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Spatially-periodic magnetic structures are widely used for generation of high-brilliance radiation in storage rings, sources of synchrotron radiation and free electron lasers. In 1947, V.L. Ginzburg suggested the first undulator scheme. An alternating magnetic field created by a planar undulator makes electrons oscillate in the transverse direction, with interference of radiation emitted from separate parts of the trajectory. The spectrum of the forward emitted radiation is enchanced due to constructive interference. The ondulator is made of the magnetized bars that are not perfect and their magnetization differs. Therefore, the electron trajectory is not purely sinusoidal and, as a result, the spectral intensity fades. The task was to find out if the precision of magnet manufacturing is sufficient. This paper presents modelling of electron motion in the measured magnetic field of the new (third) free electron laser at the Siberian Synchrotron Radiation Centre. We have managed to estimate the effect of the field errors through comparison of the resulting emitted field amplitude with the amplitude from ideal magnet bars using the hodograph method.
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