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Title: Luminosity Variations Along Bunch Trains in PEP-II

Abstract

In the spring of 2005 after a long shut-down, the luminosity of the B-Factory PEP-II decreased along the bunch trains by about 25-30%. There were many reasons studied which could have caused this performance degradation, like a bigger phase transient due to an additional RF station in the Low-Energy-Ring (LER), bad initial vacuum, electron cloud, chromaticity, steering, dispersion in cavities, beam optics, etc. The initial specific luminosity of 4.2 sloped down to 3.2 and even 2.8 for a long train (typical: 130 of 144), later in the run with higher currents and shorter trains (65 of 72) the numbers were more like 3.2 down to 2.6. Finally after steering the interaction region for an unrelated reason (overheated BPM buttons) and the consequential lower luminosity for two weeks, the luminosity slope problem was mysteriously gone. Several parameters got changed and there is still some discussion about which one finally fixed the problem. Among others, likely candidates are: the LER betatron function in x at the interaction point got reduced, making the LER x stronger, dispersion reduction in the cavities, and finding and fixing a partially shorted magnet.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
907712
Report Number(s):
SLAC-PUB-12521
TRN: US0703362
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Prepared for European Particle Accelerator Conference (EPAC 06), Edinburgh, Scotland, 26-30 Jun 2006
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; BEAM OPTICS; BETATRONS; CAVITIES; ELECTRONS; LUMINOSITY; PERFORMANCE; TRANSIENTS; Accelerators,ACCPHY

Citation Formats

Decker, F.J., Boyes, M., Colocho, W.S., Novokhatski, A., Sullivan, M.K., Turner, J.L., Weathersby, S.P., Wienands, U., Yocky, G., and /SLAC. Luminosity Variations Along Bunch Trains in PEP-II. United States: N. p., 2007. Web.
Decker, F.J., Boyes, M., Colocho, W.S., Novokhatski, A., Sullivan, M.K., Turner, J.L., Weathersby, S.P., Wienands, U., Yocky, G., & /SLAC. Luminosity Variations Along Bunch Trains in PEP-II. United States.
Decker, F.J., Boyes, M., Colocho, W.S., Novokhatski, A., Sullivan, M.K., Turner, J.L., Weathersby, S.P., Wienands, U., Yocky, G., and /SLAC. Fri . "Luminosity Variations Along Bunch Trains in PEP-II". United States. doi:. https://www.osti.gov/servlets/purl/907712.
@article{osti_907712,
title = {Luminosity Variations Along Bunch Trains in PEP-II},
author = {Decker, F.J. and Boyes, M. and Colocho, W.S. and Novokhatski, A. and Sullivan, M.K. and Turner, J.L. and Weathersby, S.P. and Wienands, U. and Yocky, G. and /SLAC},
abstractNote = {In the spring of 2005 after a long shut-down, the luminosity of the B-Factory PEP-II decreased along the bunch trains by about 25-30%. There were many reasons studied which could have caused this performance degradation, like a bigger phase transient due to an additional RF station in the Low-Energy-Ring (LER), bad initial vacuum, electron cloud, chromaticity, steering, dispersion in cavities, beam optics, etc. The initial specific luminosity of 4.2 sloped down to 3.2 and even 2.8 for a long train (typical: 130 of 144), later in the run with higher currents and shorter trains (65 of 72) the numbers were more like 3.2 down to 2.6. Finally after steering the interaction region for an unrelated reason (overheated BPM buttons) and the consequential lower luminosity for two weeks, the luminosity slope problem was mysteriously gone. Several parameters got changed and there is still some discussion about which one finally fixed the problem. Among others, likely candidates are: the LER betatron function in x at the interaction point got reduced, making the LER x stronger, dispersion reduction in the cavities, and finding and fixing a partially shorted magnet.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 18 00:00:00 EDT 2007},
month = {Fri May 18 00:00:00 EDT 2007}
}

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  • By scanning gated cameras and gated tune monitors across the bunch pattern during normal colliding-bunch operation of PEP-II, the tunes and beam sizes of individual bunches were measured simultaneously in the high and low energy storage rings of PEP-II. The measurements were made with 1561 colliding bunches in PEP-II, arranged in trains of 66 bunches, with each bunch in the train separated by 4.2 ns. The tune and beam size measurements were correlated with the current, luminosity, and specific luminosity of the bunch. The results show a vertical tune shift at the start and end of the mini-trains, a luminositymore » droop along the mini-train, and specific luminosity drop in the first and last bunches of the train, since they experience a different parasitic crossing on either side of the interaction point (IP).« less
  • No abstract prepared.
  • The PEP II B Factory requires a feedback system to damp out longitudinal synchrotron oscillations. A time-domain bunch-by-bunch feedback system has been proposed in which each bunch is treated as an oscillator being driven by disturbances from the other bunches. The phase is detected, filtered, and the feedback correction signal is applied by the kicker. Since we are damping energy oscillations using measurements of phase, the required feedback signal must be proportional to the amplitude of the phase oscillations but phase shifted by 90 degrees. This signal must be calculated for each of the 1658 bunches, in parallel. In themore » original proposal, it was estimated that a farm of approximately 480 digital signal processors (DIPS) would be required to implement the feedback system. However, using the technique of downsampling, this number can be reduced to about 50 DIPS. In what follows, we will briefly explain the basic idea of downsampling and its implementation.« less
  • The proposed PEP II B factory at SLAC requires a feedback to damp out longitudinal synchrotron oscillations. A time domain, downsampled, bunch-by-bunch feedback system in which each bunch is treated as an oscillator being driven by disturbances from other bunches is presented as we review the evolution of the system design. Results from a synchrotron oscillation damping experiment conducted at the SLAC/SSRL/SPEAR ring are also presented in this paper.
  • The PEP II B Factory requires a feedback system to damp out longitudinal synchrotron oscillations. A time-domain bunch-by-bunch feedback system has been proposed in which each bunch is treated as an oscillator being driven by disturbances from the other bunches. The phase is detected, filtered, and the feedback correction signal is applied by the kicker. Since we are damping energy oscillations using measurements of phase, the required feedback signal must be proportional to the amplitude of the phase oscillations but phase shifted by 90 degrees. This signal must be calculated for each of the 1658 bunches, in parallel. In themore » original proposal, it was estimated that a farm of approximately 480 digital signal processors (DIPS) would be required to implement the feedback system. However, using the technique of downsampling, this number can be reduced to about 50 DIPS. In what follows, we will briefly explain the basic idea of downsampling and its implementation.« less