Radiation Size and Divergence at the Hard X-ray Beamline in the PAL-XFEL

In the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL), recently, the minimum gap of the hard X-ray undulator were changed from 7.2 (undulator period: 24.4 mm) to 8.3 mm (undulator period: 26 mm). To review the physical issues related to the gap change, including the radiation size and divergence, in the PAL-XFEL, we did a simulation study with GENESIS 1.3. The saturation length in the 8.3-mm case will be increased by 10% with respect to the 7.2-mm case. The study also revealed that the divergence of the radiation in 8.3-mm case would be decreased by 4% compared with that in the 7.2-mm case. In this paper, we will present the detailed simulation results to estimate the divergence of radiation at the hard X-ray beamline in the PAL-XFEL.