SRF2023 - List of Authors (Junginger, T.)

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

MOPMB023	Magnetic Flux Expulsion in TRIUMF’s Multi-Mode Coaxial Cavities	135
SUSPB011	use link to see paper's listing under its alternate paper code
	R.R. Gregory, T. Junginger, M.W. McMullin UVIC, Victoria, Canada T. Junginger, P. Kolb, R.E. Laxdal, M.W. McMullin, Z.Y. Yao TRIUMF, Vancouver, Canada
	The external magnetic flux sensitivity of SRF cavities is an important characteristic of SRF accelerator design. Previous studies have shown that n-doped elliptical cavities are very sensitive to external fields, resulting in stringent requirements for residual field and cavity cool-down speed. Few such studies have been done on HWRs and QWRs. The impact of applied field direction and cool-down speed of flux expulsion for these cavities is poorly understood. This study explores the effect of these cool-down characteristics on TRIUMF¿s QWR using COMSOL ® simulations and experimental results. This study seeks to maximize the flux expulsion that occurs when a cavity is cooled down through its superconducting temperature. Flux expulsion is affected by the cool-down speed, temperature gradient, and orientation of the cavity relative to an applied magnetic field. It was found that for a vertically applied magnetic field the cool-down speed and temperature gradient did not have a significant effect on flux expulsion. Contrarily, a horizontal magnetic field can be nearly completely expelled by a fast, high temperature gradient cool-down.
	Poster MOPMB023 [2.191 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB023
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 30 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB038	Temperature Mapping for Coaxial Cavities at TRIUMF	183
	P. Kolb, T. Junginger, J.J. Keir, R.E. Laxdal, B. Matheson, Z.Y. Yao TRIUMF, Vancouver, Canada H. Al Hassini, T. Junginger UVIC, Victoria, Canada L. Fearn UW/Physics, Waterloo, Ontario, Canada
	Temperature mapping (T-map) on superconducting radio-frequency (SRF) cavities has been shown as a useful tool to identify defects and other abnormal sources of losses. So far T-map systems have only been realized for elliptical cavities that have an easily accessible outer surface. TEM mode cavities such as quarterwave and halfwave resonators (QWR, HWR) dissipate most of their power on the inner conductor of the coaxial structure. The limited access and constrained space are a challenge for the design of a temperature mapping system. This paper describes the mechanical and electrical design including the data acquisition of a T-map system for the TRIUMF multi-mode coaxial cavities, and first results are shown.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB038
About •	Received ※ 20 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 30 June 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUIXA04	First Results from beta-SRF- Testing SRF Samples at High Parallel Field	374
	E. Thoeng, R. Kiefl, W.A. MacFarlane, J.O. Ticknor UBC & TRIUMF, Vancouver, British Columbia, Canada M. Asaduzzaman, S.R. Dunsiger, D. Fujimoto, T. Junginger, V.L. Karner, P. Kolb, R.E. Laxdal, R. Li, R.M.L. McFadden, G. Morris, M. Stachura TRIUMF, Vancouver, Canada T. Junginger, R.M.L. McFadden UVIC, Victoria, Canada
	The new ¿-SRF facility at TRIUMF has recently been commissioned. A new 1 m extension has been added to an existing ¿-NMR beamline with a large Helmholtz coil to produce fields up to 200 mT parallel to sample surfaces. The ¿-NMR technique allows depth dependent characterization of the local magnetic field in the first 100 nm of the sample surface making the probe ideal for studying Meissner screen- ing in heat treated Niobium or layered SRF materials. First measurements of Meissner screening at fields up to 200 mT have been analyzed. The results show clear differences in the Meissner screening of baseline treatments compared to mid-T baked (O-doped) Niobium.
	Slides TUIXA04 [1.644 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIXA04
About •	Received ※ 24 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 06 July 2023 — Issue date ※ 09 July 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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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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB050	Thermal Feedback in Coaxial SRF Cavities	224
SUSPB020	use link to see paper's listing under its alternate paper code
	M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao TRIUMF, Vancouver, Canada T. Junginger UVIC, Victoria, Canada
	Funding: Natural Sciences and Engineering Research Council of Canada The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

