245 research outputs found
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
Studies on charge production from Cs2Te photocathodes in the PITZ L-band normal conducting radio frequency photo injector
This paper discusses the behavior of electron bunch charge produced in an
L-band normal conducting radio frequency cavity (RF gun) from Cs2Te
photocathodes illuminated with ps-long UV laser pulses when the laser
transverse distribution consists of a flat-top core with Gaussian-like decaying
halo. The produced charge shows a linear dependence at low laser pulse energies
as expected in the quantum efficiency limited emission regime, while its
dependence on laser pulse energy is observed to be much weaker for higher
values, due to space charge limited emission. However, direct plug-in of
experimental parameters into the space charge tracking code ASTRA yields lower
output charge in the space charge limited regime compared to measured values.
The rate of increase of the produced charge at high laser pulse energies close
to the space charge limited emission regime seems to be proportional to the
amount of halo present in the radial laser profile since the charge from the
core has saturated already. By utilizing core + halo particle distributions
based on measured radial laser profiles, ASTRA simulations and semi-analytical
emission models reproduce the behavior of the measured charge for a wide range
of RF gun and laser operational parameters within the measurement
uncertainties.Comment: 15 pages, 16 figures, 2 table
Single shot cathode transverse momentum imaging in high brightness photoinjectors
In state of the art photoinjector electron sources, thermal emittance from photoemission dominates the final injector emittance. Therefore, low thermal emittance cathode developments and diagnostics are very important. Conventional thermal emittance measurements for the high gradient gun are time-consuming and thus thermal emittance is not measured as frequently as quantum efficiency during the lifetime of photocathodes, although both are important properties for the photoinjector optimizations. In this paper, a single shot measurement of photoemission transverse momentum, i.e., thermal emittance per rms laser spot size, is proposed for photocathode rf guns. By tuning the gun solenoid focusing, the electrons' transverse momenta at the cathode are imaged to a downstream screen, which enables a single shot measurement of both the rms value and the detailed spectra of the photoelectrons' transverse momenta. Both simulations and proof of principle experiments are reported
Emittance Reduction of RF Photoinjector Generated Electron Beams by Transverse Laser Beam Shaping
Laser pulse shaping is one of the key elements to generate low emittance electron beams with RF photoinjectors. Ultimately high performance can be achieved with ellipsoidal laser pulses, but 3-dimensional shaping is challenging. High beam quality can also be reached by simple transverse pulse shaping, which has demonstrated improved beam emittance compared to a transversely uniform laser in the 'pancake' photoemission regime. In this contribution we present the truncation of a Gaussian laser at a radius of approximately one sigma in the intermediate (electron bunch length directly after emission about the same as radius) photoemission regime with high acceleration gradients (up to 60 MV/m). This type of electron bunch is used e.g. at the European XFEL and FLASH free electron lasers at DESY, Hamburg site and is being investigated in detail at the Photoinjector Test facility at DESY in Zeuthen (PITZ). Here we present ray-tracing simulations and experimental data of a laser beamline upgrade enabling variable transverse truncation. Initial projected emittance measurements taken with help of this setup are shown, as well as supporting beam dynamics simulations. Additional simulations show the potential for substantial reduction of slice emittance at PITZ. © Published under licence by IOP Publishing Ltd
Status and Objectives of the Dedicated Accelerator R&D Facility "SINBAD" at DESY
We present a status update on the dedicated R\&D facility SINBAD which is
currently under construction at DESY. The facility will host multiple
independent experiments on the acceleration of ultra-short electron bunches and
novel, high gradient acceleration methods. The first experiment is the
ARES-experiment with a normal conducting 100\,MeV S-band linac at its core. We
present the objectives of this experiment ranging from the study of compression
techniques to sub-fs level to its application as injector for various advanced
acceleration schemes e.g. the plans to use ARES as a test-site for DLA
experiments in the context of the ACHIP collaboration. The time-line including
the planned extension with laser driven plasma-wakefield acceleration is
presented. The second initial experiment is AXSIS which aims to accelerate
fs-electron bunches to 15\,MeV in a THz driven dielectric structure and
subsequently create X-rays by inverse Compton scattering.Comment: EAAC'17 conference proceeding
Report on Gun Conditioning Activities at PITZ in 2013
Recently three RF guns were prepared at the Photo Injector Test Facility at DESY, location Zeuthen PITZ for their subsequent operation at FLASH and the European XFEL. The gun 3.1 is a previous cavity design and is currently installed and operated at FLASH, the other two guns 4.3 and 4.4 were of the current cavity design and are dedicated to serve for the start up of the European XFEL photo injector. All three cavities had been dry ice cleaned prior their conditioning and hence showed low dark current levels. The lowest dark current level as low as 60 amp; 956;A at 65MV m field amplitude has been observed for the gun 3.1. This paper reports in details about the conditioning process of the most recent gun 4.4. It informs about experience gained at PITZ during establishing of the RF conditioning procedure and provides a comparison with the other gun cavities in terms of the dark currents. It also summarizes the major setup upgrades, which have affected the conditioning processes of the cavitie
Persistent post-traumatic headache: A migrainous loop or not? The clinical evidence
Background: Headache is a common complication of traumatic brain injury. The International Headache Society defines post-traumatic headache as a secondary headache attributed to trauma or injury to the head that develops within seven days following trauma. Acute post-traumatic headache resolves after 3 months, but persistent post-traumatic headache usually lasts much longer and accounts for 4% of all secondary headache disorders. Main body: The clinical features of post-traumatic headache after traumatic brain injury resemble various types of primary headaches and the most frequent are migraine-like or tension-type-like phenotypes. The neuroimaging studies that have compared persistent post-traumatic headache and migraine found different structural and functional brain changes, although migraine and post-traumatic headache may be clinically similar. Therapy of various clinical phenotypes of post-traumatic headache almost entirely mirrors the therapy of the corresponding primary headache and are currently based on expert opinion rather than scientific evidence. Pharmacologic therapies include both abortive and prophylactic agents with prophylaxis targeting comorbidities, especially impaired sleep and post-traumatic disorder. There are also effective options for non-pharmacologic therapy of post-traumatic headache, including cognitive-behavioral approaches, onabotulinum toxin injections, life-style considerations, etc. Conclusion: Notwithstanding some phenotypic similarities, persistent post-traumatic headache after traumatic brain injury, is considered a separate phenomenon from migraine but available data is inconclusive. High-quality studies are further required to investigate the pathophysiological mechanisms of this secondary headache, in order to identify new targets for treatment and to prevent disability
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