Superconducting Cavity Group



国際リニアコライダー計画(ILC)用試験加速器として建設されたSTF-2クライオモジュールには、ニオブ製1.3GHz、9-cell超伝導空洞が12台内蔵されており、運転温度2Kでパルス高加速電界での電子ビーム加速試験が行われています。2019年3月にはILCの目標値である平均加速電界32MV/mでのビーム運転が達成され、ビームエネルギーとして280MeVまでのビーム加速に成功しました。内面検査・機械研磨装置、電解研磨や高圧水洗浄などの表面処理装置、組立用クリーンルーム、空洞単体での低温性能評価を行う縦型測定システムなど、超伝導空洞開発を全工程に渡って一貫して行う設備が整っており、超伝導空洞の高性能化に重点を置いた研究活動を行っています。 特に、清浄環境下で超伝導空洞の窒素雰囲気中での真空熱処理を行うための高温真空熱処理炉が開発され、この真空熱処理炉を用いた窒素熱処理(窒素ドープ、窒素インフージョン)による高Q値・高加速電界の達成を目指した開発研究が重点的に行われています。横型クライオスタットでは超伝導電子銃空洞の冷却試験が計画され、また、陽子・重イオンを加速するための低ベータ型超伝導空洞開発が共同研究により展開されています。さらに、ニオブより高い超伝導転移温度を持つNb3SnやMgB2を用いた超伝導薄膜空洞の開発研究にも着手しています。


梅森 健成
Kensei Umemori

Cavity Group Leader

加古 永治
Eiji Kako

Professor Emeritus

阪井 寛志
Hiroshi Sakai


佐伯 学行
Takayuki Saeki

Associate Professor

山本 康史
Yasuchika Yamamoto

Associate Professor

後藤 剛喜
Takeyoshi Goto

Associate Professor

アシーシ クマール
Kumar Ashish

Assistant Professor

道前 武
Takeshi Dohmae

Assistant Professor

井藤 隼人
Hayato Ito

Assistant Professor

片山 領
Ryo Katayama

Assistant Professor

久保 毅幸
Takayuki Kubo

Assistant Professor

オメット マチュー
Mathieu Omet

Assistant Professor

荒木 隼人
Hayato Araki

Technical Associate

髙橋 光太郎
Kotaro Takahashi

Grad Student,
Research Assistant


Journal Articles

 T. Okada, E. Kako, M. Masuzawa, H. Sakai, R. Ueki, K. Umemori, and T. Tajima, Observation of quenching-induced magnetic flux trapping using a magnetic field and temperature mapping system, Phys. Rev. Accel. Beams 25, 082002 (2022).

