SRF2023 - List of Authors (Liepe, M.)

Paper	Title	Page
MOPMB015	Development of a Plasma-Enhanced Chemical Vapor Deposition System for High-Performance SRF Cavities	100
SUSPB009	use link to see paper's listing under its alternate paper code
	G. Gaitan, A.T. Holic, W.I. Howes, G. Kulina, P. Quigley, J. Sears, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Liepe Cornell University, Ithaca, New York, USA B.W. Wendland University of Minnesota, Minnesota, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, or other compound superconductors are essential for reaching enhanced RF performance levels in SRF cavities. However, optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a high-vacuum, gas, and precursor delivery system, and uses plasma to significantly reduce the required processing temperature and promote precursor decomposition. Here we present an update on the development of this system, including final system design, safety considerations, assembly, and commissioning.
	Poster MOPMB015 [1.951 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB015
About •	Received ※ 16 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 16 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB053	Theoretical Study of Thin Noble-Metal Films on the Niobium Surface	230
SUSPB021	use link to see paper's listing under its alternate paper code
	C.A. Méndez, T. Arias, M. Liepe, N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: The Center for Bright Beams, Supported by National Science Foundation award No. PHY-1549132 Recent experiments suggest that noble-metal deposition on niobium metal surfaces can remove the surface oxide and ultimately improve superconducting radio-frequency (SRF) cavities performance. In this preliminary study, we use density-functional theory to investigate the potential for noble-metal passivation of realistic, polycrystalline niobium surfaces for SRF. Specifically, we investigate the stability of gold and palladium monolayers on niobium surfaces with different crystal orientations and evaluate the impact of these impurities on superconducting properties. In particular, our results suggest that gold can grow in thin layers on the niobium surface, whereas palladium rather tends to dissolve into the niobium cavity. These results will help inform ongoing experimental efforts to passivate niobium surfaces of SRF cavities.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB053
About •	Received ※ 22 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023
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MOPMB020	A Comprehensive Picture of Hydride Formation and Dissipation	119
	N. Sitaraman, T. Arias Cornell University, Ithaca, New York, USA A.V. Harbick, M.K. Transtrum Brigham Young University, Provo, USA M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Research linking surface hydrides to Q-disease, and the subsequent development of methods to eliminate surface hydrides, is one of the great successes of SRF cavity R\&D. We use time-dependent Ginzburg-Landau to extend the theory of hydride dissipation to sub-surface hydrides. Just as surface hydrides cause Q-disease behavior, we show that sub-surface hydrides cause high-field Q-slope (HFQS) behavior. We find that the abrupt onset of HFQS is due to a transition from a vortex-free state to a vortex-penetration state. We show that controlling hydride size and depth through impurity doping can eliminate HFQS.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB020
About •	Received ※ 30 June 2023 — Revised ※ 18 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023
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MOPMB076	Surface Characterization Studies of Gold-Plated Niobium	290
SUSPB024	use link to see paper's listing under its alternate paper code
	S.G. Seddon-Stettler, M. Liepe, T.E. Oseroff, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: The National Science Foundation, Grant No. PHY-1549132 The native niobium oxide layer present on niobium has been shown to affect the performace of superconducting RF cavities. Extremely thin layers of gold on the surface of niobium have the potential to suppress surface oxidation and improve cavity performance. However, depositing uniform layers of gold at the desired thickness (sub-nm) is difficult, and different deposition methods may have different effects on the gold surface, on the niobium surface, and on the interface between the two. In particular, the question of whether gold deposition actually passivates the niobium oxide is extremely relevant for assessing the potential of gold deposition to improve RF performance. This work builds on previous research studying the RF performance of gold/niobium bilayers with different gold layer thicknesses. We here consider alternative methods to characterize the composition and chemical properties of gold/niobium bilayers to supplement the previous RF study.
	Poster MOPMB076 [1.536 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB076
About •	Received ※ 25 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
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MOPMB093	Optimizing Growth of Niobium-3 Tin Through Pre-nucleation Chemical Treatments	337
SUSPB026	use link to see paper's listing under its alternate paper code
	S.G. Arnold, G. Gaitan, M. Liepe, L. Shpani, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Arias, N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams. Nb₃Sn is a promising alternative material for SRF cavities that is close to reaching practical applications. To date, one of the most effective growth methods for this material is vapor diffusion, yet further improvement is needed for Nb₃Sn to reach its full potential. The major issues faced by vapor diffusion are tin depleted regions and surface roughness, both of which lead to impaired performance. Literature has shown that the niobium surface oxide plays an important role in the binding of tin to niobium. In this study, we performed various chemical treatments on niobium samples pre-nucleation to enhance tin nucleation. We quantify the effect that these various treatments had through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). These methods reveal information on tin nucleation density and uniformity, and a thin tin film present on most samples, even in the absence of nucleation sites. We present our findings from these surface characterization methods and introduce a framework for quantitatively comparing the samples. We plan to apply the most effective treatment to a cavity and conduct an RF test soon.
