Design of a harmonic generation FEL experiment at BNL

We present the design parameters of a harmonic generation FEL experiment to be carried out at the accelerator test facility (ATF) at BNL. This experiment will be carried out as a proof-of-principle for the proposed UV-FEL user's facility at BNL. In the experiment we plan to triple the frequency of a CO₂ seed laser by utilizing two superconducting wigglers and a dispersive section. The first wiggler will be used in conjunction with the CO₂ seed laser to generate a ponderomotive force that will bunch the electron beam. The bunching will then be enhanced by the dispersion section. The second wiggler, tuned to the third harmonic of the seed laser will follow. In the beginning of the second wiggler the bunched beam will produce superradiant emission (characterized by a quadratic growth of the radiated power), then the radiation will be amplified exponentially. The last part of the wiggler will be tapered. We plan to study the evolution of the various radiation growth mechanisms as well as the coherence of the tripled and exponentially amplified radiation.