The free-electron laser operates by the coherent axial bunching of electrons, and the interaction is extremely sensitive to random imperfections in the wiggler field. Planar wigglers can easily exhibit a random rms fluctuation of 0.5% from pole to pole. This yields a velocity fluctuation that causes a phase jitter that also detunes the wave-particle resonance. In this chapter, we explore the effects of wiggler imperfections on free-electron laser performance and compare the effects of wiggler imperfections with those of an axial energy spread.
KeywordsWiggler imperfections Phase jitter Nonlinear modeling
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