122 research outputs found
Corrugated structure insertion for extending the SASE bandwidth up to 3% at the European XFEL
The usage of x-ray free electron laser (XFEL) in femtosecond
nanocrystallography involves sequential illumination of many small crystals of
arbitrary orientation. Hence a wide radiation bandwidth will be useful in order
to obtain and to index a larger number of Bragg peaks used for determination of
the crystal orientation. Considering the baseline configuration of the European
XFEL in Hamburg, and based on beam dynamics simulations, we demonstrate here
that the usage of corrugated structures allows for a considerable increase in
radiation bandwidth. Data collection with a 3% bandwidth, a few microjoule
radiation pulse energy, a few femtosecond pulse duration, and a photon energy
of 5.4 keV is possible. For this study we have developed an analytical modal
representation of the short-range wake function of the flat corrugated
structures for arbitrary offsets of the source and the witness particles.Comment: 29 pages, 17 figure
Automatic tuning of Free Electron Lasers
Existing FEL facilities often suffer from stability issues: so electron
orbit, transverse electron optics, electron bunch compression and other
parameters have to be readjusted often to account for drifts in performance of
various components. The tuning procedures typically employed in operation are
often manual and lengthy. We have been developing a combination of model-free
and model-based automatic tuning methods to meet the needs of present and
upcoming XFEL facilities. Our approach has been implemented at FLASH
\cite{flash} to achieve automatic SASE tuning using empirical control of orbit,
electron optics and bunch compression. In this paper we describe our approach
to empirical tuning, the software which implements it, and the results of using
it at FLASH. We also discuss the potential of using machine learning and
model-based techniques in tuning methods
Calculation of wakefields in 2D rectangular structures
We consider the calculation of electromagnetic fields generated by an
electron bunch passing through a vacuum chamber structure that, in general,
consists of an entry pipe, followed by some kind of transition or cavity, and
ending in an exit pipe. We limit our study to structures having rectangular
cross-section, where the height can vary as function of longitudinal coordinate
but the width and side walls remain fixed. For such structures, we derive a
Fourier representation of the wake potentials through one-dimensional
functions. A new numerical approach for calculating the wakes in such
structures is proposed and implemented in the computer code ECHO(2D). The
computation resource requirements for this approach are moderate and comparable
to those for finding the wakes in 2D rotationally symmetric structures.
Numerical examples obtained with the new numerical code are presented.Comment: 31 pages, 10 figure
Beam Dynamics and Tolerance Studies of the THz-driven Electron Linac for the AXSIS Experiment
A dielectric-loaded linac powered by THz-pulses is one of the key parts of
the "Attosecond X-ray Science: Imaging and Spectroscopy" (AXSIS) project at
DESY, Hamburg. As in conventional accelerators, the AXSIS linac is designed to
have phase velocity equal to the speed of light which, in this case, is
realized by tuning the thickness of the dielectric layer and the radius of the
vacuum channel. Therefore, structure fabrication errors will lead to a change
in the beam dynamics and beam quality. Additionally, errors in the bunch
injection will also affect the acceleration process and can cause beam loss on
the linac wall. This paper numerically investigates the process of electron
beam acceleration in the AXSIS linac, taking into account the aforementioned
errors. Particle tracking simulations were done using the code ECHO, which uses
a low-dispersive algorithm for the field calculation and was specially adapted
for the dielectric-loaded accelerating structures.Comment: EAAC'17 conference proceeding
SCHEME FOR GENERATING AND TRANSPORTING THZ RADIATION TO THE X-RAY EXPERIMENTAL HALL AT THE EUROPEAN XFEL
Abstract We consider generation of THz radiation from the spent electron beam downstream of the SASE2 undulator in the electron beam dump area. The THz output must propagate at least for 250 meters through the photon beam tunnel to the experimental hall to reach the SASE2 X-ray hutches. We propose to use an open beam waveguide such as an iris guide as transmission line. In order to efficiently couple radiation into the iris transmission line, generation of the THz radiation pulse can be performed directly within the iris guide. The line transporting the THz radiation to the SASE2 X-ray hutches introduces a path delay of about 20 m. Since THz pump/X-ray probe experiments should be enabled, we propose to exploit the European XFEL baseline multi-bunch mode of operation, with 222 ns electron bunch separation, in order to cope with the delay between THz and X-ray pulses. We present start-to-end simulations for 1 nC bunch operation-parameters, optimized for THz pump/X-ray probe experiments. Detailed characterization of the THz and SASE X-ray radiation pulses is performed. Highly focused THz beams will approach the high field limit of 1 V/atomic size
The ice-free topography of Svalbard
We present a first version of the Svalbard ice-free topography (SVIFT1.0) using a mass-conserving approach for mapping glacier ice thickness. SVIFT1.0 is informed by more than 900’000 point-measurements of glacier thickness, totalling almost 8’300 km of thickness profiles. It is publicly available for download. Our estimate for the total ice volume is 6’253km3, equivalent to 1.6cm sea-level rise. The thickness map suggests that 13% of the glacierised area is grounded below sea-level. Thickness values are provided together with a map of error estimates that comprise uncertainties in the thickness surveys as well as in other input variables. Aggregated error estimates are used to define a likely ice-volume range of 5’200-7’400km3. The ice-front thickness of marine-terminating glaciers is a key quantity for ice-loss attribution because it controls the potential ice discharge by iceberg calving into the ocean. We find a mean ice-front thickness of 133m for the archipelago
Indirect Methods for Wake Potential Integration.
The development of the modern accelerator and free-electron laser projects requires to consider wake fields of very short bunches in arbitrary three dimensional structures. To obtain the wake numerically by direct integration is difficult, since it takes a long time for the scattered fields to catch up to the bunch. On the other hand no general algorithm for indirect wake field integration is available in the literature so far. In this paper we review the known indirect methods to compute wake potentials in rotationally symmetric and cavity-like three dimensional structures. For arbitrary three dimensional geometries we introduce several new techniques and test them numerically
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