• T. Obina, J.W. Flanagan, T. Honda, T.M. Mitsuhashi, M. Tadano, M. Tobiyama
  KEK, Ibaraki
• W.X. Cheng, J.D. Fox
  SLAC, Menlo Park, California
• D. Teytelman
  Dimtel, San Jose

A bunch-by-bunch feedback system has been developed to suppress longitudinal coupled-bunch instabilities at the KEK-PF. A generalpurpose signal processor, called iGp, has been developed by a collaboration among KEK, SLAC and INFN-LNF. A longitudinal kicker based on the DAΦNE-type over-damped cavity was designed and installed in the ring. The whole feedback loop was closed at the end of June 2007. The longitudinal dipole-mode instabilities are successfully suppressed up to 430 mA. The performance and the details of the system will be presented in this paper.

• T. Ieiri, H. Fukuma, Y. Funakoshi, K. Ohmi, M. Tobiyama
  KEK, Ibaraki

Recent high-intensity machines with a multi-bunched beam demand bunch-by-bunch beam diagnostics. Especially in a colliding machine such as KEKB, the beam-beam effect is one of the main issues from the viewpoint of beam dynamics. Recently, KEKB achieved an effective head-on collision by using of crab cavities and gained a higher specific luminosity. A gated beam-position monitor, being capable of measuring the beam phase as well as the transverse position of a specific bunch in a bunch train, has been developed and is used to measure a beam-beam kick at KEKB. The monitor detects the beam position with a resolution of a few micrometers. The monitor demonstrated the effect of the crab cavities and estimated the effective horizontal beam size at the interaction point from a linear part of a beam-beam kick. Moreover, the monitor detected a displacement of the horizontal beam position along a bunch train under the crabbing collision. We estimate that the horizontal displacement is caused by an asymmetric kick of the crab cavities, which is based on a bunch-by-bunch phase modulation due to transient beam loading.

• M. Tobiyama, J.W. Flanagan, T. Obina, M. Tadano
  KEK, Tsukuba

Button electrodes with good time response are essential for the bunch-by-bunch feedback / diagnostic systems needed for future short-bunch-spacing accelerators, such as energy recovery linacs (ERL) or a super B-factory. The impedance matching and time-domain response of electrodes, particularly around the vacuum seal, have been studied using 3-D electromagnetic codes (HFSS, MAFIA and GdfidL). Several candidates have been fabricated to examine the tolerance for mechanical pressures and heat stress due to the welding process. The real beam response from a short bunch has also been studied using a test-beam line at the KEK-PF injector beam transport section.