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Beam based alignment of the undulator section is one of the delicate issues in beam commissioning and regular beam tuning of X-FEL facilities since the tolerance on the electron beam orbit straightness is tight, typically a few micro-meters rms. A new approach based on the dipole corrector strengths is under investigation for the PSI future X-FEL facility, SwissFEL. The idea is to minimize the deviation of corrector strengths, required to steer the electron beam to the beam position monitor (BPM) centres, by varying BPM positions. The beam trajectory, if there is no dipolar error, must be fully straight with no corrector excitation, where the deviation is zero, i.e. minimized. Under dipolar errors, e.g. undulator imperfections, the minimization is performed w.r.t. their average value. The procedure requires precise BBA of quadrupoles to adjacent BPM beforehand and an orbit feedback in operation. Although these preparation works require some efforts, the method is rather simple and robust. The methodology together with expected performance from analytical estimation and simulations applied to the undulator section of SwissFEL is presented.
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