Design parameters of the high gain harmonic generation experiment using Cornell undulator at the ATF

We present the design parameters of a high gain harmonic generation (HGHG) FEL experiment to be carried out at the accelerator test facility (ATF) at BNL, in collaboration with APS. This experiment is a proof-of-principle experiment for the DUV-FEL at BNL. In the HGHG experiment we plan to double the frequency of a CO₂ seed laser by utilizing a 0.76 m long 9 period undulator (named the “Mini Undulator”), a 2 m long 60 period undulator (named the “Cornell Undulator A”), and a 0.3 m electromagnet chicane (the dispersive section). The first undulator 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 undulator, the Cornell Undulator A, tuned to the second harmonic of the seed laser will serve as the radiator. In the beginning of the radiator the bunched beam will produce coherent emission (characterized by a quadratic growth of the radiated power), then the radiation will be amplified exponentially. We plan to study the evolution of the various radiation growth mechanisms as well as the coherence of the doubled, exponentially amplified radiation