 R. Katayama, E. Kako, S. Yamaguchi, S. Michizono, and K. Umemori, Design study of compact medical accelerator using superconducting rf quadrupole for boron neutron capture therapy, Phys. Rev. Accel. Beams 25, 021601 (2022).
  T. Kubo, Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor, and depairing current density, Phys. Rev. Applied 17, 014018 (2022).
  S. Ooi, M. Tachiki, T. Konomi, T. Kubo, A. Kikuchi, S. Arisawa, H. Ito, and K. Umemori, Observation of intermediate mixed state in high-purity cavity-grade Nb by magneto-optical imaging, Phys. Rev. B 104, 064504 (2021).
 H. Ito, H. Araki, K. Takahashi, and K. Umemori, Influence of furnace baking on Q–E behavior of superconducting accelerating cavities, Prog. Theor. Exp. Phys. 2021, 071G01 (2021).
 T. Okada, E. Kako, T. Konomi, M. Masuzawa, H. Sakai, K. Tsuchiya, R. Ueki, K. Umemori, P. Pizzol, A. Poudel, and T. Tajima , "Systematic evaluation of magnetic sensitivities of anisotropic magnetoresistive sensors at liquid helium temperature for superconducting cavities" , Review of Scientific Instruments.92, 035003 (2021).
 T. Kubo, Superheating fields of semi-infinite superconductors and layered superconductors in the diffusive limit: structural optimization based on the microscopic theory, Supercond. Sci. Technol. 34, 045006 (2021).
  F. Qiu, T. Miura, D. Arakawa, N. Higashi, E. Kako, T. Matsumoto, S. Michizono, T. Miyajima, T. Obina, H. Sakai, K. Umemori, RF commissioning of the compact energy recovery linac superconducting cavities in pulse mode, Nucl. Instrum. Methods Phys. Res. A 985, 164660 (2021).
 V. Chouhan, S. Kato, Y. Ida, K. Nii, T. Yamaguchi, and H. Hayano, Chemical analysis and field emission study of electropolished niobium surface containing synthesized niobium oxide particles, Materials Chemistry and Physics 259, 124044 (2021).
 T. Kubo, Superfluid flow in disordered superconductors with Dynes pair-breaking scattering: Depairing current, kinetic inductance, and superheating field, Phys. Rev. Research 2, 033203 (2020).
 T. Kubo, Weak-field dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density, Phys. Rev. Research 2, 013302 (2020).
 H. Ito, H. Hayano, T. Kubo, and T. Saeki, Vortex penetration field measurement system based on third-harmonic method for superconducting RF materials, Nucl. Instrum. Methods Phys. Res. A 955, 163284 (2020).
 V. Chouhan, S. Kato, K. Nii, T. Yamaguchi, M. Sawabe, T. Saeki, H. Monjushiro, H. Oikawa, H. Ito, H. Hayano, and Y. Ida, Vertical electropolishing for 1.3 GHz single- and nine-cell superconducting niobium cavities: A parametric optimization and rf performance, Phys. Rev. Accel. and Beams 22, 103101 (2019).
 T. Kubo and A. Gurevich, Field-dependent nonlinear surface resistance and its optimization by surface nanostructuring in superconductors, Phys. Rev. B 100, 064522 (2019).
 T. Kubo, Optimum multilayer coating of superconducting particle accelerator cavities and effects of thickness dependent material properties of thin films, Jpn. J. Appl. Phys. 58, 088001 (2019).
 C. Z. Antoine, M. Aburas, A. Four, F. Weiss, Y. Iwashita, H. Hayano, S. Kato, T. Kubo, and T. Saeki, Optimization of tailored multilayer superconductors for RF application and protection against premature vortex penetration, Supercond. Sci. Technol. 32, 085005 (2019).
 H. Sakai, E. Cenni, K. Enami, T. Furuya, M. Sawamura, K. Shinoe, and K. Umemori, Field emission studies in vertical test and during cryomodule operation using precise x-ray mapping system, Phys. Rev. Accel. Beams 22, 022002 (2019).
 H. Oikawa, T. Higashiguchi, and H. Hayano, Design of niobium-based mushroom-shaped cavity for critical magnetic field evaluation of superconducting multilayer thin films toward achieving higher accelerating gradient cavity, Jpn. J. Appl. Phys. 58, 028001 (2019).
