Asymmetric optical klystrons for the high-gain FELs

One dimensional, time-dependent simulation study for the optimization of the klystron FEL based on the start-up from noise has been made. By considering the slippage effect and the gain-limiting effect we propose an asymmetric klystron FEL as an alternative for a high-gain FEL. Asymmetric klystron FELs consist of two different undulator sections and the dispersive section inbetween and it has advantages of higher gain and shorter saturation length, which are essential for the high-gain FELs starting from noise. The optimum operational conditions for the asymmetric klystron FEL are investigated on the parameter plane of the various undulator strengths and the dispersive section parameters with a beam energy spread.