SRF2021 - List of Authors (Longuevergne, D.)

Paper	Title	Page
SUPCAV013	Multipacting Analysis of the Quadripolar Resonator (QPR) at HZB	42
	S. Bira, D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France Y. Kalboussi CEA-IRFU, Gif-sur-Yvette, France S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany Th. Proslier CEA-DRF-IRFU, France
	Multipacting (MP) is a resonating electron discharge, often plaguing radio-frequency (RF) structures, produced by the synchronization of emitted electrons with the RF fields and the electron multiplication at the impact point with the surface structure. The electron multiplication can take place only if the secondary emission yield (SEY, i.e. the number of electrons emitted due to the impact of one incoming electron), , is higher than 1. The SEY value depends strongly on the material and the surface contamination. Multipacting simulations are crucial in high-frenquency (HF) vacuum structures to localize and potentially improve the geometry. In this work, multipacting simulations were carried out on the geometry of the Quadrupole Resonator (QPR) in operation at HZB using the Spark 3D module in Microwave Studio suite (CST). These simulations helped to understand a particular behavior observed during the QPR tests, and furthermore made it possible to suggest enhancement ways in order to limit this phenomenon and facilitate its operation.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPCAV013
About •	Received ※ 09 July 2021 — Revised ※ 09 July 2021 — Accepted ※ 09 April 2022 — Issue date ※ 07 May 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPFDV001	Investigation of an Alternative Path for SRF Cavity Fabrication and Surface Processing	319
	O. Hryhorenko, D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France C.Z. Antoine CEA-IRFU, Gif-sur-Yvette, France F. Brisset ICMMO, Orsay, France T. Dohmae KEK, Ibaraki, Japan
	The preparation of SRF cavities includes a lengthy, costly, and safety issued electrochemical polishing (EP or BCP) step to remove the damaged layer coming from the cavity fabrication. We have shown that most of the damage layer is originated from the rolling process during the preparation of the sheet material, while subsequent deep drawing tends to leave only µm thick damage layer. We propose a 2-steps mechanical process that allows us to easily get rid of the thick damage layer on the sheets before cavity forming. The process has been established on samples and extended to large disks ready for 1.3 GHz half-cell forming. The polished sheets will be then sent to KEK for half-cell forming and subsequent surface and material analysis before proceeding to half-cell welding. Former studies on the sample demonstrated that damages induced by forming can successfully be removed by recrystallization and less than 10 µm final chemistry.
	Poster MOPFDV001 [2.309 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV001
About •	Received ※ 25 June 2021 — Revised ※ 11 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 15 May 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUOFDV04	Evidence of Reduced Magnetic Sensitivities in Low Beta SRF Cavities
	D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France A. Miyazaki Uppsala University, Uppsala, Sweden
	Dedicated flux trapping experiments have been carried out on different types of low-beta superconducting accelerating cavities. The measured magnetic sensitivities of these complex geometries can be significantly lower than the predicted values calculated by commonly-used material-based models. In this paper, we suggest a new approach beyond the present material based models. Indeed, both the ambient magnetic field orientation and cavity geometry have a significant impact on the cavity performance degradation due to magnetic trapped flux. Experimental data are presented, and a new model to interpret the geometrical effect is introduced, assessed and shows as well very good agreement with data from the literature.
	Slides TUOFDV04 [1.265 MB]
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TUPCAV002	HOM Excitation in Spoke Resonator for SRF Studies	435
	D. Longuevergne, N. Bippus, F. Chatelet, V. Delpech, N. Hu, C. Joly, T. Pépin-Donat, F. Rabehasy, L. Renard Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France M. Baudrier CEA-DRF-IRFU, France E. Cenni, L. Maurice CEA-IRFU, Gif-sur-Yvette, France
	The excitation of Higher Order Modes (HOM) or Lower Order Modes (LOM) has been performed for years on multi-cell superconducting accelerating cavities as a mean to coarsely locate a quench, a defective area or ignite a plasma for surface cleaning. Moreover, such multi-mode testing is very useful to understand more accurately the frequency dependence of the surface resistance in a wide range of surface magnetic fields (0<B<150mT). In that sense, several type of dedicated non-accelerating resonators like Quadrupole Resonator (QPR), Half- or Quarter- Wave resonators have been built to specifically study new superconducting materials or new surface or heat treatments. What is proposed in this paper is to perform such multi-mode analysis (352 MHz, 720 MHz and 1300 MHz) in an existing accelerating cavity, in particular a Spoke Resonator. Baseline results will be presented and perspectives of such technique will be discussed.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUPCAV002
About •	Received ※ 22 June 2021 — Revised ※ 19 July 2021 — Accepted ※ 23 August 2021 — Issue date ※ 15 April 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPCAV002	Improvement of Chemical Etching Capabilities (BCP) for SRF Spoke Resonators at IJCLab	590
	J. Demercastel-Soulier, P. Duchesne, D. Longuevergne, G. Olry, T. Pépin-Donat, F. Rabehasy, D. Reynet, S. Roset, L.M. Vogt Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
	Buffered chemical polishing (BPC) is the reference surface polishing adopted for ESS and MYRRHA SRF spoke resonators at IJCLab. This chemical treatment, in addition to improving the RF performance, fits into the frequency adjustment strategy of the jacketed cavity during its preparation phase. In the framework of the collaboration with Fermilab for PIP-II project, IJCLab has developed a new setup to perform rotational BCP. The implementation of a rotation during chemical etching improves significantly the homogeneity and quality of surface polishing. In this paper, we present the numerical analysis based on a fluid dynamics model. The goal is to estimate the acid flow characteristics inside the cavity, determine the influence of several parameters as mass flow rate and rotation speed and propose the best configuration for the new experimental setup
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPCAV002
About •	Received ※ 23 June 2021 — Revised ※ 18 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 14 January 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FROFDV07	Material Engineering of ALD- Deposited Multilayer to Improve the Superconducting Performances of RF Cavities Under Intense RF Fields
	Y. Kalboussi CEA, DES-ISAS-DM2S, Université Paris-Saclay, Gif-sur-Yvette, France C.Z. Antoine, B. Delatte CEA-IRFU, Gif-sur-Yvette, France S. Bira, D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France D. Dragoe ICMMO, Orsay, France J. Leroy CEA/DRF/IRAMIS/SIS2M, Gif sur Yvette, France Th. Proslier CEA-DRF-IRFU, France S. Tusseau-Nenez Ecole Polytechnique, Palaiseau, France
	We are exploring an original approach to improve the performance of bulk Niobium RF cavities through surface engineering with ALD superconducting multilayer capable of screening efficiently the magnetic fields and therefore inhibiting vortices penetration in Niobium cavities. As a first step for the multilayer, we aim at replacing the deleterious niobium native oxide by a clean interface between an insulator synthesized by ALD (Al₂O₃, Y2O3 and MgO) and the Niobium metal. To that end I will present the results obtained on both flat niobium samples and 1.3 GHz elliptical cavities. Our study shows that ALD deposited films are a good diffusion barrier, resist to thermal treatments and reduce significantly the presence of the niobium native oxide on the surface. Low SEY material such as TiN was also deposited on top of the insulator film to reduce multipacting phenomena. RF test on ALD coated cavities shows already a slight improvement of the superconducting performances. In parallel we started synthesizing superconducting NbTiN alloys by ALD. I will present preliminary results on the superconducting properties of NbTiN films grown on AlN by ALD with various compositions on Nbiobium.
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Paper

