Polarization control in X-ray FELs by reverse undulator tapering

E. A. Schneidmiller; M. V. Yurkov

doi:10.1117/12.2181224

12 May 2015 Polarization control in X-ray FELs by reverse undulator tapering

E. A. Schneidmiller, M. V. Yurkov

Proceedings Volume 9512, Advances in X-ray Free-Electron Lasers Instrumentation III; 951218 (2015) https://doi.org/10.1117/12.2181224
Event: SPIE Optics + Optoelectronics, 2015, Prague, Czech Republic

Abstract

Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade one can consider an installation of a short helical (or cross-planar) afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. In this paper we propose a new method for such a suppression: an application of the reverse taper in the main undulator. We discover that in a certain range of the taper strength, the density modulation (bunching) at saturation is practically the same as in the case of non-tapered undulator while the power of linearly polarized radiation is suppressed by orders of magnitude. Then strongly modulated electron beam radiates at full power in the afterburner. Considering SASE3 undulator of the European XFEL as a practical example, we demonstrate that soft X-ray radiation pulses with peak power in excess of 100 GW and an ultimately high degree of circular polarization can be produced. The proposed method is rather universal, i.e. it can be used at SASE FELs and seeded (self-seeded) FELs, with any wavelength of interest, in a wide range of electron beam parameters, and with any repetition rate.

Citation Download Citation

E. A. Schneidmiller and M. V. Yurkov "Polarization control in X-ray FELs by reverse undulator tapering", Proc. SPIE 9512, Advances in X-ray Free-Electron Lasers Instrumentation III, 951218 (12 May 2015); https://doi.org/10.1117/12.2181224

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