A detailed study of hardware related tolerances for the undulator system for the European x-ray freeelectron laser (XFEL) has been performed. Various realistic error scenarios were taken into account. These included girder deformation under magnetic loads, the influence of temperature variation, errors caused by limited accuracy of the motion control system, and phase matching errors. Undulator errors are classified into periodic and random errors. For periodic errors, such as girder deformation, a close and universal correlation between rms phase shake and power degradation was established, while the results of random errors show more scatter in the results, which have to be evaluated statistically. For XFEL parameters the correlation is very good and can be used to evaluate the influence of different error sources without the need to do extended FEL simulations. The method was applied to reevaluate some critical tolerances on the XFEL undulator systems: girder deformation, accuracy for gap control, and the requirement on temperature stability. The results show that these tolerances could be relaxed as compared to earlier work.
In long gap tunable undulators, strong magnetic forces always lead to some amount of gap-dependent girder deformation and resulting gap-dependent phase errors. For the undulators for the European XFEL, this problem has been investigated thoroughly and quantitatively. Using the different gap dependencies of suitable shims and pole height tuning, a method is presented which can be applied to reduce the overall gap dependence of the phase error if needed. It is exemplified by tuning one of the undulator segments for the European X-Ray Free Electron Laser back to specs.
At the European X-ray Free Electron Laser there is a planar undulator system under construction called SASE3, which produces intense linearly polarized light in the wavelength range from 0.4-1.6 nm. Nevertheless there is a strong demand for circularly polarized radiation in this wavelength range. An important part of a potential solution is described in this paper. After the planar undulator the electron beam, which is completely bunched, is sent through a suitable radiator. This can be an economically and technically convenient method to generate radiation with polarization properties, which are determined only by the radiator. If in addition a bend is used to separate the light created by the linear SASE3 from that of the radiator, two beam lines may be served, one with planar and one with circular radiation. In this case the light of the helical radiator is not contaminated by the light generated by the planar system. In order to obtain coherent radiation in the radiator, the microbunching of the planar undulator must be preserved throughout the bend. This is the basic problem. In this paper a fundamental, basic study is made. Several solutions for bending systems are presented, whose complexities, wavelength ranges, and debunching effects are different. The expected circular polarization and radiation power by such a bend are simulated for a model radiator.
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