 H. Oikawa, T. Higashiguchi, and H. Hayano, Note: Design and resonant condition measurement of the mushroom-shaped Al test cavity for critical magnetic field evaluation of superconducting thin-film sample, Review of Scientific Instruments 89, 076102 (2018).
 A. Gurevich and T. Kubo, Surface impedance and optimum surface resistance of a superconductor with an imperfect surface, Phys. Rev. B 96, 184515 (2017).
 T. Dohmae, K. Umemori, M. Yamanaka, Y. Watanabe and H. Inoue, Investigation of in-house superconducting radio-frequency 9-cell cavity made of large grain niobium at KEK, Nucl. Instrum. Methods Phys. Res. A 875, 1 (2017).
 H. Shimizu, T. Dohmae, M. Egi, K. Enami, H. Inoue, E. Kako, G. T. Park, H. Sakai, K. Umemori, Y. Watanabe, S. Yamaguchi, and M. Yamanaka, Fabrication and Evaluation of Superconducting Single-Cell Cavities Manufactured Using Various Materials and Methods, IEEE Trans. Appl. Supercond. 27, 3500714 (2017).
 M. Masuzawa, A. Terashima, K. Tsuchiya and R. Ueki, Magnetic shielding for superconducting RF cavities, Supercond. Sci. Technol. 30, 034009 (2017).
 T. Kubo, Multilayer coating for higher accelerating fields in superconducting radio-frequency cavities: a review of theoretical aspects, Supercond. Sci. Technol. 30, 023001 (2017).
 S. Huang, T. Kubo, and R. L. Geng, Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through Tc, Phys. Rev. Accel. Beams 19, 082001 (2016).
 T. Kubo, Flux trapping in superconducting accelerating cavities during cooling down with a spatial temperature gradient, Prog. Theor. Exp. Phys. 2016, 053G01 (2016).
 T. Kubo, Field limit and nano-scale surface topography of superconducting radio-frequency cavity made of extreme type II superconductor, Prog. Theor. Exp. Phys. 2015, 063G01 (2015).
 T. Kubo, Magnetic field enhancement at a pit on the surface of a superconducting accelerating cavity, Prog. Theor. Exp. Phys. 2015, 073G01 (2015).
 T. Kubo, Y. Iwashita, and T. Saeki, Radio-frequency electromagnetic field and vortex penetration in multilayered superconductors, Appl. Phys. Lett. 104, 032603 (2014).
 K. Watanabe, S. Noguchi, E. Kako, K. Umemori, and T. Shishido, Development of the superconducting rf 2-cell cavity for cERL injector at KEK, Nucl. Instrum. Methods Phys. Res. A 714, 67 (2013).
 Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, and K. Watanabe, Achieving high gradient performance of 9-cell cavities at KEK for the international linear collider, Nucl. Instrum. Methods Phys. Res. A 729, 589 (2013).
 X. Zhao, R. Geng, P. V. Tyagi, H. Hayano, S. Kato, M. Nishiwaki, T. Saeki, and M. Sawabe, Surface characterization of Nb samples electropolished with real superconducting rf accelerator cavities, Phys. Rev. ST Accel. Beams 13, 124702 (2010).
 E. Kako, H. Hayano, S. Noguchi, N. Ohuchi, M. Satoh, T. Shishido, K. Watanabe, and Y. Yamamoto, Cryomodule tests of four Tesla-like cavities in the Superconducting RF Test Facility at KEK, Phys. Rev. ST Accel. Beams 13, 041002 (2010).
 M. Sawamura, T. Furuya, H. Sakai, T. Takahashi, K. Umemori, and K. Shinoe, Eccentric-fluted beam pipes to damp quadrupole higher-order modes, Phys. Rev. ST Accel. Beams 13, 022003 (2010).
 Y. Yamamoto, Cavity diagnostic system for the performance test of the 1.3 GHz superconducting 9-cell cavity, Nucl. Instrum. Methods Phys. Res. A 623, 579 (2010).
 Y. Iwashita, H. Hayano, and Y. Tajima, Development of high resolution camera for observations of superconducting cavities, Phys. Rev. ST Accel. Beams 11, 093501 (2008).
 K. Watanabe, S. Noguchi, E. Kako, T. Shishido, and H. Hayano, New HOM coupler design for ILC superconducting cavity, Nucl. Instrum. Methods Phys. Res. A 595, 299 (2008).

