SRF2015 - List of Keywords (target)

Paper	Title	Other Keywords	Page
MOPB009	Model of Flux Trapping in Cooling Down Process	cavity, interface, experiment, framework	90
	T. Kubo KEK, Ibaraki, Japan
	Recent findings that cooling conditions affect an amount of trapped magnetic flux attract much attention as a way to achieve a high-Q0 by SRF cavity,,*. Q0~210¹¹ has already been achieved by the full flux expulsion***. While much experimental studies have been conducted, not much theoretical progress followed on it. In this paper, I introduce a simple model that can explain how trapped fluxoids are expelled in cooling process. J.M.Vogt et al., PRSTAB 16, 102002 (2013) A.Romanenko et al., JAP 115, 184903 (2014) J.M.Vogt et al., PRSTAB 18, 042001 (2015) ***A.Romanenko et al., APL 105, 234103 (2014)
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MOPB093	Vertical Electropolishing Studies at Cornell	cavity, cathode, SRF, niobium	364
	F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA H. Hayano, T. Saeki KEK, Ibaraki, Japan Y.I. Ida, K.N. Nii MGH, Hyogo-ken, Japan
	Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.
	Poster MOPB093 [4.364 MB]
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MOPB101	Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, niobium, SRF, cathode	390
	M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA F. Furuta, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.D. Mammosser ORNL, Oak Ridge, Tennessee, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
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MOPB106	Analysis of High Pressure Rinsing Characteristics for SRF Cavities	cavity, experiment, SRF, niobium	414
	Y. Jung, M.O. Hyun, M.J. Joung IBS, Daejeon, Republic of Korea J. Kim, J. Seo Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea
	High pressure rinsing (HPR) treatment has been widely used in the SRF cavity fabrication. This well- known process helps remove effectively undesirable emission tips from the inner surface of cavities, which are responsible for a different level's multipaction and hellium quenching. Also, the HPR treatment can clean or polish the RF (Radio Frequency) surface, which is critically sensitive to an applied magnetic field, by removing contaminants such as an organic oil, a remnant metal debris and dirty etchants from the cavity surface. Consequently, the HPR treatment contributes to improve quality factor during the cavity operation both by decreasing various field emission sites and by removing defects from the cavity surface. In this paper, we performed HPR experiments by using a simplified cavity structure, intentionally painted with a pattern on the inner surface. Therefore, we report how the surface treatment by HPR was carried out as functions of the distance between a target to be cleaned and a nozzle, and a water pressure.
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TUPB037	Superconducting NbN-Based Multilayer and NbTiN Thin Films for the Enhancement of SRF Accelerator Cavities	lattice, cavity, SRF, niobium	638
	M.C. Burton, M. Beebe, R.A. Lukaszew, J.M. Riso The College of William and Mary, Williamsburg, Virginia, USA C.E. Reece, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Funded by: Defense Threat Reduction Agency HDTRA1-10-1-0072 Current superconducting radio frequency (SRF) technology, used in various particle accelerator facilities is reliant upon bulk Nb. Due to technological advancements in the processing of bulk Nb cavities, the facilities have reached accelerating fields very close to material-dependent limits, i.e. ~50 MV/m for bulk Nb. One possible solution to overcome this limit proposed by A. Gurevich consists of the deposition of alternating thin layers of superconducting and insulating materials on the interior surface of the cavities which may prevent early field penetration and thus delay high field breakdown. Some candidate materials proposed for this scheme are NbN and NbTiN. Here we present experimental results correlating film microstructure and surface morphology with superconducting properties on coupon samples made with NbN and NbTiN. We have achieved thin films with close to bulk-like lattice parameters and transition temperatures, while achieving Hc1 values larger than bulk for films thinner than their London penetration depths. We compare results from samples grown utilizing NbTi targets with different stoichiometries and we will show RF measurements from 2” coupon samples. A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006).
	Poster TUPB037 [0.989 MB]
