Wiggler imperfections in free-electron lasers

Abstract

A self-consistent 3-D analysis of wiggler imperfections in FELs is described using the WIGGLIN simulation code. WIGGLIN treats the electron dynamics using the 3-D Lorentz force equations, and does not rely on a wiggler-averaged formalism. In the planar wiggler model used, both the divergence and the axial component of the curl vanish identically while the transverse components of the curl are small. In describing wiggler imperfections, a random variation is chosen for the pole-to-pole variations in the amplitude and a continuous map is used between the pole faces. The average efficiency, as well as the standard deviation about the average efficiency, is determined by using an ensemble of different randomly chosen wiggler variations with a fixed rms value. The specific parameters chosen correspond to the 35-GHz ELF experiment conducted at Lawrence Livermore National Laboratory; however, the fundamental physics is relevant to a wide range of FEL experiments. On average, increases in the field imperfections cause a decrease in the efficiency; however, this is relatively benign and is certainly a much less severe constraint than that imposed by electron beam quality considerations. In addition, particular error distributions can result in efficiency enhancements.