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Observation Of Vertical Beam Blow-Up In Kekb Low Energy Ring

By Fukuma Akai Akasaka, M. Tejima, M. Tobiyama, T. Tsuboyama, N. Yamamoto, M. Yoshida, S. Yoshimoto and C. H. Yu


This paper describes an experimental study of the enlargement of the vertical beam size observed in single beam operation at the KEKB LER. 1 INTRODUCTION A blow-up of the vertical beam size is observed in the KEKB positron ring (LER)[1]. The beam size as a function of beam current starts to increase at a threshold beam current and is almost doubled at 300 mA under typical operating conditions. Thus the blow-up is one of the most serious problems limiting the luminosity of KEKB. The main characteristics of the blow-up observed in early operation period are summarized as: 1) the blow-up is a single beam and a multi-bunch effect; 2) the blow-up has a threshold intensity which is determined roughly by (bunch current)/(bunch spacing); 3) no dipole oscillation has been observed when the vertical chromaticity is high (5 to 8), though the chromaticity is as low as 2 and the bunch feedback system is turned off, a vertical dipole oscillation is excited; 4) the blow-up is almost independent of ..

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