Author: Ohmi, K.
Paper Title Page
MOPS005 Beam Dynamics Simulations of J-PARC Main Ring for Upgrade Plan of Fast Extraction Operation 598
 
  • Y. Sato, K. Hara, S. Igarashi, T. Koseki, K. Ohmi, C. Ohmori, M. Tomizawa
    KEK, Ibaraki, Japan
  • H. Hotchi
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
 
  Beam loss simulations under space charge effects are necessary to seek higher intensity proton beams. This paper presents simulations for fast extraction operation of Japan Proton Accelerator Research Complex (J-PARC) Main Ring. For upgrade plan, increasing protons per bunch and making higher repetition pattern are considered. Their optimal balance is discussed to minimize beam losses for aimed beam power considering space charge effects. We found that to optimize RF voltage pattern is a strong key to reduce beam losses for higher repetition. As benchmark works, we compare our simulations with the measured beam loss in our past operation.  
 
MOPS006 Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB 601
 
  • D.M. Zhou, K. Ohmi
    KEK, Ibaraki, Japan
  • A. Chao
    SLAC, Menlo Park, California, USA
 
  When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.  
 
MOPS007 Interference of CSR Fields in a Curved Waveguide 604
 
  • D.M. Zhou, K. Ohmi
    KEK, Ibaraki, Japan
 
  CSR fields generated by a bunched beam passing through a series of bending magnets may interfere with each other due the reflections of outer chamber wall. This kind of multi-bend interference causes sharp peaks and long-range tail in the CSR impedance and wake potentials, respectively. Using a dedicated computer code, CSRZ, we calculated the longitudinal CSR impedance in the SuperKEKB positron damping ring for purpose of demonstration. It was found that multi-bend interference may enhance the CSR fields within a distance comparable to the bunch length, which is typically in the order of several millimeters. A simple instability analysis was performed and it suggested that multi-bend interference might play a role in the single-bunch instabilities of small electron/positron rings.  
 
MOPS057 Beam-beam Interaction under External Force Oscillation 736
 
  • K. Ohmi
    KEK, Ibaraki, Japan
 
  Beam-ion interaction is strongly nonlinear. Response for external oscillation applied to beam shows characteristic feature. Simulations for external frequency scan becomes feasible for the recent computer power. We show the frequency response for beam-ion system in KEK-PF and recent low emittance rings.  
 
TUPC030 Recommendation for Mitigations of the Electron Cloud Instability in the ILC 1063
 
  • M.T.F. Pivi, L. Wang
    SLAC, Menlo Park, California, USA
  • L.E. Boon, K.C. Harkay
    ANL, Argonne, USA
  • J.A. Crittenden, G. Dugan, M.A. Palmer
    CLASSE, Ithaca, New York, USA
  • T. Demma, S. Guiducci
    INFN/LNF, Frascati (Roma), Italy
  • M.A. Furman
    LBNL, Berkeley, California, USA
  • K. Ohmi, K. Shibata, Y. Suetsugu, J. Urakawa
    KEK, Ibaraki, Japan
  • C. Yin Vallgren
    Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
 
  Funding: Work supported by the Director, Office of Science, High Energy Physics, U.S. DOE under Contract No. DE-AC02-76SF00515.
Electron cloud has been identified as one of the highest priority issues for the ILC Damping Rings (DR). A working group has evaluated the electron cloud effect and instability, and mitigation solutions for the electron cloud formation. Working group deliverables include recommendations for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron DR, which is presently assumed to be the 3.2km design. Detailed studies of a range of mitigation options including coatings, clearing electrodes, grooves and novel concepts, were carried out over the previous several years by nearly 50 researchers, and the results of the studies form the basis for the recommendation. The assessments of the benefits or risks associated with the various options were based on a systematic ranking scheme. The recommendations are the result of the working group discussions held at numerous meetings and during a dedicated workshop. The mitigation choices will be also presented in a more detailed report later in 2012. In addition, a number of items requiring further investigation were identified and studies will be carried out at CesrTA and other institutions.
 
 
TUPC098 Beam Profile Measurement using Flying Wire Monitors at the J-PARC Main Ring* 1239
 
  • S. Igarashi, K. Ohmi, Y. Sato, M.J. Shirakata, M. Tejima, T. Toyama
    KEK, Ibaraki, Japan
  • Y. Hashimoto, K. Satou
    J-PARC, KEK & JAEA, Ibaraki-ken, Japan
 
  Transverse beam profiles have been measured using flying wire monitors at the main ring of the Japan Proton Accelerator Research Complex (J-PARC). The flying wire is a beam profile monitor using a thin carbon fiber as a target. The beam is scanned with the wire target at the maximum speed of 5 m/s. The secondary particles from the beam-wire scattering are detected using a scintillation counter as a function of the wire position. The measurement has revealed a characteristic temporal change of the beam profile during the injection period of 120 ms. A multiparticle tracking simulation program, SCTR, taking account of space charge effects has successfully reproduced the beam profiles.  
 
WEPC108 CSR Impedance for an Ultrarelativistic Beam moving in a Curved Trajectory 2268
 
  • D.M. Zhou, K. Ohmi, K. Oide
    KEK, Ibaraki, Japan
 
  A dedicated computer code, CSRZ, has been developed to calculate the coherent synchrotron radiation (CSR) impedance for an ultrarelativistic beam moving in a curved trajectory. Following the pioneering work of T. Agoh and K. Yokoya*, the code solves the parabolic equation in the frequency domain in a curvilinear coordinate system. The beam is assumed to move along a vacuum chamber which has a uniform rectangular cross section but with variable bending radius. Using this code, we did investigations in calculating the longitudinal CSR impedance of a single and a series of bending magnets. The calculation results indicate that the shielding effect due to outer chamber wall can be well explained by a simple optical approximation model at high frequencies. The CSR fields reflected by the outer wall may interfere with each other in a long bending magnet and lead to sharp narrow peaks in the CSR impedance.
* T. Agoh and K. Yokoya, Phys. Rev. ST Accel. Beams, 7(5):054403 (2004).
 
 
THPZ008 Strong-strong Simulations for Super B Factories II 3696
 
  • K. Ohmi
    KEK, Ibaraki, Japan
 
  Trials for the strong-strong simulation for study of beam-beam effect in large Piwinski angle (LPA) collision adopted in Super B factories. So far a combination method of particle in cell method and soft-Gaussian model has been used. We now show complete strong-strong simulation for LPA collision scheme. Collisions between many slices of two bunches are evaluated by particle in cell method with shifted Green function.