WEOFI  —  Beam Dynamics and Electromagnetic Fields   (28-Jun-06   11:30—12:30)

Chair: P. Emma, SLAC, Menlo Park, California

   
Paper Title Page
WEOFI01 Beam Dynamics Measurements in the Vicinity of a Half-integer Resonance 1902
 
  • T. Ieiri, J.W. Flanagan, H. Fukuma, H. Ikeda, Y. Ohnishi, K. Oide, M. Tobiyama
    KEK, Ibaraki
 
  The operating point of the betatron tune set near a half-integer is a crucial parameter to make high luminosity in electron/positron ring colliders. Dynamic beam-beam effects would change the optics parameters of the colliders, depending on the betatron tune and the beam-beam parameter. On the other hand, existence of the half-integer stopband makes the beam unstable. Therefore, beam behavior near a half-integer might provide interesting issues from the viewpoint of beam dynamics. We measured a frequency response of the beam across a half-integer for measuring the betatron tune at KEKB. A sharp spike just at a half-integer was observed in the tune spectrum. We believe that the spectrum would be a nonlinear resonance caused by some off-momentum particles in a bunch, not by a coherent motion of a whole bunch. The horizontal beam size measured using a synchrotron radiation monitor indicated a slight increase when the tune approached a half-integer. The variations in the beam size are discussed, considering both dynamic beam-beam effects and a beta beat due to the half-integer stopband.  
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WEOFI02 RF Phase Modulation Studies at the LNLS Electron Storage Ring 1905
 
  • N.P. Abreu, R.H.A. Farias, P.F. Tavares
    LNLS, Campinas
 
  In this work we present a set of measurements of the effectiveness of RF phase modulation on the second harmonic of the RF frequency as a mechanism to damp longitudinal coupled-bunch instabilities. We also propose a theoretical model of the damping mechanism, in which the increase of the spread in synchrotron frequencies inside the bunches produced by phase modulation is responsible for damping the centroid dipolar coherent motion caused by an external excitation, which could be a Higher Order Mode (HOM) of the RF cavities driving the coupled bunch motion. We measured the coherent synchrotron oscillation damping of a single bunch under two circumstances, with and without phase modulation, and determined the amount of extra damping due to the modulation. With this experiment we could also measure the frequency of small oscillations around the stable islands formed by phase modulation and its behavior when the RF phase modulation amplitude and frequency are changed. We performed measurements of Beam Transfer Function (BTF) to observe the effects of phase modulation over the stable area for coherent oscillations and compared the results with a theoretical model.  
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WEOFI03 Beam Dynamics Simulation in e- Rings in SRFF Regime 1908
 
  • L. Falbo
    INFN-Pisa, Pisa
  • D. Alesini
    INFN/LNF, Frascati (Roma)
  • M. Migliorati
    Rome University La Sapienza, Roma
 
  The concept of strong RF focusing has been recently proposed to obtain locally short bunches in electron/positron colliders, by modulating the longitudinal bunch dimensions along the rings. To study the single bunch dynamics, a macroparticle numerical code has been written which simulates the effects of the objects generating broad band impedance along the ring and the effects of the coherent synchrotron radiation in dipoles and wigglers. The obtained results are shown and discussed.  
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