  We propose to use the self-seeding scheme with single crystal monochromator
at the European X-ray FEL to produce monochromatic, high-power radiation at 16
keV. Based on start to end simulations we show that the FEL power of the
transform-limited pulses can reach about 100 GW by exploiting tapering in the
tunable-gap baseline undulator. The combination of high photon energy, high
peak power, and very narrow bandwidth opens a vast new range of applications,
and includes the possibility to considerably increase the user capacity and
fully exploit the high repetition rate of the European XFEL. In fact, dealing
with monochromatic hard X-ray radiation one may use crystals as deflectors with
minimum beam loss. To this end, a photon beam distribution system based on the
use of crystals in the Bragg reflection geometry is proposed for future study
and possible extension of the baseline facility. They can be repeated a number
of times to form an almost complete (one meter scale) ring with an angle of 20
degrees between two neighboring lines. The reflectivity of crystal deflectors
can be switched fast enough by flipping the crystals with piezo-electric
devices similar to those for X-ray phase retarders at synchrotron radiation
facilities. It is then possible to distribute monochromatic hard X-rays among
10 independent instruments, thereby enabling 10 users to work in parallel. The
unmatched repetition rate of the European XFEL would be therefore fully
exploited.
