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Title: Wakefield Calculations for the LCLS in Multibunch Operation

Authors:
;
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1146450
Report Number(s):
SLAC-PUB-16039
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Journal Name: Conf.Proc.C110904:802-804,2011; Conference: Presented at the 2nd International Particle Accelerator Conference (IPAC-2011), San Sebastian, Spain, 4-9 Sep 2011
Country of Publication:
United States
Language:
English
Subject:
Accelerators,ACCSYS

Citation Formats

Bane, K.L.F., and /SLAC. Wakefield Calculations for the LCLS in Multibunch Operation. United States: N. p., 2014. Web.
Bane, K.L.F., & /SLAC. Wakefield Calculations for the LCLS in Multibunch Operation. United States.
Bane, K.L.F., and /SLAC. Mon . "Wakefield Calculations for the LCLS in Multibunch Operation". United States. doi:. https://www.osti.gov/servlets/purl/1146450.
@article{osti_1146450,
title = {Wakefield Calculations for the LCLS in Multibunch Operation},
author = {Bane, K.L.F. and /SLAC},
abstractNote = {},
doi = {},
journal = {Conf.Proc.C110904:802-804,2011},
number = ,
volume = ,
place = {United States},
year = {Mon Jul 21 00:00:00 EDT 2014},
month = {Mon Jul 21 00:00:00 EDT 2014}
}

Conference:
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  • Normally the Linac Coherent Light Source (LCLS) operates in single-bunch mode, sending a bunch of up to 250 pC charge at 120 Hz through the linac and the undulator, and the resulting FEL radiation into one of the experimental hutches. With two bunches per rf pulse, each pulse could feed either two experiments or one experiment in a pump-probe type configuration. Two-bunch FEL operation has already been briefly tested at the LCLS, and works reasonably well, although not yet routinely. In this report we study the longitudinal and transverse long-range (bunch-to-bunch) wakefields of the linacs and their effects on LCLSmore » performance in two-bunch mode, which is initially the most likely scenario. The longitudinal wake changes the average energy at the second bunch, and the transverse wake misaligns the second bunch (in transverse phase space) in the presence of e.g. transverse injection jitter or quad misalignments. Finally, we extend the study to consider the LCLS with trains of up to 20 bunches per rf pulse. In the LCLS the bunch is created in an rf gun, and then passes in sequence through Linac 0, Linac 1, Linac X, Bunch Compressor 1 (BC 1), Linac 2, BC 2, Linac 3, and finally the undulator. In the process the bunch energy reaches 13.5 GeV and peak current 3 kA. In Table 1 we present some machine and beam parameters in three of the linacs that we will use in the calculations: initial beam energy E{sub 0}, total accelerator length L, average beta function {beta}{sub y}, bunch peak current I, and rf phase (with respect to crest) {phi}; the final energy of a linac equals E{sub 0} of the following linac, and in Linac 3 is E{sub f} = 13.5 GeV. (The X-band linac, with L = 60 cm, has wake effects that are small compared to the other linacs, and will not be discussed.) In this report we limit our study to trains of equally populated, equally spaced bunches with a total length of less than 100 ns. The charge of each bunch is eN{sub b} = 250 pC.« less
  • This Paper discusses various aspects of multibunch motion in the presence of nearest neighbor wakefield coupling. Included are the solution to the problem for smooth focusing with equal bunch energies, an explanation for the apparent damping of the bunch amplitudes that is observed for weak coupling, and a treatment of the problem for discrete focusing based on the moments of the wakefield distributions in the structures.
  • This Paper discusses various aspects of multibunch motion in the presence of nearest neighbor wakefield coupling. Included are the solution to the problem for smooth focusing with equal bunch energies, an explanation for the apparent damping of the bunch amplitudes that is observed for weak coupling, and a treatment of the problem for discrete focusing based on the moments of the wakefield distributions in the structures.
  • The Cornell storage ring CESR, designed to collide one bunch of e/sup +/ with one bunch of e/sup -/ at energies up to 8 GeV each, is used almost exclusively for research on b-quark physics (the /TAU/ region, 4.5 - 5.6 GeV per beam). Here the radiation loss is less than one-quarter the design maximum--low enough to relax beam-current limitations due to total rf power, yet still high enough to provide a comfortable amount of radiation damping (/tau/ /SUB rad/ approx. = 22 ms), which helps control beam instabilities. Performance is therefore relatively good. With single bunches, the luminosity (whichmore » scales roughly as E/sup 4/) reaches about 1.6 x 10/sup 31/ cm/sup -2/s/sup -1/ at 5.4 GeV. This is achieved with bunch currents of about 17 mA, in a regime where vertical beam blowup due to the beam-beam interaction makes L alpha I rather than I/sup 2/. The beam current is limited to this level by the onset of sudden beam losses during collision. To raise the luminosity, CESR has since 1983 operated with multiple bunches in each beam. At the unwanted crossing points within the guide-field arcs, these bunches are separated in the horizontal plane: e/sup +/ and e/sup -/ orbits are oppositely distorted, ''pretzel'' fashion, by a pair of electrostatic separators near the ends of each arc. The orbits still coincide around the two interaction points, and must do so very accurately of course. The required modifications of CESR, and early experience with multibunch operation, were described previously. We report our progress here, as an example of the considerations applying when two beams are bedded sideby-side in the same aperture, separated by electrostatic steering elements. The topics are: design constraints, Sec.2; lattice-optical and orbit effects, Secs. 3 and 4; and beam performance, Secs. 5 and 6.« less