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TUPB040	High Power Impulse Magnetron Sputtering of Thin Films for Superconducting RF Cavities	power-supply, radio-frequency, scattering, vacuum	647
	S. Wilde, B. Chesca Loughborough University, Loughborough, Leicestershire, United Kingdom E. Alves Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear, Lisboa, Portugal N.P. Barradas Universidade de Lisboa, Instituto Superior Técnico, Bobadela, Portugal A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	The production of superconducting coatings for radio frequency cavities is a rapidly developing field that should ultimately lead to acceleration gradients greater than those obtained by bulk Nb RF cavities. Optimizing superconducting properties of Nb and Nb compound thin-films is therefore essential. Nb films were deposited by magnetron sputtering in pulsed DC mode onto Si (100) and MgO (100) substrates and also by high impulse magnetron sputtering (HiPIMS) onto Si (100), MgO (100) and polycrystalline Cu. HiPIMS was then used to deposit NbN and NbTiN thin films onto Si(100) and polycrystalline Cu. The films were characterised using scanning electron microscopy, x-ray diffraction, DC SQUID magnetometry and Q factor for a flat thin film sample.
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TUPB047	Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach	electron, gun, cathode, SRF	673
	C. Schlemper, X. Jiang, M. Vogel University Siegen, Siegen, Germany
	Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.
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TUPB051	Development of Nb3Sn Coatings by Magnetron Sputtering for SRF Cavities	vacuum, radio-frequency, SRF, quadrupole	691
	G.J. Rosaz, S. Calatroni, F.M. Leaux, F. Motschmann, Z. Mydlarz, M. Taborelli, W. Vollenberg CERN, Geneva, Switzerland
	Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453 Cost and energy savings are an integral requirement in the design of future particle accelerators. Very low losses SRF accelerating systems, together with high-efficiency cryogenics systems, have the potential of low running costs. The association to the capital cost reduction allowed by thin films coated copper cavities may represent the best overall cost-performance compromise. This strategy has been applied for instance in LEP, the LHC and HIE-ISOLDE with the niobium thin films technology. New materials must be considered to improve the quality factor of the cavities, such as Nb3Sn, which could also ideally operate at higher temperature thus allowing further energy savings. The study considers the possibility to coat a copper resonator with an Nb3Sn layer by means of magnetron sputtering using an alloyed target. We present the impact of the process parameters on the as-deposited layer stoichiometry. The latter is in good agreement with previous results reported in the literature and can be tuned by acting on the coating pressure. The effect of post-coating annealing temperature on the morphology, crystallinity and superconducting properties of the film was also investigated.
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THPB023	The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON	cavity, niobium, controls, accelerating-gradient	1119
	A. Gresele, M. Giaretta, A. Visentin Ettore Zanon S.p.A., Nuclear Division, Schio, Italy A.A. Sulimov, J.H. Thie DESY, Hamburg, Germany
	Serial production of superconducting cavities for European-XFEL will be completed at E.ZANON by the end of 2015. For that reason we can summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed.
	Poster THPB023 [3.227 MB]
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THPB059	Design, Fabrication and Performance of SRF-Gun Cavity	cavity, gun, SRF, cathode	1243
	T. Konomi, E. Kako, Y. Kobayashi, K. Umemori, S. Yamaguchi KEK, Ibaraki, Japan R. Matsuda Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan T. Yanagisawa MHI, Hiroshima, Japan
	The development of superconducting RF gun has been started at KEK. The performance targets are that average current is 100 mA, normalized emittance is less than 1 μm.rad, beam energy is 2 MeV and energy spread is less than 0.1 %. The SRF gun consists of 1.3 GHz and 1.5 cell elliptical cavity and backward illuminated photocathode. The cavity shape was designed by using SUPERFISH and GPT. The cavity has been fabricated by Japanese industry. Accelerating field tuning and vertical test without cathode plug was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. For next vertical test, cathode rod without photocathode is in preparation. In the workshop, the SRF-Gun concepts and vertical test results will be reported.
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Paper

