SRF2019 - List of Authors (Ito, R.)

Paper	Title	Page
TUP077	Nb₃Sn Thin Film Coating Method for Superconducting Multilayered Structure	628
	R. Ito, T. Nagata ULVAC, Inc, Chiba, Japan H. Hayano, R. Katayama, T. Kubo, T. Saeki KEK, Ibaraki, Japan H. Ito Sokendai, Ibaraki, Japan Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan
	S-I-S (superconductor-insulator-superconductor) multilayered structure has been proposed in order to increase the maximum acceleration gradient of SRF cavities. Nb₃Sn is the material most expected as a superconducting layer of the S-I-S multilayered structure because it offers both a large critical temperature and large predicted Hsh. Most important in fabricating Nb₃Sn thin films is the stoichiometry of the material produced, and the lack of tin leads to performance degradation. We have launched a new in-house DC magnetron sputtering apparatus for Nb₃Sn deposition. Nb and Sn layers were alternately and repeatedly deposited on Si wafer while adjusting the film thickness of each layer, so we successfully obtained Nb-Sn films having appropriate composition ratio. The as-deposited films were annealed under the temperature of 600 degree C for 1 hour to generate the Nb₃Sn phase. The characteristics of Nb-Sn films evaluated by XRD, XRF, FE-SEM, and so on. We also measured critical temperature of the annealed films. In this paper, the detail of the Nb₃Sn coating method and the measurement result of the Nb-Sn films will be reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP077
About •	paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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TUP078	Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK	632
SUSP013	use link to see paper's listing under its alternate paper code
	H. Ito Sokendai, Ibaraki, Japan C.Z. Antoine CEA-IRFU, Gif-sur-Yvette, France H. Hayano, R. Katayama, T. Kubo, T. Saeki KEK, Ibaraki, Japan R. Ito, T. Nagata ULVAC, Inc, Chiba, Japan Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan
	Funding: The work is supported by Japan Society for the Promotion of Science Grant-in-Aid for Young Scientist (A) No.17H04839. The multilayer thin film structure of the superconductor has been proposed by A. Gurevich to enhance the maximum gradient of SRF cavities. The lower critical field Hc1 at which the vortex start penetrating the superconducting material will be improved by coating Nb with thin film superconductor such as NbN. It is expected that the enhancement of Hc1 depends on the thickness of each layer. In order to determine the optimum thickness of each layer and to compare the measurement results with the theoretical prediction proposed by T. Kubo, we developed the Hc1 measurement system using the third harmonic response of the applied AC magnetic field at KEK. For the Hc1 measurement without the influence of the edge or the shape effects, the AC magnetic field can be applied locally by the solenoid coil of 5mm diameter in our measurement system. ULVAC made the NbN-SiO₂ multilayer thin film samples of various NbN thicknesses. In this report, the measurement result of the bulk Nb sample and NbN-SiO₂ multilayer thin film samples of different thickness of NbN layer will be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP078
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THFUA2	Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO₂ on Pure Nb Substrate	807
	R. Katayama, H. Hayano, T. Kubo, T. Saeki KEK, Ibaraki, Japan C.Z. Antoine CEA-IRFU, Gif-sur-Yvette, France H. Ito Sokendai, Ibaraki, Japan R. Ito ULVAC, Inc, Chiba, Japan Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan T. Nagata ULVAC, Inc., Tsukuba, Japan
	In recent years, it has been pointed out that the maximum accelerating gradient of a superconducting RF cavity can be increased by coating the inner surface of the cavity with a multilayer thin-film structure consisting of alternating insulating and superconducting layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices begin penetrating into the superconductor layer. This is predicted to depend on the combination of the film thickness. We made samples that have a NbN/SiO₂ thin-film structure on a pure Nb substrate with several layers of NbN film deposited using DC magnetron sputtering method. Here, we report the measurement results of effective Hc1 of NbN/SiO₂(30 nm)/Nb multilayer samples with thicknesses of NbN layers in the range from 50 nm to 800 nm by using the third-harmonic voltage method. Experimental results show that an optimum thickness exists, which increases the effective Hc1 by 23.8 %.
	Slides THFUA2 [2.333 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA2
About •	paper received ※ 03 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Nb₃Sn Thin Film Coating Method for Superconducting Multilayered Structure

