• T. Mastorides, J.D. Fox, C.H. Rivetta, D. Van Winkle
  SLAC, Menlo Park, California

The growth rates of the longitudinal higher-order impedance-driven modes beam have greatly increased since the initial PEP-II design and commissioning. This increase is attributed to the addition of 8 1.2 MW RF klystrons and 12 accelerating cavities, as well as to operations at twice the design current and almost four times the luminosity. As a result, the requirement for the longitudinal feedback has greatly increased since the design, and the feedback filters and control schemes have evolved during PEP-II operations. In this paper growth and damping rate data for the high-order cavity driven beam modes are presented and compared with historical estimates and measurements. The available margins for the 4 A LER and 2.2 HER ring case at PEP-II are estimated, and suggestions for reliable operation are also presented. The effect of noise in the feedback processing channel is also studied. Data for different gain configurations of the filter from PEP and other accelerators are presented. These data show the tradeoff between instability control and higher noise levels.

• P.S. Prieto, C.I. Briegel, R. Dysert, N. Eddy, B.J. Fellenz, E. Gianfelice-Wendt, W. Haynes, D.J. Nicklaus, R. Rechenmacher, D. Slimmer, D.C. Voy, M. Wendt
  Fermilab, Batavia
• J.C. Frisch, J. May, D.J. McCormick, J. Nelson, A. Seryi, T.J. Smith, M. Woodley
  SLAC, Menlo Park, California
• N. Terunuma, J. Urakawa
  KEK, Ibaraki

A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility (ATF) damping ring is currently in progress, carried out by a KEK/FNAL/SLAC collaboration under the umbrella of the global ILC R&D effort. The upgrade consists of a high resolution, high reproducibility read-out system, based on analog and digital downconversion techniques, digital signal processing, also implementing a novel automatic gain error correction schema. The technical concept and realization, as well as preliminary results of the beam studies are presented.