	Poster MOPMB093 [1.118 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB093
About •	Received ※ 21 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 July 2023
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MOPMB094	Design of a 1.3 GHz High-Power RF Coupler for Conduction-Cooled Systems	342
SUSPB027	use link to see paper's listing under its alternate paper code
	N.A. Stilin, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell is designing a new standalone, compact SRF cryomodule which uses cryocoolers in place of liquid helium for cooling. One of the biggest challenges in implementing such a system is designing a high-power input coupler which is able to be cooled by the cryocoolers without any additional liquid cryogenics. Due to the limited heat load capacity of the cryocoolers at 4.2 K, this requires very careful thermal isolation of the 4.2 K portion of the coupler and thorough optimization of the RF behavior to minimize losses. This paper will present the various design considerations which enabled the creating of a conduction-cooled 1.3 GHz input coupler capable of delivering up to 100 kW CW RF power.
	Poster MOPMB094 [0.964 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB094
About •	Received ※ 16 June 2023 — Revised ※ 26 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 23 July 2023
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TUIBA01	A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities	361
	M.M. Kelley, T. Arias, S. Deyo, D. Liarte, J.P. Sethna, N. Sitaraman Cornell University, Ithaca, New York, USA M. Liepe, T.E. Oseroff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called anti-Q slope. We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a ‘‘three’’-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like impurities having potential strengths informed from complementary ab initio calculations of impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off. S. Deyo, M. Kelley et al. Phys. Rev. B 106, 104502 (2022)
	Slides TUIBA01 [2.019 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIBA01
About •	Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 08 July 2023
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TUCBA01	Measurements of the Amplitude-Dependent Microwave Surface Resistance of a Proximity-Coupled Au/Nb Bilayer	369
	T.E. Oseroff, M. Liepe, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A sample host cavity is used to measure the surface resistance of a niobium substrate with a gold film deposited in place of its surface oxide. This talk will report about this measurement result. The film thickness of the gold layer was increased from 0.1 nm to 2.0 nm in five steps to study the impact of the normal layer thickness. The 0.1 nm film was found to reduce the surface resistance below its value with the surface oxide present and to enhance the quench field. The magnitude of the surface resistance increased substantially with gold film thickness. The surface resistance field-dependence appeared to be independent from the normal layer thickness. The observations reported in this work have profound implications for both low-field and high-field S.C. microwave devices. By controlling or eliminating the niobium oxide using a gold layer to passivate the niobium surface, it may be possible to improve the performance of SRF cavities used for particle acceleration. This method to reduce surface oxidation while maintaining low surface resistance could also be relevant for minimizing dissipation due to two-level systems observed in low-field low-temperature devices.
	Slides TUCBA01 [2.292 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCBA01
About •	Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 26 July 2023
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TUPTB004	Progress on Zirconium-Doped Niobium Surfaces	398
	N. Sitaraman, T. Arias, Z. Baraissov, D.A. Muller Cornell University, Ithaca, New York, USA G. Gaitan, M. Liepe, T.E. Oseroff, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the NSF under Award PHY-1549132, the Center for Bright Beams, and in part by CNF (NSF Grant NNCI-2025233), and in part by CCMR (DMR-1719875). The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB004
About •	Received ※ 30 June 2023 — Revised ※ 26 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 22 August 2023
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TUPTB006	Materials Design for Superconducting RF Cavities: Electroplating Sn, Zr, and Au onto Nb and and Chemical Vapor Deposition	401
	Z. Sun, M. Liepe, T.E. Oseroff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Z. Baraissov, D.A. Muller, M.O. Thompson Cornell University, Ithaca, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Materials scientists seek to contribute to the development of next-generation superconducting radio-frequency (SRF) accelerating cavities. Here, we summarize our achievements and learnings in designing advanced SRF materials and surfaces, including Nb₃Sn [1¿3], ZrNb(CO) [4, 5], and Au/Nb surface design [6,7]. Our efforts involve electrochemical synthesis, phase transformation, and surface chemistry, which are closely coupled with superconducting properties, SRF performance, and engineering considerations. We develop electrochemical processes for Sn, Zr, and Au on the Nb surface, an essential step in our investigation for producing high-quality Nb₃Sn, ZrNb(CO), and Au/Nb structures. Additionally, we design a custom chemical vapor deposition system to offer additional growth options. Notably, we find the second-phase NbC formation in ZrNb(CO) and in ultra-high-vacuum baked or nitrogen-processed Nb. We also identify low-dielectric-loss ZrO2 on Nb and NbZr(CO) surfaces. These advancements provide materials science approaches dealing with fundamental and technical challenges to build high-performance, multi-scale, robust SRF cavities for particle accelerators and quantum applications.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB006
