Keyword: damping
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TUB2CO03 Fokker-Planck Analysis of Transverse Collective Instabilities in Electron Storage Rings ion, impedance, simulation, synchrotron 290

• R.R. Lindberg
ANL, Argonne, Illinois, USA

Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We expand on the work of Suzuki*, writing out the linear matrix equation including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. The eigenvalues and eigenvectors determine the collective stability of the beam, and we show that the predicted threshold current for transverse instability and the profile of the unstable agree well with tracking simulations. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticity requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.
* T. Suzuki, Particle Accel., 12, 237 (1982)

Slides TUB2CO03 [1.717 MB]
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-TUB2CO03
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TUPOA17 A Longitudinal Digital Mode Damper System for the Fermilab Booster ion, booster, cavity, feedback 320

• N. Eddy, W. Pellico, A. Semenov, D.C. Voy, A.M. Waller
Fermilab, Batavia, Illinois, USA

Funding: This work was supported by the U.S. Department of Energy under contract No. DE-AC02-07CH11359.
The Fermilab Booster accelerates bunches and accelerates proton beams from 400 MeV to 8 GeV. During the acceleration the Radio Frequency (RF) cavities are swept from 38MHz to 52.8MHz and requires crossing through transition where accelerating phase is shifted 90 degrees. In order to keep the beam stable and minimize losses and emittance growth a longitudinal damping system is required. This has traditionally been done by dedicated analog electronics designed to operate on specific beam modes for frequencies of instabilities. A complete digital implementation has been developed for this same purpose. The new digital system features and performance are detailed.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-TUPOA17
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TUPOB22 Dependence of the Coupling of Dipole Motion From Bunch to Bunch Caused by Electron Clouds at CesrTA Due to Variations in Bunch Length and Chromaticity ion, electron, positron, dipole 538

• M.G. Billing, L.Y. Bartnik, M.J. Forster, N.T. Rider, J.P. Shanks, M.B. Spiegel, S. Wang
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
• R. Holtzapple
CalPoly, San Luis Obispo, California, USA
• E.C. Runburg
University of Notre Dame, Indiana, USA

The Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) has been utilized to probe the interaction of the electron cloud with a 2.1 GeV stored positron beam. Recent experiments have characterized any dependence of beam'electron cloud (EC) interactions on the bunch length (or synchrotron tune) and the vertical chromaticity. The measurements were performed on a 30-bunch positron train with 14 nsec spacing between bunches, at a fixed current of 0.75 mA/bunch. The dynamics of the stored beam, in the presence of the EC, was quantified using 20 turn-by-turn beam position monitors in CESR to measure the correlated bunch-by-bunch dipole motion. In this paper we report on the observations from these experiments and analyze the coupling of di-pole motion from bunches within the train to subsequent bunches, caused by the EC.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-TUPOB22
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TUPOB45 A Model to Simulate the Effect of a Transverse Feedback System on Single Bunch Instability Thresholds ion, simulation, feedback, kicker 596

• G. Bassi, A. Blednykh, V.V. Smaluk
BNL, Upton, Long Island, New York, USA
• Z. Yang
Auburn University, Auburn, USA

Funding: DOE Contract No. DE-AC02-98CH10886
A model to simulate the effect of a transverse feedback system is implemented in SPACE, a parallel, self-consistent code for collective effects. As an application, we discuss single bunch instability thresholds in the NSLS-II storage ring and compare the numerical results with measurements.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-TUPOB45
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WEA4CO03 Intrinsic Landau Damping of Space Charge Modes at Coupling Resonance ion, resonance, coupling, ECR 863

• A. Macridin, J.F. Amundson, A.V. Burov, P. Spentzouris, E.G. Stern
Fermilab, Batavia, Illinois, USA

Funding: This work was performed at Fermilab, operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Using Synergia accelerator modeling package and Dynamic Mode Decomposition technique, the properties of the first transverse dipole mode in Gaussian bunches with space charge are compared at transverse coupling resonance and off-resonance. The Landau damping at coupling resonance and in the strong space charge regime is a factor of two larger, while the mode's tune and shape are nearly the same. While the damping mechanism in the off-resonance case fits well with the classical Landau damping paradigm, the enhancement at coupling resonance is due to a higher order mode-particle coupling term which is modulated by the amplitude oscillation of the resonance trapped particles.

Slides WEA4CO03 [3.422 MB]
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-WEA4CO03
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WEPOB01 Lower Emittance Lattice for the Advanced Photon Source Upgrade Using Reverse Bending Magnets ion, lattice, emittance, quadrupole 877

• M. Borland, T.G. Berenc, R.R. Lindberg, V. Sajaev, Y.P. Sun
ANL, Argonne, Illinois, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
he Advanced Photon Source (APS) is pursuing an upgrade to the storage ring to a hybrid seven-bend-achromat design*. The nominal design provides a natural emittance of 67 pm. By adding reverse dipole fields to several quadrupoles**, we can reduce the natural emittance to 41 pm while simultaneously providing more optimal beta functions in the insertion devices. The improved emittance results from a combination of increased energy loss per turn and a change in the damping partition. At the same time, the nonlinear dynamics performance is very similar, thanks in part to increased dispersion in the sextupoles. This paper describes the properties, optimization, and performance of the new lattice.
* L. Farvacque et al., IPAC13, 79 (2013).
** J.P. Delahaye \em et al., PAC89, 1611 (1990); A. Streun, NIM A 737, 148 (2014).

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-WEPOB01
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