Title

Other Keywords

Page

MOPB009

Model of Flux Trapping in Cooling Down Process

cavity, interface, experiment, framework

90

T. Kubo
KEK, Ibaraki, Japan

Recent findings that cooling conditions affect an amount of trapped magnetic flux attract much attention as a way to achieve a high-Q0 by SRF cavity*,**,***. Q0~2*10¹¹ has already been achieved by the full flux expulsion****. While much experimental studies have been conducted, not much theoretical progress followed on it. In this paper, I introduce a simple model that can explain how trapped fluxoids are expelled in cooling process.
*J.M.Vogt et al., PRSTAB 16, 102002 (2013)
**A.Romanenko et al., JAP 115, 184903 (2014)
***J.M.Vogt et al., PRSTAB 18, 042001 (2015)
****A.Romanenko et al., APL 105, 234103 (2014)

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MOPB093

Vertical Electropolishing Studies at Cornell

cavity, cathode, SRF, niobium

364

F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
Y.I. Ida, K.N. Nii
MGH, Hyogo-ken, Japan

Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.

Poster MOPB093 [4.364 MB]

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MOPB101

Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid

cavity, niobium, SRF, cathode

390

M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
F. Furuta, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.D. Mammosser
ORNL, Oak Ridge, Tennessee, USA
A.M. Rowe
Fermilab, Batavia, Illinois, USA

Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process.
Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.

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MOPB106

Analysis of High Pressure Rinsing Characteristics for SRF Cavities

cavity, experiment, SRF, niobium

414

Y. Jung, M.O. Hyun, M.J. Joung
IBS, Daejeon, Republic of Korea
J. Kim, J. Seo
Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea

High pressure rinsing (HPR) treatment has been widely used in the SRF cavity fabrication. This well- known process helps remove effectively undesirable emission tips from the inner surface of cavities, which are responsible for a different level's multipaction and hellium quenching. Also, the HPR treatment can clean or polish the RF (Radio Frequency) surface, which is critically sensitive to an applied magnetic field, by removing contaminants such as an organic oil, a remnant metal debris and dirty etchants from the cavity surface. Consequently, the HPR treatment contributes to improve quality factor during the cavity operation both by decreasing various field emission sites and by removing defects from the cavity surface. In this paper, we performed HPR experiments by using a simplified cavity structure, intentionally painted with a pattern on the inner surface. Therefore, we report how the surface treatment by HPR was carried out as functions of the distance between a target to be cleaned and a nozzle, and a water pressure.

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TUPB037

Superconducting NbN-Based Multilayer and NbTiN Thin Films for the Enhancement of SRF Accelerator Cavities

lattice, cavity, SRF, niobium

638

M.C. Burton, M. Beebe, R.A. Lukaszew, J.M. Riso
The College of William and Mary, Williamsburg, Virginia, USA
C.E. Reece, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Funded by: Defense Threat Reduction Agency HDTRA1-10-1-0072
Current superconducting radio frequency (SRF) technology, used in various particle accelerator facilities is reliant upon bulk Nb. Due to technological advancements in the processing of bulk Nb cavities, the facilities have reached accelerating fields very close to material-dependent limits, i.e. ~50 MV/m for bulk Nb. One possible solution to overcome this limit proposed by A. Gurevich consists of the deposition of alternating thin layers of superconducting and insulating materials on the interior surface of the cavities which may prevent early field penetration and thus delay high field breakdown*. Some candidate materials proposed for this scheme are NbN and NbTiN. Here we present experimental results correlating film microstructure and surface morphology with superconducting properties on coupon samples made with NbN and NbTiN. We have achieved thin films with close to bulk-like lattice parameters and transition temperatures, while achieving Hc1 values larger than bulk for films thinner than their London penetration depths. We compare results from samples grown utilizing NbTi targets with different stoichiometries and we will show RF measurements from 2” coupon samples.
*A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006).