About •	Received ※ 30 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
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TUPTB026	Measurements of High Values of Dielectric Permittivity Using Transmission Lines	447
	V.D. Shemelin, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE Usage of lossy materials is necessary for absorption of higher order modes excited in the RF cavities. Presently, measurements of lossy materials with usage of transmission lines give errors rapidly increasing with increase of the dielectric permittivity. A method is presented for measurements of high values of dielectric permittivity epsilon in a waveguide at high frequencies with lower errors. This method supplements the method of measurements evolved for low values of epsilon and is close to resonant methods, when a sample is placed into a cavity and the measurement is done at one only frequency. The new approach with use of Microwave Studio simulations makes possible to measure this value in several frequency points at one measurement.
	Poster TUPTB026 [0.872 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB026
About •	Received ※ 20 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 02 July 2023
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WEIAA04	Development of High-performance Niobium-3 Tin Cavities at Cornell University	600
	L. Shpani, S.G. Arnold, G. Gaitan, M. Liepe, T.E. Oseroff, R.D. Porter, N.A. Stilin, Z. Sun, N.M. Verboncoeur Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA N. Sitaraman Cornell University, Ithaca, New York, USA
	Funding: Work supported by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beam and U.S. DOE grant No. DE-SC0008431. Niobium-3 tin is a promising material for next-generation superconducting RF cavities due to its high critical temperature and high theoretical field limit. There is currently significant worldwide effort aiming to improve Nb₃Sn growth to push this material to its ultimate performance limits. This talk will present an overview of Nb₃Sn cavity development at Cornell University. One approach we are pursuing is to further advance the vapor diffusion process through optimized nucleation and film thickness. Additionally, we are exploring alternative Nb₃Sn growth methods, such as the development of a plasma-enhanced chemical vapor deposition (CVD) system, as well as Nb₃Sn growth via electrochemical synthesis.
	Slides WEIAA04 [5.260 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIAA04
About •	Received ※ 29 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 21 August 2023 — Issue date ※ 22 August 2023
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WEPWB108	Update on Cornell High Pulsed Power Sample Host Cavity	841
SUSPB029	use link to see paper's listing under its alternate paper code
	N.M. Verboncoeur, A.T. Holic, M. Liepe, T.E. Oseroff, R.D. Porter, J. Sears, L. Shpani Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA R.D. Porter SLAC, Menlo Park, California, USA
	The Cornell High Pulsed Power Sample Host Cavity (CHPPSHC) is designed to measure the temperature-dependent superheating fields of future SRF materials and thereby gain insights into the ultimate limits of their performance. Theoretical estimation of the superheating fields of SRF materials is challenging and mostly has been done for temperatures near the critical temperature or in the infinite kappa limit. Experimental data currently available is incomplete, and often impacted by material defects and their resulting thermal heating, preventing finding the fundamental limits of theses materials. The CHPPSHC system allows reaching RF fields in excess of half a Tesla within microseconds on material samples by utilizing high pulsed power, thereby outrunning thermal effects. We are principally interested in the superheating field of Nb₃Sn, a material of interest for the SRF community, and present here the current fabrication and assembly status of the CHPPSHC as well as early results.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB108
About •	Received ※ 27 June 2023 — Revised ※ 20 July 2023 — Accepted ※ 20 August 2023 — Issue date ※ 22 August 2023
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THIXA05	Conduction-Cooled SRF Cavities: Opportunities and Challenges	973
	N.A. Stilin, H. Conklin, T. Gruber, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Thanks to improvements in the performance of both commercial cryocoolers and Nb₃Sn-coated superconducting radio-frequency (SRF) cavities, it is now possible to design and build compact, SRF cryomodules without the need for liquid cryogenics. In addition, these systems offer robust, non-expert, turn-key operation, making SRF technology significantly more accessible for smaller-scale applications in fields such as industry, national security, medicine, environmental sustainability, etc. To fully realize these systems, many technical and operational challenges must be overcome. These include properly cooling the SRF cavity via thermal conduction and designing high-power (~ 100 kW continuous) RF couplers which dissipate minimal heat (~ 1 W) at 4.2 K. This presentation will discuss these challenges and the solutions which have been developed at Cornell University and elsewhere.
	Slides THIXA05 [7.219 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-THIXA05
About •	Received ※ 27 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 04 July 2023 — Issue date ※ 08 July 2023
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Paper

