Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41709 Publications

A physical model for electromagnetic control of local temperature gradients in a Czochralski system

Cramer, A.; Röder, M.; Pal, J.; Gerbeth, G.

Abstract

The shape of the solidification front and the related mono-crystalline growth in the Czochralski crystal growth process is thought of being strongly influenced by the ratio of the horizontal and the vertical temperature gradient r* = deltaT_h / deltaT_v at the triple point liquid-solid-atmosphere, which ratio desirably should be in the order of unity. A liquid metal model experiment was therefore built that allows studying r* under the influence of magnetic fields. The cylindrical liquid metal column was homogeneously heated from below, whereas on top the heat was extracted in a centrical region covering only one third of the surface in order to simulate the growing crystal. Without flow control, r* ≈ 3 is far removed from unity. It was then possible to reach the target value r* = 1 for any temperature difference between the bottom and the top at a moderate field strength while applying a rotating magnetic field.

Keywords: crystal growth; Czochralski process; flow control; electromagnetic processing of materials; magnetic fields

  • Lecture (Conference)
    International Scientific Colloquium on Modelling for Material Processing, 16.-17.09.2010, Riga, Lettland
  • Contribution to proceedings
    International Scientific Colloquium Modelling for Material Processing, 16.-17.09.2010, Rīga, Latvija
    Proceedings of the 6th International Scientific Colloquium Modelling for Material Processing, 978-9984-45-223-4, 41-46
  • Magnetohydrodynamics 46(2010), 353-362

Permalink: https://www.hzdr.de/publications/Publ-14651


Magnetic field controlled single crystal growth and surface modification of titanium alloys exposed for biocompatibility

Hermann, R.; Calin, M.; Uhlemann, M.; Wendrock, H.; Gerbeth, G.; Büchner, B.; Eckert, J.

Abstract

The aim of the work is the growth and characterisation of Ti55Nb45 (wt %) single crystals with the floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced via additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. As a result, a tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards to outwards flows. Due to their attractive properties such as light, strong and totally biocompatible, titanium is one of few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations (-1,0,0) and (1,0,1) normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly define crystal orientation and orientation changes in the crystallographic textures. The elastic modulus, the shear modulus and the bulk modulus were determined in dependence on the crystal orientation using ultrasonic measurements. Moreover, the oxide formation behavior on Ti surfaces in dependence on the grain orientation was investigated, performed anodically from fluoride containing electrolyte.

Permalink: https://www.hzdr.de/publications/Publ-14650


Thermophysical properties of intermetallic Ti-Al alloys in the liquid state

Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.

Abstract

TiAl intermetallic alloys were developed as potential materials for high temperature applications because of their excellent chemical and physical properties such as low density, high modulus and corrosion resistance. These characteristics are attractive for applications in aerospace and automotive industries but also for chemical and biomedical application. However, their low ductility at room temperature limits their application. Also microscopic factors like volume fraction of the apparent phases, the distribution of orientation variants, fineness of the microscopic structure strongly affect the mechanical properties.

  • Lecture (Conference)
    Liquid and Amorphous Metals Conference (LAM 14), 11.-16.07.2010, Rom, Italy

Permalink: https://www.hzdr.de/publications/Publ-14649


Thermophysical and structure-sensitive properties of low-temperature ternary liquid metal eutectics

Plevachuk, Y.; Sklyarchuka, V.; Gerbeth, G.; Eckert, S.

Abstract

Investigation of thermophysical and structure-sensitive properties of liquid low-temperature ternary metal eutectic alloys are stimulated both by pure academic as well as by applied science. In particular, there exist few reliable experimental data on the electrophysical, transport and surface properties of multicomponent alloys and, therefore, they are often estimated with analytical approaches. In order to prove any theory, experimental results are needed.
The favorable combination of the technical characteristics of Ga-based melts brought about their extensive application as sliding contacts, the working medium of magnetohydrodynamic devices, heat-sensitive elements of liquid-metal thermometers and thermocouples, and the base for conducting magnetic fluids. The GaInSn eutectic alloy is a suitable alternative to mercury since it exhibits an equilibrium melting point of 284 K. Bi-Pb-Sn liquid eutectics are chosen as model substances for experimental

  • Poster
    XIV Liquid and Amorphous Metals Conference (LAM 14), 11.-16.07.2010, Rom, Italy

Permalink: https://www.hzdr.de/publications/Publ-14648


Saturation correction of an ionization chamber for short and intense beam pulses

Karsch, L.; Richter, C.; Pawelke, J.

Keywords: saturation correction; ionization chamber; short and intense beam pulse

  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14647


An integrated dosimetry and cell irradiation device for in vitro cell experiments with laser accelerated protons

Richter, C.; Akhmadaliev, S.; Dammene, Y.; Karsch, L.; Reinhardt, S.; Sobiella, M.; Schürer, M.; Weber, A.; Pawelke, J.

Keywords: dosimetry; cell irradiation; in vitro cell experiments; laser accelerated protons

  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14646


Liquid metal modelling of continuous steel casting

Gerbeth, G.; Eckert, S.; Timmel, K.; Miao, X.

Abstract

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present the new experimental facility CONCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, experimental results will be presented on the impact of a steady magnetic field on the outlet flow from the nozzle, obtained at a smaller-scale set-up working with the room-temperature alloy GaInSn. Local velocities in both facilities are measured by Ultrasound Doppler Velocimetry and contactless inductive flow tomography. The latter is attractive also for real-scale steel casting.

  • Lecture (Conference)
    TMS Annual meeting "Jim Evans Honorary Symposium", 14.-18.02.2010, Seattle, USA
  • Contribution to proceedings
    TMS Annual meeting, 14.-18.02.2010, Seattle, USA
    "Jim Evans Honorary Symposium", 55-62

Permalink: https://www.hzdr.de/publications/Publ-14645


Radiobiological preparation of in vitro cell experimentes with laser accelerated protons

Beyreuther, E.; Dammene Debbih, Y.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Richter, C.; Schürer, M.; Pawelke, J.

Keywords: in vitro cell experimentes; laser accelerated protons

  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14644


Influence of ultra-high pulse dose rate on biological effectiveness of laser accelerated electrons

Laschinsky, L.; Beyreuther, E.; Karsch, L.; Leßmann, E.; Naumburger, D.; Richter, C.; Schürer, M.; Pawelke, J.

Keywords: ultra-high pulse dose rate; biological effectiveness; laser accelerated electrons

  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14643


Biological effectiveness of laser-accelerated electrons in comparison to conventional accelerated electrons

Naumburger, D.; Beyreuther, E.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H. P.; Baumann, M.

Keywords: biological effectiveness; laser-accelerated electrons; electrons

  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14642


Research of the laser-radiooncology (onCOOPtics) group

Pawelke, J.

Keywords: laser radiooncology

  • Invited lecture (Conferences)
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14641


Modelling, Simulation and Experiments to Boiling in Pressurized Water Reactors in the framework of the R&D program “Energie 2020+”

Krepper, E.

Abstract

Der Vortrag gibt einen Überblick zu diesem Verbundprojekt. Die im Rahmen des Förderprogramms Energie 2020+ durch das Bundesministerium für Bildung und Forschung geförderten und gemeinsam von den Partnern Forschungszentrum Dresden-Rossendorf (FZD), Technische Universität Dresden (TUD), Hochschule Zittau/Görlitz (HSZG), Karlsruher Institut für Technologie (KIT), Ruhr-Universität Bochum (RUB), Technische Universität München (TUM) und ANSYS Germany durchgeführten Arbeiten sind der Weiterentwicklung und Validierung von CFD-Modellen für Siedevorgänge in Druckwasserreaktoren, vom Blasensieden bis hin zu Phänomenen des Filmsiedens, gewidmet. Das auf die Grundlagen orientierte Vorhaben schließt die Modellentwicklung, die Simulation und Experimente in verschiedenen Maßstäben ein. Kleinskalige Experimente an den Hochschulen dienen der Aufklärung mikroskopischer Phänomene. An der Großversuchsanlage TOPFLOW wird ein Bündelexperiment zur integralen Validierung der Modelle aufgebaut. Die Ausrüstung dieses Experiments mit schneller Röntgentomographie wird störungsfrei zeitlich und räumlich hoch aufgelöste Daten liefern, die für die Entwicklung und Validierung von CFD-Modellen geeignet sind. Die TU Dresden wird den Einfluss chemischer Zusätze auf die Ausprägung kritischer Siedezustände an der Versuchsanlage BORAN untersuchen. Durch den Einsatz neuester und zum Teil eigens zu entwickelnder Messtechnik wird ein signifikanter Erkenntniszuwachs gegenüber dem Stand von Wissenschaft und Technik erreicht werden.

Keywords: CFD; boiling; model development; small scale experiments; large scale tests

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    Sitzung des CFD-Verbundes, 21.-22.07.2010, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14640


CFD modelling of boiling in rod bundles

Krepper, E.; Rzehak, R.

Abstract

The presentation shows the application of the CFD wall boiling model on the computation of a rod bundle. The data of the OECD/NEA Benchmark Based on NUPEC PWR Subchannel and Bundle Test (PSBT) were used. Besides the parameters of the wall boiling model the simulation of turbulence in the narrow channels is essential.

Keywords: CFD; two phase flow; wall boiling; rod bundle; OECD benchmark PSBT

  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14639


Development and validation of the wall boiling model in ANSYS CFD

Frank, T.; Lifante, C.; Burns, A.; Krepper, E.; Rzehak, R.

Abstract

The presentation shows the actual state of model implementation of a wall boiling model in the code ANSYS/CFX. Publisherd experimental data are used to validate the model

Keywords: CFD; two phase flow; wall boiling; model development; validation

  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14638


Contactless inductive flow tomography: principles and applications

Wondrak, T.; Stefani, F.; Gerbeth, G.; Gundrum, T.

Abstract

There is a growing interest in the determination of the velocity field of metal or semiconductor melts in many industrial applications, such as steel casting and silicon growth. Due to the opaqueness of those fluids optical methods are not applicable. Furthermore these fluids are often very hot or chemically aggressive, so a contactless measuring technique would be highly desirable. Interestingly, those metal and semiconductor melts are characterized by a relatively high electrical conductivity. Exposing the flow of such melts to an externally applied magnetic field, electrical currents are induced which give rise to a perturbation of the applied field. This flow induced field perturbation, which is detectable outside the fluid volume, contains information about the flow structure and can be exploited to reconstruct the velocity field. By applying consecutively the external magnetic field in different directions, different induced currents and magnetic fields can be produced from the same velocity. This enables a tomographic reconstruction of the flow field. Such a contactless inductive flow tomography (CIFT) was proposed, and later verified experimentally. The determination of the velocity from the measured induced magnetic field is an ill-posed linear inverse problem. One of the key problems is the inherent non-uniqueness of the reconstruction. For the velocity reconstruction we circumvent this non-uniqueness problem by using Tikhonov regularization and the method of the L-curve to identify automatically the best regularization parameter. At the point of strongest curvature (the knee) of the L-curve one expects the most reasonable compromise between the fit of the modeled magnetic fields to the measured ones on one hand, and the minimum kinetic energy on the other hand. One possible application of CIFT is the continuous casting process which is widely used in the steel producing industry. The flow structure in the mould, where the steel starts to solidify, is of particular interest since it is mainly responsible for the quality of the produced steel slabs. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external field. We show that the CIFT method is able to reconstruct a numerically determined flow field with an empirical correlation coefficient of about 75 per cent. Then we apply the method to different flow configurations in a real model and show that typical flow features can be reliably detected.

Keywords: velocity measurement; liquid metals; continuous casting; inverse problems

  • Lecture (Conference)
    5th International Conference: Inverse Problems: Modeling and Simulation, 24.-29.05.2010, Antalya, Türkei

Permalink: https://www.hzdr.de/publications/Publ-14637


Use of electromagnetic induction tomography for monitoring liquid metal/gas flow regimes on a model of an industrial steel caster

Terzija, N.; Yin, W.; Peyton, A.; Gerbeth, G.; Stefani, F.; Timmel, K.; Wondrak, T.

Abstract

Monitoring of the steel flow through the submerged entry nozzle (SEN) during continuous casting presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould. Electromagnetic inductance tomography (EMT) presents an attractive tool to visualize the steel flow profile within the SEN.
In this paper, we investigate various flow regimes over a range of stopper positions and gas volume flow rates on a model of a submerged entry nozzle. A scaled (approx. 10:1) experimental rig consisting of a tundish, stopper rod, nozzle and mould was used. Argon gas was injected through the centre of the stopper rod and the behaviour of the two phase GaInSn / Argon flow was studied. The experiments were performed with GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at the room temperature. The electromagnetic system used in our experiments to monitor the behavior of the two phase GaInSn / Argon flow consisted of an array of 8 equally spaced inductive coils arranged around the object, a data acquisition system and a host computer. The present system operates with a sinusoidal excitation waveform with a frequency of 20 kHz and the system has a capture rate of 40 frames per second.
The results show the ability of the system to distinguish the different flow regimes and to detect the individual bubbles. Sample tomographic images given in the paper clearly illustrate the different flow regimes.

Keywords: two­phase flow study; electromagnetic inductance tomography; industrial steel caster model

Permalink: https://www.hzdr.de/publications/Publ-14636


Contactless inductive flow tomography: principles and application to a model of continuous casting

Wondrak, T.; Stefani, F.; Timmel, K.; Galindo, V.; Gundrum, T.; Gerbeth, G.

Abstract

In many metal casting processes the flow structure in the mould is very important for the produced material. For instance the flow field in the mould in the continuous casting process plays an important role for slug entrainment and surface defects. The measurement of that velocity field is very difficult due to the opaqueness and the high temperature of the liquid steel. One possible measurement technique is the contactless inductive flow tomography (CIFT), which is able to reconstruct the three dimensional velocity field in electrically conducting melts from externally measured induced magnetic fields.
Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external magnetic field and to measure the induced fields at the narrow faces of the mould. We utilize CIFT for visualizing the flow of GaInSn in a model of continuous steel casting. In a first step we show that a numerically determined flow field can be reconstructed by CIFT with an empirical correlation coefficient of nearly 80 per cent. Then we apply the method to the real model and show that typical flow features can be reliably detected.

