Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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Wissenschaftlich-technische Berichte / Forschungszentrum Rossendorf e. V. / FZR
No full textUnregelmäßig erscheinende Berichte über wissenschaftliche Ergebnisse aus den einzelnen Forschungsbereichen der zum FZR gehörenden Institute
Wissenschaftlich-technische Berichte / Forschungszentrum Dresden - Rossendorf / FZD
No full textUnregelmäßig erscheinende Berichte über wissenschaftliche Ergebnisse aus den einzelnen Forschungsbereichen der zum FZD gehörenden Institute
High-Yield Optical Undulators Scalable to Optical Free-Electron Laser Operation by Traveling-Wave Thomson-Scattering
Full text linkAll across physics research, incoherent and coherent light sources are extensively utilized.
Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources.
But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays.
This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources.
The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems.
TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources.
Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized.
Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods.
This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems.
The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range.
These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis.
It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser.
Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed.
The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups.
An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, to
Parallelisierung des Wellenfrontrekonstruktionsalgorithmus auf Multicore-Prozessoren
Full text linkZiel dieser Arbeit war die Beschleunigung des von Elena-Ruxandra Cojocaru und Sébastien Bérujon in Python implementierten Wellenfrontrekonstruktionsalgorithmus. Dieser berechnet aus zwei Bildern einer Probe pixelweise die Fronten der elektromagnetischen Welle eines Röntgenlasers. Die Bilder werden hierbei von zwei hochempfindlichen Röntgen-CCD-Sensoren aufgenommen, welche in einem festen Abstand zueinander und zur Probe positioniert sind. Treffen Strahlen des Röntgenlasers auf diese, so lässt sich aus den so aufgenommenen Streubildern die Wellenfront rekonstruieren, was Rückschlüsse auf die Struktur der Probe zulässt. Auf Basis von Performance-Analysen der Python-Implementierung wurden Optimierungen und Parallelisierungsmöglichkeiten für die kritischen Programmabschnitte ermittelt, implementiert und evaluiert. Die schnellste vorgestellte Lösung basiert auf der Verteilung der Bildpaare auf mehrere Rechenkerngruppen und der Parallelisierung der Berechnung der Bildpaare auf diesen, was eine Skalierung über mehrere Knoten erlaubt. Kombiniert mit der Nutzung optimierter Bibliotheken und dem Übersetzen des Python-Codes wurde eine Beschleunigung von bis zu vier gegenüber der Referenzimplementierung mit gleicher Kernanzahl erreicht. Wurden 120 Kerne verwendet, so war eine Beschleunigung auf das bis zu 133-fache gegenüber der Referenz auf einem Kern möglich. Die Referenzdaten hierfür wurden an der Beamline BM05 der European Synchrotron Radiation Facility aufgenommen.The goal of this thesis was the acceleration of the wavefront reconstruction algorithm which was developed in Python by Elena-Ruxandra Cojocaru and Sébastien Bérujon. This algorithms calculates the electromagnetic wavefront of an X-ray laser from two images of a target pixelwise. The images were captured by two highly sensitive X-ray CCD sensors, which were positioned in a fixed distance to each other and the target. When the refracted X-ray beam hits these detectors a distortion image is generated from which the wavefront can be reconstructed. The result can be used to draw conclusions about the structure of the target. On the basis of performance measurements of the Python implementation optimization and parallelization possibilities for critical sections were determined, implemented and evaluated. The fastest proposed solution is based on the distribution of the image pairs onto CPU core groups and the parallelization of the calculation of the image pairs on these which allows scaling the problem over multiple nodes. This combined with the use of optimized libraries and the compilation of the Python code resulted in a speedup of up to four towards the reference implementation without the use of more cores. When using 120 cores a speedup of up to 133 towards the reference implementation running on a single core could be achieved. The here used datasets were recorded at Beamline BM05 of the European Synchrotron Radiation Facility
Hydrogen burning: Study of the 22Ne(p,gamma)23Na, 3He(alpha,gamma)7Be and 7Be(p, gamma)8B reactions at ultra-low energies
