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Title: Electron Beam Alignment Strategy in the LCLS Undulators

Abstract

The x-ray FEL process puts very tight tolerances on the straightness of the electron beam trajectory (2 {micro}m rms) through the LCLS undulator system. Tight but less stringent tolerances of 80 {micro}m rms vertical and 140 {micro}m rms horizontally are to be met for the placement of the individual undulator segments with respect to the beam axis. The tolerances for electron beam straightness can only be met through beam-based alignment (BBA) based on electron energy variations. Conventional alignment will set the start conditions for BBA. Precision-fiducialization of components mounted on remotely adjustable girders and the use of beam-finder wires (BFW) will satisfy placement tolerances. Girder movement due to ground motion and temperature changes will be monitored continuously by an alignment monitoring system (ADS) and remotely corrected. This stabilization of components as well as the monitoring and correction of the electron beam trajectory based on BPMs and correctors will increase the time between BBA applications. Undulator segments will be periodically removed from the undulator Hall and measured to monitor radiation damage and other effects that might degrade undulator tuning.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
896941
Report Number(s):
SLAC-PUB-12098
TRN: US200705%%82
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Invited talk at 28th International Free Electron Laser Conference (FEL 2006), Berlin, Germany, 27 Aug - 1 Sep 2006
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ALIGNMENT; ELECTRON BEAMS; ELECTRONS; FREE ELECTRON LASERS; GROUND MOTION; MONITORING; MONITORS; RADIATIONS; STABILIZATION; TUNING; WIGGLER MAGNETS; Other,XFEL

Citation Formats

Nuhn, H.-D., Emma, P.J., Gassner, G.L., LeCocq, C.M., Peters, E., Ruland, R.E., and /SLAC. Electron Beam Alignment Strategy in the LCLS Undulators. United States: N. p., 2007. Web.
Nuhn, H.-D., Emma, P.J., Gassner, G.L., LeCocq, C.M., Peters, E., Ruland, R.E., & /SLAC. Electron Beam Alignment Strategy in the LCLS Undulators. United States.
Nuhn, H.-D., Emma, P.J., Gassner, G.L., LeCocq, C.M., Peters, E., Ruland, R.E., and /SLAC. Wed . "Electron Beam Alignment Strategy in the LCLS Undulators". United States. doi:. https://www.osti.gov/servlets/purl/896941.
@article{osti_896941,
title = {Electron Beam Alignment Strategy in the LCLS Undulators},
author = {Nuhn, H.-D. and Emma, P.J. and Gassner, G.L. and LeCocq, C.M. and Peters, E. and Ruland, R.E. and /SLAC},
abstractNote = {The x-ray FEL process puts very tight tolerances on the straightness of the electron beam trajectory (2 {micro}m rms) through the LCLS undulator system. Tight but less stringent tolerances of 80 {micro}m rms vertical and 140 {micro}m rms horizontally are to be met for the placement of the individual undulator segments with respect to the beam axis. The tolerances for electron beam straightness can only be met through beam-based alignment (BBA) based on electron energy variations. Conventional alignment will set the start conditions for BBA. Precision-fiducialization of components mounted on remotely adjustable girders and the use of beam-finder wires (BFW) will satisfy placement tolerances. Girder movement due to ground motion and temperature changes will be monitored continuously by an alignment monitoring system (ADS) and remotely corrected. This stabilization of components as well as the monitoring and correction of the electron beam trajectory based on BPMs and correctors will increase the time between BBA applications. Undulator segments will be periodically removed from the undulator Hall and measured to monitor radiation damage and other effects that might degrade undulator tuning.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 03 00:00:00 EST 2007},
month = {Wed Jan 03 00:00:00 EST 2007}
}

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  • To maintain gain in the 100 m long linac-driven Linac Coherent Light Source (LCLS) FEL undulator, the electron and photon beams must propagate colinearly to within -5 {micro}m rms over distances comparable to the 11.7 m FEL gain length in the 6 mm diameter undulator vacuum chamber. The authors have considered a variety of intercepting and non-intercepting position monitor technologies to establish and maintain this beam alignment. They present a summary discussion of the applicability and estimated performance of monitors detecting synchrotron radiation, transition and diffraction radiation, fluorescence, photoemission or bremsstrahlung from thin wires, Compton scattering from laser beams, andmore » image currents from the electron beam. They conclude that: (1) non-intercepting RF cavity electron BPMs, together with a beam based alignment system, the best suited for this application; and (2) insertable intercepting wire monitors are valuable for rough alignment, for beam size measurements, and for simultaneous measurement of electron and photon beam position by detecting bremsstrahlung from electrons and diffracted x-rays from the photo beam.« less
  • Interaction of an electron beam with external field or its own radiation has widespread applications ranging from coherent-radiation generation, phase space cooling or formation of temporally-structured beams. An efficient coupling mechanism between an electron beam and radiation field relies on the use of a magnetic undulator. In this contribution we detail our plans to build short (11-period) undulators with 7-cm period refurbishing parts of the aladdin U3 undulator [1]. Possible use of these undulators at available test facilities to support experiments relevant to cooling techniques and radiation sources are outlined.
  • In order to reach the high peak current required for an x-ray FEL, two separate magnetic dipole chicanes are used in the LCLS accelerator to compress the electron bunch length in stages. In these bunch compressors, coherent synchrotron radiation (CSR) can be emitted-induced either by a short electron bunch, or by any longitudinal density modulation that may be on the bunch. We present measurements, simulations, and analysis of (1) the CSR-induced energy loss, (2) the related transverse emittance growth, and (3) the microbunching-induced CSR directly observed at optical wavelengths.