Keywords: velocity measurement; liquid metals; continuous casting

  • Lecture (Conference)
    6th World Congress on Industrial Process Tomography, 06.-9.9.2010, Peking, China
  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography, 06.-9.9.2010, Peking, China
    6th World Congress on Industrial Process Tomography, 1051-1066

Permalink: https://www.hzdr.de/publications/Publ-14635


Contribution of Lattice Vibrations to the Thermodynamics of Vacancy Clusters in bcc-Fe

Talati, M.; Posselt, M.; Bonny, G.; Al-Motasem, A. T.; Bergner, F.

Abstract

During the long operation time of nuclear reactors, vacancies and vacancy clusters (VC) may play an intermediary role in the formation of copper-rich precipitates (CRP), which are considered to be the main cause of hardening and embrittlement of Cu-bearing RPV steels since these defects act as obstacles to dislocation motion within the grains of polycrystalline bcc-Fe. The effect of irradiation on the microstructure of RPV steels and consequently on their mechanical properties is a multiscale phenomenon. The evolution of VCs over realistic time and length scales can be effectively studied by rate theory. However, many parameters used, such as the free binding energies of precipitates, are not very well known from experimental investigations. Atomic-level computer simulations can provide these data. The few previous attempts to include the effect of lattice vibrations into thermodynamics of Cu-precipitates in bcc-Fe did not lead to consistent results [1, 2].The present investigations are focused on the phonon contributions to the thermodynamics of VCs. In all calculations the Mendelev potential for bcc Fe is used [3]. Molecular dynamics simulations at different temperatures are performed in order to determine the velocity autocorrelation function which can be transformed into the vibrational density of states (VDOS). VDOS is also obtained using dynamical matrix method under harmonic approximation. This quantity is then used to calculate the contributions of lattice vibrations to the total free energy of bcc-Fe as well as to the free energy of formation and free binding energy of VCs. The vibrational contribution to the total free energy of bcc-Fe is compared with available CALPHAD data and with the values obtained using other interatomic potentials. At a temperature of 600 K the vibrational contribution to the free binding energy leads to a reduction of the absolute value of the corresponding zero-Kelvin free binding energy of the VC by about 10%.

[1] K. Yuge, A. Seko, I. Tanaka, S. R. Nishitani, Phys. Rev. B 72 (2005) 174201.
[2] K. Yuge, A. Seko, K. Kobayashi, T. Tatsuoka, S. R. Nishitani, H. Adachi, Mater. Trans. 45 (2004) 1473.
[3] M. I. Mendelev, S. Han, D. J. Srolovitz, G. Ackland, D. Y. Sun, M. Asta, Philo. Mag. 83 (2003) 3977.

Keywords: Vibrational Density of States; Total free energy; Free binding energy; bcc-Fe; Thermodynamics; Molecular Dynamics Simulation

  • Poster
    The fifth International Conference on Multiscale Materials Modeling (MMM-2010), 04.-08.10.2010, Freiburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-14634


Boiling models for CFD

Rzehak, R.; Krepper, E.

Abstract

CFD for Boiling Flows requires models to represent bubble dynamics during ebullition cycle. At present, mostly empirical correlations are used to this end, which have only a limited range of applicabiblity. Hence, there is a strong desire to replace these correlations by physical models. A survey of available approaches to this issue is given and need for further research identified.

Keywords: CFD; boiling

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14633


Measurement technique developments for LBE flows

Buchenau, D.; Eckert, S.; Gerbeth, G.; Stieglitz, R.; Dierckx, M.

Abstract

We report on the development of measurements techniques for flows in lead-bismuth eutectic alloys (LBE). This paper covers the test results of newly developed contact-less flow rate sensors as well as the development and test of the LIDAR technique for operational free surface level detection. The flow rate sensors are based on the flow-induced disturbance of an externally applied AC magnetic field which manifests itself by a modified amplitude or a modified phase of the AC field. Another concept of a forcefree contactless flow meter uses a single cylindrical permanent magnet. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The operation of those sensors has been demonstrated at liquid metal test loops for which comparative flow rate measurements are available, as well as at the LBE loops THESYS at KIT and WEBEXPIR at SCK-CEN. For the level detection a commercial LIDAR system was successfully tested at the WEBEXPIR facility in Mol and the THEADES loop in Karlsruhe.

Keywords: Liquid metal; LBE; Phase-shift sensor; EMFM; Rotating magnet; LIDAR

  • Lecture (Conference)
    Int. DEMETRA Workshop, 02.-04.03.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14632


Interfacial heat and mass tansfer models

Krepper, E.; Scheuerer, G.

Abstract

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

Keywords: CFD; Two fluid model; heat transfer; mass transfer; boiling; cavitation

  • Invited lecture (Conferences)
    7th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 26.-28.05.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland
  • Invited lecture (Conferences)
    9th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 08.-10.06.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14629


CFD models for the description of particle transport, deposition and (re)mobilization of deposited particles at walls

Barth, T.; Krepper, E.

Abstract

Radioactive aerosol deposition and the assessment of its resuspension during a design basis accident (DBA) in the primary circuit have been revealed in the past as a key issue in the development and certification of advanced pebble bed High Temperature Reactors (HTRs). The report describes the particle parametres to be expected. Actual CFD methods to model particle deposition and particle resuspension are reported.

Keywords: CFD; Euler/Lagrange; Particles; Deposition; Resuspension

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    FZD\FWS\2010\06
    22 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-14625


Extension of the MUSIG approach by considering gas/liquid-mass transfer

Krepper, E.; Lucas, D.; Schmidtke, M.

Abstract

The report describes the derivation of the corresponding equation and validations on the TOPFLOW condensation experiments (test series K16). The evolution of the cross-sectional averaged void fraction along the pipe were compared with experimental results. In the test K16_118 the condensation of steam was prevailing. The influence of the heat transfer model bubble – liquid (Ranz-Marshall, Hughmark, Tomiyama) was investigated and the influence of the initial bubble size distribution was shown. In the tests K16_140 reevaporation caused by decreasing hydrostatic pressure was found in the experiments and simulated.

Keywords: CFD; two phase flow; bubble population balance; mass transfer

Involved research facilities

  • TOPFLOW Facility
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    FZD\FWS\2010\05
    22 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-14624


Improvement of the turbulence modelling in Euler/Eulerian CFD simulation of gas/liquidflow

Krepper, E.; Schmidtke, M.; Lucas, D.

Abstract

In the Euler/Eulerian approach simulating bubbly flow, the influence of the bubbles on the turbulence of the liquid has to be modelled. Vice versa, the structures of the turbulent liquid flow influence the gas void fraction distribution, which is expressed as a turbulent dispersion force. Reliable models for turbulence are an urgent precondition for the improvement of models describing bubble coalescence and bubble breakup in any population balance model. In the present work the different approaches simulating the influence of bubbles on the turbulence are revised and compared to measurements using ANSYS-CFX. Models for the turbulent dispersion force are validated.

Keywords: CFD; two phase flow; turbulence

Involved research facilities

  • TOPFLOW Facility
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    FZD\FWS\2010\04
    18 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-14623


Die supraleitende HF-Fotoelektronenquelle am ELBE-Beschleuniger im FZD

Teichert, J.

Keywords: SRF Gun; Cs2Te; electron injector

Involved research facilities

Related publications

  • Lecture (others)
    MAMI Seminar, 28.01.2010, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-14622


Study of gas-liquid two-phase flow in pipes with ultrafast electron beam X-ray CT

Fischer, F.; Hampel, U.

Abstract

Electron beam X-ray CT is capable of fast measurement of multi-phase flows with frame rates of 1000 images per second and higher. The principle is based on the creation of a moving X-ray spot by electromagnetic deflection of a high-intensity electron beam across a circular target within an evacuated scanner enclosure. Together with a fixed fast X-ray detector this setup allows scanning of objects at frame rates well beyond that of classical CT machines. Our group has developed a scanner that is capable of scanning at up to 7 kHz frame rate and approximately 1 mm spatial resolution. The technique allows visualizing and measuring multiphase flows in vessels of moderate size. We have applied this fast electron X-ray tomography to the study of gas-liquid flow in a vertical pipe of 50 mm inner diameter. Different two-phase flow regimes from bubbly flow to churn-turbulent flow were produced and scanned. The data were processed using self-made image reconstruction software which implements the filtered backprojection technique and further post-processing algorithms for determination of gas-phase parameters, such as temporal and radial gas fraction profiles.

Keywords: Electron beam tomography; X-ray tomography; flow measurement; two-phase flow

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    6th World Congress of Industrial Process Tomography, 06.-09.09.2010, Peking, China

Permalink: https://www.hzdr.de/publications/Publ-14619


Alfven wave experiments with liquid rubidium

Gundrum, T.; Hüller, J.; Stefani, F.; Gerbeth, G.; Galindo, V.; Herrmannsdörfer, T.; Arnold, F.; Putzke, C.

Abstract

Since their discovery by Hannes Alfvén in 1942, Alfvén waves have played an ever increasing role in explaining many phenomena in astrophysical and fusion related plasmas. The experimental investigation of Alfvén waves had started shortly after Alfvéns prediction, with first experiments using mercury and liquid sodium. Since those times, many Alfvén wave experiments have been carried out, both in liquid metals and, even more extensively, in plasmas.
Interestingly, the recent developments in reaching pulsed magnetic fields above 50 Tesla open up quite new prospects for Alfvén wave experiments with liquid metals. At those field strengths it happens that the Alfvén speed in higher alkalis metals reaches the sound speed (the threshold is 51 T for Caesium and 55 T for Rubidium). This threshold is of upmost importance for the character of Alfvén waves and its relation to slow and fast magnetoacoustic waves, and its crossing has been made responsible for the corona heating.In order to check the feasibility of experiments with higher alkali metals, we have carried out at Dresden High Magnetic Field Laboratory a preliminary experiment. This first test experiment has yielded a proof of concept, and first promising results have been achieved.

Keywords: Alfven; MHD; Rubidium; magnetoacoustic wave; liquid metal; high magnetic field

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Lecture (Conference)
    Science in High Magnetic Fields, 05.-11.09.2010, Ameland, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-14618


Use of Superconducting LINACS for Positron Generation: The EPOS System at Research Center Dresden-Rossendorf

Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.

Abstract

Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting Linac-based accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system at the Research Center Dresden-Rossendorf, will be described.

Involved research facilities

Related publications

  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques, 01.-06.08.2010, North Queensland, Australia
  • Contribution to proceedings
    12th International Workshop on Slow Positron Beam Techniques, 01.-06.08.2010, North Queensland, North Queensland
    Use of Superconducting LINACS for Positron Generation: The EPOS System at Research

Permalink: https://www.hzdr.de/publications/Publ-14617


SRF Gun Experiments

Teichert, J.; Arnold, A.; Büttig, H.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staats, G.; Xiang, R.; Kneisel, P.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.

Involved research facilities

Related publications

  • Lecture (others)
    EuCARD-SRF Annual Review 2010, 07.-09.04.2010, Daresbury, UK

Permalink: https://www.hzdr.de/publications/Publ-14616


High Rep Rate Guns: FZD Superconducting RF Photogun

Teichert, J.; Arnold, A.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staats, G.; Staufenbiel, F.; Tietze, H.; Xiang, R.; Kneisel, P.; von der Horst, B.; Matheisen, A.; Stephan, J.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.; Volkov, V.

Abstract

A RF photo injector with a superconducting cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. This new and promising injector type allows CW operation and has the potential for the production of high-brightness electron beams. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed. In November 2007 the first beam was produced. In 2008 beam parameter measurements with Cs2Te photo cathodes were carried out. Due to problems during the cleaning of the cavity, the design gradient could not be reached. Thus the SRF gun is operating now with a peak field of 17.5 MV/m which corresponds to electron energy of 3 MeV. In 2009 the cathode transfer system was upgraded, the bunch lengths measurement based on Cherenkov radiation was put into operation, and the connection beamline to ELBE was installed in the winter shutdown. In February, the first beam of the SRF gun was injected to ELBE and accelerated. Parallel to the commissioning and operation of the SRF gun, an improved design for the gun cavity was created and two now cavities, one made of RRR300 Nb and one made of high-grain Nb was fabricated in collaboration with JLab.

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    FLS 2010 – ICFA Beam Dynamic Workshop, 01.-05.03.2010, Menlo Park, USA

Permalink: https://www.hzdr.de/publications/Publ-14615


Dynamics of a trapped Brownian particle in shear flows

Holzer, L.; Bammert, J.; Rzehak, R.; Zimmermann, W.

Abstract

The Brownian motion of a particle in a harmonic potential, which is simultaneously exposed either to a linear shear flow or to a plane Poiseuille flow is investigated. In the shear plane of both flows the probability distribution of the particle becomes anisotropic and the dynamics is changed in a characteristic manner compared to a trapped particle in a quiescent fluid. The particle distribution takes either an elliptical or a parachute shape or a superposition of both depending on the mean particle position in the shear plane. Simultaneously, shear-induced cross-correlations between particle fluctuations along orthogonal directions in the shear plane are found. They are asymmetric in time. In Poiseuille flow thermal particle fluctuations perpendicular to the flow direction in the shear plane induce a shift of the particle’s mean position away from the potential minimum. Two complementary methods are suggested to measure shear-induced cross-correlations between particle fluctuations along orthogonal directions.

Keywords: Brownian motion; shear flow; fluctuations; correlation; colloids

Permalink: https://www.hzdr.de/publications/Publ-14613


Validierung des Inhomogenen MUSIG-Modells mit Phasenübergang

Schmidtke, M.; Krepper, E.; Lucas, D.

Abstract

Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in a 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a wire mesh sensor. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapour void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.

Keywords: steam bubble; condensation; Inhomogeneous MUSIG; TOPFLOW; phase transfer; Nusselt number

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    3. Meilenstein Workshop / CFD-Forschungsverbund Entwicklung und Anwendung von Computational Fluid Dynamics (CFD) Programmen für Phänomene im Kühlkreislauf und Sicherheitseinschluss von Leichtwasserreaktoren, 23.09.2010, München-Holzkirschen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14612


CFD Simulation zum Eintrag von Mineralwolle in den Reaktorkern

Höhne, T.; Grahn, A.; Kliem, S.; Weiss, F. P.

