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Title: Tracking Studies of a Higher-Harmonic Bunch-Lengthening Cavity for the APS Upgrade

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Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: 6th International Particle Accelerator Conference (IPAC 2015), 05/03/15 - 05/08/15, Richmond, VA
Country of Publication:
United States

Citation Formats

Borland, M., Berenc, T., Lindberg, R., and Xiao, A. Tracking Studies of a Higher-Harmonic Bunch-Lengthening Cavity for the APS Upgrade. United States: N. p., 2015. Web.
Borland, M., Berenc, T., Lindberg, R., & Xiao, A. Tracking Studies of a Higher-Harmonic Bunch-Lengthening Cavity for the APS Upgrade. United States.
Borland, M., Berenc, T., Lindberg, R., and Xiao, A. 2015. "Tracking Studies of a Higher-Harmonic Bunch-Lengthening Cavity for the APS Upgrade". United States. doi:.
title = {Tracking Studies of a Higher-Harmonic Bunch-Lengthening Cavity for the APS Upgrade},
author = {Borland, M. and Berenc, T. and Lindberg, R. and Xiao, A.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 1

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  • Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be curedmore » with more effective HOM damping or a longitudinal feedback system.« less
  • The proposed Advanced Photon Source (APS) multibend achromat (MBA) lattice includes a passive bunchlengthening cavity to alleviate lifetime and emittance concerns. Feedback in the main radio-frequency (rf) system affects the overall impedance presented to the beam in this double rf system. To aid beam stability studies, a realistic model of rf feedback has been developed and implemented in elegant and Pelegant.
  • It has been suggested that the phase of the beam excited voltage in the harmonic cavity can be controlled by detuning its resonant frequency from the beam current harmonic. Unfortunately the detuning needed to flatten the acceleration waveform also corresponds to the region of Robinson instability for the harmonic cavity. Therefore, lengthening the bunch may be followed by large amplitude synchrotron oscillation of the bunch center of mass. Bunch lengthening is discussed in this note from several points of view. There follows a simple review of single electron oscillations in a quartic potential. Then equations are developed for the coupledmore » oscillations of a cavity and a rigid bunch as a fully nonlinear, time dependent initial value problem. Next, a computer program that solves these equations for one, two or more cavities, with and without externally driven fields, is described and some simulations of the harmonic cavity interaction are shown. Finally, the fully nonlinear equations are linearized to derive a dispersion relation for the case of beam excitation in the harmonic cavity. 6 refs., 5 figs.« less
  • NSLS-II is a new ultra-bright 3 GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. Ion clearing gaps are required to suppress ion effects on the beam. The natural bunch length of 3mm is planned to be lengthened by means of a third harmonic cavity in order to increase the Touschek limited lifetime. After an extensive investigation of different cavity geometries, a passive, superconducting two-cell cavity has been selected for prototyping. The cavity is HOM damped with ferrite absorbers on the beam pipes.more » The two-cell cavity simplifies the tuner design, compared to having two independent cells. Tradeoffs between the damping of the higher order modes, thermal isolation associated with the large beam tubes, and overall cavity length are described. A copper prototype has been constructed, and measurements of fundamental and higher order modes will be compared to calculated values.« less