Investigation of electron energy spread effects on the intracavity MIR-FEL power at the PBP-CMU electron linac laboratory

At the PBP-CMU Electron Linac Laboratory, the existing linear accelerator system is under developing to produce electron beams with suitable properties for generation of oscillator mid-infrared free-electron laser (MIR-FEL) and super-radiant terahertz (THz) undulator radiation. This work focuses on the simulation of the oscillator MIR-FEL with expected electron beam energy of 20 – 25 MeV to evaluate the required electron beam parameters. To achieve FEL saturation, the single-pass FEL simulation using the code GENESIS 1.3 was performed to estimate the laser wavelength, FEL gain and electron macro-pulse duration. In the simulation, electron beams with energy spread of 0, 0.5 and 1.0 %, and the electron peak current of 25 and 50 A were considered. As a result, the electron beam with energy of 20 – 25 MeV can produce the FEL wavelengths of 13.5 – 21.2 µm using a 1.6-m undulator with maximum undulator parameter of 1.07. The largest FEL gain is 216% when using electron beam energy and peak current of 20 ± 0% MeV and 50 A, which requires the electron macro-pulse duration of 1.6 µs to saturate FEL. Due to the possible macro-pulse duration at our facility of 6 µs, the operation of electron beam with energy spread of 0.5% and peak current of higher than 25 A is required to saturate FEL. Results from this single-pass simulation can be used as a based information for further practical consideration with multi-pass simulation.