Abstract

Es wurden CFD-Analysen zum Eintrag von Mineralwolle in den Kern bei Sumpfbetrieb der Kernnotkühlung durchgeführt. Ziel der CFD-Rechnungen war der qualitative Nachweis der so genannten Durchbruchkanäle, die experimentell an der Versuchsanlage UPTF beobachtet wurden und durch die das heißseitig eingespeiste Notkühlwasser in den Kern gelangt, auch unter den Massenstrom- und Druckverhältnissen bei Ansaugung aus dem Sumpf. Zunächst wurde ohne Belastung des Kühlmittels mit Isoliermaterial gerechnet, während weiterführende Rechnungen die teilweise Belegung der oberen Abstandshalterebene durch eingetragene Mineralwollfasern berücksichtigten. Dafür musste die Verteilung der Ablagerung der Mineralwollfasern auf der oberen Abstandshalterebene ermittelt werden. Die Rechnungen zeigen eine zunächst bevorzugte Ablagerung der Fasern im Bereich der Durchbruchkanäle.

Keywords: CFD; Kernnotkühlung; Durchbruchkanäle; UPTF

  • Contribution to proceedings
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland-Fachtagung der KTG-Fachgruppen, 07.-08.10.2010, Forschungszentrum Dresden-Rossendorf, Deutschland
    CD-ROM
  • Invited lecture (Conferences)
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland-Fachtagung der KTG-Fachgruppen, 07.-08.10.2010, Forschungszentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14611


Thermal fluid dynamics research at Forschungszentrum Dresden-Rossendorf - sensors, systems and applications

Hampel, U.

Abstract

Understanding and modeling multiphase flows requires sophisticated imaging tools which can disclose physical information of such flows with high temporal and spatial resolution. At FZD a number of sensors and imaging systems are being developed and applied, which are able to obtain phase distribution information from multiphase flows with superior resolution and speed. Within the presentation we will introduce and discuss the methods of wire mesh imaging, gamma ray tomography and ultra fast X-ray tomography with respect to their functional principles and application in energy and process engineering.

Keywords: multiphase flow measurement; wire mesh sensor; computed tomography

Involved research facilities

  • TOPFLOW Facility
  • Lecture (others)
    Meeting on the application of multiphase flow measurement techniques in reactor engineering, 28.09.2010, Eindhoven, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-14610


Thermal fluid dynamics research and multiphase flow measurement and imaging techniques at FZD

Hampel, U.

Abstract

The presentation gives an overview over the research activities in thermal fluid dynamics research at FZD. A focus is given on experiments on steam-water two-phase flows and innovative tomographic instrumentation. Research is carried out at the TOPFLOW thermal hydraulic test facility where steam-water flows under authentic nuclear reactor conditions can be investigated. In the recent past, new imaging sensors and technologies, such as wire mesh sensors and fast X-ray tomography have been developed and are being applied for such studies.

Keywords: two-phase flow; flow measurement; thermal fluid dynamics

Involved research facilities

  • TOPFLOW Facility
  • Invited lecture (Conferences)
    Multiphase flow and microbubbles in oil and gas production: Son of DIPSS “Ideas Factory”, 27.09.2010, Sheffield, UK

Permalink: https://www.hzdr.de/publications/Publ-14609


The THz-FEL FELBE at the Radiation Source ELBE

Seidel, W.

Abstract

Two free-electron lasers (FELBE; 4-21 μm and 18-250 μm, respectively) have been in routine user operation for a wide range of IR experiments at the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf for several years. The lasers are driven by a superconducting RF linac that permits the generation of a cw-beam with a repetition rate of 13 MHz and a high average beam power. In addition, operation in a macropulse modus (pulse duration >100 µs, repetition rate ≤ 25 Hz) is possible. A few important experiments using the cw-operation are discussed. Furthermore, an outlook is given on the experiments which use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD provides pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.

Involved research facilities

Related publications

  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010
  • Invited lecture (Conferences)
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden

Permalink: https://www.hzdr.de/publications/Publ-14608


A Laser-Activated Plasma Switch for the Extraction of Single FELBE Radiation Pulses

Seidel, W.; Winnerl, S.

Abstract

In order to decrease the average radiation power of the Rossendorf free-electron laser FELBE, as required for certain experiments (high pulse energies but moderate or low average power), the FEL repetition rate can be reduced from 13 MHz to 1 kHz. To this end, plasma switching of FEL radiation pulses was demonstrated for cw operation. The plasma switch is based on the principle of photo-induced reflectivity by an optically excited electron-hole plasma. Germanium or silicon serves as semiconductor material for the switch. The semiconductor was illuminated by a Nd:YAG laser amplifier system (1 kHz, wavelength 1064 nm, pulse duration16 ps, 1Watt), generating an electron-hole plasma on the front surface of the semiconductor. To integrate this plasma-switch into the existing experimental set-up we build an additional by-pass to the Germanium or Silicon slab which is under Brewster’s angle. To get a high contrast in the switched beam we adjust the polarization plane of the incoming beam to the right direction by using an additional polarization rotator. We will report on first results at different wavelength. Submitted as a poster to the FEL 2010 conference.

Involved research facilities

Related publications

  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Permalink: https://www.hzdr.de/publications/Publ-14606


Conceptual Design of a THz Facility at the ELBE Radiation Source

Lehnert, U.; Helm, M.; Michel, P.; Schneider, H.; Seidel, W.; Winnerl, S.; Aksoy, A.

Abstract

To extend the wavelength range of possible experiments from the FIR into the THz region a dedicated beamline is planned at the ELBE Radiation Source. The beamline will deliver coherent transition radiation and coherent synchrotron radiation as broad-band (essentially single-cycle) radiation. Superradiant undulator radiation will be produced for a tunable narrow-band radiation source in the 100GHz to 3THz range. This requires a compression of the ELBE electron beam down to 150fs bunchlength. The beam transport and bunch compression scheme as well as the properties of the produced radiation are presented in detail.

Involved research facilities

Related publications

  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Permalink: https://www.hzdr.de/publications/Publ-14605


A Tapered-Undulator Experiment at the ELBE FIR Oscillator FEL

Lehnert, U.; Asgekar, V. B.; Michel, P.

Abstract

A tapered undulator experiment was carried out at the Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The main motivation was to see whether the presence of a dispersive medium due to the partially waveguided resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering (i.e. a decrease of undulator field amplitude over the beam path) proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.

Involved research facilities

Related publications

  • Poster
    Free Elektron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    FEL Conference 2010, 23.-27.08.2010, Malmö, Schweden
    Proceedings of the FEL 2010

Permalink: https://www.hzdr.de/publications/Publ-14604


Im Kern die Sicherheit

Weiss, F.-P.

Abstract

Wirtschafts- und Klimafaktor Kernenergie; Ausbau der Kernenergie-globaler Trend; Sicherheit von Kernkraftwerken; Anforderungen an die (Sicherheits-)Forschung im aktuellen Kontext; Zukunftsvision der nuklearen Sicherheitsforschung

  • Invited lecture (Conferences)
    FDP Technologieforum, 27.05.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14603


The Fritz Haber Institute THz FEL Status

Bluem, H.; Dowell, D.; Park, J.; Todd, A. M. M.; Christina, V.; Rathke, J.; Young, L. M.; Douglas, D.; Dalesio, L. B.; Gewinner, S.; Junkes, H.; Meijer, G.; Schöllkopf, W.; von Helden, G.; Zhang, W. O.; Lehnert, U.; Michel, P.; Seidel, W.; Wuensch, R.; Jordan, K.; Gottschalk, S. C.; Kelly, R. N.

Abstract

The Fritz Haber Institute of the Max Planck Society in Berlin, Germany will celebrate its Centennial in 2011. Coincident with this event, they will christen a THz Free Electron Laser (FEL) that will operate from 3 to 300 microns. A linac with a gridded thermionic gun is required to operate from 15 to 50 MeV at 200 pC while delivering a transverse rms emittance of 20 mm-mrad in a 1 psec rms, 50 keV rms energy spread bunch at the wigglers. Mid-IR and far-IR wigglers enable this electron beam to deliver the required radiation spectrum. In addition to the longitudinal emittance, a key design requirement is the minimization of the micropulse and macropulse jitter to ensure radiation wavelength stability and timing consistency for pump probe experiments. We present the completed physics and engineering design that delivers the required performance for this device. Shipment is scheduled for the end of the calendar year and the status of fabrication will be summarized.

Involved research facilities

Related publications

  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of FEL 2010
  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden

Permalink: https://www.hzdr.de/publications/Publ-14602


ELBE and the upgrade project towards a National Centre for High Power Radiation Sources 4th National Congress on Particle Accelerators and Applications

Michel, P.

Abstract

A superconducting *E*lectron *L*inac with high *B*rilliance and low *E*mittance (ELBE) which provides an average beam current of 1 mA with maximum beam energy of 36 MeV was constructed in the Forschungszentrum Dresden-Rossendorf, Germany. The electron beam is used to generate infrared light (Free Electron Lasers), MeV-Bremsstrahlung, X-rays (electron channelling), fast neutrons and positrons. The ELBE secondary beams are used for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations.
Furthermore a 150 TW Ti:Sa Laser delivers high intense and very short laser pulses used for laser plasma acceleration of electrons and protons.

Until 2014 ELBE will be upgraded to a Centre for High Power Radiation Sources. The concept contains additional broad and narrow band coherent THz sources and the development of a 500 TW Ti:Sa Laser and even a 2 PW diode pumped Laser system. Laser plasma electron acceleration and proton acceleration experiments for medical applications are planed.
Additionally coupled electron laser beam experiments like Thomson scattering or injection of ELBE electron into the laser plasma will be done.

Keywords: Superconducting Electron; infrared light; 500 TW Ti:Sa Laser; X-rays; MeV Bremsstrahlung

Involved research facilities

Related publications

  • Lecture (Conference)
    Congress on Particle Accelerators and Applications (UPHUK-4), 30.08.-01.09.2010, Bodrum, Turkey

Permalink: https://www.hzdr.de/publications/Publ-14601


Modeling of Ruddlesden-Popper surfaces and oxygen vacancies in strontium titanate

Zschornak, M.; Gutmann, E.; Stöcker, H.; Shakverdova, I.; Meyer, D. C.; Gemming, S.

Abstract

Strontium titanate (STO) is an oxide crystallizing with cubic perovskite-type of structure that exhibits a high tunability of dielectric, electric, mechanical and optical properties by means of defects. Apart from dopants, also intrinsic oxygen vacancies or ordered stacking faults, e.g. Ruddlesden-Popper (RP) phases SrO(SrTiO3)n, influence these properties.
We have investigated structural stability, electronic properties and surface energies of such RP phases up to n = 5 by means of density-functional theory. We find a significant gain of formation energy up to n = 3 and can approximate the interaction range of neigh-boring stacking faults to 11.7 Angs.. Surfaces in [001] and [100] direction with all possible unreconstructed crystal terminations have been modeled and stability is compared. In contrast to pure STO, the near-surface SrO-OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO2 surface rumpling, to stabilize SrO termination in SrO-rich surrounding or to increase the band gap for TiO2 termination.
Further, we have theoretically verified a rever-sible elastic softening along an O-deficient 001 direction recently found in nano-inden-tation of SrTiO3 under influence of an electric field. Results from an isotropic and anisotropic model of a SrTiO3-d super cell are discussed.

Keywords: ferroelectrics; surface; Ruddlesden-Popper; STO; strontium titanate; DFT; density-functional; stacking faults; planar defect; complex oxide

  • Poster
    ICAMM 2010 - International Conference on Advanced Materials Modelling, 07.-10.07.2010, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-14600


Density-functional investigation of the electronic structure at surfaces and interfaces of gallium phosphide

Schreiber, M.; Steinbach, G.; Gemming, S.

Abstract

Gallium phosphide is a compound semiconductor with an indirect band gap of 2.26 eV. It is commonly employed for manufacturing low-cost red, orange, and green light-emitting diodes (LEDs) with low to medium brightness. As pure material GaP is transparent for yellow and red light, thus GaP is a better suited as substrate for GaAsP LEDs than GaAs. GaP itself may also be employed as active LED material, which emits green light in the pure phase and shifts to yellow-green upon nitrogen-doping and further to the red by doping with zinc-oxide. Thus, GaP thin films on cheaper silicon substrates promise a high application potential for LED engineering.
The present study addresses both material discontinuities which occur at the boundaries of such a GaP thin functional layer, the surface and the interface with the silicon substrate. Density-functional calculations have been performed with the pseudopotential plane-wave code ABINIT [1]. The most stable (001) surface is P-terminated and exhibits the formation of P dimers in analogy with the common (1x1)-, (2x1)-, and c(4x2)-symmetric reconstructions known for the Si(001) surface. Those reconstructions give rise to STM patterns with differing symmetries, especially when terminated by additional hydrogen atoms. At the interface with the silicon substrate both the Ga-rich and the P-rich terminations of the GaP layer are studied along with partially Si-occupied boundary layers. Substantially negative values of the work of separation are obtained for all investigated interfaces, which indicate the high stability and the low remanent stresses at the GaP-Si interface.

[1] www.abinit.org.

Keywords: GaP; gallium phosphide; surface; interface; silicon; semi-conductor; DFT; density-functional

  • Poster
    STC 2010, 27.-30.09.2010, Münster, Deutschland
  • Lecture (others)
    Arbeitstreffen GaP-based Devices, 12.11.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14598


Nanostructures - Small and Beautiful

Gemming, S.; Erbe, A.; Facsko, S.

Abstract

Spatial confinement effects induce fascinating new phenomena in nanostructured media, which are based on structure- and interface-controlled modifications of the bulk material properties. A thorough understanding of the resulting properties and an assessment of the application potential ideally relies on a combination of experimental and modelling techniques, which cover the whole range of nanostructure creation, characterization and applicative integration into larger functional elements. Thus, we apply self-organized patterning by ion-beam-induced surface modifications and top-down electron ltihographic techniques to generate nano-scale functional elements and combine it with nanometrology methods on specific structural, mechanical, optical and transport phenomena and with scale-adapted as well as multi-scale modeling.

Transport properties on the small scale, for instance, have traditionally been addressed by a classical master equation approach for the motion of the different charge carrier species, which is based on rate theory. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics, local potential changes at interfaces, and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. We have combined both approaches to study electron transport in several material systems with different degrees of structural and electronic complexity. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures [1], for a mechanically triggered metal-insulator transition in nanowires [2], and for the enhanced conductivity at multiferroic domain walls [3].

[1] Kunze, T.; et al.; Phys. Rev. B 81, 115401 (2010).
[2] Popov, I.; et al.; Nano Lett. 8, 4093-4097 (2008).
[3] Seidel, J.; et al.; Nature Materials 8, 229-234 (2009).

