Collimator system of SLEGS beamline at Shanghai Light Source

Shanghai laser electron gamma source (SLEGS) is an energy-variable gamma-ray source developed based on the inverse Compton scattering of 10640 nm photons from a 100 W CO${}_2$ laser on 3.5 GeV electrons from the Shanghai Light Source. It produces gamma-rays in the energy range of 0.4–21.7 MeV with a flux of 10${}^5$–10${}^7$ photons/s. A collimator system was designed to produce quasimonochromatic gamma-ray beams with a best possible bandwidth of 1.1%–4.4% and filter out the substandard gamma-rays. The collimator system composed of coarse and fine collimators, constitutes a critical component of the SLEGS. By Geant4 simulations, we show that the collimator system is effective in tuning beam bandwidths and regular dodecagonal beam spots at the target position.