• 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.

• W.X. Cheng, W.J. Corbett, A.S. Fisher
  SLAC, Menlo Park, California

A dual-axis, synchroscan streak camera was used to measure temporal bunch profiles in three storage rings at SLAC: the PEP-II low-energy and high-energy rings, and SPEAR3. At high currents, both PEP rings exhibit a transient shift in synchronous phase along the bunch train due to RF-cavity loading. Bunch length and profile asymmetry were measured along the train for a range of beam currents. To avoid the noise of a dual-axis sweep, we accumulated a single-axis synchroscan image over multiple turns while applying a 50-ns gate to the microchannel plate. To improve the extinction ratio, we synchronized this 2-kHz gate with an upstream mirror pivoting at 1 kHz to deflect light from other bunches off the axis. At SPEAR3 we compared the bunch length as a function of current for several lattices: achromatic, low-emittance and low momentum compaction. In the first two cases, resistive and reactive impedance components were extracted from the longitudinal bunch profiles. In the low-alpha configurations, we observed natural bunch lengths approaching the camera resolution, requiring special care to remove instrumental effects, and saw evidence of instability and periodic bursting.