Keywords: nanostructures; ion-beam; surface modification; ripples; transport; break junction; DFT; classical rate theory

Involved research facilities

Related publications

  • Lecture (others)
    Physikalisches Kolloquium, 07.07.2010, Freiberg (S), Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14597


Oxygen vacancy contribution on the polarization dependent DAFS of Rutile TiO2

Zschornak, M.; Richter, C.; Novikov, D.; Stöcker, H.; Leisegang, T.; Gemming, S.; Meyer, D. C.

Abstract

In order to develop a method to reconstruct the density of unoccupied electronic states in between Fermi energy and vacuum level, we performed combined anisotropic anomalous scattering and diffraction anomalous fine structure (AAS-DAFS) scans. Examining the energy dependence of the dipole-dipole transition near the Ti-K absorption edge in rutile TiO2 [2], special interest was given to the stability of the symmetry restrictions imposed by the Ti site symmetry m.mm on the dipole-dipole transition. Here we present new results, extending former findings from studying the sample orientation dependent, diffracted intensity on different allowed and forbidden reflections at the specific resonance photon energy of E = 4985 eV exclusively [3], in respect to the energy dependence.

Keywords: DAFS; rutile; O vacancy; point defect; X-Ray; simulation

  • Poster
    European Crystallographic Meeting, ECM-26, 30.08.-02.09.2010, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14596


Correlation of structure and conductance in nanowires

Gemming, S.

Abstract

In nanostructured materials spatial confinement effects lead to structure-dependent deviations from the bulk transport properties. Such modifications may in part be accounted for by classical transport simulations, but a microscopically more detailed and mostly parameter-free picture is obtained from quantum-mechanical density-functional theory (DFT). DFT calculations yield the atom arrangement and electronic structure of nanotubes and nanowires in the electronic ground state. Additionally, an extension by a Green’s function formalism leads to the determination and analysis of electronic transport through contacted nanostructures. A combination of both approaches allows to correlate structural and transport properties of nanostructures. The applicability of this approach will be demonstrated for a mechanically triggered metal-insulator transition in nanowires.
Kibsgaard et al. Nano Lett 8 (2008) 3928; [2] Popov et al. Nano Lett 8 (2008) 4093.

Keywords: transport; nanotubes; nanowires; crystallography; DFT; transition metal chalcogenides; MoS; molybdenum sulfide

  • Poster
    European Crystallographic Meeting, ECM-26, 30.08.-02.09.2010, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14595


Transport in Nanostructured Materials

Gemming, S.

Abstract

In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.

Keywords: transport; calculation DFT; simulation; multi-scale; nano-electronics; molecular electronics; multiferroics

  • Invited lecture (Conferences)
    FAHL Academia 2010: Transparent and flexible Electronics, 28.09.2010, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14594


Anisotropy of magnetic interactions in the spin-ladder compound (C5H12N)2CuBr4

Čižmár, E.; Ozerov, M.; Wosnitza, J.; Thielemann, B.; Krämer, K. W.; Rüegg, C.; Piovesana, O.; Klanjšek, M.; Horvatić, M.; Berthier, C.; Zvyagin, S. A.

Abstract

Magnetic excitations in the spin-ladder material (C5H12N)2CuBr4 (BPCB) are probed by high-resolution multifrequency electron spin resonance (ESR) spectroscopy. Our experiments provide a direct evidence for a pronounced anisotropy (~5% of the dominant exchange interaction), that is in contrast to a fully isotropic spin-ladder model employed for this system previously. It is argued that this anisotropy in BPCB is caused by spin-orbit coupling, which appears to be important for describing magnetic properties of this compound. The zero-field zone-center gap in the excitation spectrum of BPCB, Δ0/kB = 16.5 K, is detected directly. Furthermore, an ESR signature of the interladder exchange interactions is obtained. The detailed characterization of the anisotropy in BPCB completes the determination of the full spin hamiltonian of this exceptional spin-ladder material and shows ways to study anisotropy effects in spin ladders.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-14593


Superconductivity in Gallium-doped Germanium

Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Poster
    2nd EuroMagNET Summer School 2010 at Ameland, 05.-11.09.2010, Ameland, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-14592


The Dresden High Magnetic Field Laboratory - Recent Research Results

Wosnitza, J.

Abstract

The Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), situated at the outskirts of Dresden, has opened its doors for external users in 2007. Since then, an increasing number of scientists from all over the world applied for magnet time and had, after approval, the possibility to conduct their high-field research in the pulsed fields at the HLD. A variety of magnets with pulsed fields up to 70 T are available and a European record field of 87.2 T has been reached. Numerous experimental methods are available allowing to measure electrical transport, magnetization, magnetostriction, ultrasound, ESR, and even NMR, often with very high resolution. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented. This includes e.g. the detection of Shubnikov-de Haas oscillations in electron-doped high-temperature superconductors that allowed to unravel a drastic change of the Fermi-surface topology upon doping. Furthermore, pulsed-field experiments at the HLD allowed to observe the field-induced conductance switching in single-walled carbon nanotubes.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    Seminar at the National Institute for Materials Science, 21.09.2010, Tsukuba, Japan

Permalink: https://www.hzdr.de/publications/Publ-14591


Electron Injectors, The Determining Part For Beam Quality At Accelerators

Arnold, A.

Abstract

The electron source essentially determines the properties of the entire accelerator system. As part of the 1st doctoral seminar in Oybin (Zittauer Gebirge), the talk explains the working principles of two different electron sources. The first part is dealing with the established thermionic source of ELBE (Electron Linac for beams with high Brilliance and low Emittance). While in the second part the benefits of the new superconducting electron source (SRF gun) are presented.

Keywords: electron; source; SRF; Gun

Involved research facilities

Related publications

  • Lecture (others)
    1st FZD Graduate Students PhD Seminar, 11.-13.10.2006, Oybin, Germany

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Permalink: https://www.hzdr.de/publications/Publ-14590


Overview On Superconducting Photo Injectors

Arnold, A.; Teichert, J.

Abstract

The success of most of the proposed energy recovery linac (ERL) based electron accelerator projects for future storage ring replacements (SRR) and high power IR-FELs largely depends on the development of an appropriate source. E.g., to meet the FEL specifications [J. W. Lewellen, SPIE 5534, 22-36 (2004)] electron beams with an unprecedented combination of high brightness, low emittance (0.1 μmrad) and high average current (hundreds of mA) are required. An elegant way to create a beam of such quality is to combine the high beam quality of a normal conducting RF photoinjector with the superconducting technology, i.e., to build a superconducting RF photoinjector (SRF gun). SRF gun R&D programs based on different approaches have been launched at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Substantial progress was achieved in recent years and first long term operation was demonstrated at FZD [R. Xiang et al., in Proceedings of FEL09, Liverpool, GB, 2009]. In the near future SRF guns are expected to play an important role for LINAC driven FEL facilities. In the present paper we will review the concepts, the design parameters and the status of the major SRF gun projects.

Keywords: Superconducting; Electron; Injector; SRF; Gun; ERL; FEL; AES; Beijing University; BESSY; BNL; DESY; FZD; TJNAF; Niowave; NPS; Wisconsin University

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Permalink: https://www.hzdr.de/publications/Publ-14589


Bunch Length Measurements at the Radiation Source ELBE

Kaya, C.

Abstract

At the ELBE Free Electron Laser (FEL) at Forschungszentrum Dresden Rossendorf (FZD) electron bunches having lengths between 1 to 4 ps are generated. It is required to compress these electron bunches to lenghts below 1 ps which necessitates diagnosis of the electron bunch parameters. We use a Martin-Puplett interferometer (MPI) which is a modification of the Michelson interferometer, where the beams are linearly polarized at specific orientations. It measures the autocorrelation function of the coherent transition radiation (CTR) from a view screen which is an optical replication of the electron bunch.
The interferometer setup consists of various optical components like polarizers, beam splitter, mirrors and Golay cell detectors. In our measurement a wire grid was used as a polarizer and also as a beam splitter. A thorough understanding of the response of the optical components, as a function of the CTR wavelength range of our interest, is required for correct analysis of the measured signal. We have therefore simulated the response of the entire interferometer setup including the diffraction losses and the window transmission and compared the results to experimental measurements.

Keywords: electron bunch length; Martin-Puplett interferometer

Involved research facilities

Related publications

  • Poster
    DIPAC 2009, 25.-27.05.2009, Basel,, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-14588


Longitudinal Electron Bunch Profile Measurement with Electro Optic Sampling at the Radiation Source ELBE

Kaya, C.

Abstract

At the ELBE Accelerator at the Forschungszentrum Dresden (FZD) we want to perform longitudinal electron bunch profile measurement with Electro Optic Sampling (EOS) technique. We present the preliminary measurement results. The EOS technique is based on the change in the optical characteristics of a birefringent crystal due to the electric field induced by the passage of electrons in the vicinity of the crystal. Therefore we use femtosecond laser (Ti:Sa) pulses to probe the change of birefringence in the electro-optic ZnTe crystal. The resolution in the experiment is limited to about 250 fs by the bandwidth of the detection equipment.
One of the important steps in the measurement is to synchronize the Ti:Sa laser pulses emitted with a repetition frequency of 78 MHz with the 13 MHz radio frequency from the superconducting accelerator with low time jitter. The set-up required for determination of the temporal overlap of the femtosecond laser pulse with the real electron bunch was assembled with a OTR sensitive photodiode. The last synchronization step was tuning the time delay of the femtosecond laser relative to the electron bunch by an optical delay unit. By splitting the signal from the ZnTe crystal in a balance detector we achieve information about the longitudinal electron bunch profile.

Keywords: Electro Optic Sampling; bunch length; ZnTe

Involved research facilities

Related publications

  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Germany

Permalink: https://www.hzdr.de/publications/Publ-14587


Bunch Length Measurements at the Radiation Source ELBE

Kaya, C.

Abstract

At the ELBE Free Electron Laser (FEL) at Forschungszentrum Dresden Rossendorf (FZD) electron bunches having lengths between 1 to 4 ps are generated. It is required to compress these electron bunches to lenghts below 1 ps which necessitates diagnosis of the electron bunch parameters. We use a Martin-Puplett interferometer (MPI) which is a modification of the Michelson interferometer, where the beams are linearly polarized at specific orientations. It measures the autocorrelation function of the coherent transition radiation (CTR) from a view screen which is an optical replication of the electron bunch.
The interferometer setup consists of various optical components like polarizers, beam splitter, mirrors and Golay cell detectors. In our measurement a wire grid was used as a polarizer and also as a beam splitter. A thorough understanding of the response of the optical components, as a function of the CTR wavelength range of our interest, is required for correct analysis of the measured signal. We have therefore simulated the response of the entire interferometer setup including the diffraction losses and the window transmission and compared the results to experimental measurements.

Keywords: electron bunch; Martin-Puplett interferometer

Involved research facilities

Related publications

  • Lecture (Conference)
    DIPAC 2009, 25.-27.05.2009, Basel, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-14586


Morphology Induced Magnetic Anisotropy of Thin Films on Nanoscale MgO- and Si-Ripples

Lenz, K.; Körner, M.; Liedke, M. O.; Fritzsche, M.; Cizmar, E.; Ranjan, M.; Facsko, S.; Fassbender, J.

Abstract

Ion beam erosion techniques allow for the creation of well ordered ripple patterns with nanometer periodicity. Moreover, the periodicity can be tuned over a wide range by changing the ion beam energy [1]. The ripple pattern is directly transferred to the surface of films grown on these substrates. This offers the possibility of tailoring the magnetic properties by inducing additional magnetic anisotropy as well as modifying the intrinsic magnetic damping by adding relaxation mechanisms due to the structural modifications.
We study the influence of rippled vs. flat Si substrates for 10 nm thin Fe and Co films, as well as technologically relevant Heusler alloys (Fe3Si and Co2FexMn1-xSi). The magnetic anisotropy as well as damping is measured by frequency and angle-dependent vector network analyzer ferromagnetic resonance. The ripple morphology of the magnetic layers induces a strong uniaxial magnetic anisotropy. The intrinsic magnetic damping is influenced by mosaicity related inhomogeneous broadening and additional two-magnon scattering.
This work was supported by DFG grant no. FA 314/6-1.

Keywords: Magnetism; Magnetic Anisotropy; Nanoscale; Ripples

Involved research facilities

Related publications

  • Poster
    IEEE 7th International Symposium on Metallic Multilayers (MML 2010), 19.-24.09.2010, Berkeley, CA, USA

Permalink: https://www.hzdr.de/publications/Publ-14585


electron bunch length measurement at the radiation source ELBE

Kaya, C.

Abstract

In this study, measurement of electron bunch length at the ELBE Free Electron Laser (FEL) in the Forschungszentrum Dresden (FZD) is represented. Transition radiation is emitted when an electron passes the interface of two mediums of different dielectric constants. In case that the wavelength of the radiation is longer than the bunch length, coherent transition radiation (CTR) is emitted. The time profile of the CTR is a copy of the electron bunch longitudinal profile. The Martin- Puplett interferometer (MPI) is used to measure the autocorrelation function of the CTR pulse. The power spectrum and the bunch length information is obtained by Fourier transforming the measured autocorrelation function. There are different approaches for obtaining the bunch length from the MPI measurements. The data can be evaluated in the time domain as well as in the frequency domain. We can derive the longitudinal shapes of the electron bunch by analyzing the frequency information. The Measurement of the longitudinal electron bunch length is compared with the frequency domain method.

Keywords: electron bunch length

Involved research facilities

Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung 2009, 09.-13.03.2009, Munich, Germany

Permalink: https://www.hzdr.de/publications/Publ-14584


A Diplexer to Operate Two Cavity Eigen modes in Parallel

Arnold, A.

Abstract

To fulfil the demand of future high power and high luminosity FEL and storage ring sources, an intensive electron beam with short bunch length, small emittance and large bunch charge is required. Normal conducting (NC) laser driven radio frequency (RF) photocathode guns can deliver 1 nC bunches with an emittance of 1 π µrad. But to realize the demand on high average currents, a superconducting (SC) RF gun appears to be the best solution. First long term operation has been demonstrated at FZD [1]. In difference to the NCRF guns, the application of static magnetic fields near the cathode is not possible. Instead, the use of the magnetic field of a transverse electric (TE) mode in parallel to the accelerating mode was proposed. Numerical simulations have shown that this RF focusing can be applied to compensate the emittance growth [2].
This contribution will introduce a possibility to use the existing coaxial RF coupler of TESLA like cavities, as a RF power input for TE modes in parallel to its normal operation. The additional coupler component outside the module accomplishes the task of combining two different frequencies from different sources to one load. Thus, it corresponds to the working principle of a high power RF diplexer. Based on the 31/2 cell Rossendorf SRF-Gun [3], a concrete technical implementation and results of its operation at the cold SRF-Gun cavity will be presented.

