Microbunch preserving bending system for a helical radiator at the European X-ray Free Electron Laser

Abstract

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.

Generation of attosecond coherent X-ray radiation through modulation compression

“…Such a prebunched beam can be used to generate coherent attosecond hard X-ray radiation for applications such as core electron ultrafast dynamics studies [20]. Careful lattice design is needed in order to preserve the prebunched microstructure of the electron beam before entering the undulator for X-ray radiation [21].…”

Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam

“…7 requires only magnetic optics that are already present in an undulator line. This contrasts with the elegant but lengthy achromatic systems envisioned to rotate and preserve microbunches through a bend [15,32,33].…”

“…The result, demonstrated by the wavelength scaling in Eq. (15), is a critical angle of ∼2 μRad at 1.5 Å.…”

“…With a carefully chosen undulator K parameter in the Delta undulator, a powerful diverted beam was observed at several times the intrinsic beam divergence. It is generally understood that a transverse kick does not change the microbunch orientation, and hence suppresses the coherent radiation emitted in the direction of the electron motion [14,15]. This understanding has been formalized into a theory of far-field radiation from a kicked beam [16,17], but is inconsistent with Delta undulator experiments.…”

Lattice design of the integrable optics test accelerator and optical stochastic cooling experiment at Fermilab

“…We assume there is no horizontal-vertical coupling in where l and δ are the longitudinal offset and momentum deviation. Following the steps outlined Section 5.3, the sample lengthening due to second-order effects (ignoring terms proportional to l) is [30]:…”