• J. Xu, J.D. Fox, D. Van Winkle
  SLAC, Menlo Park, California

Bunched beam signals from button-style Beam-Position Monitor (BPM) electrodes can have spectral content up to 20-30 GHz and time-domain structure of narrow impulsive trains. Multi-bunch feedback systems require receivers to process such beam signals and generate ΔX, ΔY, and ΔZ beam motion signals. To realistically test these receivers, we have developed a 4-bunch programmable impulse generator, which mimics the signals from a multi-bunch beam. Based on step-recovering diode techniques, this simulator produces modulated 100-ps impulse signals. The programmable nature of the system allows us to mimic Betatron and Synchrotron signals from 4 independent bunches with adjustable beam spacing from 1 to 8 ns. Moreover, we can observe nonlinear effects and study the noise floor and the resolution of the receiver. This paper presents the design of the system and shows typical achieved results.

J. Xu, J.D. Fox, D. Van Winkle
Stanford Linear Accelerator Center
Stanford, CA 94309, U.S.A.

• 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. Gasior, A. Boccardi, O.R. Jones, R.J. Steinhagen
  CERN, Geneva

The unprecedented intensity and energy of the LHC proton beams will require an excellent control of the transverse beam dynamics in order to limit particle loss in the superconducting systems. Due to restricted tolerances of the machine protection system and tight beam emittance blow-up budget only small beam excitation is allowed, making precise measurements of the transverse beam parameters very challenging. This paper describes the systems measuring the tune, coupling and chromaticity of the LHC beams. As manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that can be safely and reliably operated only with automatic feedback systems for controlling the transverse beam dynamics. An outline of these systems is also presented.

• V. Kamerdzhiev, V.A. Lebedev, A. Semenov
  Fermilab, Batavia

Monitoring the tunes of individual proton and antiproton bunches is crucial to understanding and mitigating the beam-beam effects in the Tevatron collider. To obtain a snapshot of the evolving bunch-by-bunch tune distribution a simultaneous treatment of all the bunches is needed. The digital tune monitor (DTM) was designed to fulfill these requirements. It uses a standard BPM as a pickup. The vertical proton monitor is installed and allows us to gain valuable operational experience. A major upgrade is underway to implement an automatic bunch-by-bunch gain and offset adjustment to maintain the highest possible sensitivity under real operational conditions. We present the concept of the DTM along with its technical realization as well as the latest experimental results. Major challenges from the design and operation point of view are discussed.