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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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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Paper

Title

Page

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

Cite •

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

MOPMB023

Magnetic Flux Expulsion in TRIUMF’s Multi-Mode Coaxial Cavities

135

SUSPB011

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

R.R. Gregory, T. Junginger, M.W. McMullin
UVIC, Victoria, Canada
T. Junginger, P. Kolb, R.E. Laxdal, M.W. McMullin, Z.Y. Yao
TRIUMF, Vancouver, Canada

The external magnetic flux sensitivity of SRF cavities is an important characteristic of SRF accelerator design. Previous studies have shown that n-doped elliptical cavities are very sensitive to external fields, resulting in stringent requirements for residual field and cavity cool-down speed. Few such studies have been done on HWRs and QWRs. The impact of applied field direction and cool-down speed of flux expulsion for these cavities is poorly understood. This study explores the effect of these cool-down characteristics on TRIUMF¿s QWR using COMSOL ® simulations and experimental results. This study seeks to maximize the flux expulsion that occurs when a cavity is cooled down through its superconducting temperature. Flux expulsion is affected by the cool-down speed, temperature gradient, and orientation of the cavity relative to an applied magnetic field. It was found that for a vertically applied magnetic field the cool-down speed and temperature gradient did not have a significant effect on flux expulsion. Contrarily, a horizontal magnetic field can be nearly completely expelled by a fast, high temperature gradient cool-down.

Poster MOPMB023 [2.191 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB023

About •

Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 30 July 2023

Cite •

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

MOPMB038

Temperature Mapping for Coaxial Cavities at TRIUMF

183

P. Kolb, T. Junginger, J.J. Keir, R.E. Laxdal, B. Matheson, Z.Y. Yao
TRIUMF, Vancouver, Canada
H. Al Hassini, T. Junginger
UVIC, Victoria, Canada
L. Fearn
UW/Physics, Waterloo, Ontario, Canada

Temperature mapping (T-map) on superconducting radio-frequency (SRF) cavities has been shown as a useful tool to identify defects and other abnormal sources of losses. So far T-map systems have only been realized for elliptical cavities that have an easily accessible outer surface. TEM mode cavities such as quarterwave and halfwave resonators (QWR, HWR) dissipate most of their power on the inner conductor of the coaxial structure. The limited access and constrained space are a challenge for the design of a temperature mapping system. This paper describes the mechanical and electrical design including the data acquisition of a T-map system for the TRIUMF multi-mode coaxial cavities, and first results are shown.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB038

About •

Received ※ 20 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 30 June 2023

Cite •

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

TUIXA04

First Results from beta-SRF- Testing SRF Samples at High Parallel Field

374

E. Thoeng, R. Kiefl, W.A. MacFarlane, J.O. Ticknor
UBC & TRIUMF, Vancouver, British Columbia, Canada
M. Asaduzzaman, S.R. Dunsiger, D. Fujimoto, T. Junginger, V.L. Karner, P. Kolb, R.E. Laxdal, R. Li, R.M.L. McFadden, G. Morris, M. Stachura
TRIUMF, Vancouver, Canada
T. Junginger, R.M.L. McFadden
UVIC, Victoria, Canada

The new ¿-SRF facility at TRIUMF has recently been commissioned. A new 1 m extension has been added to an existing ¿-NMR beamline with a large Helmholtz coil to produce fields up to 200 mT parallel to sample surfaces. The ¿-NMR technique allows depth dependent characterization of the local magnetic field in the first 100 nm of the sample surface making the probe ideal for studying Meissner screen- ing in heat treated Niobium or layered SRF materials. First measurements of Meissner screening at fields up to 200 mT have been analyzed. The results show clear differences in the Meissner screening of baseline treatments compared to mid-T baked (O-doped) Niobium.

Slides TUIXA04 [1.644 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIXA04

About •

Received ※ 24 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 06 July 2023 — Issue date ※ 09 July 2023

Cite •

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

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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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

Cite •

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

MOPMB050

Thermal Feedback in Coaxial SRF Cavities

224

SUSPB020

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

M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada

Funding: Natural Sciences and Engineering Research Council of Canada
The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050

About •

Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023

Cite •

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

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

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

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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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