Characterization and use of the spent beam for serial operation of LCLS

Boutet, S.; Foucar, L.; Barends, T.R.M.; Botha, S.; Doak, R.B.; Koglin, J.E.; Messerschmidt, M.; Nass, K.; Schlichting, I.; Seibert, M.M.; Shoeman, R.L.; Williams, G.J.

doi:10.1107/S1600577515004002

Figure 4
Refocused beam profile characterization at ∼7.6 keV. The results are shown on the same scale as the simulations of Fig. 3

for ease of comparison. The results are shown in red for the vertical profile and in black for the horizontal profile. Each of the small colored dots represents an LCLS shot to which a two-dimensional Gaussian profile was fitted to the measured profile. The solid lines represent the average of the fitted spots within certain central photon energy bin. The slope at which the FWHM increases with deviations from the ideal photon energy is smaller than expected from simulations. This could be an indication that the spectral bandwidth of the beam was larger than expected. The beam profile at the optimally focused energy is fairly consistent with the expected 0.2% bandwidth beam with a Gaussian source propagating through the CXI beamline. A larger measured spot size than simulated is not so surprising given that perfect optics were used for the simulation. The data are consistent with both expectations of larger foci due to optical aberrations and a potentially larger than expected bandwidth but do not allow us to claim one over the other.

JOURNAL OF
SYNCHROTRON
RADIATION

ISSN: 1600-5775

Volume 22| Part 3| May 2015| Pages 634-643

https://doi.org/10.1107/S1600577515004002

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