Title

Page

MOPMB015

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

100

SUSPB009

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

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

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

Poster MOPMB015 [1.951 MB]

DOI •

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

About •

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

Cite •

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

MOPMB053

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

230

SUSPB021

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

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

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

DOI •

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

About •

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

Cite •

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

MOPMB020

A Comprehensive Picture of Hydride Formation and Dissipation

119

N. Sitaraman, T. Arias
Cornell University, Ithaca, New York, USA
A.V. Harbick, M.K. Transtrum
Brigham Young University, Provo, USA
M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Research linking surface hydrides to Q-disease, and the subsequent development of methods to eliminate surface hydrides, is one of the great successes of SRF cavity R\&D. We use time-dependent Ginzburg-Landau to extend the theory of hydride dissipation to sub-surface hydrides. Just as surface hydrides cause Q-disease behavior, we show that sub-surface hydrides cause high-field Q-slope (HFQS) behavior. We find that the abrupt onset of HFQS is due to a transition from a vortex-free state to a vortex-penetration state. We show that controlling hydride size and depth through impurity doping can eliminate HFQS.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB020

About •

Received ※ 30 June 2023 — Revised ※ 18 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023

Cite •

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

MOPMB076

Surface Characterization Studies of Gold-Plated Niobium

290

SUSPB024

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

S.G. Seddon-Stettler, M. Liepe, T.E. Oseroff, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
N. Sitaraman
Cornell University, Ithaca, New York, USA

Funding: The National Science Foundation, Grant No. PHY-1549132
The native niobium oxide layer present on niobium has been shown to affect the performace of superconducting RF cavities. Extremely thin layers of gold on the surface of niobium have the potential to suppress surface oxidation and improve cavity performance. However, depositing uniform layers of gold at the desired thickness (sub-nm) is difficult, and different deposition methods may have different effects on the gold surface, on the niobium surface, and on the interface between the two. In particular, the question of whether gold deposition actually passivates the niobium oxide is extremely relevant for assessing the potential of gold deposition to improve RF performance. This work builds on previous research studying the RF performance of gold/niobium bilayers with different gold layer thicknesses. We here consider alternative methods to characterize the composition and chemical properties of gold/niobium bilayers to supplement the previous RF study.

Poster MOPMB076 [1.536 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB076

About •

Received ※ 25 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023

Cite •

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

MOPMB093

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

337

SUSPB026

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

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

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

Poster MOPMB093 [1.118 MB]

DOI •

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

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

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MOPMB094

Design of a 1.3 GHz High-Power RF Coupler for Conduction-Cooled Systems

342

SUSPB027

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N.A. Stilin, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell is designing a new standalone, compact SRF cryomodule which uses cryocoolers in place of liquid helium for cooling. One of the biggest challenges in implementing such a system is designing a high-power input coupler which is able to be cooled by the cryocoolers without any additional liquid cryogenics. Due to the limited heat load capacity of the cryocoolers at 4.2 K, this requires very careful thermal isolation of the 4.2 K portion of the coupler and thorough optimization of the RF behavior to minimize losses. This paper will present the various design considerations which enabled the creating of a conduction-cooled 1.3 GHz input coupler capable of delivering up to 100 kW CW RF power.

