DESIGN STUDY OF AN ISOCHRONOUS BEND FOR A HELICAL RADIATOR AT THE EUROPEAN XFEL

The planar SASE3 undulator system of the European XFEL will produce linearly polarized radiation in the wavelength range 0.4 to 1.6 nm. There is, however, a strong demand for circular polarized radiation in this wavelength range. After the planar undulator the electron beam is completely bunched. Sending it through a suitable radiator is an economically and technically convenient method to generate radiation with polarization properties fully determined by the radiator. If a bend is used to separate the light created by the linear SASE3 from that of the radiator there are two independent light sources. In this case the light of the radiator is not contaminated by the light of the upstream linear FEL. The micro bunching of the planar undulator must be preserved through the bend. In this paper, a first order isochronous bend is presented, which uses beta function matching to minimize nonlinear aberrations. This solution is capable to preserve micro bunching at wave lengths larger than 1.6nm.