Compensation of thermal loss in free-electron laser with optimal tapering and pre-bunching

Abstract

AbstractIncreasing the output power of a long-wavelength free-electron laser (FEL), despite the destroying effects of beam energy spread, is studied using the optimal pre-bunching of the thermal electron beam along with the optimal tapering of the planar wiggler magnetic field. A set of self-consistent coupled nonlinear differential equations in three dimensional that describe the evolution of radiation and electron beam in the interaction zone are solved numerically by the Runge–Kutta method. The axial energy spread is considered and it degrades the FEL performance by reducing the saturation power and increasing the saturation length. To compensate these destroying effects, the optimum function or degree of electron beam pre-bunching and optimum parameters of wiggler tapering are found by the successive runs of the simulation code.