BEAM OPTICS AND PARAMETER DESIGN OF THE XFEL/SPRING-8

The transverse optics of the XFEL/SPring-8 is designed using newly introduced linear formulation of the beam envelope including acceleration effects. The beam optics of the main linac and undulator section is based on a FODO-like lattice. To avoid the FEL gain reduction due to a longitudinal kink in the bunch, the horizontal beta function is set small at bending magnets to minimize the CSR effect. Since the accelerator of XFEL/SPring-8 uses a thermionic gun with an 1 A initial beam current, the total bunch compression ratio reaches about 3000, which is one order higher than a photocathode system. For nonlinearity compensation in the bunch compression, two correction cavities are installed, which are operated at the same frequency as the linac and not at its harmonic. In this paper, the XFEL/SPring-8 accelerator layout and its expected beam parameters are shown to achieve the 0.1 nm x-ray FEL.