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Title: Linac Coherent Light Source Electron Beam Collimation

Abstract

This paper describes the design and simulation of the electron beam collimation system in the Linac Coherent Light Source (LCLS). Dark current is expected from the gun and some of the accelerating cavities. Particle tracking of the expected dark current through the entire LCLS linac, from gun through FEL undulator, is used to estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction. A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an estimate of average continuous beam power lost. In addition, the transverse wakefield alignment tolerances are calculated for each collimator.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
902721
Report Number(s):
SLAC-PUB-12489
TRN: US0703083
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; LINEAR ACCELERATORS; COLLIMATORS; DESIGN; ELECTRON BEAMS; LIGHT SOURCES; WIGGLER MAGNETS; COMPUTERIZED SIMULATION; ELECTRON GUNS; FREE ELECTRON LASERS; Accelerators,ACCPHY

Citation Formats

Wu, J., Dowell, D., Emma, P., Limborg-Deprey, C., Schmerge, J.F., and /SLAC. Linac Coherent Light Source Electron Beam Collimation. United States: N. p., 2007. Web.
Wu, J., Dowell, D., Emma, P., Limborg-Deprey, C., Schmerge, J.F., & /SLAC. Linac Coherent Light Source Electron Beam Collimation. United States.
Wu, J., Dowell, D., Emma, P., Limborg-Deprey, C., Schmerge, J.F., and /SLAC. Fri . "Linac Coherent Light Source Electron Beam Collimation". United States. doi:. https://www.osti.gov/servlets/purl/902721.
@article{osti_902721,
title = {Linac Coherent Light Source Electron Beam Collimation},
author = {Wu, J. and Dowell, D. and Emma, P. and Limborg-Deprey, C. and Schmerge, J.F. and /SLAC},
abstractNote = {This paper describes the design and simulation of the electron beam collimation system in the Linac Coherent Light Source (LCLS). Dark current is expected from the gun and some of the accelerating cavities. Particle tracking of the expected dark current through the entire LCLS linac, from gun through FEL undulator, is used to estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction. A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an estimate of average continuous beam power lost. In addition, the transverse wakefield alignment tolerances are calculated for each collimator.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Apr 27 00:00:00 EDT 2007},
month = {Fri Apr 27 00:00:00 EDT 2007}
}

Conference:
Other availability
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  • The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) based on the final kilometer of the Stanford Linear Accelerator. The tight tolerances for positioning the electron beam close to the undulator axis calls for the introduction of Beam Finder Wire (BFW) device. A BFW device close to the upstream end of the undulator segment and a quadrupole close to the down stream end of the undulator segment will allow a beam-based undulator segment alignment. Based on the scattering of the electrons on the BFW, we can detect the electron signal in the main dump bends aftermore » the undulator to find the beam position. We propose to use a threshold Cherenkov counter for this purpose. According to the signal strength at such a Cherenkov counter, we then suggest choice of material and size for such a BFW device in the undulator.« less
  • The Linac Coherent Light Source (LCLS), currently under design, requires accurate alignment between the electron beam and each undulator's magnetic centerline. A beam finder wire (BFW) instrument has been developed to provide beam location information that is used to move the undulators to their appropriate positions. A BFW instrument is mounted at each of the 33 magnets in the undulator section. Beam detection is achieved by electrons impacting two carbon fiber wires and then sensing the downstream radiation. The wires are mounted vertically and horizontally on a wire card similar to that of a traditional wire scanner instrument. The developmentmore » of the BFW presents several design challenges due to the need for high accuracy of the wires locations and the need for removal of the wires during actual operation of the LCLS (30 microns repeatability is required for the wire locations). In this paper, we present the technical specification, design criteria, mechanical design, and results from prototype tests for the BFW.« less
  • The Linac Coherent Light Source (LCLS), currently under design, requires beam diagnostic instruments between the magnets in the beam undulator section. Ten wire scanners are planned as one of the primary instruments to characterize electron beam properties. The development of these wire scanners presents several design challenges due to the need for high accuracy and resolution of the wire motion (3-{micro}m tolerance, typical) and the high intensity of the beam (1 nC, 3400-A peak, over an area of 30-{micro}m rms radius at 120 Hz). In this paper, we present the technical specification and design criteria for the scanners. We willmore » also present the mechanical design of the UHV-compatible drive and its engineering analysis. Lastly, we present the wire card design and discuss associated thermal and mechanical issues originating from the highly intense x-ray and electron beams.« less
  • A linac configuration providing a low emittance high peak current electron beam is under study for a potential Linac Coherent Light Source (LCLS) based on the SLAC accelerator. The parameters of the final electron bunch are nearing the technological limits of present accelerators in both transverse and longitudinal phase space. In this note we describe a layout of the RF gun, linac, and bunch compressors to deliver the required bunch properties. We consider a bunch that is generated by an rf gun and accelerated to 7 GeV in 900 m of SLAC linac structure before it enters the wiggler. Wemore » assume that the rf gun generates a gaussian beam with an energy of 10 MeV, a population N = 6 {times} 10{sup 9}e{sup {minus}}, an rms length {sigma}{sub z} = 0.5 mm, an rms energy spread {sigma}{sub {delta}} = 0.2%, and normalized rms emittances {gamma}{epsilon}{sub x,y} = 3 mm-mrad. At the end of the linac, we require that the peak current {cflx I} {approx_gt} 2.5 kA and the peak-to-peak energy spread {Delta}{delta} {approx_lt} 0.2%. To obtain the required high peak current, we need to compress the bunch length by a factor greater than 10. In deciding at what position in the linac to compress we need to consider three issues: the longitudinal wakefield in the linac, this increases the beam`s energy spread and is harder to compensate with short bunches, the transverse wakefield and rf deflections in the linac, these increase the transverse emittance of the beam and are more severe for long bunches, and the effects of phase and current jitter which will change the bunch length and therefore the peak current of the beam. In this paper, we will describe how we compress the bunch to meet these three criteria. Then, we will briefly describe the bunch compressor optics and finally we will mention some details specific to the SLAC site.« less
  • The LCLS is a novel high-brightness x-ray source designed to operate in the 300--400 eV range. In contrast to conventional synchrotron radiation sources, its output pulses will be characterized by unprecedented levels of brevity and peak power. In this paper we present recently-developed beam line layouts and design features intended to optimize the delivery of the LCLS photons to various experimental stations.