Abstract
A hard x-ray self-seeding (HXRSS) setup will soon be available at the European X-ray Free Electron Laser (XFEL). The availability of high repetition rate x-ray pulses poses novel challenges in the setup development, compared to the choices made at other facilities, mainly crystal heat-load and radiation-damage issues. However, high-repetition rate is expected to allow for unprecedented output characteristics. A two-chicane HXRSS setup is found to be optimal for the European XFEL. In this paper we discuss the physical choices peculiar to that facility and simulations done, which allow us to fix the parameter for the setup design.
Highlights
Hard x-ray self-seeding (HXRSS) based on single crystal monochromators [1,2] is an active filtering technique allowing for an increased spectral density and longitudinal coherence at hard x-ray FELs that usually exploit the selfamplified spontaneous emission (SASE) mechanism as a baseline mode of operation.A HXRSS setup based on single crystal monochromators will soon be installed at the SASE2 FEL line of the European X-ray Free Electron Laser (XFEL)
In the following parts of this paper, aside from confirming the effect of signal-to-noise ratio (SNR) increase by simulations, we will focus our attention on two main questions: first, where is the optimal location for the HXRSS monochromators along the SASE2 undulator and, second, what performance we can expect from a two-chicane HXRSS setup, where we allow a certain maximum pulse energy to impinge on the crystals
In this paper we investigated and optimized the overall performance of the forthcoming HXRSS setup at the European XFEL
Summary
Hard x-ray self-seeding (HXRSS) based on single crystal monochromators [1,2] is an active filtering technique allowing for an increased spectral density and longitudinal coherence at hard x-ray FELs that usually exploit the selfamplified spontaneous emission (SASE) mechanism as a baseline mode of operation. Recent studies [4,5,6] suggest that the use of a two-chicane scheme brings no advantage over a single chicane In contrast to those claims, in this paper we show, both theoretically and by means of simulations, that a two-chicane solution allows for an increased signalto-noise ratio, the signal being the seeded FEL pulse, and the noise being, in this case, the underlying shotnoise amplification. The HXRSS setup designed for the European XFEL is expected to operate from below 5 keV (theoretically down to 3 keV, with probable limitations due to heat load) up to 14.4 keV (and above, if one considers the option of tuning part of the radiator to a harmonic of the fundamental [9]), with different nominal electron charges 20, 100, 250, 500, and 1 nC and working energies 8.5, 12, 14, and 17.5 GeV.
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