Title

Page

Multipacting Analysis of the Quadripolar Resonator (QPR) at HZB

42

S. Bira, D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
Y. Kalboussi
CEA-IRFU, Gif-sur-Yvette, France
S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
Th. Proslier
CEA-DRF-IRFU, France

Multipacting (MP) is a resonating electron discharge, often plaguing radio-frequency (RF) structures, produced by the synchronization of emitted electrons with the RF fields and the electron multiplication at the impact point with the surface structure. The electron multiplication can take place only if the secondary emission yield (SEY, i.e. the number of electrons emitted due to the impact of one incoming electron), , is higher than 1. The SEY value depends strongly on the material and the surface contamination. Multipacting simulations are crucial in high-frenquency (HF) vacuum structures to localize and potentially improve the geometry. In this work, multipacting simulations were carried out on the geometry of the Quadrupole Resonator (QPR) in operation at HZB using the Spark 3D module in Microwave Studio suite (CST). These simulations helped to understand a particular behavior observed during the QPR tests, and furthermore made it possible to suggest enhancement ways in order to limit this phenomenon and facilitate its operation.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPCAV013

About •

Received ※ 09 July 2021 — Revised ※ 09 July 2021 — Accepted ※ 09 April 2022 — Issue date ※ 07 May 2022

Cite •

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

MOPFDV001

Investigation of an Alternative Path for SRF Cavity Fabrication and Surface Processing

319

O. Hryhorenko, D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
F. Brisset
ICMMO, Orsay, France
T. Dohmae
KEK, Ibaraki, Japan

The preparation of SRF cavities includes a lengthy, costly, and safety issued electrochemical polishing (EP or BCP) step to remove the damaged layer coming from the cavity fabrication. We have shown that most of the damage layer is originated from the rolling process during the preparation of the sheet material, while subsequent deep drawing tends to leave only µm thick damage layer. We propose a 2-steps mechanical process that allows us to easily get rid of the thick damage layer on the sheets before cavity forming. The process has been established on samples and extended to large disks ready for 1.3 GHz half-cell forming. The polished sheets will be then sent to KEK for half-cell forming and subsequent surface and material analysis before proceeding to half-cell welding. Former studies on the sample demonstrated that damages induced by forming can successfully be removed by recrystallization and less than 10 µm final chemistry.

