Author: Ohmi, K.
Paper Title Page
MOPPC002 Local Chromatic Correction Scheme and Crab-waist Collisions for an Ultra-low β* at the LHC 118
  • J.L. Abelleira, S. Russenschuck, R. Tomás, F. Zimmermann
    CERN, Geneva, Switzerland
  • J.L. Abelleira
    EPFL, Lausanne, Switzerland
  • C. Milardi, M. Zobov
    INFN/LNF, Frascati (Roma), Italy
  • K. Ohmi
    KEK, Ibaraki, Japan
  • D.N. Shatilov
    BINP SB RAS, Novosibirsk, Russia
  Funding: Work supported by the European Commission under the FP7 Research Infrastructures project Eu- CARD, grant agreement no. 227579.
We discuss potential merits and the parameter range of interest for a possible crab-waist collision scheme at the LHC, and report preliminary optics studies of a local chromatic correction scheme with flat beams (βx*>>βy*), which could boost the LHC luminosity by about an order of magnitude and would also allow for crab-waist collisions.
TUOBC02 Small-Beta Collimation at SuperKEKB to Stop Beam-Gas Scattered Particles and to Avoid Transverse Mode Coupling Instability 1104
  • H. Nakayama, Y. Funakoshi, K. Kanazawa, K. Ohmi, Y. Ohnishi, Y. Suetsugu
    KEK, Ibaraki, Japan
  • H. Nakano
    Tohoku University, Graduate School of Science, Sendai, Japan
  At SuperKEKB, beam particles which are Coulomb-scattered by the residual gas molecular change direction and will be eventually lost by hitting beam pipe inner wall. Due to large vertical beta function and small beam pipe radius just before IP, most of Coulomb-scattered particles are lost there and are very dangerous for the Belle-II detector. To stop such particles before the IP, vertical collimators are installed in the ring. However, such vertical collimators should be placed very close (few mm) to the beam and therefore induce transverse mode coupling instability. To avoid beam instability and achieve collimation at the same time, we need to install vertical collimators where vertical beta function is SMALL, since maximum collimator width determined by aperture condition is proportional to β1/2, and minimum collimator width determined by instability is proportional to β2/3. We present our strategy to stop beam-gas scattered particles and simulated loss rate in the interaction region. We will also show dedicated vertical collimator design to achieve less instability.  
slides icon Slides TUOBC02 [2.196 MB]  
TUPPC017 Orbit and Optics Correction to Realize Designed Machine Performance 1194
  • Y. Seimiya, S. Kamada, A. Morita, K. Ohmi, K. Oide
    KEK, Ibaraki, Japan
  It is difficult for actual accelerators to achieve the designed machine performance without appropriate correction or adjustment of magnet errors. By correction as magnets are aligned to design orbit, we aim to be realized the designed machine performance. However, it is not easy to estimate the design orbit in real accelerators. In KEKB and PF, beam position monitor(BPM) can be calibrated to the center of quadrupole magnet(QM). BPM and QM misalignments (except rotation misalignment) referring to design orbit can be estimated using assumption that these misalignments are coincident. This is, design orbit at BPM and QM can be derived.  
TUPPC019 Beam Dynamics Simulations of J-PARC Main Ring for Damage Recovery from the Tohoku Earthquake in Japan and Upgrade Plan of Fast Extraction Operation 1200
  • Y. Sato, K. Hara, S. Igarashi, T. Koseki, K. Ohmi, C. Ohmori
    KEK, Ibaraki, Japan
  • H. Hotchi
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  Magnets of Japan Proton Accelerator Research Complex (J-PARC) were shaken by the Tohoku Earthquake in Japan on March 11th, 2011. The alignment of J-PARC Main Ring (MR) received 20 mm displacement horizontally and 6 mm vertically. Beam dynamics simulations were performed to estimate the effect of the displacement on closed orbit distortions and beam loss in fast extraction (FX) operation of J-PARC MR. Based on the simulation results, we concluded that re-alignment of J-PARC MR was needed to achieve high-power beam. The re-alignment of MR was finished on October 28th, 2011. We also considered the effects of the earthquake on the upstream of MR to establish our upgrade plan, which was based on beam dynamics simulations optimizing collimator balance of injection beam transport (3-50BT) and MR, and RF patterns. J-PARC MR FX operation was resumed from December 2011.  
WEPPR004 Effect of Beam-beam Interactions on Stability of Coherent Oscillations in a Muon Collider 2940
  • K. Ohmi
    KEK, Ibaraki, Japan
  • Y. Alexahin
    Fermilab, Batavia, USA
  In order to achieve the peak luminosity of a muon collider in the 1035 cm-2 s-1 range the number of muons per bunch should be of the order of a few units of 1012 rendering the beam-beam parameter as high as 0.1 per IP. Such strong beam-beam interaction can be a source of instability if the working point is chosen close to a coherent beam-beam resonance. On the other hand, the beam-beam tune spread can provide a mechanism of suppression of the beam-wall driven instabilities. In this report the coherent instabilities driven by beam-beam and beam-wall interactions are studied with the help of BBSS code for the case of 1.5 TeV c.o.m muon collider.  
