SRF2015 - List of Authors (Kubo, T.)

Paper	Title	Page
MOPB008	Theoretical Field Limit and Cavity Surface Conditions: Nano-Scale Topography and Sub-millimeter Pit	86
	T. Kubo KEK, Ibaraki, Japan
	The recent two theoretical papers,* are briefly introduced. The former addresses the superheating field (Bs) suppression due to nano-defects distributing almost continuously on the cavity surface. We introduce a model of the nano-defect. An analytical formula for Bs suppression factor is derived. By using the formula, suppression factors of bulk or multilayer superconductors and those after various surface processing technologies can be evaluated. An application to the dirty Nb processed by EP is also presented as an example. The latter address the magnetic field enhancement (MFE) at the sub-millimeter pit on the surface of cavity, which is thought to cause quench. There exists the famous well-type pit model, but many of pits are not well-type but have gentle slopes. Impacts of the slope angle on MFE have not been well understood. We introduce a model that can describe a pit with an arbitrary slope angle. A formula to evaluate the MFE factor is derived. A pit with a gentle slope angle yields a much smaller MFE factor than the well-type pit. The formula can be applied to the calculation of MFE factors of real pits with arbitrary slope angles. T. Kubo, Prog. Theor. Exp. Phys. 2015,063G01(2015). ** T. Kubo, Prog. Theor. Exp. Phys. 2015,073G01(2015).
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MOPB009	Model of Flux Trapping in Cooling Down Process	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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TUBA07	Theory of Multilayer Coating for Proof-of-Concept Experiments
	T. Kubo KEK, Ibaraki, Japan
	Structures of alternating layers of superconducting (SC) and insulating layers formed on a bulk SC are actively discussed these years, because of their great possibility in realizing a high-field and high-Q SCRF cavity. In 2013, theoretical studies of an ideal system with a single SC layer and a single insulator layer formed on a bulk SC were carried out, by which appropriate combinations of materials and optimum thicknesses of SC and insulator layers that can enhance field limit were revealed. A more realistic model with nano-scale surface defects on the SC layer was also studied in 2014. As of this year, a sample-experiment-oriented theoretical study is in progress towards proof-of-concept experiments. Theories are becoming realistic every year. In this talk, I will review progresses after 2013 and provide theoretical equipages to tackle experiments of the multilayer coating(). A.Gurevich, Appl. Phys. Lett.88,012511(2006); T.Kubo et al.,Appl. Phys. Lett.104,032603(2014); T.Kubo, Prog. Theor. Exp.Phys.2015,063G01(2015); T.Kubo, Prog. Theor. Exp.Phys.2015,073G01(2015).
	Slides TUBA07 [2.080 MB]
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TUPB062	Evaluation of Sc Property Coated on a Surface	723
	Y. Iwashita, Y. Fuwa Kyoto ICR, Uji, Kyoto, Japan M. Hino Kyoto University, Research Reactor Institute, Osaka, Japan T. Kubo, T. Saeki KEK, Ibaraki, Japan
	Funding: This work was supported by JSPS KAKENHI Grant Number 26600142. We are trying to deposit thin superconducting material on a substrate for higher accelerating field gradients. In order to evaluate the deposit method, surface properties are under measurement. Some results on measurements at DC and a preparation status toward RF measurement will be reported.
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THAA04	Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities	1006
	K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.
	Slides THAA04 [2.810 MB]
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THPB046	Design and Development of Superconducting Spoke Cavity for Compact Photon Source	1196
	M. Sawamura Japan Atomic Energy Agency (JAEA), Gamma-ray Non-Destructive Assay Research Group, Tokai-mura, Ibaraki-ken, Japan E. Cenni CEA/IRFU, Gif-sur-Yvette, France R. Hajima JAEA, Ibaraki-ken, Japan H. Hokonohara, Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan T. Kubo, T. Saeki KEK, Ibaraki, Japan
	Funding: This study is supported by Photon and Quantum Basic Research Coordinated Development Program of MEXT, Japan. The spoke cavity is expected to have advantages for compact ERL accelerator for X-ray source based on laser Compton scattering. We have been developing the spoke cavity under a research program of MEXT, Japan to establish the fabrication process. Since our designed shape of the spoke cavity is complicated due to increase the RF properties, we have been designing the mold including the process of press work and the support parts for vacuum tolerance with the mechanical simulation. In this paper we present status of the spoke cavity fabrication.
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Paper

Title

Page

Theoretical Field Limit and Cavity Surface Conditions: Nano-Scale Topography and Sub-millimeter Pit

