative effort between IJCLab, CEA/Irfu, HZB, and KEK in order to develop innovative surface processing and cavity fabrication protocols capable of meeting stringent requirements for SRF surfaces, including the reduction of safety risks and ecological footprint, enhancing reliability, improving the surface roughness, and potentially allowing cost reduction. The research findings will be disclosed.

Slides WEIXA06 [7.469 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA06

About •

Received ※ 16 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 14 July 2023

Cite •

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

WEIXA07

Review of Thermal Treatments: Effects, Reliability, and Open Questions

S. Posen
Fermilab, Batavia, Illinois, USA

Over years of research and development, a variety of thermal treatments have been developed for bulk niobium cavities, providing different high performance capabilities for SRF resonators depending on the application. Key considerations include maximum field, quality factor at a desired field, sensitivity to trapped flux, and reproducibility of performance. In this talk, we overview the last decade of development of heat treatments, as well as what is reliability achieved at different laboratories, and open questions.

Slides WEIXA07 [6.423 MB]

Cite •

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