WEPPR005 Study of Electron Cloud Instability in Fermilab Main Injector 2943
  • K. Ohmi
    KEK, Ibaraki, Japan
  • R.M. Zwaska
    Fermilab, Batavia, USA
  Electron cloud has been observed in Fermilab main injector. Electron signal is enhanced near the transition. The slippage factor which suppress instabilities approach to zero at the transition. Instabilities must be most serious near the transition. The instability caused by the electron cloud is an important issue for high intensity operation and the future toward Project-X. Simulations of electron cloud instability near the transition is presented.  
WEYA02 Studies at CesrTA of Electron-Cloud-Induced Beam Dynamics for Future Damping Rings 2081
  • G. Dugan, M.G. Billing, K.R. Butler, J.A. Crittenden, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, K.G. Sonnad, H.A. Williams
    CLASSE, Ithaca, New York, USA
  • R.F. Campbell, R. Holtzapple, M. Randazzo
    CalPoly, San Luis Obispo, California, USA
  • J.Y. Chu
    CMU, Pittsburgh, Pennsylvania, USA
  • J.W. Flanagan, K. Ohmi
    KEK, Ibaraki, Japan
  • M.A. Furman, M. Venturini
    LBNL, Berkeley, California, USA
  • M.T.F. Pivi
    SLAC, Menlo Park, California, USA
  Funding: US National Science Foundation PHY-0734867, PHY-1002467, and PHY-1068662; US Dept. of Energy DE-FC02-08ER41538; and the Japan/US Cooperation Program.
Electron clouds can adversely affect the performance of accelerators, and are of particular concern for the design of future low emittance damping rings. Studies of the impact of electron clouds on the dynamics of bunch trains in CESR have been a major focus of the CESR Test Accelerator program. In this paper, we report measurements of coherent tune shifts, emittance growth, and coherent instabilities carried out using a variety of bunch currents, train configurations, beam energies, and transverse emittances, similar to the design values for the ILC damping rings. We also compare the measurements with simulations which model the effects of electron clouds on beam dynamics, to extract simulation model parameters and to quantify the validity of the simulation codes.
slides icon Slides WEYA02 [2.033 MB]  
WEPPR052 Octupole Magnets for the Instability Damping at the J-PARC Main Ring 3045
  • S. Igarashi, T. Koseki, K. Ohmi, M.J. Shirakata, H. Someya, T. Toyama
    KEK, Ibaraki, Japan
  • A. Ando
    J-PARC, KEK & JAEA, Ibaraki-ken, Japan
  Octupole magnets have been installed for the instability damping at the J-PARC main ring. The transverse instability was observed during the injection and acceleration periods and caused the beam losses. The chromaticity tuning and bunch-by-bunch feedback system have been applied to suppress the instability. Octupole magnets were considered to create a larger amplitude dependent betatron tune shift and to supply additional option for the instability damping. The side effects of the dynamic aperture reduction and the resonances have been studied.  
WEPPR054 Calculation of Coherent Wiggler Radiation using Eigenfunction Expansion Method 3048
  • D. Zhou, Y.H. Chin, K. Ohmi
    KEK, Ibaraki, Japan
  • G.V. Stupakov
    SLAC, Menlo Park, California, USA
  An analytic method originated by Y. H. Chin* was extended to calculate the electromagnetic fields and the longitudinal impedance due to coherent wiggler radiation (CWR) in a rectangular chamber. The method used dyadic Green functions based on eigenfunction expansion method in electromagnetic theory and was rigorous for the case of straight chamber. We re-derived the theory and did find the full expressions for the longitudinal impedance of a wiggler with finite length. With shielding of chamber, the CWR impedance indicated resonant properties which were not seen in the theory for CWR in free space.
* Y.H. Chin, LBL-29981, 1990.
THYB01 Beam-beam Limit in a Hadron Collider 3208
  • K. Ohmi
    KEK, Ibaraki, Japan
  Beam-beam limit phenomenon is observed in degradation of luminosity lifetime and/or beam life time in hadron colliders, especially in LHC. We focus the luminosity degradation in this paper. Various effects to degrade the luminosity grow severe in a high beam intensity. Coherent beam-beam instability, incoherent beam-beam emittance growth and those cupeled with lattice errors, external noises, intra-beam scattering. The beam-beam limit in an ideal machine and a machine with above errors is discussed with theory and simulation. Experimental results are reviewed and compare with the theory and simulations.  
slides icon Slides THYB01 [4.712 MB]  
THPPP005 Space Charge Effect in the Presence of x-y Coupling in J-PARC MR 3731
  • K. Ohmi
    KEK, Ibaraki, Japan
  • S. Hatakeyama
    JAEA/J-PARC, Tokai-mura, Japan
  It is crucial issue to suppress beam loss due to space charge force in J-PARC MR. We focus x-y coupling as a source of the beam loss. x-y coupling is measured by turn-by-turn beam position monitors in J-PARC MR. A space charge simulation under the measured x-y coupling evaluates the beam loss. Tolerance of x-y coupling and how to improve the beam loss are discussed.