628

R. Ito, T. Nagata
ULVAC, Inc, Chiba, Japan
H. Hayano, R. Katayama, T. Kubo, T. Saeki
KEK, Ibaraki, Japan
H. Ito
Sokendai, Ibaraki, Japan
Y. Iwashita
Kyoto ICR, Uji, Kyoto, Japan

S-I-S (superconductor-insulator-superconductor) multilayered structure has been proposed in order to increase the maximum acceleration gradient of SRF cavities. Nb₃Sn is the material most expected as a superconducting layer of the S-I-S multilayered structure because it offers both a large critical temperature and large predicted Hsh. Most important in fabricating Nb₃Sn thin films is the stoichiometry of the material produced, and the lack of tin leads to performance degradation. We have launched a new in-house DC magnetron sputtering apparatus for Nb₃Sn deposition. Nb and Sn layers were alternately and repeatedly deposited on Si wafer while adjusting the film thickness of each layer, so we successfully obtained Nb-Sn films having appropriate composition ratio. The as-deposited films were annealed under the temperature of 600 degree C for 1 hour to generate the Nb₃Sn phase. The characteristics of Nb-Sn films evaluated by XRD, XRF, FE-SEM, and so on. We also measured critical temperature of the annealed films. In this paper, the detail of the Nb₃Sn coating method and the measurement result of the Nb-Sn films will be reported.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP077

About •

paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

Export •

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

TUP078

Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK

632

SUSP013

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

H. Ito
Sokendai, Ibaraki, Japan
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
H. Hayano, R. Katayama, T. Kubo, T. Saeki
KEK, Ibaraki, Japan
R. Ito, T. Nagata
ULVAC, Inc, Chiba, Japan
Y. Iwashita, H. Tongu
Kyoto ICR, Uji, Kyoto, Japan

Funding: The work is supported by Japan Society for the Promotion of Science Grant-in-Aid for Young Scientist (A) No.17H04839.
The multilayer thin film structure of the superconductor has been proposed by A. Gurevich to enhance the maximum gradient of SRF cavities. The lower critical field Hc1 at which the vortex start penetrating the superconducting material will be improved by coating Nb with thin film superconductor such as NbN. It is expected that the enhancement of Hc1 depends on the thickness of each layer. In order to determine the optimum thickness of each layer and to compare the measurement results with the theoretical prediction proposed by T. Kubo, we developed the Hc1 measurement system using the third harmonic response of the applied AC magnetic field at KEK. For the Hc1 measurement without the influence of the edge or the shape effects, the AC magnetic field can be applied locally by the solenoid coil of 5mm diameter in our measurement system. ULVAC made the NbN-SiO₂ multilayer thin film samples of various NbN thicknesses. In this report, the measurement result of the bulk Nb sample and NbN-SiO₂ multilayer thin film samples of different thickness of NbN layer will be discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP078

About •

paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

Export •

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

THFUA2

Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO₂ on Pure Nb Substrate

807

R. Katayama, H. Hayano, T. Kubo, T. Saeki
KEK, Ibaraki, Japan
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
H. Ito
Sokendai, Ibaraki, Japan
R. Ito
ULVAC, Inc, Chiba, Japan
Y. Iwashita, H. Tongu
Kyoto ICR, Uji, Kyoto, Japan
T. Nagata
ULVAC, Inc., Tsukuba, Japan

In recent years, it has been pointed out that the maximum accelerating gradient of a superconducting RF cavity can be increased by coating the inner surface of the cavity with a multilayer thin-film structure consisting of alternating insulating and superconducting layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices begin penetrating into the superconductor layer. This is predicted to depend on the combination of the film thickness. We made samples that have a NbN/SiO₂ thin-film structure on a pure Nb substrate with several layers of NbN film deposited using DC magnetron sputtering method. Here, we report the measurement results of effective Hc1 of NbN/SiO₂(30 nm)/Nb multilayer samples with thicknesses of NbN layers in the range from 50 nm to 800 nm by using the third-harmonic voltage method. Experimental results show that an optimum thickness exists, which increases the effective Hc1 by 23.8 %.

Slides THFUA2 [2.333 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA2

About •

paper received ※ 03 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019

Export •

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