Author: Den Hartog, P.K.
Paper Title Page
THP068 LCLS-II Extruded Aluminum Undulator Vacuum Chambers — New Approaches to an Improved Aperture Surface Finish 719
  • G.E. Wiemerslage, P.K. Den Hartog, J. Qian, M. White
    ANL, Lemont, Illinois, USA
  Funding: Work at Argonne National Laboratory is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract # DE-AC02-06CH11357.
The Linac Coherent Light Source, (LCLS) the world’s first x-ray free electron laser (FEL) became operational in 2009. The Advanced Photon Source contributed to the original project by designing and building the undulator line. Two slightly different variations of these chambers were required for LCLS-II: one for a soft X-ray (SXR) undulator line, and one for a hard X-ray (HXR) undulator line. Because of the extremely short electron bunch length, a key physics requirement was to achieve the best possible surface finish within the chamber aperture. Improvements to our earlier fabrication methods allowed us to meet the critical surface roughness finish defined by RF impedance requirements. We were able to improve the surface finish from an average of 812 nm rms to 238 nm rms. The average longitudinal surface roughness slope of all chambers was to be less than 20 mrad. We achieved an average longitudinal surface roughness slope of 8.5 mrad with no chamber exceeding 20 mrad. In the end, sixty-four undulator vacuum chambers and alignment systems were delivered to SLAC for the LCLS-II Upgrade project. Here we will report on the process improvements for the fabrication of these chambers.
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About • paper received ※ 16 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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