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Abstract:The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0

We demonstrate a hard-X-ray self-seeded (HXRSS) free-electron laser (FEL) at Pohang Accelerator Laboratory with an unprecedented peak brightness (3.2 × 10 35 photons/(s•mm 2 •mrad 2 •0.1%BW)). The self-seeded FEL generates hard X-ray pulses with improved spectral purity; the average pulse energy was 0.85 mJ at 9.7 keV, almost as high as in SASE mode; the bandwidth (0.19 eV) is about 1/70 as wide, the peak spectral brightness is 40 times higher than in self-ampli ed spontaneous emission (SASE) mode, and the stability is excellent with > 94% of shots exceeding the average SASE intensity. Using this self-seeded XFEL, we conducted serial femtosecond crystallography (SFX) experiments to map the structure of lysozyme protein; data-quality metrics such as R split , multiplicity, and signal-to-noise ratio for the SFX were substantially increased. We precisely map out the structure of lysozyme protein with substantially better statistics for the diffraction data and signi cantly sharper electron density maps compared to maps obtained using SASE mode.

The Pohang Light Source (PLS) has operated for 14 years successfully. To meet the request of the increasing user community, the PLS-II that is the upgrade project of PLS has been completed. Main goals of the PLS-II are to increase beam energy to 3 GeV, to increase number of insertion devices by the factor of two (20 IDs), to increase beam current to 400 mA and to reduce beam emittance below 10 nm with existing PLS tunnel and injection system. The PLS-II had been commissioned over the six months. During commissioning, we achieved 14 insertion devices operation and top-up operation with 100 mA beam current and 5.8 nm beam emittance. In this paper, we report the experimental results from the PLS-II commissioning.

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