Keywords: RF; Diplexer; TE-Mode; Magnetic Mode; Focussing; Emittance; Compensation; SRF; Gun; Accelerator; Injector

Involved research facilities

Related publications

  • Poster
    25th Linear Accelerator Conference (LINAC10), 12.-17.09.2010, Tsukuba, Japan
  • Contribution to proceedings
    25th Linear Accelerator Conference (LINAC10), 12.-17.09.2010, Tsukuba, Japan
    A Diplexer to Operate Two Cavity Eigen modes in Parallel
  • Lecture (others)
    Work in Progress (WIP) Seminar Serie, 29.05.2009, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-14583


Short Overview of Superconducting Photo Injectors

Arnold, A.; Teichert, J.

Abstract

The success of most of the proposed ERL based electron accelerator projects for future storage ring replacements (SRR) and high power IR-FELs is contingent upon the development of an appropriate source. Electron beams with an unprecedented combination of high brightness, low emittance and high average current (hundreds of mA) are required to meet future FEL specifications.
An elegant way to create such an unique beam is to combine the high beam quality of a normal conducting RF photo guns with the superconducting technology. Such superconducting RF photo injectors (SRF gun) based on different approaches are under investigation at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Lot of progress could be achieved during the last years and first long term operation was demonstrated at the FZD.

Keywords: ERL; FEL; SRF; Gun; Injector; Electron; Superconducting

Involved research facilities

Related publications

  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-14582


Druckabfall an verstopften Ansaugsieben, Stand der Modellierung

Grahn, A.

Abstract

Der Kühlmittelverluststörfall im Primärkühlkreislauf eines Kernreaktors lässt sich in eine Früh- und eine Spätphase unterteilen. In der Frühphase wird Isoliermaterial in der Umgebung des Lecks durch das unter hohem Druck ausströmende Kühlmedium ausgetragen und gelangt weiter in den Containmentsumpf. Dort befinden sich die Ansaugkammern der Umwälzpumpen des Notkühlkreislaufs. Gitterroste oder Lochbleche am Ende der Ansaugkammern dienen als Rückhaltevorrichtungen, an denen Feststoffe vom Kühlmedium abgetrennt und am Weitertransport über die Pumpen zurück in den Reaktorkern gehindert werden sollen. An diesen Rückhaltevorrichtungen bilden sich Packungen des Feststoffs, die unter dem Einfluss des Strömungswiderstandes kompaktiert werden und den Druckverlust erhöhen. In der Spätphase, wenn die Bildung der Feststoffpackungen bereits abgeschlossen ist, bilden sich durch den Kontakt des Kühlmediums mit metallischen und nichtmetallischen Oberflächen des Containments sowie seiner Einbauten Partikelsuspensionen, die in die Feststoffpackungen an den Rückhaltevorrichtungen eindringen und über längere Zeiträume zu einem weiteren Anstieg des Druckverlusts führen. Die Feststoffpackungen wirken in der Spätphase demnach als Tiefenfiltrationsmedium. Im Vortrag werden die Fortschritte bei der Modellierung des Druckabfalls an der Rückhaltevorrichtung in beiden Phasen des Störfalls berichtet. Es wird die Implementierung eines Siebmodells und dessen Einbettung in den Strömungssimulationscode ANSYS-CFX dargestellt. Transiente Testrechnungen zeigen die Anwendbarkeit des Siebmodells zur der Simulation des Druckaufbaus an ungleichmäßig beladenen Rückhaltevorrichtungen. Die Implementierung eines Tiefenfiltrationsmodells wird vorgestellt, mit dessen Hilfe der Differenzdruckanstieg in der Spätphase durch Eintrag von Partikelsuspensionen berechnet werden kann. Des Weiteren wird die Vorgehensweise bei der experimentellen Parameterbestimmung der verwendeten empirischen Modellgleichungen erläutert.

  • Lecture (Conference)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 "Isolationsmaterialbelastete Kühlmittelströmung", 03.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14581


Coupling of the CFD code ANSYS CFX with the 3D neutron kinetic core model DYN3D

Kliem, S.; Grahn, A.; Rohde, U.; Schütze, J.; Frank, T.

Abstract

The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled within the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for two small-size test problems confirm the correctness of the implementation of the prototype coupling. The first test problem was a mini-core consisting of nine real-size fuel assemblies with quadratic cross section. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the DYN3D/ANSYS CFX codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power in the same mini-core. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.
The same calculations were carried for a mini-core with seven real-size fuel assemblies with hexagonal cross section in order to prove the applicability of the coupled code to cores with hexagonal fuel assemblies. The differences between the results of coupled calculations and those of the stand-alone DYN3D code are in the same range as for the quadratic mini-core.

  • Lecture (Conference)
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
  • Contribution to proceedings
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
    Proceedings of the 20th Symposium of AER on VVER Reactor Physics and Reactor Safety, CDROM paper 5.5, Budapest: KFKI AEKI

Permalink: https://www.hzdr.de/publications/Publ-14580


AER Working Group D on VVER Safety Analysis – report of the 2010 meeting

Kliem, S.

Abstract

The AER Working Group D on VVER reactor safety analysis held its 19th meeting in Pisa, Italy, during the period 15-16 April, 2010. The meeting was hosted by the San Piero a Grado Nuclear Research Group of the University of Pisa and was held in conjunction with the second workshop on the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and the fourth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 12 participants attended the meeting of the working group D, 8 from AER member organizations and 4 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.

The meeting started with a general information exchange about the recent activities in the participating organizations.

The given presentations and the discussions can be attributed to the following topics:

  • Code validation and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP
  • Safety analyses and code developments
  • Future activities

A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files can be obtained from the chairman.

  • Lecture (Conference)
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
  • Contribution to proceedings
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
    Proceedings of the 20th Symposium of AER on VVER Reactor Physics and Reactor Safety, CDROM paper 5.1, Budapest: KFKI AEKI

Permalink: https://www.hzdr.de/publications/Publ-14579


Operation of the superconducting RF photo gun at ELBE

Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.

Abstract

As the first superconducting rf photo-injector (SRF gun) in practical operation, the FZD SRF gun has been successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for the users of ELBE radiation source. The SRF gun consists of a 3½ 1.3GHz SC cavity and a normal conducting photocathode. A modified 3½ niobium cavity has been fabricated and tested, which will increase the RF gradient in the gun and thus improve the beam parameters further. The electron beam of 3 MeV with the max bunch charge of about 400pC has been routinely produced for conditioning. In this paper the status of the SRF gun injection to the linac will be presented, and the latest results of the beam experiments will be discussed.

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Related publications

Permalink: https://www.hzdr.de/publications/Publ-14578


Temperaturfeldmessung und Detektion von Hotspots in Schüttungen

Schäfer, T.; Schubert, M.; Kryk, H.; Hampel, U.

Abstract

Mehrphasenreaktoren mit katalytisch aktiven Festbetten werden in vielen Prozessen der chemischen bzw. petrochemischen Industrie eingesetzt. Katalysatorausnutzung und Reaktoreffizienz sinken durch Fehlverteilungen der Gas- und Flüssigphasen im durchströmten Packungsquerschnitt sowie durch Kanalbildung und Bypassströme. Derartige Fehlverteilungen können außerdem zur Ausbildung lokaler thermischer Hotspots in der Schüttung führen. Hotspots mindern die Produktausbeute und -qualität, stellen ein erhebliches Sicherheitsrisiko dar und können bis zum Durchgehen des Reaktors führen. Die messtechnische Erfassung signifikanter Temperaturgradienten in der Packung ist dabei Voraussetzung zur optimierten Prozessführung und für die Einleitung regeltechnischer Sicherheitsmaßnahmen.
Basierend auf den von Prasser et al. (1998) entwickelten Gittersensoren zur Erfassung von Phasenverteilungen wurde ein neuer Temperaturgittersensor entwickelt, bei dem PT2000-Widerstandsthermometer in den Kreuzungspunkten eines 32x8 Leiterplatten-Arrays installiert sind. Exemplarisch wird die Anwendbarkeit eines flächigen Temperatursensors in einer Katalysatorschüttung demonstriert. Es werden lokale Wärmequellen erzeugt und deren Ausbreitungsdynamik in Abhängigkeit von den Strömungsbedingungen untersucht. Der entwickelte Temperaturflächensensor ermöglicht die Visualisierung des zeitlich und örtlich aufgelösten Temperaturfeldes im Reaktor.

Keywords: temperature array sensor; temperature wire-mesh sensor; packed-bed reactor; trickle bed reactor; temperature field; temperature distribution; hotspots; hotspot detection; temperatur field visualization

  • Abstract in refereed journal
    Chemie Ingenieur Technik 82(2010)9, 1428-1428
    DOI: 10.1002/cite.201050198
    ISSN: 0009-286X/1522-2640
  • Poster
    ProcessNet-Jahrestagung 2010 und 28. DECHEMA-Jahrestagung der Biotechnologen, 21.-23.09.2010, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14577


Modelling the resuspensions of fibres in the racetrack channel

Cartland Glover, G.

Abstract

Presentation of the progress made in modelling fibre agglomerate transport in the racetrack channel. Fibre agglomerates can be generated through the disruption of insulation materials during LOCA in NPPs. The fibres can make their way to the containment sump strainers and lead to their blockage. This blockage can lead to an increase in the pressure drop acting across the strainers, which can lead to cavitation behind the strainer and in the recirculation pumps. This will lead to a loss of ECC water reaching the reactor. A small proportion of the fibres may also reach the reactor vessel. Therefore reliable numerical models of the three-dimensional flow behaviour of the fibres must be developed. The racetrack channel offers the chance to validate such models. The presentation describes the techniques involved and the results obtained from transient simulations of the whole channel.

Keywords: Fibre agglomerates; CFD; Racetrack channel

  • Lecture (Conference)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 "Isolationsmaterialbelastete Kühlmittelströmung", 03.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14576


Interactive 3D ELBE Simulator for Educational Use

Arnold, A.

Abstract

The paper presents a novel approach to communicate scientific issues based on realistic and interactive 3D simulations. To demonstrate the versatility of this concept, a virtual copy of the electron accelerator ELBE, situated at the Forschungszentrum Dresden Rossendorf (FZD), was created. For programming we used the Open Source Engine Ogre3D, the modeling tool 3Ds Max and the programming environment Visual Studio. The intention of the work is a freely explorable replica of the reality, which is characterized by the interactivity of most of its components and their mouse click retrievable information. The resulting visualization is to our knowledge so far unique in the world and thus exploring completely new ways of imparting knowledge.

Keywords: Interactive; ELBE; Simulation; Education

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    International Workshop - Innovation Information Technology - Theory and Practice, 06.-10.09.2010, Dresden, Germany
  • Contribution to proceedings
    International Workshop - Innovation Information Technology - Theory and Practice, 06.-10.09.2010, Dresden, Germany
    Proceedings of the International Workshop "Innovation Information Technology: Theory and Practice", Dresden: Forschungszentrum Dresden - Rossendorf, 978-3-941405-10-3, 83-85
  • Lecture (others)
    Work in Progress (WIP) Seminar Serie, 26.03.2010, FZD, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-14575


Towards a precision measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis

Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Kempe, M.; Kögler, T.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schramm, G.; Schwengner, R.; Sobiella, M.; Stach, D.; Wagner, A.; Yakorev, D.

Abstract

Experimental data for the reaction p(n,γ)d are scarce at energies relevant to Big Bang nucleosynthesis. In network calculations, the reaction rate used relies on theoretical models constrained by nucleon-nucleon scattering data, the capture cross section for thermal neutrons and experimental data of the inverse reaction d(γ,n)p. The latter reaction - the photodissociation of the deuteron - is also sparsely investigated at Big-Bang energies. A comparison of measurements with precise calculations is difficult due to large experimental uncertainties.
To address the need for precise experimental data we started to measure the cross section of the reaction d(γ,n)p. We use high-intensity bremsstrahlung with an endpoint energy of 5.0 MeV generated at the superconducting electron accelerator ELBE at Forschungszentrum Dresden-Rossendorf. The incoming photon flux is determined by photon scattering at 27Al by measuring the well known transitions at 2.2 and 3.0 MeV with high-purity germanium detectors. With a pulse length of a few ps and an adjustable repetition rate, ELBE offers ideal conditions for precise time-of-flight experiments. For neutron detection we use plastic scintillators read out on two sides by high-gain photomultipliers. With this setup we can measure neutrons between 20 keV and 1.4 MeV with an energy resolution of about 4 %. The statistical uncertainty reached so far is about 5 %, the analysis of systematic effects is ongoing.

Keywords: Big Bang nucleosynthesis; bremsstrahlung; gamma-ray spectroscopy; neutron time-of-flight; nuclear astrophysics; photon scattering

Involved research facilities

Related publications

  • Poster
    11th Symposium on Nuclei in the Cosmos, 19.-23.07.2010, Heidelberg, Germany
  • Contribution to proceedings
    11th Symposium on Nuclei in the Cosmos, 19.-23.07.2010, Heidelberg, Germany
    PoS (NIC-XI) 090: Proceedings of Science

Permalink: https://www.hzdr.de/publications/Publ-14574


Energy scaling of laser accelerated protons and proton emission from reduced mass targets

Metzkes, J.; Zeil, K.; Kraft, S. D.; Bock, S.; Bussmann, M.; Helbig, U.; Karsch, L.; Kluge, T.; Pawelke, J.; Richter, C.; Cowan, T. E.; Sauerbrey, R.; Schramm, U.

