Design considerations for SASE-FEL at PLS

The infrared (IR) free-electron laser (FEL) which is in design stage at Pohang Light Source is a self-amplified spontaneous emission (SASE) system that is driven by a 60 MeV to 100 MeV test linac facility. We present results of the numerical simulation for the design of the IR SASE-FEL at the PLS. It is shown that high-gain SASE-FEL with 1.5 mum radiation wavelength is driven by a 61 MeV electron beam from the S-band rf linac and a about 5 m long undulator. The generation of third harmonic from bunching at the fundamental wavelength is also investigated as a purpose toward enhancing the usefulness of the IR SASE-FEL facility at the PLS. In this paper, we investigate sensitivity of the beam parameters, emittance, energy spread, beam energy and peak beam current, to the performance of the designed IR SASE-FEL by a simulation code GINGER. We also investigate the influence of beam parameters on the bunching of fundamental and nonlinear third harmonic, and show that the third harmonic emission results in the same trend as that of the fundamental