Poster TUPB037 [0.989 MB]

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TUPB040

High Power Impulse Magnetron Sputtering of Thin Films for Superconducting RF Cavities

power-supply, radio-frequency, scattering, vacuum

647

S. Wilde, B. Chesca
Loughborough University, Loughborough, Leicestershire, United Kingdom
E. Alves
Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear, Lisboa, Portugal
N.P. Barradas
Universidade de Lisboa, Instituto Superior Técnico, Bobadela, Portugal
A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G.B.G. Stenning
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

The production of superconducting coatings for radio frequency cavities is a rapidly developing field that should ultimately lead to acceleration gradients greater than those obtained by bulk Nb RF cavities. Optimizing superconducting properties of Nb and Nb compound thin-films is therefore essential. Nb films were deposited by magnetron sputtering in pulsed DC mode onto Si (100) and MgO (100) substrates and also by high impulse magnetron sputtering (HiPIMS) onto Si (100), MgO (100) and polycrystalline Cu. HiPIMS was then used to deposit NbN and NbTiN thin films onto Si(100) and polycrystalline Cu. The films were characterised using scanning electron microscopy, x-ray diffraction, DC SQUID magnetometry and Q factor for a flat thin film sample.

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TUPB047

Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach

electron, gun, cathode, SRF

673

C. Schlemper, X. Jiang, M. Vogel
University Siegen, Siegen, Germany

Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.

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TUPB051

Development of Nb3Sn Coatings by Magnetron Sputtering for SRF Cavities

vacuum, radio-frequency, SRF, quadrupole

691

G.J. Rosaz, S. Calatroni, F.M. Leaux, F. Motschmann, Z. Mydlarz, M. Taborelli, W. Vollenberg
CERN, Geneva, Switzerland

Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453
Cost and energy savings are an integral requirement in the design of future particle accelerators. Very low losses SRF accelerating systems, together with high-efficiency cryogenics systems, have the potential of low running costs. The association to the capital cost reduction allowed by thin films coated copper cavities may represent the best overall cost-performance compromise. This strategy has been applied for instance in LEP, the LHC and HIE-ISOLDE with the niobium thin films technology. New materials must be considered to improve the quality factor of the cavities, such as Nb3Sn, which could also ideally operate at higher temperature thus allowing further energy savings. The study considers the possibility to coat a copper resonator with an Nb3Sn layer by means of magnetron sputtering using an alloyed target. We present the impact of the process parameters on the as-deposited layer stoichiometry. The latter is in good agreement with previous results reported in the literature and can be tuned by acting on the coating pressure. The effect of post-coating annealing temperature on the morphology, crystallinity and superconducting properties of the film was also investigated.

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THPB023

The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON

cavity, niobium, controls, accelerating-gradient

1119

A. Gresele, M. Giaretta, A. Visentin
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
A.A. Sulimov, J.H. Thie
DESY, Hamburg, Germany

Serial production of superconducting cavities for European-XFEL will be completed at E.ZANON by the end of 2015. For that reason we can summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed.

Poster THPB023 [3.227 MB]

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THPB059

Design, Fabrication and Performance of SRF-Gun Cavity

cavity, gun, SRF, cathode

1243

T. Konomi, E. Kako, Y. Kobayashi, K. Umemori, S. Yamaguchi
KEK, Ibaraki, Japan
R. Matsuda
Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan
T. Yanagisawa
MHI, Hiroshima, Japan

The development of superconducting RF gun has been started at KEK. The performance targets are that average current is 100 mA, normalized emittance is less than 1 μm.rad, beam energy is 2 MeV and energy spread is less than 0.1 %. The SRF gun consists of 1.3 GHz and 1.5 cell elliptical cavity and backward illuminated photocathode. The cavity shape was designed by using SUPERFISH and GPT. The cavity has been fabricated by Japanese industry. Accelerating field tuning and vertical test without cathode plug was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. For next vertical test, cathode rod without photocathode is in preparation. In the workshop, the SRF-Gun concepts and vertical test results will be reported.

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