86

T. Kubo
KEK, Ibaraki, Japan

The recent two theoretical papers*,** are briefly introduced. The former addresses the superheating field (Bs) suppression due to nano-defects distributing almost continuously on the cavity surface*. We introduce a model of the nano-defect. An analytical formula for Bs suppression factor is derived. By using the formula, suppression factors of bulk or multilayer superconductors and those after various surface processing technologies can be evaluated. An application to the dirty Nb processed by EP is also presented as an example. The latter address the magnetic field enhancement (MFE) at the sub-millimeter pit on the surface of cavity, which is thought to cause quench**. There exists the famous well-type pit model, but many of pits are not well-type but have gentle slopes. Impacts of the slope angle on MFE have not been well understood. We introduce a model that can describe a pit with an arbitrary slope angle. A formula to evaluate the MFE factor is derived. A pit with a gentle slope angle yields a much smaller MFE factor than the well-type pit. The formula can be applied to the calculation of MFE factors of real pits with arbitrary slope angles.
* T. Kubo, Prog. Theor. Exp. Phys. 2015,063G01(2015).
** T. Kubo, Prog. Theor. Exp. Phys. 2015,073G01(2015).

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MOPB009

Model of Flux Trapping in Cooling Down Process

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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TUBA07

Theory of Multilayer Coating for Proof-of-Concept Experiments

T. Kubo
KEK, Ibaraki, Japan

Structures of alternating layers of superconducting (SC) and insulating layers formed on a bulk SC are actively discussed these years, because of their great possibility in realizing a high-field and high-Q SCRF cavity. In 2013, theoretical studies of an ideal system with a single SC layer and a single insulator layer formed on a bulk SC were carried out, by which appropriate combinations of materials and optimum thicknesses of SC and insulator layers that can enhance field limit were revealed. A more realistic model with nano-scale surface defects on the SC layer was also studied in 2014. As of this year, a sample-experiment-oriented theoretical study is in progress towards proof-of-concept experiments. Theories are becoming realistic every year. In this talk, I will review progresses after 2013 and provide theoretical equipages to tackle experiments of the multilayer coating(*).
*A.Gurevich, Appl. Phys. Lett.88,012511(2006); T.Kubo et al.,Appl. Phys. Lett.104,032603(2014); T.Kubo, Prog. Theor. Exp.Phys.2015,063G01(2015); T.Kubo, Prog. Theor. Exp.Phys.2015,073G01(2015).

Slides TUBA07 [2.080 MB]

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TUPB062

Evaluation of Sc Property Coated on a Surface

723

Y. Iwashita, Y. Fuwa
Kyoto ICR, Uji, Kyoto, Japan
M. Hino
Kyoto University, Research Reactor Institute, Osaka, Japan
T. Kubo, T. Saeki
KEK, Ibaraki, Japan

Funding: This work was supported by JSPS KAKENHI Grant Number 26600142.
We are trying to deposit thin superconducting material on a substrate for higher accelerating field gradients. In order to evaluate the deposit method, surface properties are under measurement. Some results on measurements at DC and a preparation status toward RF measurement will be reported.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA04

Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities

1006

K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan
A. Hocker
Fermilab, Batavia, Illinois, USA
T. Tajima
LANL, Los Alamos, New Mexico, USA

In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.

Slides THAA04 [2.810 MB]

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THPB046

Design and Development of Superconducting Spoke Cavity for Compact Photon Source

1196

M. Sawamura
Japan Atomic Energy Agency (JAEA), Gamma-ray Non-Destructive Assay Research Group, Tokai-mura, Ibaraki-ken, Japan
E. Cenni
CEA/IRFU, Gif-sur-Yvette, France
R. Hajima
JAEA, Ibaraki-ken, Japan
H. Hokonohara, Y. Iwashita, H. Tongu
Kyoto ICR, Uji, Kyoto, Japan
T. Kubo, T. Saeki
KEK, Ibaraki, Japan

Funding: This study is supported by Photon and Quantum Basic Research Coordinated Development Program of MEXT, Japan.
The spoke cavity is expected to have advantages for compact ERL accelerator for X-ray source based on laser Compton scattering. We have been developing the spoke cavity under a research program of MEXT, Japan to establish the fabrication process. Since our designed shape of the spoke cavity is complicated due to increase the RF properties, we have been designing the mold including the process of press work and the support parts for vacuum tolerance with the mechanical simulation. In this paper we present status of the spoke cavity fabrication.

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reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)