Abstract
X-ray free-electron lasers (XFELs) are cutting-edge scientific instruments for a wide range of disciplines. Conventionally, the narrow bandwidth is pursued in an XFEL. However, in recent years, the large-bandwidth XFEL operation schemes are proposed for X-ray spectroscopy and X-ray crystallography, in which over-compression is a promising scheme to produce broad-bandwidth XFEL pulses through increasing the electron beam energy chirp. In this paper, combining with the beam yaw correction to overcome the transverse slice misalignment caused by the coherent synchrotron radiation, finding out the over-compression working point of the linac is treated as a many-objective (having four or more objectives) optimization problem, thus the non-dominated sorting genetic algorithm III is applied to the beam dynamic optimization for the first time. Start-to-end simulations demonstrate a full bandwidth of 4.6% for Shanghai soft x-ray free-electron laser user facility.
Highlights
X-ray free electron lasers (XFELs) are leading-edge instruments in a wide range of research fields that can provide short wavelength radiation with high brightness and ultra-fast time structures [1]
In the baseline design of the soft x-ray free-electron laser (SXFEL) user facility, 0.5 nC electron bunches with 130 MeVare generated in the injector section which includes two S-band accelerating structures and a laser heater
Electron beams are accelerated at the off-crest phase of a S-band accelerating section to create an energy chirp and an X-band rf cavity is used to linearize the chirp
Summary
X-ray free electron lasers (XFELs) are leading-edge instruments in a wide range of research fields that can provide short wavelength radiation with high brightness and ultra-fast time structures [1]. The relative bandwidth of the SASEXFEL pulses at saturation is of the order of the Pierce parameter [8], with values between 10−3 and 10−4. To generate fully coherent XFEL pulses, several schemes [9] have been proposed to further decrease the XFEL bandwidth. In addition to narrow bandwidth XFEL pulses, the large-bandwidth XFEL operation has attracted increasing attention. Broad-bandwidth XFEL pulses are very useful in many spectroscopy experiments [10,11], multi-wavelength anomalous diffraction [12,13], and x-ray crystallography [14,15]. In the large-bandwidth mode, the XFEL wavelength can be adjusted by applying a monochromator without changing any parameters on the accelerator side
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