Wake monochromator in asymmetric and symmetric Bragg and Laue geometry for self-seeding the European X-ray FEL

TL;DR

This paper explores the use of wake monochromators with asymmetric and symmetric Bragg and Laue geometries in diamond crystals to enhance self-seeding at the European X-ray FEL, enabling fully coherent TW power pulses for bio-imaging.

Contribution

It proposes a novel upgrade concept for the European X-ray FEL using wake monochromators with optimized crystal geometries and configurations to improve coherence and spectral coverage.

Findings

Feasible photon energy range from 3 keV to 13 keV.

Maximal spatial shift occurs at small Bragg angles.

Using four crystal planes allows broad spectral tunability.

Abstract

We discuss the use of self-seeding schemes with wake monochromators to produce TW power, fully coherent pulses for applications at the dedicated bio-imaging bealine at the European X-ray FEL, a concept for an upgrade of the facility beyond the baseline previously proposed by the authors. We exploit the asymmetric and symmetric Bragg and Laue reflections (sigma polarization) in diamond crystal. Optimization of the bio-imaging beamline is performed with extensive start-to-end simulations, which also take into account effects such as the spatio-temporal coupling caused by the wake monochromator. The spatial shift is maximal in the range for small Bragg angles. A geometry with Bragg angles close to pi/2 would be a more advantageous option from this viewpoint, albeit with decrease of the spectral tunability. We show that it will be possible to cover the photon energy range from 3 keV to 13 keV by using four different planes of the same crystal with one rotational degree of freedom.