Abstract

In the last years, high power laser systems in the 100 TW range with ultrashort pulses (~30 fs) and repetition rates of up to 10 Hz have come into operation. In order to investigate the laser proton acceleration in this laser regime we have performed a series of experiments using plain few-micron-thick metal targets and mass-limited silicon targets. The targets were irradiated with 30 fs pulses from the new 150 TW DRACO Laser facility at the Forschungszentrum Dresden-Rossendorf which show a contrast level of 10-10 in the picosecond and 10-9 up to 10-10 in the nanosecond range.
For both target types, proton spectra have been measured with a magnetic spectrometer and radiochromic film stacks. In addition, two magnetic electron spectrometers at different angles have yielded information on the electrons emitted from the non-irradiated target rear side.
Using plain metal foil targets, we have observed a linear scaling of the maximum proton energy with laser power and could show that this behaviour is explained consistently by Schreiber’s analytical scaling model [1] in the limiting case of ultrashort laser pulses [2]. Despite the high laser contrast we have found that a slight deformation of the target rear side results in a predictable deflection of the emission of energetic protons away from the target normal direction [2].
The mass limited targets tested in the experiment were micromachined silicon foils with lateral sizes of 20x20 µm2 to 100x100 µm2 mounted on tiny stalks. Their thickness of 2 μm corresponded to the optimum target thickness for proton acceleration at DRACO. Depending on the size of the targets strong influences of the stalks as well as the target edges were found which could both increase or decrease the maximum proton energy in comparison to a plain foil.

[1] J. Schreiber et al., PRL 97, 045005 (2006)
[2] K. Zeil et al., NJP 12, 045015 (2010)

  • Poster
    31st European Conference on Laser Interaction with Matter, ECLIM 2010, 06.-10.09.2010, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-14572


Corrosion chemistry of galvanized steel in boric acid media

Hoffmann, W.; Kryk, H.; Weiß, F.-P.

Abstract

The corrosion of hot-dip galvanized steel in boric acid media has been investigated by different corrosion experiments at increased temperatures using galvanized steel samples. The related experiments are designed to aid the risk management of safety of nuclear power stations. The results of additional potentiodynamic measurements are used for the explanation of the corrosion mechanism by cathodic protection of steel. The surfaces of samples as well as the composition of solutions were examined by different analytical methods. No significant amounts of suspended solid corrosion products were detected up to 70 °C. However, on samples obtained at 90 °C, a solid corrosion product was formed which was identified as zinc borate. The fast corrosion of zinc in boric acid solution decreases with the reaction time as well as with increasing pH of the solution. After two days, a nearly constant level of zinc ion concentration reduces the further corrosion of zinc significantly. The local corrosion of galvanized steel is influenced by the double layer structure of the zinc coating.

  • Lecture (Conference)
    EUROCORR 2010, 13.-17.09.2010, Moscow, Russia
  • Contribution to proceedings
    EUROCORR 2010, 13.-17.09.2010, Moscow, Russia
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-14571


Status of the SRF Gun operation at ELBE

Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Kamps, R. X. T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.

Abstract

The superconducting RF photo-injector (SRF gun) at FZD is the first operating electron injector of its kind. The gun with a 3½-cell cavity operating and a frequency of 1.3 GHz produces an electron beam of 3 MeV with a maximum bunch charge of about 400 pC. Also the design values for the acceleration gradient could not be reached with the cavity which is in use at present the SRF gun will improve the beam quality for ELBE users. End of 2009 the beamline was installed which connects the SRF gun with ELBE accelerator. We will report on the first test and on the progress in applying the SRF gun for user operation.

Involved research facilities

Related publications

  • Contribution to proceedings
    Free Elektron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    FEL 2010 Conference
  • Poster
    Free Elektron Laser Conference, 23.-27.08.2010, Malmö, Sweden

Permalink: https://www.hzdr.de/publications/Publ-14570


Investigation of the corrosion chemistry of hot-dip galvanized steel at LOCA condition

Hoffmann, W.; Kryk, H.; Weiß, F.-P.

Abstract

The loss of coolant accident (LOCA) is assumed to be one of the most severe accidents during pressurized water reactor (PWR) operation. Strainers in the reactor sump prevent the transport of fibres formed by fragmentation of insulation material to the reactor core for maintaining save cooling. Additionally, the coolant flow may be reduced or blocked by corrosion products resulting from reaction of primary circuit fluid with metallic components such as hot-dip galvanized steel gratings. The chemical behaviour of special designed galvanized steel samples was tested by means of batch experiments and in a tailored corrosion test facility under post LOCA conditions. Pure water, boric acid solution and a boric acid solution with additional LiOH for adjusting pH are used as liquid media. Only in solutions containing boric acid, the zinc ion concentration shows a significant increase within the first two days but no head loss occurred. Depending on reaction conditions, the zinc-concentration increases more slowly in the corrosion test facility than in batch experiments. At 45°C, concentrations up to 90 mg Zn/l are reached. It is remarkable that no significant amount of corrosion products of the basic material (Fe) were determined. Local damage of the outer pure zinc layer is observed especially in the trickled region of galvanized gratings.

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-14569


Ergebnisse der Batchversuche und Experimente an der KorrVA zur Korrosion von verzinkten Stahlproben und dem Verhalten der Korrosionsprodukte

Hoffmann, W.; Kryk, H.

Abstract

Mit feuerverzinkten Stahlproben wurden Korrosionsexperimente unter Kühlmittelverluststörfall-Bedingungen durchgeführt. Ziel dieser Arbeiten ist die Untersuchung des Einfluss von Korrosionsprodukten auf das Verhalten der Mineralwolleablagerungen an den Sieben der Sumpfabsaugung des Notkühlsystems eines Druckwasserreaktors (DWR). Dadurch soll eine Datenbasis zu diesem sicherheitsrelevanten Vorgang für die numerische Strömungsmodellierung bereitgestellt werden. Mit Hilfe von Batchversuchen, bei denen eine verzinkte Stahlprobe in eine gerührte Borsäurelösung tauchte, wurden bei 45, 70 und 90°C grundlegende Untersuchungen zur Korrosion im Kühlmittel des Primärkreislaufs eines DWR ohne Isoliermaterial ausgeführt, wobei neben Oberflächenuntersuchungen der Probe auch die Zusammensetzung des Mediums analysiert wurde. Im Gegensatz zu reinem Wasser findet in Borsäurelösungen eine deutliche Zinkauflösung statt, ohne dass sich wesentliche Mengen an festen Korrosionsprodukten bilden. Nur bei 90°C entstehen auf der Zinkoberfläche kugelförmige Korrosionsproduktablagerungen, die durch Laser-Raman-Spektroskopie als Zinkborat identifiziert wurden. Die Experimente wurden auf eine spezielle Versuchsanlage KorrVA übertragen, die in Anlehnung an die Sumpfgeometrie mit 65l Badvolumen bei vergleichbarer Strömungsgeschwindigkeit eine Untersuchung von beregneten oder getauchten Gitterrostproben (30x30cm) ermöglicht. Die Faserablagerung nach einem Störfall wird durch separat hergestelltes Faserbett aus fragmentierten Isoliermaterialfasern nachgebildet und als für die Praxis relevante Größe, der sich bildende Differenzdruck registriert. Eine im Verhältnis zu den Batchversuchen langsamere Zunahme der Zinkkonzentration in der Lösung ist durch den weniger intensiven Kontakt der Medien bei Beregnung zu erklären, ebenso wie durch noch geringeren Kontakt bei Durchströmung eines getauchten Gitterrosts. Eine wesentliche Zunahme des Differenzdrucks über das Faserbett wurde bei diesen Versuchen nicht festgestellt, da die Sättigungskonzentration von Zinkborat offensichtlich nicht erreicht ist und die Bedingungen für die Bildung der beiden schwerer löslichen Zinkkorrosionsprodukte basisches Zinkcarbonat und Zinkhydroxid bzw. Zinkoxid nicht erreicht werden. Wie Schliffbilder zeigen, erfolgt an den direkt beregneten Kreuzungspunkten am Gitterrost eine narbenförmige Korrosion der obersten Zinkschicht (Reinzink) bis auf das darunter liegende Hartzink (Zn-Fe Legierung). Korrosionsprodukte des Eisens aus dem Basismaterial werden unter diesen Bedingungen nicht gebildet.

  • Lecture (Conference)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 „Isolationsmaterialbelastete Kühlmittelströmung“, 03.03.2010, Dresden, Deutschland
  • Contribution to proceedings
    Fachkolloquium zum BMWi-Vorhaben 150 1363 „Isolationsmaterialbelastete Kühlmittelströmung“, 03.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14568


Dose-dependent biological damage of tumour cells by laser-accelerated proton beams

Kraft, S. D.; Zeil, K.; Richter, C.; Beyreuther, E.; Bussmann, M.; Enghardt, W.; Karsch, L.; Kluge, T.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Pawelke, J.; Sauerbrey, R.; Cowan, T. E.; Schramm, U.

Abstract

Cancer therapy using protons or heavier ions such as carbon plays a more and more important rolein oncology. We report on the first experiments, showing dose dependent biological damage of tumour cells by laser accelerated protons.

  • Lecture (Conference)
    31st European Conference on Laser Interaction with Matter, 06.-10.09.2010, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-14567


Dosimetry of laser-accelerated particle beams used for in-vitro cell irradiation experiments

Richter, C.; Dammene, Y.; Kaluza, M.; Karsch, L.; Kraft, S.; Metzkes, J.; Schlenvoigt, H.; Schramm, U.; Schürer, M.; Sobiella, M.; Wachs, R.; Weber, A.; Woithe, J.; Zeil, K.; Pawelke, J.

Abstract

Introduction: Before the novel technology of laser-based particle acceleration can be used for clinical applications, several requirements have to be fulfilled. These are the supply of stable and reliable particle beams with reproducible properties, sufficient particle intensity and useable energy spectra. Additionally, a precise dose delivery and the exposure of a desired irradiation field are needed. Beside these demands, consequences on dosimetry as well as on the radiobiological effect have to be investigated for ultra-short and ultra-intense pulsed laser-accelerated particle beams.
Material and Methods: Before conducting experiments with laser-accelerated particles, the response of different solid state dosimeters (TLD, OSL, diamond ionization chamber, EBT radiochromic films) to short, intense pulses of MeV electrons have been measured. After these successful characterizations, the worldwide first systematic radiobiological cell irradiations with laser-accelerated electrons have been performed with the JeTi laser system at the FSU Jena. The electron beam was controlled and monitored by means of a Roos ionization chamber (PTW Freiburg, Freiburg, Germany) and an in-house Faraday Cup for a defined dose delivery of the prescribed dose. Moreover, the precise absolute dose delivered to each cell sample was determined by an EBT film (ISP Corp., Wayne, NJ, USA) positioned in front of the cell sample. Furthermore, the energy spectrum of the laser-accelerated electron beam was determined both from measurements with an electromagnetic spectrometer and calculated from depth dose distributions measured with EBT film stacks.
In a next step, cell irradiation experiments with laser-accelerated protons have been prepared. Therefore, an Integrated Dosimetry and Cell Irradiation Device (IDCID) was developed. It can be installed at different laser and conventional accelerators and is used for both dosimetry and cell irradiations. The device consists of an ionization chamber made of ultra-thin foils (total thickness of 22.5 µm) for online dose information and a Faraday Cup inset for absolute dosimetry that can be replaced with a cell holder inset for cell irradiations. Moreover, EBT films or CR-39 solid state track detectors can be placed in the cell holder inset matching the plane of the cell mono layer. The IDCID was thoroughly tested and characterized with monoenergetic protons of energies between 5-9 MeV at a conventional Tandem accelerator. The design of the Faraday Cup (FC) was adopted from Cambria et al. Its absolute calibration (signal to charge correlation) was performed on 3 independent ways: (1) electronic calibration by applying a defined charge to the FC amplifier, (2) dose calibration against an established absolute dosimetry at a clinical proton facility (Helmholtz Zentrum Berlin, Germany) and (3) a calibration with CR-39. As the device presented excellent working capabilities, first cell irradiations using the IDCID were performed at the DRACO 150 TW laser system at the FZD.
As radiochromic films were used for different dosimetric aspects and beam qualities, both EBT and EBT2 films have been calibrated for several beam qualities, e.g. proton, electron and photon beams of different energies, partially presented in Richter et al.
Results: Both a laser-accelerated electron and proton beam have been optimized, monitored and controlled in terms of dose homogeneity, stability and absolute dose delivery and were used for sys-tematic radiobiological cell experiments. A combi-nation of different dosimetric components were used to provide both a online beam- and dose-monitoring and a precise absolute dosimetry. These dosimeters have been thoroughly tested, characterized, precisely calibrated, and finally applied successful.
Conclusion: A precise dosimetric characterization, optimization and control of laser-accelerated and therefore ultra-short pulsed, intense particle beams is possible, allowing radiobiological experiments and meeting all necessary requirements like homogeneity, stability and precise dose delivery. In order to fulfill the much higher dosimetric requirements for clinical application, several improvements concerning i.e. proton energy, spectral shaping and patient safety have been identified.
References:
Cambria, R., Hérault, J., Brassart, N., Silari, M. and Chauvel, P., 1997, Phys Med Biol 42 1185-1196
Richter, C., Karsch, L., Woithe, J. and Pawelke, J., 2009, Med Phys 36, 5506-5514

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Related publications

  • Lecture (Conference)
    SSD16, 19.-24.09.2010, Sydney, Australia
  • Contribution to proceedings
    SSD16, 17.-24.09.2010, Sydney, Australia
    SSD16 - Abstract Book, 43-43

Permalink: https://www.hzdr.de/publications/Publ-14566


Sculpting nanoscale precipitation patterns in nanocomposite thin films via hyperthermal ion deposition

Abrasonis, G.; Kovács, G. J.; Tucker, M.; Heller, R.; Krause, M.; Guenette, M.; Munnik, F.; Lehmann, J.; Tadich, A.; Cowie, B. C. C.; Thomsen, L.; Bilek, M. M. M.; Möller, W.

Abstract

Control of the morphology of self-organized nanostructures is the key issue in bottom-up approaches. Here, morphological transitions of precipitation patterns in C:Cu nanocomposite films are studied. The films have been grown by oblique incidence ionized physical vapour deposition. We show that the ion energy and directionality are transferred into the C-Cu phase separation process resulting in nanopattern formation and tilt. Increasing metal content induces the ‘tilted’-‘lying’ transition accompanied with Cu nanoparticle prolate-spherical-oblate shape transformations. The results allow the identification of metal sub-plantation as the key atomistic mechanism, and demonstrate the possibility to achieve nanoscale sculpting via energetic ion deposition.

