Author: Ohmi, K.
Paper Title Page
TUOCB1 Progress in the Design of Beam Optics for FCC-ee Collider Ring* 1281
 
  • K. Oide, K. Ohmi
    KEK, Ibaraki, Japan
  • M. Benedikt, H. Burkhardt, B.J. Holzer, A. Milanese, J. Wenninger, F. Zimmermann
    CERN, Geneva, Switzerland
  • A.P. Blondel, M. Koratzinos
    DPNC, Genève, Switzerland
  • A.V. Bogomyagkov, E.B. Levichev, D.N. Shatilov
    BINP SB RAS, Novosibirsk, Russia
  • M. Boscolo
    INFN/LNF, Frascati (Roma), Italy
 
  The beam optics for the FCC-ee collider has been updated: (a) the layout is adjusted to a new footprint of FCC-hh, (b) the design around the interaction point is refined considering a number of machine-detecor interface issues, (c) the arc lattice is refined taking realistic magnet designs into account, (d) the β* and betatron tunes are re-optimized according to recent results of the beam-beam simulations, and more. These changes make the collider design more realistic without performance degradation.  
slides icon Slides TUOCB1 [4.891 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUOCB1  
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TUPIK059 Recent Progress of Dithering System at SuperKEKB 1827
 
  • Y. Funakoshi, H. Fukuma, T. Kawamoto, M. Masuzawa, S. Nakamura, K. Ohmi, T. Oki, S. Uehara
    KEK, Ibaraki, Japan
  • P. Bambade, D. El Khechen, D. Jehanno, V. Kubytskyi, C. Rimbault
    LAL, Orsay, France
  • A.S. Fisher
    SLAC, Menlo Park, California, USA
  • U. Wienands
    ANL, Argonne, Illinois, USA
 
  Recent progress of the dithering system at SuperKEKB is described. Some details of the system layout are shown. Beam orbit and optics related issues are discussed. Preliminary tests of the some components in the Phase 1 beam commissioning or in the bench are described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPIK059  
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WEPIK073 Three Dimensional Wake Field for an Electron Moving in Undulator 3098
 
  • K. Ohmi
    KEK, Ibaraki, Japan
 
  Electro-magnetic field for given trajectory of an electron is calculated by Lienard-Wiechert potential. The field near the electron moving in an undulator is presented. The field is regarded as a wake field in the undulator. Motion of a bunch is studied in the wake field.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK073  
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WEPIK074 Twiss Parameter Measurement and Application to Space Charge Dynamics 3101
 
  • K. Ohmi, S. Igarashi, T. Toyama
    KEK, Tokai, Ibaraki, Japan
  • H. Harada, S. Hatakeyama
    JAEA/J-PARC, Tokai-mura, Japan
  • N. Kuroo
    UTTAC, Tsukuba, Ibaraki, Japan
  • Y. Sato
    J-PARC, KEK & JAEA, Ibaraki-ken, Japan
  • R. Tomás, A. Wegscheider
    CERN, Geneva, Switzerland
 
  We are looking for feasible and quantitative method to evaluate space charge induced beam loss in J-PARC MR. One possible way is space charge simulation and theory based on measured Twiss parameter. Twiss parameter measurement using turn-by-turn monitors is presented. Resonance strengths of lattice magnets and space charge force are estimated by the measured Twiss parameters. Emittance growth and beam loss under the resonance strengths are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK074  
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WEPIK075 Electron Cloud Instability in SuperKEKB Phase I Commissioning 3104
 
  • K. Ohmi, J.W. Flanagan, H. Fukuma, H. Ikeda, E. Mulyani, K. Shibata, Y. Suetsugu, M. Tobiyama
    KEK, Ibaraki, Japan
 
  Beam size blow-up due to electron cloud has been observed in Phase I commissioning of SuperKEKB. Vacuum chambers in LER (low energy positron ring) were cured by antechamber and TiN coating for electron cloud. Some parts, bellows, were not cured by the coating. In the early stage of Phase I commissioning, beam size blow up has been observed above a threshold current. The blow up was suppressed by weak permanent magnets generating longitudinal field, which cover the bellows. Electron cloud current have been monitored during the commissioning. The thresholds for the electron cloud induced fast head-tail instability have been simulated in the operating beam conditions. Coupled bunch instability caused by electron cloud has been measured in the operating beam conditions and installation of the permanent magnets. The measurement and simulation results are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK075  
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THPAB021 Wake Field and Head-Tail Instability in Beam-Beam Collision with a Large Crossing Angle 3738
 
  • K. Ohmi, D. Zhou
    KEK, Ibaraki, Japan
  • N. Kuroo
    UTTAC, Tsukuba, Ibaraki, Japan
  • K. Oide, F. Zimmermann
    CERN, Geneva, Switzerland
 
  Head-tail type of coherent beam-beam instability has been seen in a strong-strong beam-beam simulation for collision with a large Piwinski angle σzθ/σx>>1, where θ is a half crossing angle. Beta x* is key parameter for the instability. The instability is not serious for SuperKEKB, but can be seen in phase II commissioning stage. It has a large impact for design of FCC-ee. We introduce wake field due to the beam-beam collision. The wake field gives turn-by-turn correlation of head-tail mode. Head-tail instability caused by the wake field explains that seen in the strong-strong beam-beam simulation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB021  
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THPAB022 Ion Instability in SuperKEKB Phase I Commissioning 3741
 
  • K. Ohmi, H. Fukuma, Y. Suetsugu, M. Tobiyama
    KEK, Ibaraki, Japan
 
  Ion instability has been observed in SuperKEKB phase I commissioning. Unstable modes, their growth rates, tune shift were measured. Frequency of the unstable modes is slower than theoretical prediction and the growth rate is also slower. We discuss possible model to explain the measurements.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB022  
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THPVA010 Electron Cloud Simulations for the Main Ring of J-PARC 4436
 
  • B. Yee-Rendón, R. Muto, K. Ohmi, K. Satou, M. Tomizawa, T. Toyama
    KEK, Ibaraki, Japan
 
  The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams. At Main Ring (MR) of J-PARC, signals related to the electron cloud have been observed during the slow beam extraction mode. Hence, several studies were conducted to investigate the mechanism that produces it, the results confirmed a strong dependence on the beam intensity and the bunch structure in the formation of the electron cloud, however, the precise explanation of its trigger conditions remains incomplete. To shed light on the problem, electron cloud simulations were done using an updated version of the computational model developed from previous works at KEK. The code employed the signals of the measurements to reproduce the events seen during the surveys.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA010  
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THPVA012 Transverse Impedance Measurement in SuperKEKB 4442
 
  • N. Kuroo
    UTTAC, Tsukuba, Ibaraki, Japan
  • T. Ishibashi, T. Mimashi, K. Ohmi, Y. Ohnishi, K. Shibata, Y. Suetsugu, S. Terui, M. Tobiyama, D. Zhou
    KEK, Ibaraki, Japan
 
  In KEK(Japan), SuperKEKB project is progressing toward upgrade. This project aims improvement luminosity (8×1035 cm-2s- 1) which is 40 times of the performance of the KEKB accelerator. In Phase 1 of this project, a performance test as storage ring was carried out. Understanding of ring Impedance/wake is an important subject in phase I. Measurement of Head Tail Damping using Turn by Turn monitor was performed to evaluate impedance/wake. Betatron motion is excited by kicker and its damping is measured for several parameters sets of bunch current and chromaticity in both HER and LER. The wake field was calculated from the decrement of betatron amplitude. We present the wake field which is cross-checked with tune shift based on the current dependence.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA012  
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