Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

The proposed next generation accelerator and synchrotron light facilities will require active feedback systems to control multi-bunch instabilities. These feedback systems must operate in machines with thousands of circulating bunches and with short (2-4 ns) interbunch intervals. The functional requirements for transverse (betatron) and longitudinal (synchrotron) feedback systems are presented. Several possible implementation options are discussed and system requirements developed. Results are presented from a digital signal processing based synchrotron oscillation damper operating at the SSRL/SLAC SPEAR storage ring.

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“…The saturated processing has been shown to suppress the growth of coherent instabilities from injection-like initial conditions. 1,13 "ri…”

Section: Signal Processing Optionsmentioning

confidence: 99%

Multibunch feedback—Strategy, technology, and implementation options

Fox

Eisen

Hindi

et al. 1992

AIP Conference Proceedings

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“…The limiting function allows injection (and large-amplitude excitation of the injected bunch) while still damping neighboring bunches in a linear regime. The saturated processing has been shown to suppress the growth of coherent instabilities from injection-like initial conditions [12].…”

Section: N Signal Processing Optionsmentioning

confidence: 99%

Feedback control of coupled-bunch instabilities [particle accelerators]

Fox

Eisen

Hindi

et al.

Proceedings of International Conference on Particle Accelerators

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The next generation of synchrotron light murces and particle accelerators will require active feedback systems to control multi-bunch instabilities [1,2,3]. Stabilizing hundreds or thousands of potentially unstable modes in these accelerator designs presents many technical challenges.Feedback system to stabiliee' coupled-bunch instabilities may be understood in the frequency domain (modeb a d f d b a c k ) or in the time domain (bunch-by-bunch feedback). In both approaches an external amplifier system is wed to create damping fields that prevent coupledbunch d a t i o n s from growing without bound. The system requirements for transverse (betatron) and longitudinal (synchrotron) feedback are presented, and possible implementation options developed. Feedback system designs based on digital signal-processing techniques are described. Experimental results are shown from a synchrotron oecillation damper in the SSRL/SLAC storage ring SPEAR that uses digital signal-processing techniques. I. A CLASSICAL ANALOGYThe dynamics of coupled-bunch motion can be illustrated by the-mechanical analog of coupled pendulums. In Figure 1 this aniogy is applied to the charged particle bunches in a storage Sng, with each pendulum representing the oscillatory motion (synchrotron or betatron) of a bunch. The coupling springs represent the impedances of the accelerating cavities and vacuum structures. Bunchj+i and subsequent bunches are driven from the excitations of bunchi, much as pendulumj drives pendulumsj+k through the coupling springs [4]. xi' hl 1+2 k3 695 -' 7U?& Figure 1. Coupled pendulum analogy. * Work supported by Department of Energy contract DE-AC03-76s F005 1 5.In a storage ring with many bunches and many external higher-order mode resonators, the resulting motion can be found by coherently summing the driving terms and considering the periodic excitation due to the orbit of the particles [5,6]. Unstable, growing Oscillatory motion can result, in which the motion of a few bunches can excite an unstable normal mode. Thee instabilities can be controlled by reducing the magnitude and number of external, parasitic higher-order modes, carefully controlling the resonant frequenciea of the parssitic resonators to avoid coupling to the beam, and by adding damping to the motion of each bunch.External beam-feedback systems do the latter. In the analogy of Figure 1, they act to add dashpots to each pendulum. Each bunch can be thought of aa a harmonic cecillator obeying the equation of motion where wo is the bunch synchrotron (longitudinal) or betatron (transverse) frequency, f(t) is an external driving term and y is a damping term. An external feedback system acts on the beam, contributing to this damping term, and allowing control of external disturbances ,f(t) driving the beam. 11. TIME DOMAIN VS. FREQUENCY DOMAIN PROCESSINGThe action of the feedback system can be understood in either the time or frequency domains [7]. If each unstable normal-mode frequency is identified, a single narrowband feedback channel for each mode can be impl...

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“…A time-domain computer simulation of the longitudinal motion of a multibunch beam [3] ,has been used in order to study the performance of the ALS LFB system under a variety of conditions. The simulation is useful for studying many issues which theoretical methods on coupledbunch beam stability can only estimate.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the ALS longitudinal multibunch feedback system

Byrd

Proceedings of International Conference on Particle Accelerators

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Longitudinal coupled bunch growth rates in the Advanced Light Source (ALS), a 1.5 GeV electron storage ring for producing synchrotron radiation, indicate the need for damping via a feedback (FB) system. The design of the system is based on the proposed PEP-II longitudinal FB system which uses a digital filter to provide the required phase and amplitude response. We report the results of a detailed computer simulation of the ,FB system including single particle longitudinal beam dynamics, measured RF cavity fundamental and higher order modes, and response of major FB components such as the power amplifier and kicker. The simulation addresses issues such as required FB power and gain, noise, digital filter effects, and varying initial bunch conditions.

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Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

Cited by 6 publications

References 1 publication

Multibunch feedback—Strategy, technology, and implementation options

Multibunch feedback—Strategy, technology, and implementation options

Feedback control of coupled-bunch instabilities [particle accelerators]

Simulation of the ALS longitudinal multibunch feedback system

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