SRF2023 - List of Keywords (plasma)

Paper	Title	Other Keywords	Page
MOIAA05	Commissioning of the Second JLAB C75 Cryomodule & Performance Evaluation of Installed C75 Cavities	cavity, cryomodule, SRF, controls	14
	M.D. McCaughan, G. Ciovati, G.K. Davis, M.A. Drury, T. Powers, A.V. Reilly JLab, Newport News, Virginia, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. JLAB has long been a hub of SRF technology with the CEBAF accelerator as one of its first large scale adopters. As SRF technology has advanced, the C50 and C100 programs have allowed for the extension of CEBAF’s total energy to 6 GeV and nearly 12 GeV respectively. Along with the increase in energy reach, rates of accelerating gradient degradation have been extracted for these cryomodule designs. A plan to mitigate these losses & maintain robust gradient headroom to deliver the 12 GeV program ¿ the CEBAF Performance Plan¿ established a multi-year effort of cryomodule refurbishments and replacements. Part of this plan included a cost optimization of the C50 program with more modern processing techniques and the replacement of existing cavities with larger grain boundary cavities produced from ingot Niobium (dubbed C75 for 75 MeV gain). Reports have been made on the prototype pair of C75 cavities installed in a C50 cryomodule and the first full C75 cryomodule installed in 2017 and 2021. This paper reports on the results from the qualification of the cavities for the second C75 module in both a vertical cryostat and the commissioning results of the cryomodule in the CEBAF tunnel.
	Slides MOIAA05 [1.810 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOIAA05
About •	Received ※ 19 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 02 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMB009	Plasma Electrolytic Polishing Technology Progress Development for Nb and Cu Substrates Preparation	cavity, cathode, experiment, SRF	75
	E. Chyhyrynets, O. Azzolini, R. Caforio, D. Fonnesu, D. Ford, G. Keppel, C. Pira, A. Salmaso, F. Stivanello INFN/LNL, Legnaro (PD), Italy G. Marconato Università degli Studi di Padova, Padova, Italy
	Funding: Work supported by the INFN CSNV experiment SAMARA. Fundings from the EU’s Horizon 2020 Research and Innovation programme under Grant Agreement N 101004730. PNRR MUR project PE0000023-NQSTI. Superconducting radio frequency (SRF) cavity performance is highly dependent on surface preparation. Conventionally, electropolishing (EP) is used to achieve a clean surface and low roughness for both Nb and Cu substrates, but it requires harsh and corrosive solutions like concentrated acids. Plasma Electrolytic Polishing (PEP) is a promising alternative that uses only diluted salt solutions and has several advantages over EP. PEP can replace intermediate steps like mechanical or chemical polishing, thanks to its superior removal rate of up to 2-8 um/min of Nb and 3-30 um/min of Cu. It achieves Ra roughness of 100 nm for both substrates and has a higher smoothing effect than EP. PEP is also suitable for normal conducting cavities and other accelerator components, including couplers. We demonstrate the effectiveness of PEP on SRF substrates and analyse substrate defect evaluation. We demonstrate the application of PEP onto SRF substrates and analyse the substrate’s defect evaluation. The ongoing work includes Nb bulk and Nb on Cu QPR treatments and RF tests in collaboration with HZB.
	Poster MOPMB009 [11.877 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB009
About •	Received ※ 17 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)

MOPMB015	Development of a Plasma-Enhanced Chemical Vapor Deposition System for High-Performance SRF Cavities	cavity, SRF, vacuum, controls	100
	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)

