Accelerating the convergence of free electron laser simulations by retrieving a spatially-coherent component of microbunching

Abstract: A simple method to reduce the numerical cost in free electron laser (FEL) simulations is presented, which is based on retrieving a spatially-coherent component of microbunching to suppress artifact effects that can potentially overestimate the FEL gain; this significantly reduces the number of macroparticles to reach the numerical convergence and enables the direct computation of amplified radiation without solving the wave equation. Examples of FEL simulations performed to demonstrate the proposed method show that the computation time to get a reliable result is reduced by 1-2 orders of magnitude depending on the simulation condition.