Others (日本語で書かれた解説記事)

 井藤隼人, Furnace Baking 法による超伝導加速空洞の高Q値・高加速勾配化について, 加速器 19, 18 (2022).
 山本康史, 福田将史, 松本利広, 森川祐, ILCに向けたSTF-2クライオモジュールによる33 MV/m でのビーム加速実証, 加速器 18, 143 (2021).
 久保毅幸, 対破壊電流密度概観, 低温工学 56, 277 (2021).
 山本明, 素粒子物理実験・加速器・超伝導技術との歩み― 未来への願い ―, 低温工学 54, 485 (2019).
 加古永治, 超伝導空洞を用いた加速器の現状と展望, 低温工学 54, 257 (2019).
 梅森健成, 超伝導加速空洞の性能向上に向けた技術開発, 低温工学 54, 267 (2019).
 久保毅幸, 超伝導加速空洞の物理と課題、そして性能向上への理論的示唆, 低温工学 54, 275 (2019).
 中西功太, 早野仁司, 福田将史, 松本利広, 森 川祐, 山本康史, STF-2加速器のビームコミッショニング, 高エネルギーニュース 38, 47 (2019).
 久保毅幸, 超伝導空洞の物理と窒素インフュージョン: 国際リニアコライダー計画の実現 に向けて, 加速器 15, 40 (2018).
 山本康史, From the European XFEL Accelerator to the International Linear Collider, 高エネルギーニュース 36, 157 (2018).
 山本康史, ILCに向けたSTF Phase-2計画の進展, 高エネルギーニュース 34, 277 (2016).
 加古永治, 超伝導空洞技術:技術研修会 (1), 加速器 13, 2 (2016).
 加古永治, 超伝導空洞技術:技術研修会 (2), 加速器 13, 70 (2016).
 阪井寛志, 本田洋介, ERL試験加速器のビームコミッショニング, 高エネルギーニュース 33, 205 (2014).
 佐伯学行, ILC 用超伝導加速空洞の量産化に向けた製造の研究, 加速器 11, 161 (2014).
 佐伯学行, KEKにおけるILCのための超伝導9セル空洞製造の研究, 高エネルギーニュース 32, 178 (2013).
 山本明, 国際リニアコライダー・技術設計書の完成と今後の展開, 高エネルギーニュース 31, 314 (2013).
 加古永治, ILC用超伝導空洞の開発, 低温工学 48, 415 (2013).
 加藤茂樹, 佐伯学行, 沢辺元明, 西脇みちる, 早野仁司, 両角祐一, 渡邊謙, Puneet Veer TYAGI, 岩下芳久, 超伝導加速空洞の高電界化に向けた研究(その1), 加速器 7, 95 (2010).
 加藤茂樹, 佐伯学行, 沢辺元明, 西脇みちる, 早野仁司, 両角祐一, 渡邊謙, Puneet Veer TYAGI, 岩下芳久, 超伝導加速空洞の高電界化に向けた研究(その2), 加速器 7, 199 (2010).
 斎藤健治, ニオブ超伝導空洞と材料・表面科学―50 MV/m 高電界超伝導空洞開発,この20年 の闘い―, 加速器 2, 479 (2005).

