| Paper |
Title |
Page |
| MOPCH048 |
Linac Coherent Light Source Electron Beam Collimation
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148 |
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- J. Wu, D. Dowell, P. Emma, C. Limborg-Deprey, J.F. Schmerge
SLAC, Menlo Park, California
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This paper describes the design and preliminary simulations of the electron beam collimation system in the Linac Coherent Light Source (LCLS) linac. 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 L0-linac exit to FEL undulator entrance, 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 on each individual collimator. In addition, the transverse wakefield alignment tolerances are calculated for each collimator.
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| THPCH193 |
Comparison between H-ion and Heat Cleaning of Cu-metal Cathodes
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3245 |
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- D. Dowell, F. King, R.E. Kirby, J.F. Schmerge
SLAC, Menlo Park, California
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Understanding the quantum efficiency (qe) of a metal photocathode in an s-band RF gun is important to limit the drive laser energy requirement and provide the best quality electron beam. Systematic measurements of the qe vs. wavelength for varying surface contamination have been performed on copper samples using x-ray photoelectron spectroscopy (XPS). The sample is first cleaned to the theoretical limit of qe using a 1 keV hydrogen ion beam. The H-ion beam cleans an area approximately 1cm in diameter and has no effect on the surface roughness while removing essentially all contaminants and lowering the work function to 4.3eV. The sample is then exposed to atmospheric contaminants (nitrogen and oxygen) and measured again with XPS to determine the degree of contamination and the effect on the qe. The goal is to determine the best procedure for transferring and installing cathodes in an s-band gun. These results and comparison with a heat cleaned cathode are presented.
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