Speaker
Description
We present results of modeling of the FEL radiation used in pump probe experiment at BL3 at SACLA free electron laser. 160 pC, 8 GeV electron bunch produces two photon pulses with different photon energies (color1: 8 keV and color 2: 9 keV) when consecutively passing two undulator sections. First color is filtered by Si111 monochromator to the bandwidth of 0.02% (pulse energy is 0.1 uJ). Second color is used as is with fwhm spectrum width of 0.3% (pulse energy is 70 uJ). Width of the radiation spectrum is mainly defined by the space charge induced energy chirp along the electron bunch. Our analysis shows that parameters of SASE FEL in the experiment correspond to a large value of diffraction parameter, B ~ 400 which prevent formation of the transverse coherence for both colors. An important feature of the radiation is significant slice spatial distortions of the fields and poor pointing stability for the color 1 arising from fundamental reasons - start up of the amplification from the shot noise and radiation mode degeneration arising from large values of diffraction parameter. We perform simulations of the radiation pulses with three dimensional, time dependent FEL simulation code FAST. Then simulated data are stored in the XPD-FAST, data base of photon properties hosted by the European XFEL and DESY, and finally used for modeling of experiment. The FEL simulation results will be used for a detailed analysis of X-ray crystal diffraction data from the two-color experiment.
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