MOPMB049	Plasma Processing: Ignition Testing and Simulation Models for a 172 MHz HWR Cavity	cavity, vacuum, simulation, SRF	219
	M.E. McIntyre, B.R. Blomberg, M.P. Kelly, J.T. McLain, K.M. Villafania, G.P. Zinkann ANL, Lemont, Illinois, USA Z. Wei GIT, Atlanta, Georgia, USA
	Maintenance and cleaning of superconducting RF cavities is labor intensive task that involves disassembling the cryostat holding the resonators and removing them to be cleaned. At the Argonne Tandem Linac Accelerating System (ATLAS) at Argonne National Laboratory, a project is underway to research cleaning the cavities in-situ by plasma processing. Previous plasma processing research by SNS, MSU, FNAL, and IJCLab has been successful in improving field emissions post processing. It is advantageous to pursue research in this method, allowing for possible use on modern ATLAS cryomodules, A-tank and G-tank quarter-wave resonators. The results presented show initial plasma ignition testing and plasma simulations for the coupled E and B fields, both done on a 172 MHz HWR cavity previously designed as early R&D for FRIB. Future plans are also included, laying out next steps to test plasma processing on the same HWR cavity and eventually a QWR.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB049
About •	Received ※ 05 July 2023 — Revised ※ 25 July 2023 — Accepted ※ 24 September 2023 — Issue date ※ 24 September 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPTB006	Materials Design for Superconducting RF Cavities: Electroplating Sn, Zr, and Au onto Nb and and Chemical Vapor Deposition	cavity, SRF, controls, niobium	401
	Z. Sun, M. Liepe, T.E. Oseroff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Z. Baraissov, D.A. Muller, M.O. Thompson Cornell University, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Materials scientists seek to contribute to the development of next-generation superconducting radio-frequency (SRF) accelerating cavities. Here, we summarize our achievements and learnings in designing advanced SRF materials and surfaces, including Nb₃Sn [1¿3], ZrNb(CO) [4, 5], and Au/Nb surface design [6,7]. Our efforts involve electrochemical synthesis, phase transformation, and surface chemistry, which are closely coupled with superconducting properties, SRF performance, and engineering considerations. We develop electrochemical processes for Sn, Zr, and Au on the Nb surface, an essential step in our investigation for producing high-quality Nb₃Sn, ZrNb(CO), and Au/Nb structures. Additionally, we design a custom chemical vapor deposition system to offer additional growth options. Notably, we find the second-phase NbC formation in ZrNb(CO) and in ultra-high-vacuum baked or nitrogen-processed Nb. We also identify low-dielectric-loss ZrO2 on Nb and NbZr(CO) surfaces. These advancements provide materials science approaches dealing with fundamental and technical challenges to build high-performance, multi-scale, robust SRF cavities for particle accelerators and quantum applications.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB006
About •	Received ※ 30 June 2023 — Revised ※ 11 August 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPWB053	Simulation of the Dynamics of Gas Mixtures during Plasma Processing in the C75 Cavity	cavity, electron, simulation, SRF	696
	N.K. Raut, P. Dhakal, T.D. Ganey, T. Powers JLab, Newport News, Virginia, USA
	Funding: The work is supported by SC Nuclear Physics Program through DOE SC Lab funding announcement DE-FOA-0002670 & is authored by JSA, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177 Plasma processing using a mixture of noble gas and oxygen is a technique that is currently being used to reduce field emission and multipacting in accelerating cavities. Plasma is created inside the cavity when the gas mixture is exposed to an electromagnetic field that is generated by applying RF power through the fundamental power or higher-order mode couplers. Oxygen ions and atomic oxygen are created in the plasma which breaks down the hydrocarbons on the surface of the cavity and the residuals from this process are removed as part of the process gas flow. Removal of hydrocarbons from the surface increases the work function and reduces the secondary emission coefficient. This work describes the initial results of plasma simulation, which provides insight into the ignition process, distribution of different species, and interactions of free oxygen and oxygen ions with the cavity surfaces. The simulations have been done with an Ar/¿2 plasma using COMSOL® multiphysics. These simulations help in understanding the dynamics and control of plasma inside the cavity and the exploration of different gas mixtures.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB053
About •	Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 29 June 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPWB054	In Situ Plasma Processing of Superconducting Cavities at JLab, 2023 Update	cavity, cryomodule, HOM, radiation	701
	T. Powers, N.C. Brock, T.D. Ganey JLab, Newport News, Virginia, USA
