The Full Potential of the Baseline SASE Undulators of the European XFEL

TL;DR

This paper demonstrates that optimizing the undulator gap configuration in the European XFEL can significantly enhance SASE X-ray beam performance, achieving up to tenfold increases in peak power and spectral density without extra hardware.

Contribution

It introduces a method to improve XFEL output by undulator gap optimization, highlighting the potential of tapering in the SASE regime.

Findings

Up to tenfold increase in peak power achieved.

Enhanced photon spectral density demonstrated.

Optimization can be done without additional hardware.

Abstract

The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure simply consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the soft X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime. We illustrate this fact for the SASE3 beamline. The FEL code Genesis has been extensively used for these studies. Based on these findings we suggest that the requirements for the SASE3 instrument (SCS, SQS) and for the SASE3 beam transport system be updated.