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Figure 7
The effect of space charge on measured wavelength as a function of target gas pressure, FLASH2 repetition rate and beam size. The panels show wavelength results for the 30 bunches of the pulse train at [\lambda_{\rm{und}}] = 13.5 nm for different target gas pressures. (a) A considerable wavelength shift increasing over the pulse train is found at high repetition rate of 1 MHz and a large aperture (uncropped beam). (b) Reduced space charge effect when the beam size is reduced by means of a smaller aperture. (c) Almost no space charge effect if, in addition, the repetition rate is lowered to 100 kHz. The residual slope of λ along the bunch train in the curves for [p_{\rm{OPIS}}\le 4\times10^{-7}] reflects a real trend in FEL wavelength. For all measurements the bunch wavelength tool described in §3.1[link] has been used.

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 25| Part 1| January 2018| Pages 3-15
https://doi.org/10.1107/S1600577517013893
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