Poster MOPFDV001 [2.309 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPFDV001

About •

Received ※ 25 June 2021 — Revised ※ 11 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 15 May 2022

Cite •

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

TUOFDV04

Evidence of Reduced Magnetic Sensitivities in Low Beta SRF Cavities

D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
A. Miyazaki
Uppsala University, Uppsala, Sweden

Dedicated flux trapping experiments have been carried out on different types of low-beta superconducting accelerating cavities. The measured magnetic sensitivities of these complex geometries can be significantly lower than the predicted values calculated by commonly-used material-based models. In this paper, we suggest a new approach beyond the present material based models. Indeed, both the ambient magnetic field orientation and cavity geometry have a significant impact on the cavity performance degradation due to magnetic trapped flux. Experimental data are presented, and a new model to interpret the geometrical effect is introduced, assessed and shows as well very good agreement with data from the literature.

Slides TUOFDV04 [1.265 MB]

Cite •

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

TUPCAV002

HOM Excitation in Spoke Resonator for SRF Studies

435

D. Longuevergne, N. Bippus, F. Chatelet, V. Delpech, N. Hu, C. Joly, T. Pépin-Donat, F. Rabehasy, L. Renard
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
M. Baudrier
CEA-DRF-IRFU, France
E. Cenni, L. Maurice
CEA-IRFU, Gif-sur-Yvette, France

The excitation of Higher Order Modes (HOM) or Lower Order Modes (LOM) has been performed for years on multi-cell superconducting accelerating cavities as a mean to coarsely locate a quench, a defective area or ignite a plasma for surface cleaning. Moreover, such multi-mode testing is very useful to understand more accurately the frequency dependence of the surface resistance in a wide range of surface magnetic fields (0<B<150mT). In that sense, several type of dedicated non-accelerating resonators like Quadrupole Resonator (QPR), Half- or Quarter- Wave resonators have been built to specifically study new superconducting materials or new surface or heat treatments. What is proposed in this paper is to perform such multi-mode analysis (352 MHz, 720 MHz and 1300 MHz) in an existing accelerating cavity, in particular a Spoke Resonator. Baseline results will be presented and perspectives of such technique will be discussed.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUPCAV002

About •

Received ※ 22 June 2021 — Revised ※ 19 July 2021 — Accepted ※ 23 August 2021 — Issue date ※ 15 April 2022

Cite •

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

WEPCAV002

Improvement of Chemical Etching Capabilities (BCP) for SRF Spoke Resonators at IJCLab

590

J. Demercastel-Soulier, P. Duchesne, D. Longuevergne, G. Olry, T. Pépin-Donat, F. Rabehasy, D. Reynet, S. Roset, L.M. Vogt
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

Buffered chemical polishing (BPC) is the reference surface polishing adopted for ESS and MYRRHA SRF spoke resonators at IJCLab. This chemical treatment, in addition to improving the RF performance, fits into the frequency adjustment strategy of the jacketed cavity during its preparation phase. In the framework of the collaboration with Fermilab for PIP-II project, IJCLab has developed a new setup to perform rotational BCP. The implementation of a rotation during chemical etching improves significantly the homogeneity and quality of surface polishing. In this paper, we present the numerical analysis based on a fluid dynamics model. The goal is to estimate the acid flow characteristics inside the cavity, determine the influence of several parameters as mass flow rate and rotation speed and propose the best configuration for the new experimental setup

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPCAV002

About •

Received ※ 23 June 2021 — Revised ※ 18 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 14 January 2022

Cite •

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

FROFDV07

Material Engineering of ALD- Deposited Multilayer to Improve the Superconducting Performances of RF Cavities Under Intense RF Fields

Y. Kalboussi
CEA, DES-ISAS-DM2S, Université Paris-Saclay, Gif-sur-Yvette, France
C.Z. Antoine, B. Delatte
CEA-IRFU, Gif-sur-Yvette, France
S. Bira, D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
D. Dragoe
ICMMO, Orsay, France
J. Leroy
CEA/DRF/IRAMIS/SIS2M, Gif sur Yvette, France
Th. Proslier
CEA-DRF-IRFU, France
S. Tusseau-Nenez
Ecole Polytechnique, Palaiseau, France

We are exploring an original approach to improve the performance of bulk Niobium RF cavities through surface engineering with ALD superconducting multilayer capable of screening efficiently the magnetic fields and therefore inhibiting vortices penetration in Niobium cavities. As a first step for the multilayer, we aim at replacing the deleterious niobium native oxide by a clean interface between an insulator synthesized by ALD (Al₂O₃, Y2O3 and MgO) and the Niobium metal. To that end I will present the results obtained on both flat niobium samples and 1.3 GHz elliptical cavities. Our study shows that ALD deposited films are a good diffusion barrier, resist to thermal treatments and reduce significantly the presence of the niobium native oxide on the surface. Low SEY material such as TiN was also deposited on top of the insulator film to reduce multipacting phenomena. RF test on ALD coated cavities shows already a slight improvement of the superconducting performances. In parallel we started synthesizing superconducting NbTiN alloys by ALD. I will present preliminary results on the superconducting properties of NbTiN films grown on AlN by ALD with various compositions on Nbiobium.

Cite •

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