Experimental study based on direct in-situ observation of normal-conducting RF accelerating cavities for elucidating the breakdown-trigger mechanism

• Project/Area Number: 15H03671
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: High Energy Accelerator Research Organization
• Principal Investigator: Abe Tetsuo 大学共同利用機関法人高エネルギー加速器研究機構, 加速器研究施設, 准教授 (70370070)
• Project Period (FY): 2015-04-01 – 2018-03-31
• Project Status: Completed (Fiscal Year 2017)
• Budget Amount: ¥17,420,000 (Direct Cost: ¥13,400,000、Indirect Cost: ¥4,020,000); Fiscal Year 2017: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000); Fiscal Year 2016: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000); Fiscal Year 2015: ¥12,740,000 (Direct Cost: ¥9,800,000、Indirect Cost: ¥2,940,000)
• Keywords: ブレークダウン / 真空放電 / 加速空洞 / マイクロ波 / 高周波 / 高電界 / 粒子加速 / 加速器 / 高周波加速空洞

Outline of Final Research Achievements

Normal-conducting RF accelerating cavities, made of copper, are hearts of many particle accelerators, where vacuum arcs in the cavities (breakdowns) could limit accelerator performance; however, we do not know what the real source of cavity breakdowns is. Performing experimental breakdown study based on direct in-situ observation, we demonstrated that cavity breakdown was caused by an explosion of a bright spot which maintained its intensity during high-power operation until the explosion, or by a spot-type explosion not originating from a stable bright spot. In this study, using higher-spec cameras, we have discovered that the bright spots were high-temperature (> 1000 degC) microparticles made of material(s) other than copper, and that spot-type explosions can be understood to be results of impact of flying high-temperature microparticles on cavity surface.

Research Products

• [Journal Article] Direct Observation of Breakdown Trigger Seeds in a Normal-Conducting RF Accelerating Cavity (2018)
  • Author(s): 阿部 哲郎、影山 達也、坂井 浩、竹内 保直、吉野 一男
  • Journal Title: Physical Review Accelerators and Beams Volume: 21 Issue: 12 Pages: 122002-122002
  • DOI: 10.1103/physrevaccelbeams.21.122002
  • Peer Reviewed / Open Access
• [Journal Article] Breakdown Study Based on Direct In-Situ Observation of Inner Surfaces of an RF Accelerating Cavity during a High-Gradient Test" (2016)
  • Author(s): Tetsuo Abe, Tatsuya Kageyama, Hiroshi Sakai, Yasunao Takeuchi, and Kazuo Yoshino
  • Journal Title: Physical Review Accelerators and Beams Volume: 19 Issue: 10 Pages: 102001-102001
  • DOI: 10.1103/physrevaccelbeams.19.102001
  • Peer Reviewed / Open Access
• [Presentation] Updated Results of Breakdown Study for a 509-MHz Continuous-Wave Accelerating Cavity based on Direct In-situ Observation (2018)
  • Author(s): 阿部 哲郎
  • Organizer: 7th International Workshop on Mechanisms of Vacuum Arcs (MeVArc 2018)
• [Presentation] 加速空洞内部の直接観察によるブレークダウン引き金機構の解明研究 (2018)
  • Author(s): 阿部 哲郎、影山 達也、坂井 浩、竹内 保直、吉野 一男
  • Organizer: 第15回 日本加速器学会年会
• [Presentation] ハイパースペクトルイメージングを用いた粒子加速器用 高周波加速空洞のブレークダウン引き金機構の解明研究 (2018)
  • Author(s): 阿部 哲郎
  • Organizer: ハイパースペクトル・マルチスペクトルデータの計測と産業応用研究会
• [Presentation] High-Gradient Testing of Single-Cell Test Cavities at KEK / Nextef (2016)
  • Author(s): 阿部 哲郎
  • Organizer: 日本加速器学会
  • Place of Presentation: 幕張メッセ 国際会議場（千葉県千葉市）
  • Year and Date: 2016-08-08
• [Presentation] RF Accelerating Cavity for SuperKEKB Damping Ring and its Breakdown Study (2015)
  • Author(s): 阿部 哲郎
  • Organizer: MeVArc 2015 (5th International Workshop on Mechanisms of Vacuum Arcs)
  • Place of Presentation: ラップランド（フィンランド）
  • Year and Date: 2015-09-02
  • Int'l Joint Research
• [Presentation] KEK/Nextef における高電界加速構造の基礎研究 (2015)
  • Author(s): 阿部 哲郎
  • Organizer: 第12回日本加速器学会年会
  • Place of Presentation: 敦賀市福祉総合センターあいあいプラザ（福井県・敦賀市）
  • Year and Date: 2015-08-05
• [Remarks] 高周波加速空洞のブレークダウンの瞬間を「見た」！
  • URL: http://www2.kek.jp/accl/topics/topics161005.html