	Jefferson Lab has an ongoing R&D program in plasma processing which just completed a round of production processing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. Unlike helium processing which relies on ion bombardment of the field emitters, plasma processing uses free oxygen produced in the plasma to break down the hydrocarbons on the surface of the cavity. The initial focus of the effort was processing C100 cavities by injecting RF power into the HOM coupler ports. Results from processing cryomodules in the CEBAF accelerator as well as vertical test results will be presented. The goal will be to improve the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon-oxygen gas mixture as well as a helium-oxygen gas mixture. Before and after plasma processing results will also be presented. Funding provided by SC Nuclear Physics Program through DOE SC Lab funding announcement DE-FOA-0002670.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB054
About •	Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 01 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPWB119	Additive Manufacturing of Pure Niobium and Copper Using Laser Powder Bed Fusion for Particle Accelerator Applications	cavity, niobium, laser, SRF	872
	D. Ford, R. Caforio, E. Chyhyrynets, G. Keppel, C. Pira INFN/LNL, Legnaro (PD), Italy M. Bonesso, S. Candela, V. Candela, R. Dima, G. Favero, A. Pepato, P. Rebesan, M. Romanato INFN- Sez. di Padova, Padova, Italy M. Pozzi Rösler Italiana s.r.l., Concorezzo, Italy
	Funding: This project has received funding from the European Union¿s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Work supported by the INFN CSNV experiment SAMARA. In this study, Metal Additive Manufacturing (MAM) was evaluated as a viable method for producing seamless 6 GHz pure copper and niobium prototypes without the use of internal supports. Preliminary tests were performed to evaluate printability, leading to further investigations into surface treatments to reduce surface roughness from 35 µm to less than 1 µm. Additional prototypes were printed using different powders and machines, exploring various printing parameters and innovative contactless supporting structures to improve the quality of downward-facing surfaces with small inclination angles. These structures enabled the fabrication of seamless SRF cavities with a relative density greater than 99.8%. Quality testing was conducted using techniques such as tomography, leak testing, resonant frequency assessment, and internal inspection. The results of this study are presented herein.
	Poster WEPWB119 [9.235 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB119
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 18 July 2023
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WEPWB127	Investigation of Coupler Breakdown Thresholds for Plasma Processing of FRIB Quarter-Wave Resonators with Fundamental and Higher-Order Modes	cavity, electron, HOM, simulation	893
	P.R. Tutt, W. Hartung, S.H. Kim, T. Xu FRIB, East Lansing, Michigan, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics and used resources of the Facility for Rare Isotope Beams (FRIB) under Award Number DE-SC0000661. FRIB is developing plasma processing techniques for in-situ recovery of cavity performance in linac cryomodules during long-term user operation. While plasma processing has been shown to be effective for high-frequency (0.8 - 1.5 GHz) elliptical cavities, one of the challenges for FRIB is to avoid plasma breakdown in the fundamental input coupler (FPC), which has relatively weak coupling strength (Q_ext ranging from 2E6 to 1E7). FRIB cavities are not equipped with higher-order-mode (HOM) couplers; however, in preliminary tests, we found that HOMs are suitable for plasma processing of FRIB Quarter-Wave Resonators (QWRs) driven via the FPC. In this study, we investigated plasma breakdown thresholds in the fundamental and the first 2 HOMs for the FRIB β = 0.085 QWRs. Electric field distributions in the FPC region and cavity region were calculated for the room-temperature case using CST Microwave Studio’s frequency domain solver (FDS). Simulation results will be presented, with comparison of breakdown thresholds inferred from the RF modeling to the experimental results.
	Poster WEPWB127 [5.068 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB127
About •	Received ※ 19 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 11 August 2023
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THIXA01	Investigation of Plasma Processing for Coaxial Resonators	cavity, SRF, HOM, coupling	960
	W. Hartung, W. Chang, K. Elliott, S.H. Kim, T. Konomi, K. Saito, P.R. Tutt, T. Xu FRIB, East Lansing, Michigan, USA
	Plasma processing has been investigated by several facilities as a method to mitigate degradation of SRF cavity performance. It provides an alternative to removal and disassembly of cryomodules for refurbishment of each cavity via repeat etching and rinsing. Promising results have been obtained by several groups. Studies of plasma processing for quarter-wave resonators (QWRs) and half-wave resonators (HWRs) were undertaken at FRIB, where a total of 324 such resonators are presently in operation. Plasma ignition and optimization measurements were done with room-temperature-matched input couplers. Plasma cleaning tests were done on several QWRs using the fundamental power coupler (FPC) to drive the plasma. We investigated the usefulness of higher-order modes (HOMs) to drive the plasma. HOMs allow for less mismatch at the FPC and hence lower field in the coupler relative to the cavity. Before-and-after cold tests showed a significant reduction in field emission X-rays with judicious application of plasma processing.
	Slides THIXA01 [2.060 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-THIXA01
About •	Received ※ 01 September 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