Full text linkThe neon-sodium cycle (NeNa cycle) of hydrogen burning is active in stars of the Asymptotic Giant Branch, in classical novae, and in supernovae of type Ia. The thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction is determined by a large number of resonances, and it represents the most uncertain rate in the NeNa cycle. This PhD thesis reports on an experiment to study tentative 22Ne(p,γ)23Na resonances at Elab = 71 and 105 keV, as well as the direct capture component of the reaction rate for Elab ≤ 400 keV. The measurements were performed deep underground at the Laboratory for Un- derground Nuclear Astrophysics - LUNA (Gran Sasso, Italy), taking advantage of the strong reduction in the cosmic ray induced background. The LUNA-400-kV electrostatic accelerator and a differentially pumped, windowless gas target of iso- topically enriched 22Ne gas were used. The γ-rays from the reaction were detected with a 4π bismuth germanate scintillator. The data show upper limits on the strengths of the resonances at Elab = 71 and 105 keV of 5.8 × 10−11 and 7.0 × 10−11 eV respectively. The resonances at Elab = 156.2, 189.5 and 259.7 keV have been re-studied and show 20% higher strength than the literature. The present experiment did not show any evidence for the direct capture process at the low energies studied. In addition to the experimental work at LUNA, the 3He(α, γ)7Be and 7Be(p, γ)8B reactions were studied using the most recent solar neutrino data available. Based on the standard solar model and the experimentally measured fluxes of solar 7Be and 8B neutrinos, the astrophysical S-factors of both reactions were evaluated directly in the solar Gamow peak
WTZ Russland - Transientenanalysen für schnelle Reaktoren: WTZ Russland - Transientenanalysen für schnelle Reaktoren
Full text linkDer Reaktordynamikcode DYN3D wird für Kernanalysen von Natrium-gekühlten schnellen Reaktoren (SFR) erweitert. In diesem Bericht werden neu implementierte thermomechanische Modelle für die adäquate Simulation von SFR-Transienten beschrieben, die die Simulation der axialen Wärmeausdehnung von Brennstäben und die radiale Ausdehnung des Reaktorkerns umfassen. Darüber hinaus wurde das Verfahren zur Erstellung von Querschnittsbibliotheken für DYN3D für SFR-Analysen erweitert. Die Verifizierung der neuen Modelle und der Querschnittserstellung erfolgte auf Vollkern-Ebene mit stationären Experimenten von der BFS-Testanlage des IPPE Obninsk und Daten des großen oxidischen Kerns des OECD/NEA-Benchmark und den Experimenten zum Zyklusende des Phenix-Kerns. Die DYN3D-Ergebnisse wurden mit der Monte-Carlo-Referenzlösung verglichen, die durch den SERPENT-Code berechnet wurde. Die Testergebnisse zeigen, dass die neu entwickelten Modelle die Wärmeausdeh-nungseffekte der Kernstruktur genau berücksichtigen können. Das neu entwickelte Verfahren zur Erstellung von Querschnittsbibliotheken wurde ebenfalls auf der Basis von SERPENT-Ergebnissen erfolgreich verifiziert. Zur Validierung wurden mehrere Tests, die sowohl stationäre als auch transiente Fälle aus den Phenix-Experimenten enthalten, mit DYN3D berechnet. Die DYN3D-Lösungen weisen eine gute Übereinstimmung mit den experimentellen Daten auf, was die Anwendbarkeit der Codes für Kernanalysen von Natrium-gekühlten schnellen Reaktoren bestätigt
Annual Report 2017 - Institute of Resource Ecology
Full text linkTHE INSTITUTE OF RESOURCE ECOLOGY (IRE) IS ONE of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors
Experiments on vertical gas-liquid pipe flows using ultrafast X-ray tomography
Full text linkFor the qualification and validation of two-phase CFD-models for medium and large-scale industrial applications dedicated experiments providing data with high temporal and spatial resolution are required. Fluid dynamic parameter like gas volume fraction, bubble size distribution, velocity or turbulent kinetic energy should be measured locally. Considering the fact, that the used measurement techniques should not affect the flow characteristics, radiation based tomographic methods are the favourite candidate for such measurements. Here the recently developed ultrafast X-ray tomography, is applied to measure the local and temporal gas volume fraction distribution in a vertical pipe. To obtain the required frame rate a rotating X-ray source by a massless electron beam and a static detector ring are used.
Experiments on a vertical pipe are well suited for development and validation of closure models for two-phase flows. While vertical pipe flows are axially symmetrically, the boundary conditions are well defined. The evolution of the flow along the pipe can be investigated as well.
This report documents the experiments done for co-current upwards and downwards air-water and steam-water flows as well as for counter-current air-water flows. The details of the setup, measuring technique and data evaluation are given. The report also includes a discussion on selected results obtained and on uncertainties
Gefüge und Eigenschaften des warmfesten Chromstahls P91
Full text linkAufgabenstellung:
Aus einem Rohrstück des Materials P91 soll nach der Erarbeitung eines Probenplans zunächst das Gefüge in allen 3 Orientierungen metallographisch charakterisiert werden. Anschließend wird das Material mechanisch - technologisch sowie bruchmechanisch und fraktographisch untersucht. Die daraus erhaltenen Werkstoffkennwerte sollen mit dem Gefüge und dem fraktographischen Befund in Beziehung gesetzt werden