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Permalink: https://www.hzdr.de/publications/Publ-14565


(i)PVD growth of carbon-transition metal nanocomposites: from energetic condensation to spin-dependent transport

Abrasonis, G.

Abstract

(i)PVD growth of carbon-transition metal nanocomposites: from energetic condensation to spin-dependent transport

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Radiation Interaction with Material and its Use in Technologies 2010 (Interaction'2010), 20.-22.09.2010, Kaunas, Lithuania

Permalink: https://www.hzdr.de/publications/Publ-14564


Synthesis and tilting of precipitation patterns in carbon-transition metal nanocomposite thin films by hyperthermal ion deposition

Abrasonis, G.; Oates, T. W. H.; Kovacs, G. J.; Tucker, M.; Grenzer, J.; Persson, P. O. A.; Heinig, K. H.; Martinavicius, A.; Jeutter, N.; Baehtz, C.; Bilek, M. M. M.; Möller, W.

Abstract

The structure control, especially at the nanoscale, is of the utmost importance in the field of the materials science of thin films. Here, the hyperthermal ion induced self-organization caused by phase separation during the carbon-transition metal (Ni, Cu) thin film growth is reported. The films have been grown by ionized physical vapour deposition using filtered cathodic vacuum arc. Influence of the metal type, film composition, ion energy and incidence angle is studied. The film morphology has been determined by transmission electron microscopy and grazing incidence small angle x-ray scattering. At these growth conditions, atomic displacements are caused solely by impacting energetic ions, resulting in phase separation in an advancing surface layer. If the metal amount surpasses some critical value, this layer switches to an oscillatory mode and a nanoscale precipitation pattern emerges. We demonstrate that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for the oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. We establish a dependence of the nanopattern morphology on the growth parameters and demonstrate a method for controlling the nanopatterning. Application of this concept opens new ways for the bottom-up nanostructure control for composite materials.

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Related publications

  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM), 22.-27.08.2010, Montréal, Québec, Canada

Permalink: https://www.hzdr.de/publications/Publ-14563


Development and validation of models for bubble coalescence and breakup

Liao, Y.; Lucas, D.

Abstract

New models were prosposed for bubble coalescence and breakup. They were implemented and validated for the case of air-water pipe flow in the Test Solver and CFX, respectively. The results were compared with the TOPFLOW L12 experimental data as well as the standard models in CFX. It was observed that good agreements with experimental data and substantial improvements in contrast to the standard models were achieved. In addition, the influence of bubble-induced turbulence models was studied. Large discrepancies show that modeling of bubble induced turbulence through additional source terms is still an open question.

Keywords: new models; bubble coalescence and breakup; validation; CFX; Test solver

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    3rd Milestone-Workshop, CFD-Network on Nuclear Reactor Safety Research, 23.09.2010, Grosshartpenning (bei Holzkirchen), Germany

Permalink: https://www.hzdr.de/publications/Publ-14562


TOPFLOW-II - Aktueller Stand, wichtige Ergebnisse und Pläne zur Weiterführung der Arbeiten

Lucas, D.; Beyer, M.; Schmidtke, M.; Zhang, D.; Krepper, E.; Höhne, T.; Deendarlianto, F. B.; Seidel, T.; Vallée, C.; Schleicher, E.; Zippe, C.; Weiß, F.-P.

Abstract

Im Vortrag wird ein Überblick über den aktuellen Bearbeitungsstand des Vorhabens "TOPFLOW-Experimente, Modellentwicklung und Validierung von CFD-Codes für Dampf/Wasser-Strömungen mit Phasenübergang " (gefördert durch das BMWi, Projektnummer 150 1329) sowie über wichtige, im letzten Jahr erreichte Ergebnisse und Pläne zur Weiterführung des Vorhabens gegeben.

Keywords: Zweiphasenströmung; Experiment; CFD

Involved research facilities

  • TOPFLOW Facility
  • Lecture (others)
    3. Meilenstein-Workshop des CFD-Forschungsverbunds "Entwicklung und Anwendung von Computational Fluid Dynamics (CFD) Programmen für Phänomene im Kühlkreislauf und Sicherheitseinschluss von Leichtwasserreaktoren", 23.09.2010, Großhartpenning, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14561


Hardening and microstructure of neutron- and ion-irradiated Fe-Cr alloys

Heintze, C.; Altstadt, E.; Bergner, F.; Hernández Mayoral, M.; Xie, M.; Birkenheuer, U.

Abstract

Understanding the irradiation behaviour of binary Fe-Cr alloys is basic for the optimization of ferritic/martensitic chromium steels for future applications under conditions of high neutron exposures. In this work self-ion irradiation with the ion beam scanned over the sample was used in order to simulate neutron damage in Fe-12.5at%Cr. The material irradiated at 300°C up to a damage level of 1 dpa was exposed to isochronal annealing treatments in the range from 300 to 550°C and the indentation hardness was measured as a function of annealing temperature. We have found the presence of two recovery steps. The first one takes place at 300°C, i.e. at irradiation temperature, and gives rise to a 45% recovery of the irradiation-induced hardness increase. The second step occurs in the range from 400 to 550°C and gives rise to full recovery. The findings are discussed in terms of the dissolution of hardening features, such as dislocation loops and ’-phase particles. In addition, rate theoretical considerations were used to investigate possible flux effects caused by the pulsed irradiation experienced by the material due to the scanning ion beam. It was found, that no significant additional flux effects arise from the pulsing.

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Related publications

  • Contribution to proceedings
    OECD Nuclear Energy Agency International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-2), 31.08.-03.09.2010, Daejeon, Republic of Korea

Permalink: https://www.hzdr.de/publications/Publ-14560


Simulation der Einströmung des heißseitig eingespeisten Notkühlwassers in den Kern mit Faserablagerungen

Höhne, T.

Abstract

In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue. Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs, since the Barsebäck event . Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode. Nevertheless, it cannot be completely ruled out, that a limited amount of small fractions of the insulation material is transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling.
The CFD simulations show that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “brake through channels” located at the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that the fibres are not uniformly deposited over the core cross section.

Keywords: Strainer; Core; RPV; CFD

  • Lecture (others)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 "Isolationsmaterialbelastete Kühlmittelströmung", 03.03.2010, Forschungszentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14559


Scaling of proton energies in ultrashort pulse laser plasma acceleration

Zeil, K.; Kraft, S.; Metzkes, J.; Richter, T.; Bock, S.; Helbig, U.; Bussmann, M.; Kluge, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.

Abstract

We present a systematic investigation of ultra-short pulse laser acceleration of protons yielding unprecedented maximum proton energies of 17 MeV using the Ti:Sa lased high power laser of 100 TW Draco at the Research Centre Dresden-Rossendorf. For plain few micron thick foil targets a linear scaling of the maximum proton energy with laser power is observed and attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from target normal towards the laser direction. The change of the emission characteristics are compared to analytical modelling and 2D PIC simulations.

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Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) 2010, 10.03.2010, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14558


Ionenimplantierte Halbleiterstrukturen fuer die Strahlungssensorik

von Borany, J.; Schmidt, B.

Abstract

Die Anwendung der Ionenimplantation und anderer halbleitertechnologischer Prozessschritte hat die Fertigungstechnologie von Silizium-Detektoren für die Strahlungssensorik in den zurueckliegenden Jahren wesentlich vorangetrieben. Dies ermöglicht einerseits die kostenguenstige Herstellung von „Standard“-Sensoren, andererseits aber die Entwicklung anwendungsspezifischer Sonderkonfigurationen oder die Umsetzung innovativer neuer Loesungen. Der Vortrag gibt einen kurzgefassten Ueberblick über die Arbeiten des FZD bei der Entwicklung und Fertigung von ionenimplantierter Strahlungsdetektoren fuer ionisierende Teilchen und Photonen. Im Mittelpunkt stehen dabei Loesungen fuer die Spektroskopie von Alpha-Teilchen mit bester Energieaufloesung und Fotodioden mit angepasster spektraler Empfindlichkeit. Die Erzeugung und Optimierung dotierter Gebiete in den Detektorstrukturen mittels spezieller Implantationstechniken (flache pn-Uebergaenge, vergrabene Strukturen) und Kurzzeit- Temperverfahren ist oftmals von ausschlaggebender Bedeutung. Bedingt durch die Verfuegbarkeit elektrostatischer Beschleuniger ist die Anwendung der Hochenergie-Ionenimplantaion fuer spezielle Detektorstrukturen zu einem Markenzeichen der Rossendorfer Entwicklungen geworden. Dazu zaehlen Detektoren für schwere Ionen, Elektronenstrahlen hoher Intensitaet oder spezielle Avalanche- Photodetektoren. Der Vortrag skizziert an einigen praxisrelevanten Beispielen die Anwendung dieser Detektoren auf verschiedenen Gebieten der Sensorik.

Keywords: silicon radiation detectors; high-energy implantation

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Related publications

  • Lecture (others)
    Innovationsforum Sonden fuer Hydrogeologie und Rohstofferkundung, 24.09.-25.10.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14557


Versuchsanlagen für die Untersuchung von Korrosionsprozessen

Kryk, H.; Hoffmann, W.; Härting, H.-U.

Abstract

Das Ziel des BMWi-Forschungsvorhabens besteht in der Beschreibung von Kühlmittelströmungen mit Feststoffpartikeln (Isolationsmaterial und Korrosionsprodukte) im Sumpf (DWR) oder der Kondensationskammer (SWR) eines LWR. Dabei stehen die Entwicklung und Validierung von CFD-Modellen hinsichtlich Fasertransport, Agglomeration/Resuspension sowie Sieb- und Sumpfgeometrie-Modellierung auf Basis der Ergebnisse von Experimenten an Großversuchsanlagen des Projektpartners HS Zittau/Görlitz im Vordergrund. Weiterhin sollen CFD-Modellkomponenten entwickelt werden, die die Verblockungseigenschaften von mit Isoliermaterial belegten Sumpfansaugsieben durch partikelförmige Korrosionsprodukte unter Einbeziehung vereinfachter Modelle der Korrosionsprozesse beschreiben. Zur Aufklärung der Korrosions- und Verblockungsmechanismen werden Einzeleffekt-Experimente im FZD durchgeführt, wofür drei spezielle Versuchsanlagen im Labormaßstab entwickelt und errichtet wurden. In einer Batch-Versuchsanlage (Rührkesselreaktor) werden grundlegende Untersuchungen zu elektrochemischen Korrosionsmechanismen und zur Wasserchemie durchgeführt. Ein Korrosionsversuchsstand für Langzeit-Experimente dient der Aufklärung der Korrosions- und Partikelbildungsvorgänge unter prozessähnlichen Bedingungen sowie dem Monitoring des Differenzdruckaufbaus an den Sumpfansaugsieben. Die Experimente zur Parametrierung und Validierung von Tiefenfiltrationsmodellen für die numerische Beschreibung der Partikelanlagerung an die Sumpfansaugsiebe und dem daraus folgenden Differenzdruckaufbau werden an einem speziellen Tiefenfiltrationsversuchsstand durchgeführt. Im Rahmen des Vortrages werden, ausgehend von grundlegenden Korrosionsmechanismen, Versuchsstrategien vorgestellt und die Versuchsanlagen, Versuchsparameter und Versuchsdurchführungen detailliert erläutert.

  • Lecture (Conference)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 „Isolationsmaterialbelastete Kühlmittelströmung“, 03.03.2010, Rossendorf, Deutschland
  • Contribution to proceedings
    Fachkolloquium zum BMWi-Vorhaben 150 1363 „Isolationsmaterialbelastete Kühlmittelströmung, 03.03.2010, Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14554


Use of superconducting LINACs for positron generation

Krause-Rehberg, R.; Jungmann, M.; Werlich, B.; Pohl, A.; Brauer, G.; Anwand, W.; Butterling, M.; Krille, A.; Buettig, H.; Kosev, K. M.; Wagner, A.; Cowan, T. E.

Abstract

Recently, superconducting LINACs became available to obtain high-energy electron beams [1]. The advantage of these rather compact accelerators is the high electron bunch charge at very high repetition rates up to > 20 MHz under cw operating conditions. Moreover, the electron bunch length is extremely short (< 5 ps). A single accelerator stage containing several RF cavities may supply beam energies as large as 20 MeV. Thus, such electron beams are ideal hosts for the generation of bunched, intense sources of either slow or fast positrons. The Radiation Source ELBE [2] at the Research Centre Dresden-Rossendorf (FZD) has two accelerator stages providing an electron beam of 40 MeV with 26 MHz maximum repetition rate, and an average electron current of 1 mA. In close collaboration of the University Halle and the FZD the positron source EPOS (ELBE Positron Source) is under construction [3]. The recent progress of the EPOS project will be demonstrated. EPOS consists of a digital, pulsed monoenergetic positron beam (MePS), a conventional lifetime/Doppler spectrometer (CoPS), and a setup for gamma-induced positron annihilation spectroscopy (GiPS). While the CoPS and GiPS systems are available for user operation, the MePS system is still under construction. First positrons were moderated and fed into the positron lab. In the moment, the chopper/buncher/accelerator system is under assembly. The GiPS system has now been used in several regular user sessions. Positrons are generated inside the sample by an intense, pulsed photon beam (up to 20 MeV). Thus, the whole sample volume will be investigated even for rather thick samples up to a sample volume of 20x20x20 mm3. This is very useful for liquids, coarse powders, biological tissue, NDT experiments, and other bulky samples. GiPS as well as CoPS are operated in the moment with analogue detector systems. However, the development of digital systems is close to be completed.
[1] http://elan.desy.de/
[2] http://www.fzd.de/db/Cms?pNid=144
[3] http://positron.physik.uni-halle.de/EPOS/

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  • Invited lecture (Conferences)
    12th International Workshop on Positron Beam Techniques for Solids and Surfaces (SLOPOS 12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia

Permalink: https://www.hzdr.de/publications/Publ-14553


Enhanced laser ion acceleration from mass-limited foils

Kluge, T.; Enhardt, W.; Kraft, S. D.; Schramm, U.; Zeil, K.; Cowan, T. E.; Bussmann, M.

Abstract

This paper reports on simulations of solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020 W/cm²) laser pulses with targets of diameter down to 1 m is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. Our results suggest that the most significant ion energy enhancement to should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.

