THE EFFECTS OF WIGGLER ERRORS ON FREE-ELECTRON-LASER PERFORMANCE

The effects of random wiggler magnetic-field errors on free electron lasers are analyzed analytically adn computationally. Wiggler field errors perturb the electron beam as it propagates and lead to a random walk of the beam centroid, δx, as well as cause deviations in the parallel-beam energy, δγ∥, and in the relative phase of the electrons in the ponderomotive wave, δΨ. The phase deviation δΨ is identified as the single most important parameter charaterizing the detrimental effects of wiggler errors. In order to avoid significant reduction in gain, it is necessary for the phase deviation to be small compared to 2π. It is shown that transverse focusing of the electron beam is not effective in reducing the phase deviation. Furthermore, it is shown that beam steering at the wiggler entrance reduces the average phase deviation at the end of the wiggler by 1 3. The detrimental effects of wiggler errors may be reduced by arranging the magnet poles in an optimal ordering such that the magnitude of the phase deviation is minimized. © 1990.