## 5 Summary and Future Plans  
We reported the PAL-XFEL's efforts to improve the performance of the facility and provide a better experimental environment for users. The FEL pulse energy has been increased continuously to provide more photons for beamline experiments, and FELs with energies of more than 1.2 mJ are delivered in all photon energy ranges. The maximum photon energy was increased from 12 keV to 20 keV using a higher electron beam energy and lower undulator parameter K. To overcome the limitations of an SASE FEL, self-seeding  
Figure 12: Schematics of the time-resolved FTH (**a**) and ITOF (**b**) setup. (**a**) After a laser pump, a CCD records the interference between X-rays scattered at the sample and passed through the reference hole. (**b**) XFEL ionizes the products of the photoreaction at a time delay. The electrical field accelerates the ionized particles between the repeller and extractor, and the accelerated particles’ flight to the MCP. The mass of the ionized particle is determined by its flight time and charge.  
was prepared, and the peak brightness was improved tenfold compared to SASE FEL in all photon energy ranges. Two-color FEL generation was applied to extend the research capabilities, and two FEL pulses with a 200 eV energy difference were generated by using a different undulator parameter K in the upstream and downstream undulators of the self-seeding section. In beamline experiments, it is expected that the extended pump laser wavelengths of the XSS beamline will make it possible to study various materials and access more physical degrees of freedom. Furthermore, improving the experimental time resolution at the FXL endstation will be an essential step for studying many veiled ultrafast phenomena. Lastly, the newly developed sample injector for the SFX and the capability of the XES/XAS endstation for various sample phases will lead to new research areas and increase the number of XFEL users.  
The user beamtime of the PAL-XFEL will increase to 190 days in 2022, thereby increasing the number of beamtime shifts available to users. Accordingly, the burden of the supporting staff at the PAL-XFEL should be eased in line with the increased user experiments. As one possible approach, we plan to introduce techniques to increase the convenience and stability of the experiment, such as an automatic sample exchange system, remote control for wavelength, polarization, and intensity of the optical laser, and RF phase shifter for time-delay control.  
I.E. and C.K. planed the article and organized sections, and the following authors contributed to each section. Section 2.1: C.K., Section 2.2: I.E., 3: H.Y., I.N., M.H.C., C.H.S., G.K., C.-K.M., H.H., H.-S.K. and C.K., Section 4.1: S.H.C. and I.E. Section 4.2: J.H.L., D.N. and R.M., Section 4.3: J.P. and S.P., Section 4.4: S.H.P. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Ministry of Science and Information, Communications & Technology (ICT) of Korea (grant number 2018R1A6B4023605). D.N. was also supported by the National Research Foundation of Korea (grants NRF-2019R1A6B2A02098631 and NRF-2021R1F1A1051444). J.P. was also supported by National Research Foundation of Korea (grant No. NRF-2017M3A9F6029736). The authors acknowledge all PAL-XFEL staff members who participated in operations and R & D.  
The authors declare no conflict of interest.