It is a prospective technical route to generate UV coherent radiation using external high-power laser to pre-bunch ultra-relativistic electron beam provided by storage ring and then amplifying its harmonic components with the super-radiation method. In this paper, based on the primary parameters of Hefei Storage Ring (NSRL) FEL system, firstly we made the simulation to the electron beam energy modulation process in an optical klystron, the simulation parameters include: γ = 1000, the relativistic factor of the electron beam; the wavelength and power of the injected external laser are, λ_s = 0.353 μm and 100 MW; the period number and wavelength of the undulators are N_u = 20, and λ_u = 7.2 cm (we have the same structure for the modulator and radiator); and the normalized amplitude of the magnetic field is K = 4.2. An effective energy modulation can be achieved when the rms energy spread for the electron beam is less than 10~(-4), i.e., σ_γ/γ ≤10~(-4). Then density modulation for the energy-modulated electron beam in the dispersive section is also simulated. Under the above-mentioned conditions when the dispersive parameter N_d ≌ 76, a good density modulation results can be obtained. Finally, we also give the harmonic super radiation output power components P_3, P_5, P_7 in the radiator section.
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