MOIAA05

Commissioning of the Second JLAB C75 Cryomodule & Performance Evaluation of Installed C75 Cavities

cavity, cryomodule, SRF, controls

14

M.D. McCaughan, G. Ciovati, G.K. Davis, M.A. Drury, T. Powers, A.V. Reilly
JLab, Newport News, Virginia, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
JLAB has long been a hub of SRF technology with the CEBAF accelerator as one of its first large scale adopters. As SRF technology has advanced, the C50 and C100 programs have allowed for the extension of CEBAF’s total energy to 6 GeV and nearly 12 GeV respectively. Along with the increase in energy reach, rates of accelerating gradient degradation have been extracted for these cryomodule designs. A plan to mitigate these losses & maintain robust gradient headroom to deliver the 12 GeV program ¿ the CEBAF Performance Plan¿ established a multi-year effort of cryomodule refurbishments and replacements. Part of this plan included a cost optimization of the C50 program with more modern processing techniques and the replacement of existing cavities with larger grain boundary cavities produced from ingot Niobium (dubbed C75 for 75 MeV gain). Reports have been made on the prototype pair of C75 cavities installed in a C50 cryomodule and the first full C75 cryomodule installed in 2017 and 2021. This paper reports on the results from the qualification of the cavities for the second C75 module in both a vertical cryostat and the commissioning results of the cryomodule in the CEBAF tunnel.

Slides MOIAA05 [1.810 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOIAA05

About •

Received ※ 19 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 02 July 2023

Cite •

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

MOPMB009

Plasma Electrolytic Polishing Technology Progress Development for Nb and Cu Substrates Preparation

cavity, cathode, experiment, SRF

75

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

Funding: Work supported by the INFN CSNV experiment SAMARA. Fundings from the EU’s Horizon 2020 Research and Innovation programme under Grant Agreement N 101004730. PNRR MUR project PE0000023-NQSTI.
Superconducting radio frequency (SRF) cavity performance is highly dependent on surface preparation. Conventionally, electropolishing (EP) is used to achieve a clean surface and low roughness for both Nb and Cu substrates, but it requires harsh and corrosive solutions like concentrated acids. Plasma Electrolytic Polishing (PEP) is a promising alternative that uses only diluted salt solutions and has several advantages over EP. PEP can replace intermediate steps like mechanical or chemical polishing, thanks to its superior removal rate of up to 2-8 um/min of Nb and 3-30 um/min of Cu. It achieves Ra roughness of 100 nm for both substrates and has a higher smoothing effect than EP. PEP is also suitable for normal conducting cavities and other accelerator components, including couplers. We demonstrate the effectiveness of PEP on SRF substrates and analyse substrate defect evaluation. We demonstrate the application of PEP onto SRF substrates and analyse the substrate’s defect evaluation. The ongoing work includes Nb bulk and Nb on Cu QPR treatments and RF tests in collaboration with HZB.

