The Effects of Wiggler Errors on Free Electron Laser Performance
NAVAL RESEARCH LAB WASHINGTON DC
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The effects of random wiggler magnetic field errors on free electron lasers is analyzed analytically and computationally. Wiggler field errors perturb the electron beam as it propagates and lead to a random walk of the beam centroid delta x as well as cause deviations in the parallel beam energy delta gamma parallel and in the relative phase of the electrons in the ponderomotive wave delta psi. The phase deviation delta psi is identified as the single most important parameter characterizing 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 pi. It is shown that transverse focusing of the electron beam is not effective in reducing the phase deviation i.e., transverse focusing reduces the average phase deviation by 12. Furthermore, it is shown that the results of beam steering at the wiggler entrance reduces the average phase deviation at the end of the wiggler by 13. 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. Keywords Free electron lasers Random field errors.
- Lasers and Masers