Poster MOPMB094 [0.964 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB094

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Received ※ 16 June 2023 — Revised ※ 26 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 23 July 2023

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TUIBA01

A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities

361

M.M. Kelley, T. Arias, S. Deyo, D. Liarte, J.P. Sethna, N. Sitaraman
Cornell University, Ithaca, New York, USA
M. Liepe, T.E. Oseroff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called anti-Q slope. We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a ‘‘three’’-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like impurities having potential strengths informed from complementary ab initio calculations of impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off.
S. Deyo, M. Kelley et al. Phys. Rev. B 106, 104502 (2022)

Slides TUIBA01 [2.019 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIBA01

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Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 08 July 2023

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TUCBA01

Measurements of the Amplitude-Dependent Microwave Surface Resistance of a Proximity-Coupled Au/Nb Bilayer

369

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

A sample host cavity is used to measure the surface resistance of a niobium substrate with a gold film deposited in place of its surface oxide. This talk will report about this measurement result. The film thickness of the gold layer was increased from 0.1 nm to 2.0 nm in five steps to study the impact of the normal layer thickness. The 0.1 nm film was found to reduce the surface resistance below its value with the surface oxide present and to enhance the quench field. The magnitude of the surface resistance increased substantially with gold film thickness. The surface resistance field-dependence appeared to be independent from the normal layer thickness. The observations reported in this work have profound implications for both low-field and high-field S.C. microwave devices. By controlling or eliminating the niobium oxide using a gold layer to passivate the niobium surface, it may be possible to improve the performance of SRF cavities used for particle acceleration. This method to reduce surface oxidation while maintaining low surface resistance could also be relevant for minimizing dissipation due to two-level systems observed in low-field low-temperature devices.

Slides TUCBA01 [2.292 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCBA01

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Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 26 July 2023

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TUPTB004

Progress on Zirconium-Doped Niobium Surfaces

398

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

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

DOI •

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

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

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TUPTB006

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

401

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

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

DOI •

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

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

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TUPTB026

Measurements of High Values of Dielectric Permittivity Using Transmission Lines

447

V.D. Shemelin, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: DOE
Usage of lossy materials is necessary for absorption of higher order modes excited in the RF cavities. Presently, measurements of lossy materials with usage of transmission lines give errors rapidly increasing with increase of the dielectric permittivity. A method is presented for measurements of high values of dielectric permittivity epsilon in a waveguide at high frequencies with lower errors. This method supplements the method of measurements evolved for low values of epsilon and is close to resonant methods, when a sample is placed into a cavity and the measurement is done at one only frequency. The new approach with use of Microwave Studio simulations makes possible to measure this value in several frequency points at one measurement.

Poster TUPTB026 [0.872 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB026

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Received ※ 20 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 02 July 2023

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WEIAA04

Development of High-performance Niobium-3 Tin Cavities at Cornell University

600

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

Funding: Work supported by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beam and U.S. DOE grant No. DE-SC0008431.
Niobium-3 tin is a promising material for next-generation superconducting RF cavities due to its high critical temperature and high theoretical field limit. There is currently significant worldwide effort aiming to improve Nb₃Sn growth to push this material to its ultimate performance limits. This talk will present an overview of Nb₃Sn cavity development at Cornell University. One approach we are pursuing is to further advance the vapor diffusion process through optimized nucleation and film thickness. Additionally, we are exploring alternative Nb₃Sn growth methods, such as the development of a plasma-enhanced chemical vapor deposition (CVD) system, as well as Nb₃Sn growth via electrochemical synthesis.

Slides WEIAA04 [5.260 MB]

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

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

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WEPWB108

Update on Cornell High Pulsed Power Sample Host Cavity

841

SUSPB029

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

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

DOI •

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

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

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THIXA05

Conduction-Cooled SRF Cavities: Opportunities and Challenges

973

N.A. Stilin, H. Conklin, T. Gruber, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Thanks to improvements in the performance of both commercial cryocoolers and Nb₃Sn-coated superconducting radio-frequency (SRF) cavities, it is now possible to design and build compact, SRF cryomodules without the need for liquid cryogenics. In addition, these systems offer robust, non-expert, turn-key operation, making SRF technology significantly more accessible for smaller-scale applications in fields such as industry, national security, medicine, environmental sustainability, etc. To fully realize these systems, many technical and operational challenges must be overcome. These include properly cooling the SRF cavity via thermal conduction and designing high-power (~ 100 kW continuous) RF couplers which dissipate minimal heat (~ 1 W) at 4.2 K. This presentation will discuss these challenges and the solutions which have been developed at Cornell University and elsewhere.

Slides THIXA05 [7.219 MB]

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reference for this paper ※ doi:10.18429/JACoW-SRF2023-THIXA05

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Received ※ 27 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 04 July 2023 — Issue date ※ 08 July 2023

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