Poster MOPMB009 [11.877 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB009

About •

Received ※ 17 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)

MOPMB015

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

cavity, SRF, vacuum, controls

100

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)

MOPMB049

Plasma Processing: Ignition Testing and Simulation Models for a 172 MHz HWR Cavity

cavity, vacuum, simulation, SRF

219

M.E. McIntyre, B.R. Blomberg, M.P. Kelly, J.T. McLain, K.M. Villafania, G.P. Zinkann
ANL, Lemont, Illinois, USA
Z. Wei
GIT, Atlanta, Georgia, USA

Maintenance and cleaning of superconducting RF cavities is labor intensive task that involves disassembling the cryostat holding the resonators and removing them to be cleaned. At the Argonne Tandem Linac Accelerating System (ATLAS) at Argonne National Laboratory, a project is underway to research cleaning the cavities in-situ by plasma processing. Previous plasma processing research by SNS, MSU, FNAL, and IJCLab has been successful in improving field emissions post processing. It is advantageous to pursue research in this method, allowing for possible use on modern ATLAS cryomodules, A-tank and G-tank quarter-wave resonators. The results presented show initial plasma ignition testing and plasma simulations for the coupled E and B fields, both done on a 172 MHz HWR cavity previously designed as early R&D for FRIB. Future plans are also included, laying out next steps to test plasma processing on the same HWR cavity and eventually a QWR.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB049

About •

Received ※ 05 July 2023 — Revised ※ 25 July 2023 — Accepted ※ 24 September 2023 — Issue date ※ 24 September 2023

Cite •

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

TUPTB006

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

cavity, SRF, controls, niobium

401

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

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

DOI •

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

About •

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

Cite •

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

WEPWB053

Simulation of the Dynamics of Gas Mixtures during Plasma Processing in the C75 Cavity

cavity, electron, simulation, SRF

696

N.K. Raut, P. Dhakal, T.D. Ganey, T. Powers
JLab, Newport News, Virginia, USA

Funding: The work is supported by SC Nuclear Physics Program through DOE SC Lab funding announcement DE-FOA-0002670 & is authored by JSA, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177
Plasma processing using a mixture of noble gas and oxygen is a technique that is currently being used to reduce field emission and multipacting in accelerating cavities. Plasma is created inside the cavity when the gas mixture is exposed to an electromagnetic field that is generated by applying RF power through the fundamental power or higher-order mode couplers. Oxygen ions and atomic oxygen are created in the plasma which breaks down the hydrocarbons on the surface of the cavity and the residuals from this process are removed as part of the process gas flow. Removal of hydrocarbons from the surface increases the work function and reduces the secondary emission coefficient. This work describes the initial results of plasma simulation, which provides insight into the ignition process, distribution of different species, and interactions of free oxygen and oxygen ions with the cavity surfaces. The simulations have been done with an Ar/¿2 plasma using COMSOL® multiphysics. These simulations help in understanding the dynamics and control of plasma inside the cavity and the exploration of different gas mixtures.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB053

About •

Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 29 June 2023

Cite •

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

WEPWB054

In Situ Plasma Processing of Superconducting Cavities at JLab, 2023 Update

cavity, cryomodule, HOM, radiation

701

T. Powers, N.C. Brock, T.D. Ganey
JLab, Newport News, Virginia, USA

Jefferson Lab has an ongoing R&D program in plasma processing which just completed a round of production processing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. Unlike helium processing which relies on ion bombardment of the field emitters, plasma processing uses free oxygen produced in the plasma to break down the hydrocarbons on the surface of the cavity. The initial focus of the effort was processing C100 cavities by injecting RF power into the HOM coupler ports. Results from processing cryomodules in the CEBAF accelerator as well as vertical test results will be presented. The goal will be to improve the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon-oxygen gas mixture as well as a helium-oxygen gas mixture. Before and after plasma processing results will also be presented.
Funding provided by SC Nuclear Physics Program through DOE SC Lab funding announcement DE-FOA-0002670.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB054

