Parameter study for enhanced high gain harmonic generation scheme

An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in the new scheme, including the electron energy detuning, initial electron-beam energy spread, seeding laser power, dispersive field strength and amount of the phase shift, etc. The numerical results from GENESIS （3D-code） are presented and show that the new scheme has acceptable parameters tolerance requirements and is no more or even less sensitive to the system parameters than that of the existing scheme; With the electron energy above the resonance, the efficiency is enhanced for both the new scheme and the existing scheme compared with the resonant energy case.