56 research outputs found
X-ray Free-Electron Laser accelerator to study on Quantum Electro-Dynamics
X-ray free-electron lasers (XFELs) utilize high-density and high-energy
electron bunches which are well-suited to produce Compton back-scattering
radiation. Here we study study interaction of such electron bunches during
head-on collision with retroreflected X-ray pulses, emitted by an XFEL. Such
collisions allow one to conduct experiments on electron-positron pair
production, both through trident and gamma-gamma colliding processes. We
discuss cost-effective setups to study such processes, taking advantage of the
existing conventional as well as proposed X-ray FEL infrastructure. We estimate
parameters of the proposed experiments and compare them with other projects
under construction
Proposal to generate 10 TW level femtosecond x-ray pulses from a baseline undulator in conventional SASE regime at the European XFEL
Output characteristics of the European XFEL have been previously studied
assuming an operation point at 5 kA peak current. In this paper we explore the
possibility to go well beyond such nominal peak current level. In order to
illustrate the potential of the European XFEL accelerator complex we consider a
bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An
advantage of operating at such high peak current is the increase of the x-ray
output peak power without any modification to the baseline design. Based on
start-to-end simulations, we demonstrate that such high peak current, combined
with undulator tapering, allows one to achieve up to a 100-fold increase in a
peak power in the conventional SASE regime, compared to the nominal mode of
operation. In particular, we find that 10 TW-power level, femtosecond x-ray
pulses can be generated in the photon energy range between 3 keV and 5 keV,
which is optimal for single biomolecule imaging. Our simulations are based on
the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline,
and indicate that one can achieve diffraction to the desired resolution with 15
mJ (corresponding to about 3e13 photons) in pulses of about 3 fs, in the case
of a 100 nm focus at the photon energy of 3.5 keV
Effects of energy spread on Brightness and Coherence of undulator sources
The (spectral) brightness for partially transverse coherent sources as
Synchrotron Radiation (SR) and Free-Electron Laser (FEL) sources can be defined
as the maximum of the Wigner distribution. Then, the brightness includes
information on both coherence and wavefront characteristics of the radiation
field. For undulator sources, it is customary to approximate the
single-electron electric field at resonance with a Gaussian beam, leading to
great simplifications. Attempts to account for the modified spatial and angular
profile of the undulator radiation in the presence of detuning due to energy
spread currently build on the simplified brightness expression derived under
the assumption of Gaussian beams. The influence of energy spread on undulator
radiation properties is becoming important in view of diffraction-limited rings
with ultralow emittance coming on-line. Here we discuss the effects of energy
spread on the brightness of undulator radiation at resonance, as well as
relevant relations with coherence properties.Comment: Preprint accepted for publication in the Journal of Synchrotron
radiation, 30 pages, 8 figure
Extension of SASE bandwidth up to 2% as a way to increase the efficiency of protein structure determination by x-ray nanocrystallography at the European XFEL
Femtosecond x-ray nanocrystallography exploiting XFEL radiation is an
emerging method for protein structure determination using crystals with sizes
ranging from a few tens to a few hundreds nanometers. Crystals are randomly hit
by XFEL pulses, producing diffraction patterns at unknown orientations. One can
determine these orientations by studying the diffraction patterns themselves,
i.e. by indexing the Bragg peaks. The number of indexed individual images and
the SASE bandwidth are inherently linked, because increasing the number of
Bragg peaks per individual image requires increasing the bandwidth of the
spectrum. This calls for a few percent SASE bandwidth, resulting in an increase
in the number of indexed images at the same number of hits. Based on
start-to-end simulations for the baseline of the European XFEL, we demonstrate
here that it is possible to achieve up to a tenfold increase in SASE bandwidth,
compared with the nominal mode of operation. This provides a route for further
increasing the efficiency of protein structure determination at the European
XFEL. We illustrate this concept with simulations of lysozyme nanocrystals
Perspectives of Imaging of Single Protein Molecules with the Present Design of the European XFEL. - Part I - X-ray Source, Beamlime Optics and Instrument Simulations
The Single Particles, Clusters and Biomolecules (SPB) instrument at the
European XFEL is located behind the SASE1 undulator, and aims to support
imaging and structure determination of biological specimen between about 0.1
micrometer and 1 micrometer size. The instrument is designed to work at photon
energies from 3 keV up to 16 keV. This wide operation range is a cause for
challenges to the focusing optics. In particular, a long propagation distance
of about 900 m between x-ray source and sample leads to a large lateral photon
beam size at the optics. The beam divergence is the most important parameter
for the optical system, and is largest for the lowest photon energies and for
the shortest pulse duration (corresponding to the lowest charge). Due to the
large divergence of nominal X-ray pulses with duration shorter than 10 fs, one
suffers diffraction from mirror aperture, leading to a 100-fold decrease in