About •

Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 01 July 2023

Cite •

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

WEPWB119

Additive Manufacturing of Pure Niobium and Copper Using Laser Powder Bed Fusion for Particle Accelerator Applications

cavity, niobium, laser, SRF

872

D. Ford, R. Caforio, E. Chyhyrynets, G. Keppel, C. Pira
INFN/LNL, Legnaro (PD), Italy
M. Bonesso, S. Candela, V. Candela, R. Dima, G. Favero, A. Pepato, P. Rebesan, M. Romanato
INFN- Sez. di Padova, Padova, Italy
M. Pozzi
Rösler Italiana s.r.l., Concorezzo, Italy

Funding: This project has received funding from the European Union¿s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. Work supported by the INFN CSNV experiment SAMARA.
In this study, Metal Additive Manufacturing (MAM) was evaluated as a viable method for producing seamless 6 GHz pure copper and niobium prototypes without the use of internal supports. Preliminary tests were performed to evaluate printability, leading to further investigations into surface treatments to reduce surface roughness from 35 µm to less than 1 µm. Additional prototypes were printed using different powders and machines, exploring various printing parameters and innovative contactless supporting structures to improve the quality of downward-facing surfaces with small inclination angles. These structures enabled the fabrication of seamless SRF cavities with a relative density greater than 99.8%. Quality testing was conducted using techniques such as tomography, leak testing, resonant frequency assessment, and internal inspection. The results of this study are presented herein.

Poster WEPWB119 [9.235 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB119

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

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WEPWB127

Investigation of Coupler Breakdown Thresholds for Plasma Processing of FRIB Quarter-Wave Resonators with Fundamental and Higher-Order Modes

cavity, electron, HOM, simulation

893

P.R. Tutt, W. Hartung, S.H. Kim, T. Xu
FRIB, East Lansing, Michigan, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics and used resources of the Facility for Rare Isotope Beams (FRIB) under Award Number DE-SC0000661.
FRIB is developing plasma processing techniques for in-situ recovery of cavity performance in linac cryomodules during long-term user operation. While plasma processing has been shown to be effective for high-frequency (0.8 - 1.5 GHz) elliptical cavities, one of the challenges for FRIB is to avoid plasma breakdown in the fundamental input coupler (FPC), which has relatively weak coupling strength (Q_ext ranging from 2E6 to 1E7). FRIB cavities are not equipped with higher-order-mode (HOM) couplers; however, in preliminary tests, we found that HOMs are suitable for plasma processing of FRIB Quarter-Wave Resonators (QWRs) driven via the FPC. In this study, we investigated plasma breakdown thresholds in the fundamental and the first 2 HOMs for the FRIB β = 0.085 QWRs. Electric field distributions in the FPC region and cavity region were calculated for the room-temperature case using CST Microwave Studio’s frequency domain solver (FDS). Simulation results will be presented, with comparison of breakdown thresholds inferred from the RF modeling to the experimental results.

Poster WEPWB127 [5.068 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB127

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Received ※ 19 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 11 August 2023

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THIXA01

Investigation of Plasma Processing for Coaxial Resonators

cavity, SRF, HOM, coupling

960

W. Hartung, W. Chang, K. Elliott, S.H. Kim, T. Konomi, K. Saito, P.R. Tutt, T. Xu
FRIB, East Lansing, Michigan, USA

Plasma processing has been investigated by several facilities as a method to mitigate degradation of SRF cavity performance. It provides an alternative to removal and disassembly of cryomodules for refurbishment of each cavity via repeat etching and rinsing. Promising results have been obtained by several groups. Studies of plasma processing for quarter-wave resonators (QWRs) and half-wave resonators (HWRs) were undertaken at FRIB, where a total of 324 such resonators are presently in operation. Plasma ignition and optimization measurements were done with room-temperature-matched input couplers. Plasma cleaning tests were done on several QWRs using the fundamental power coupler (FPC) to drive the plasma. We investigated the usefulness of higher-order modes (HOMs) to drive the plasma. HOMs allow for less mismatch at the FPC and hence lower field in the coupler relative to the cavity. Before-and-after cold tests showed a significant reduction in field emission X-rays with judicious application of plasma processing.

Slides THIXA01 [2.060 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-THIXA01

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Received ※ 01 September 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023

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