# X-ray Free Electron Laser Accelerator Lattice Design Using Laser-Assisted Bunch Compression
## 7 Conclusions  
Footprint designs of the accelerator lattices for MaRIE X-ray free electron lasers (XFELs) that utilized a specific set of parameters for laser-assisted bunch compression (LABC) have been presented in this paper, with two different configurations of the first bunch compressor. The accelerator lattices were able to transport and process the electron beam from the photoinjector exit to the entrance of the X-ray undulator. The properties of the electron beam met the MaRIE requirements for X-ray lasing. The presented LABC method was based on and shares the same architecture with the ESASE scheme, but the design goals and the operating parameters, including the microbunch phase space manipulation, were more advanced.  
The presented LABC approach was achievable in our simulations by using a laser modulator in the form of a magnet undulator, downstream of the first bunch compressor at 750 MeV, in which the electron beam was modulated by a 3.4-GW 1-\(\upmu\)m wavelength laser, and the second bunch compressor, with a smaller magnitude of the \(R_{56}\) value, after the acceleration of the electron beam to a final energy of 12 GeV.  
The LABC accelerator lattices shown in this work demonstrated the suppression of both MBI and URWW. The emittance dilution and the electron beam profile deformation caused by the CSR effects were reduced to a satisfactory level by a longer overall beam length, which was intrinsic to the LABC method, by the optimized matching optics, and specially in lattice 2, by the carefully designed double C-chicane in BC1.  
Two configurations of the first bunch compressor were investigated. The conventional C-chicane configuration had a streamlined design with a much shorter length; it also led to a better alignment of the horizontal centroid distribution of the beam at the entrance of the X-ray undulator. The double C-chicane configuration occupied more space and added to the complication of the lattice, but it enabled the electron beam to have minimal transverse momentum shifts throughout the beam and to have a much smaller projected horizontal emittance as the beam exited the first bunch compressor. This comparatively smaller projected horizontal emittance was also noted at the entrance of the X-ray undulator, where the beam exhibits trivial horizontal momentum shifts along the length.  
This study showed that the MaRIE XFEL accelerator lattice could be established at a length of approximately 200 m, promoting the feasibility of hosting XFEL facilitiesat a smaller scale, e.g., on university campuses, as opposed to only being available at national laboratories.  
Conceptualization, B.E.C., P.M.A. and Q.R.M.; methodology, P.M.A. and H.X.; formal analysis, P.M.A., Q.R.M. and H.X.; investigation, H.X., L.D.D. and R.R.R.; writing--original draft preparation, H.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the U.S. Department of Energy through the Laboratory Directed Research and Development program of the Los Alamos National Laboratory, under project number 20200287 ER.  
Not applicable.  
The data presented in this study are available upon request from the corresponding author.  
The authors declare no conflict of interest.