Phase Slip in an Undulator with Pole and BPM Errors

摘要

A statistical analysis of a corrected electron trajectory through a planar FELundulator is used to predict the optimal beam position monitor (BPM) spacing. The undulator is composed of modular sections, each containing many dipoles with random field and roll angle errors. Located between each section are inaccurate BPMs, steering correctors, and possibly quadrupole magnets. An analytical formula for electron-to-photon phase errors is derived and used to estimate the best BPM spacing. The results are applied to the LCLS FEL undulator, which has demanding requirements on electron trajectory straightness.