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Funakoshi, Y.

Paper Title Page
MOPLS030 Recent Progress of KEKB 610
 
  • Y. Funakoshi
    KEK, Ibaraki
  
  We summarize the machine operation of KEKB during the past one year, focusing on progress for this period.  
MOPLS031 Beam Orbit Control System for the KEKB Crab Cavities 613
 
  • M. Masuzawa, Y. Funakoshi, T.T. Nakamura, J.-I. Odagiri
    KEK, Ibaraki
  
  KEKB is an electron-positron collider with an 8 GeV electron ring (HER) and a 3.5 GeV positron ring (LER). The two beams currently collide at one interaction point with a finite horizontal crossing angle of 11 mrad. The design luminosity of 10 /nb/sec was first reached in May 2003 and the peak luminosity exceeded 16 /nb/sec in December 2005. Simulations predict a luminosity boost if a crab crossing scheme is introduced. The installation of two superconducting crab cavities, one in each ring, is scheduled in March 2006 in order to implement the crab crossing scheme. For stable operation, the horizontal beam position in the crab cavity must be carefully controlled. This is needed to avoid loss of control of the crabbing mode field due to beam loading. A beam position feedback system at the crab cavity has been prepared and tested. Its performance will be discussed in this report.  
MOPLS033 Beam-beam Limit and Feedback Noise 619
 
  • K. Ohmi, Y. Funakoshi, S. Hiramatsu, K. Oide, M. Tobiyama
    KEK, Ibaraki
  
  Beam-beam interaction is strongly nonlinear, therefore particles in the beam experience chaotic motion. A small noise can be enhanced by the chaotic nature, with the result that unexpected emittance growth can be observed. We study the noise of transverse bunch by bunch feedback system and related luminosity degradation. Similar effects caused by crab cavity noise is also discussed.  
THPCH050 Further Studies on Betatron Sidebands due to Electron Clouds 2898
 
  • J.W. Flanagan, H. Fukuma, Y. Funakoshi, S. Hiramatsu, T. Ieiri, H. Ikeda, K. Ohmi, K. Oide, M. Tobiyama
    KEK, Ibaraki
  
  We have observed vertical betatron sidebands in the transverse beam spectra of positron bunches at the KEKB LER which are associated with the presence of electron clouds in single-beam studies*, and which are also associated with a loss of luminosity when the KEKB beams are in collision**. The sidebands may be signals of a fast head-tail instability due to short-range wakes within the electron cloud, providing a diagnostic for exploring the mechanism for transverse beam blow-up due to electron clouds. We report here on further studies on the behavior of the sidebands under varying beam conditions, including varying initial beam size below the beam blow-up threshold, chromaticity, RF voltage and fill pattern.

*J. W. Flanagan et al. PRL 94, 054801 (2005).**J. W. Flanagan et al. Proc. PAC05, p. 680 (2005).