fluence at photon energies around 4 keV, which are ideal for imaging of single
biomolecules. The nominal SASE1 output power is about 50 GW. This is very far
from the level required for single biomolecule imaging, even assuming perfect
beamline and focusing efficiency. Here we demonstrate that the parameters of
the accelerator complex and of the SASE1 undulator offer an opportunity to
optimize the SPB beamline for single biomolecule imaging with minimal
additional costs and time. Start to end simulations from the electron injector
at the beginning of the accelerator complex up to the generation of diffraction
data indicate that one can achieve diffraction without diffraction with about
0.5 photons per Shannon pixel at near-atomic resolution with 1e13 photons in a
4 fs pulse at 4 keV photon energy and in a 100 nm focus, corresponding to a
fluence of 1e23 ph/cm^2. This result is exemplified using the RNA Pol II
molecule as a case study
Superradiant Undulator Radiation for Selective THz Control Experiments at XFELs
The generation of frequency-tunable, narrow-bandwidth and
carrier-envelope-phase stable THz pulses with fields in the MV/cm regime that
can be appropriately timed to the femtosecond X-ray pulses from
free-electron-lasers is of highest scientific interest. It will enable to
follow the electronic and structural dynamics stimulated by (non)linear
selective excitations of matter on few femtosecond time and {\AA}ngstrom length
scales. In this article, a scheme based on superradiant undulator radiation
generated just after the XFEL is proposed. The concept utilizes cutting edge
superconducting undulator technology and provides THz pulses in a frequency
range between 3 and 30 THz with exceptional THz pulse energies. Relevant
aspects for realization and operation are discussed point by point on the
example of the European XFEL
Novel opportunities for sub-meV inelastic X-ray scattering at high-repetition rate self-seeded X-ray free-electron lasers
Inelastic X-ray scattering (IXS) is an important tool for studies of
equilibrium dynamics in condensed matter. A new spectrometer recently proposed
for ultra-high-resolution IXS (UHRIX) has achieved 0.6~meV and 0.25~nm
spectral and momentum transfer resolutions, respectively. However, further
improvements down to 0.1~meV and 0.02~nm are required to close the gap
in energy-momentum space between high and low frequency probes. We show that
this goal can be achieved by further optimizing the X-ray optics and by
increasing the spectral flux of the incident X-ray pulses. UHRIX performs best
at energies from 5 to 10 keV, where a combination of self-seeding and undulator
tapering at the SASE-2 beamline of the European XFEL promises up to a
hundred-fold increase in average spectral flux compared with nominal SASE
pulses at saturation, or three orders of magnitude more than possible with
storage-ring based radiation sources. Wave-optics propagation shows that about
~ph/s in a -eV bandwidth can be achieved on the
sample. This will provide unique new possibilities for dynamics studies by IXS.Comment: 17 pages, 14 figure
Development of a hard X-ray split-and-delay line and performance simulations for two-color pump-probe experiments at the European XFEL
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 89, 063121 (2018) and may be found at https://doi.org/10.1063/1.5027071.A hard X-ray Split-and-Delay Line (SDL) under construction for the Materials Imaging and Dynamics station at the European X-Ray Free-Electron Laser (XFEL) is presented. This device aims at providing pairs of X-ray pulses with a variable time delay ranging from −10 ps to 800 ps in a photon energy range from 5 to 10 keV for photon correlation and X-ray pump-probe experiments. A custom designed mechanical motion system including active feedback control ensures that the high demands for stability and accuracy can be met and the design goals achieved. Using special radiation configurations of the European XFEL’s SASE-2 undulator (SASE: Self-Amplified Spontaneous Emission), two-color hard x-ray pump-probe schemes with varying photon energy separations have been proposed. Simulations indicate that more than 109 photons on the sample per pulse-pair and up to about 10% photon energy separation can be achieved in the hard X-ray region using the SDL.BMBF, 05K13KT4, Verbundprojekt FSP 302 - Freie-Elektronen-Laser: Nanoskopische Systeme. Teilprojekt 1: Split-and-Delay Instrument für die European XFEL Beamline Materials Imaging and DynamicsBMBF, 05K16BC1, Split-and-Delay Instrument für die European XFEL Beamline Materials Imaging and Dynamic
Multiple-core-hole resonance spectroscopy with ultraintense X-ray pulses
Understanding the interaction of intense, femtosecond X-ray pulses with heavy
atoms is crucial for gaining insights into the structure and dynamics of
matter. One key aspect of nonlinear light-matter interaction was, so far, not
studied systematically at free-electron lasers -- its dependence on the photon
energy. Using resonant ion spectroscopy, we map out the transient electronic
structures occurring during the complex charge-up pathways. Massively hollow
atoms featuring up to six simultaneous core holes determine the spectra at
specific photon energies and charge states. We also illustrate how the
influence of different X-ray pulse parameters that are usually intertwined can
be partially disentangled. The extraction of resonance spectra is facilitated
by the fact that the ion yields become independent of the peak fluence beyond a
saturation point. Our study lays the groundwork for novel spectroscopies of
transient atomic species in exotic, multiple-core-hole states that have not
been explored previously.Comment: Supplementary information is include
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