At the Pohang Accelerator Laboratory (PAL), there is a 2.5 GeV S-band linac which is under operating as a full energy injector for the Pohang Light Source (PLS) storage ring. By installing a new electron gun, a new 0.5 GeV linac, and two new bunch compressors, the PLS linac can be used as an FEL driver for the PAL XFEL project. To saturate 0.3 nm wavelength PAL XFEL SASE source, we should supply high quality electron beams to a 60 m long undulator. In this paper, we describe a new linac layout for the PAL XFEL project and its various start-to-end simulations from the cathode to the end of the linac.

PAL is operating a 2.5-GeV electron linac as a full-energy injector to the PLS storage ring. The PAL linac can be converted to a SASE-XFEL facility (PAL-XFEL) that supplies coherent X-rays down to 0.3-nm wavelength. It requires a 3-GeV driver linac and a 60-m long in-vacuum undulator with a 3-mm gap and a 12.5-mm period to realize a hard X-ray SASE-FEL. The linac should supply highly bright beams with emittance of 1.5 mm-mrad, a peak current of 4 kA, and a low energy spread of 0.02%. FEL performance is very sensitive to electron beam parameters. The beam quality is degraded along the undulator trajectory due to the energy loss and the wake field. Also the FEL gain is reduced by errors in the undulator fields and beam trajectories. The preliminary design details for the 0.3-nm PAL-XFEL are presented with parametric analysis.