Conferences Activities



 T. Okada et al., Observation of Precise Distribution of Trapped Magnetic Flux due to Quench by H&T Mapping System, SRF2021, virtual (2021)
 K. Umemori, High-performance Large-grain Cavities for the ILC, SRF2021, virtual (2021)
 T. Konomi, Overview on Worldwide Development of SRF-gun Cavities, SRF2021, virtual (2021)
 H. Sakai, Stable Beam Operation in cERL for Medical and Industrial Application at KEK, SRF2021, virtual (2021)
 H. Ito, Systematic Investigation of Mid-T Furnace Baking for High-Q Performance, SRF2021, virtual (2021)
 K. Takahashi et al., Design and Construction of Nb3Sn Vapor Diffusion Coating System at KEK, SRF2021, virtual (2021), SUPCAV008
 K. Takahashi et al., First Nb3Sn Coating and Cavity Performance Result at KEK, SRF2021, virtual (2021), SUPCAV009
 R. Katayama et al., Design Study of Compact Medical Accelerator Using Superconducting RFQ for BNCT, SRF2021, virtual (2021), MOPTEV016
 R. Katayama et al., High-Q/high-G R&D at KEK Using 9-Cell Tesla Shape Niobium Cavities, SRF2021, virtual ( 2021), MOPCAV006
 A. Kumar et al., Mechanical Properties of Directly Sliced Medium Grain Niobium for 1.3 GHz SRF Cavity, SRF2021, virtual (2021), MOPCAV004
 T. Dohmae et al., Fabrication of 1.3GHz SRF Cavities Using Medium Grain Niobium Discs Directly Sliced from Forged Ingot, SRF2021, virtual (2021), MOPCAV012
 Y. Iwashita et al., High Density Mapping Sytems for SRF Cavities, SRF2021, virtual (2021), MOPFDV002
 Y. Iwashita et al., Instrumentation R&D at KEK and Kyoto University, SRF2021, virtual (2021), TUPFDV008
 Y. Yamamoto et al., Stable Beam Operation at 33 MV/m in STF-2 Cryomodules at KEK, SRF2021, virtual (2021) , TUPFAV003
 F. Eozénou et al., Vertical Electro-Polishing of 704MHz Resonators Using Ninja Cathode: First Results, SRF2021, virtual (2021), TUPCAV001
 M. Yamanaka and K. Enami, Tensile Tests of Large Grain Ingot Niobium at Liquid He Temperature, SRF2021, virtual (2021), WEPFDV005
 Y. Yamamoto et al., Research on Ceramic for RF Window, SRF2021, virtual (2021), THPFDV008
 K. Nii et al., Impact of Vertical Electropolishing With Flipping System on Removal Uniformity and Surface State: Study With 9-Cell Niobium Coupon Cavity, SRF2021, virtual (2021), THPCAV003
 M. Omet et al., Recent Activities Regarding 9-Cell TESLA-Type Cavities at KEK, SRF2021, virtual (2021), THPCAV006



 K. Umemori et al., Study on Nitrogen Infusion using KEK New Furnace, SRF2019, Dresden, Germany (2019), MOP027
 T. Okada et al., Development of Temperature and Magnetic Field Mapping System for Superconducting Cavities at KEK, SRF2019, Dresden, Germany (2019), TUP060
 H. Sakai et al., Improvement of a Clean Assembly Work for Superconducting RF Cryomodule and Its Application to the KEK-STF Cryomodule, SRF2019, Dresden, Germany (2019), TUP104
 Y. Yamamoto et al., Successful Beam Commissioning in STF-2 Cryomodules for ILC, SRF2019, Dresden, Germany (2019), WETEA6
 T. Dohmae et al., Investigation on 1, 3 and 9-Cell SRF Elliptical Cavities made of Large Grain Niobium, SRF2019, Dresden, Germany (2019), FRCAA6
 T. Konomi et al., Development of High Intensity, High Brightness, CW SRF Gun with Bi-Alkali Photocathode, SRF2019, Dresden, Germany (2019), FRCAB4
 T. Saeki et al., Fabrication of 3.0-GHz Single-cell Cavities for Thin-film Study, SRF2019, Dresden, Germany (2019), MOP054
 H. Ito et al., Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK, SRF2019, Dresden, Germany (2019), TUP078
 R. Katayama et al., Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO2 on Pure Nb Substrate, SRF2019, Dresden, Germany (2019), THFUA2
 Y. Yamamoto and S. Michizono, Ceramic Study on RF Windows for Power Coupler, Waveguide, and Klystron in Particle Accelerator, SRF2019, Dresden, Germany (2019), MOP077
 T. Kubo and A. Gurevich, Field-Dependent Nonlinear Surface Resistance and Its Optimization by Surface Nano-Structuring of the SRF Cavities, SRF2019, Dresden, Germany (2019), THFUA4

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