RF feedback simulation results for PEP-II

Tighe, R.; Corredoura, P.

doi:10.1109/pac.1995.505653

Cited by 4 publications

(4 citation statements)

References 2 publications

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“…To study, model and optimize these LLRF, rf and beam systems several simulation methods have been developed. In this work we use a time-domain simulation method that was originally developed for PEP-II [10][11][12] and subsequently expanded for high-current operation in PEP-II [13,14], and study of the LHC and HL-LHC machines [15].…”

Section: Methodsmentioning

confidence: 99%

Beam gap transient analysis and mitigations in high-current storage rings for an electron-ion collider

Mastoridis

Fox

Guo

et al. 2020

Phys. Rev. Accel. Beams

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The U.S. electron ion collider will utilize high current electron and ion storage rings with many bunches and large rf systems. Because of the dissimilarity of the two rings, the rf transients created by gaps or variations in the current distributions will be very different in the two rings. These transients cause a shift in the synchronous phase of the beams as a function of rf bucket position, can impact the luminosity through shifts in longitudinal position of the IP, will affect the performance of the rf and LLRF control loops, and may require significant rf power overhead to control. A machine design that uses superconducting crab cavities will also have sensitivity to gap transients and synchronous phase variations along the bunch train with variations in crab cavity voltage seen by each bunch, since the high Q of the crab cavities precludes modulating them to compensate for the time of arrival shifts caused by the gap transients in the main rf systems. All these effects make the problem of managing gap transients crucial to the operation of the EIC. This work presents methods to study the dynamics of the rf and LLRF systems for these heavily beam loaded facilities. An illustrative machine design example is presented and used to investigate the expected magnitudes of the rf gap transients, and exploration of various possible remedies to match the gap transients in the two dissimilar EIC rings. In addition to the study of the power required and gap transients, this work also estimates longitudinal coupled-bunch instabilities due to the baseline cavity fundamental impedance. The work is motivated to emphasize the importance of tools and methods to estimate these effects as part of the early design phase of the Electron-Ion Collider or any high current storage ring design.

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Section: Methodsmentioning

confidence: 99%

Beam gap transient analysis and mitigations in high-current storage rings for an electron-ion collider

Mastoridis

Fox

Guo

et al. 2020

Phys. Rev. Accel. Beams

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“…The top level Simulink block system for PEP-II is shown in Figure 4.2. Some simulation elements were based on earlier work developed by R. Tighe [45]. The Matlab algorithms for the LHC implementation of the time-domain simulation have been published in [46].…”

Section: Model Descriptionmentioning

confidence: 99%

“…One application of this simulation is that the free growth rates can then be compared to the expected effective feedback damping rate ∆ l from the longitudinal loop, providing a quantitative measure of stability margins for each mode (in contrast to earlier work [45]). The effective feedback damping rate ∆ l is used as a metric because it is in the first order proportional to the beam current, until other effects become dominant at higher currents.…”

Section: Growth Rate Measurement Techniquesmentioning

confidence: 99%

Radio Frequency Station - Beam Dynamics Interaction in Circular Accelerators

Mastoridis

2010

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The longitudinal beam dynamics in circular accelerators is mainly defined by the interaction of the beam current with the accelerating Radio Frequency (RF) stations.For stable operation, Low Level RF (LLRF) feedback systems are employed to reduce coherent instabilities and regulate the accelerating voltage. The LLRF system design has implications for the dynamics and stability of the closed-loop RF systems as well as for the particle beam, and is very sensitive to the operating range of accelerator currents and energies. Stability of the RF loop and the beam are necessary conditions for reliable machine operation.This dissertation describes theoretical formalisms and models that determine the longitudinal beam dynamics based on the LLRF implementation, time domain simulations that capture the dynamic behavior of the RF station-beam interaction, and measurements from the Positron-Electron Project (PEP-II) and the Large Hadron Collider (LHC) that validate the models and simulations. These models and simulations are structured to capture the technical characteristics of the system (noise contributions, non-linear elements, and more). As such, they provide useful results and insight for the development and design of future LLRF feedback systems. They also provide the opportunity to study diverse longitudinal beam dynamics effects such as coupled-bunch impedance driven instabilities and single bunch longitudinal emittance growth.Coupled-bunch instabilities and RF station power were the performance limiting effects for PEP-II. The sensitivity of the instabilities to individual LLRF parameters, the effectiveness of alternative operational algorithms, and the possible tradeoffs between RF loop and beam stability were studied. New algorithms were implemented, iv with significant performance improvement leading to a world record current during the last PEP-II run of 3212 mA for the Low Energy Ring.Longitudinal beam emittance growth due to RF noise is a major concern for LHC. Simulations studies and measurements were conducted that clearly show the correlation between RF noise and longitudinal bunch emittance, identify the major LLRF noise contributions, and determine the RF component dominating this effect.With these results, LHC upgrades and alternative algorithms are evaluated to reduce longitudinal emittance growth during operations.The applications of this work are described with regard to future machines and analysis of new technical implementations, as well as to possible future work which would continue the directions of this dissertation.v

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“…The RF systems in PEP-II use room temperature copper cavities, with HOM damping and complex LLRF feedback loops to control the impedances seen by the circulating beam [1,2]. This RF system has been successfully operated at design currents, though the growth rates of low longitudinal modes within the RF system bandwidth have been measured to be significantly (factors of 5 to 20) higher than estimated by simulations during system design [3]. To control these low longitudinal modes the systems have been using a processing channel [4] to extract low mode longitudinal motion signals from the broadband control path and inject this correction signal in the RF system itself, using the klystrons as a power source to make correction fields.…”

Section: Introductionmentioning

confidence: 99%