Permalink: https://www.hzdr.de/publications/Publ-14552


Theoretical Understanding of Enhanced Proton Energies from Laser-Cone Interactions

Kluge, T.; Gaillard, S. A.; Bussmann, M.; Flippo, K. A.; Burris-Mog, T.; Gall, B.; Geissel, M.; Kraft, S. D.; Lockard, T.; Metzkes, J.; Offermann, D. T.; Rassuchine, J.; Schollmeier, M.; Schramm, U.; Sentoku, Y.; Zeil, K.; Cowan, T. E.

Abstract

For the past ten years, the highest proton energies accelerated with high-intensity lasers was 58 MeV, observed in 2000 at the LLNL NOVA Petawatt laser, using flat foil targets. Recently, 67.5 MeV protons were observed in experiments at the Los Alamos National Laboratory (LANL) Trident laser, using one-fifth of the PW laser pulse energy, incident into novel conical targets. We present a focused study of new theoretical understanding of this measured enhancement from collisional Particle-in-Cell simulations, which shows that the hot electron temperature, number and maximum energy, responsible for the Target Normal Sheath Acceleration (TNSA) at the cone-top, are significantly increased when the laser grazes the cone wall. This is mainly due to the extraction of electrons from the cone wall by the laser electric field, and their boost in the forward direction by the v×B term of the Lorentz force. This result is in contrast to previous predictions of optical collection and wall-guiding of electrons in angled cones. This new wall-grazing mechanism offers the prospect to linearly increase the hot electron temperature, and thereby the TNSA proton energy, by extending the length over which the laser interacts in a grazing fashion in suitably optimized targets. This may allow achieving much higher proton energies for interesting future applications, with smaller, lower energy laser systems that allow for a high repetition rate.

Keywords: laser; proton; ion; acceleration; flat top cone; maximum energy

  • Contribution to proceedings
    Advanced Accelerator Concepts Workshop, 13.-19,06,2010, Annaplolis, USA
    1299: AIP Conference Proceedings, 715

Permalink: https://www.hzdr.de/publications/Publ-14551


Stretching the Neck Towards Higher Energies

Kluge, T.; Gaillard, S.; Flippo, K.; Kraft, S. D.; Metzkes, J.; Zeil, K.; Schramm, U.; Enghardt, W.; Sauerbrey, R.; Bussmann, M.; Cowan, T.

Abstract

We present a new theoretical understanding of and selected results from experiments performed in 2009 at the TRIDENT laser at Los Alamos National lab. Those experiments yielded the wolrd's highest proton energies from laser-solid interaction and were based on novel flat-top copper cone targets. Simulations show that a new mechanism of laser-plasma interaction was responsible for the observed high proton energies and suggest that an optimization of the cone geometry may further enhance the achievable proton energies.

  • Poster
    FZD PhD Seminar, 22.-24.09-2010, Krögis, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14550


A comprehensive study of the p-type conductivity formation in radio frequency magnetron sputtering grown arsenic-doped ZnO film

Fan, J. C.; Zhu, C. Y.; Yang, B.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Wong, K. S.; Zhong, Y. C.; Ling, C. C.

Abstract

As-doped ZnO films were grown by the radio frequency magnetron sputtering method at different substrate temperature TS. For each of the TS’s, the average carrier concentration and mobility were obtained from samples grown by eight independent runs of growth through the Hall measurement. ZnO films grown on SiO2, Si and glass exhibited similar conductivity dependence on TS. As a typical example shown in the figure illustrating the carrier concentration of ZnO:As/SiO2, n-type high resistive films were yielded at low TS (i.e. 200°C). Those grown at TS=350°C and 400°C were p-type, though had large deviations from individual runs of growth. Reproducible p-type films having h~6x1017cm-3 and µ~6 cm2V-1s-1 were fabricated at high enough TS of 450°C. Conversion of the n-type ZnO:As film grown at TS=200°C to p-type film (p~1017cm-3) was observed upon the 450°C post-growth annealing in Ar.
The ZnO:As films grown at different TS’s were studied by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), positron annihilation spectroscopy (PAS) and nuclear reaction analysis (NRA). The XPS and the 10K PL results showed that majority of the As-atoms occupied the Zn-site of the lattice and the As-related acceptor had an activation energy Ea=155 meV. The correlated increase of S-parameter (obtained from the PAS study) showed that the p-type conductivity was associated with the Vzn-related defect and/or its increased open volume. These results were in consistent with Limijumnong et al’s AsZn-2VZn shallow acceptor model [Phys. Rev. Lett. 92, 155504 (2004)], which proposed an Ea=0.15 eV and a VZn volume increase due to atomic relaxation. An anti-correlation between the H-density and the p-type conductivity was also observed in the NRA study. Our results thus suggested that the p-type conductivity was associated with the thermally induced AsZn-2VZn shallow acceptor formation and the H-donor reduction.

This work was supported by the GRF (No.7031/08P) of RGC HKSAR, G_HK026/07 of RGC HKSAR and DAAD Germany, and the UDF of HKU HKSAR.

  • Invited lecture (Conferences)
    6th International Workshop on Zinc Oxide and Related Materials, 05.-07.08.2010, Changchun, China

Permalink: https://www.hzdr.de/publications/Publ-14549


Nanocap arrays of granular CoCrPt:SiO2 films on silica particles: tailoring of the magnetic properties by Co+ irradiation

Krone, P.; Brombacher, C.; Makarov, D.; Lenz, K.; Ball, D.; Springer, F.; Rohrmann, H.; Fassbender, J.; Albrecht, M.

Abstract

An approach for tailoring the magnetic properties by ion irradiation of granular perpendicular CoCrPt:SiO2 films grown on silica particles with sizes down to 10 nm was investigated. The as-prepared samples reveal an intriguing scaling dependence of the coercive field and remnant magnetization: both parameters are found to decrease with decreasing particle size. However, Co+ irradiation at a low fluence of 0.5 x 1014 cm-2 already results in an opposite scaling behavior. It is assumed that this modification is due to the enhancement of the intergranular magnetic exchange coupling of the granular CoCrPt:SiO2 film initiated by Co+ irradiation resulting in a modified reversal behavior. Further increase of the irradiation fluence beyond 1.6 x 1014 ions cm-2 leads to a degradation of the magnetic layer properties, lowering the remnant magnetization and the coercive field in the easy-axis direction. Moreover, the local magnetic properties of the samples were analyzed by magnetic force microscopy revealing magnetic multi-domain cap structures.

Keywords: magnetism; granular media; perpendicular recording; ion irradiation

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Permalink: https://www.hzdr.de/publications/Publ-14548


Developing Highly Scalable Particle-Mesh Codes for GPUs: A Generic Approach

Juckeland, G.; Bussmann, M.

Abstract

Dive deep into a multi-parallel Particle in Cell code that utilizes MPI, pthreads, and CUDA. Around this specific application a general C++ framework for transparent data transfers between GPUs has been developed and will be presented. Further techniques employed include interleaving of communication and computation, particle tiling and a study of how well CUDA performance can be transferred to OpenCL.

Keywords: gpu; particle-in-cell; pic; algorithm; cuda; simulation; performance; current deposition; cluster; mpi; opencl

Permalink: https://www.hzdr.de/publications/Publ-14546


Arsenic speciation in sulfidic waters: Consolidation of contradictory spectroscopic and chromatographic evidence

Planer‐Friedrich, B.; Suess, E.; Scheinost, A. C.; Wallschläger, D.

Abstract

In recent years, analytical methods have been developed that have demonstrated that soluble arsenic‐sulfur species constitute a major fraction of dissolved arsenic in sulfidic waters. However, an intense debate is going on about the exact chemical nature of these compounds, since X‐ray absorption spectroscopy (XAS) data generated at higher (mmol/L) concentrations suggest the presence of (oxy)thioarsenites in such waters, while ion chromatographic (IC) and mass spectroscopic data at lower (μmol/L to nmol/L) concentrations indicate the presence of (oxy)thioarsenates. In this contribution, we connect and explain these two apparently different types of results. We show by XAS that thioarsenites are the primary reaction products of arsenite and sulfide in geochemical model experiments in the complete absence of oxygen. However, thioarsenites are extremely instable towards oxidation, and convert rapidly into thioarsenates when exposed to atmospheric oxygen, e.g. while waiting for analysis on the chromatographic autosampler. This problem can only be eliminated when the entire chromatographic process is conducted inside a glove box. We also show that thioarsenites are instable towards sample dilution, which is commonly employed prior to chromatographic analysis when ultra‐sensitive detectors like ICP‐MS are used. This instability has two main reasons: if pH changes during dilution, then equilibria between individual arsenic‐sulfur species rearrange rapidly due to their different stability regions within the pH range, and if pH is kept constant during dilution, then this changes the ratio between OH‐ and SH‐ in solution, which in turn shifts the underlying speciation equilibria. This problem is avoided by analyzing samples undiluted. Our studies show that thioarsenites appear as thioarsenates in IC analyses if oxygen is not excluded completely, and as arsenite if samples are diluted in alkaline anoxic medium. This also points out that thioarsenites are necessary intermediates in the formation of thioarsenates.

Keywords: arsenic; XAFS; IC-ICP-MS; speciation

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Permalink: https://www.hzdr.de/publications/Publ-14544


3D-Visualisierung und Quantifizierung von Fluidströmungen in Salinargestein mittels Positronen-Emissions-Tomographie

Wolf, M.; Kulenkampff, J.; Enzmann, F.; Gründig, M.; Richter, M.; Lippmann-Pipke, J.; Mittmann, H.

Abstract

Anhand der Bergbaufolgeschäden des ehemaligen Kali- und Steinsalzbergbau im Raum Staßfurt (Sachsen-Anhalt) wurden im Rahmen des Forschungsverbundvorhaben Dynamik abgesoffener oder gefluteter Salzbergwerke und ihres Deckgebirgsstockwerks Ursachen, Prozesse und Auswirkungen der Bergschäden exemplarisch und umfassend untersucht.
Ein verbessertes Prozessverständnis, das auf kleinskaligen experimentellen Untersuchung der Strukturen und Prozesse im Labormaßstab und damit verbundenen Modellierungen beruht, soll zur Aufklärung des Geschehens und möglicher Folgen beitragen.
Zu diesem Zweck wurde in enger Zusammenarbeit mit dem Teilvorhaben zur strukturbezogenen Prozessmodellierung eine Methode zur direkten räumlich aufgelösten und quantitativen Prozessbeobachtung entwickelt und angewendet. Hierfür wurde als bildgebendes Verfahren die Positronen-Emissions-Tomographie (PET) eingesetzt. Hierfür wird ein Teil des injizierten Fluids mit Spuren eines Radiotracers markiert. Die Tracerkonzentration kann zerstörungsfrei, mit höchstmöglicher Empfindlichkeit und einem geeignetem Auflösungsvermögen in Raum und Zeit abgebildet werden. Der Prozess wird durch den Tracer auf geringst mögliche Weise beeinflusst und es wird ein realistisches Bild der Tracerverteilung, bzw. des Fließverhaltens, mit einer räumlichen Auflösung von 1 mm und einer zeitlichen Auflösung von 60s erzeugt.
Dieses Fließverhalten lässt sich mit räumlich heterogenen und prozessabhängigen Verteilungen von Parametern, wie effektiven Volumina, Permeabilitäten, Abstandsgeschwindigkeiten und Dispersionsraten beschreiben. Einem besseren Prozessverständnis dient insbesondere der Abgleich mit mit Lattice-Boltzmann-Simulationen der Fließprozesse, die auf hochauflösenden computertomographischen (µXCT) Messungen der internen Struktur der identischen Bohrkerne beruhen. Dieser Vergleich von PET-Messdaten mit Lattice-Boltzmann - Simulationsdaten, der zugleich eine Skalenübertragung um etwa drei Größenordnungen bedeutet, erfolgt mit geostatistischen Methoden.
Nicht in jedem Fall war dieser Abgleich zwischen Simulation und Experiment möglich: Während in klüftig-porösen Materialien gewöhnlich mit beiden Methoden räumlich stark differenzierte präferentielle Fließwege im Kluftsystem gefunden wurden, konnte in eher mikrostrukturell ausgeprägten Materialien trotz messbarer Permeabilität gelegentlich kein verbundener Porenraum aus den CT-Bildern segmentiert und somit keine LBM-Simulation durchgeführt werden. In diesem Fall zeigte die PET-Untersuchung ein diffuses Ausbreitungsverhalten des Tracers.

Keywords: positron emission tomography; imaging; saline rock; Lattice Boltzmann simulation; preferential flow

  • Contribution to proceedings
    Staßfurt 2010 - Erkennen, analysieren, bewerten und prognostizieren der zukünftigen Entwicklung der Bergbaufolgeschäden, 18.-20.11.2010, Staßfurt, Deutschland
    EDGG Exkursionsführer & Tagungspublikationen 244(2010), Hannover: Deutschen Gesellschaft für Geowissenschaften e.V, ISBN: 978-3-986944-028-6, 200-212

Permalink: https://www.hzdr.de/publications/Publ-14543


Optimization of induction heating for container-less melt extraction from a metallic sheet

Park, J.-S.; Pal, J.; Cramer, A.; Gerbeth, G.

Abstract

This work examines the induction heating of a metal sheet to be used for multiple instance melt extraction from the lower edge. The task formulation of heating the edge in first place while keeping the release of Joule heat along that edge as homogeneous as possible, i.e., the avoidance of end effects, is solved numerically with a parametric study. A set of factors is also modeled physically in the framework of an experimental series. Subject to variation are (1) the extension of the copper block, which simulates the extraction wheel, in both directions parallel and perpendicular to the inductor; (2) the protrusion depth of the edge of the sheet below the lower face of the inductor; and (3) the shape of the inductor. It is shown that this shape adopted from the floating zone crystal growth technique in a previous work,[1] albeit acting effectively, is removed from optimum. In this article, a more efficient solution is proposed. The numerical simulations also suggest that the vertical position of the inductor must be significantly above that one in Reference 1 to increase the efficiency of the process. Reasonable conformity may be stated between the calculated and the experimental results.

Keywords: container-less melt extraction; induction heating

Permalink: https://www.hzdr.de/publications/Publ-14541


Transport of hot electron currents in solid targets irradiated by high intensity short laser pulses

Antici, P.; Andebert, P.; Borghesi, M.; Cowan, T.; Gremillet, L.; Sentoku, Y.; Fuchs, J.

Abstract

Abstract. We have analyzed the transport of hot electrons generated in the interaction between a short-pulse, ultra-high intensity laser beam (pulse duration t1018 W.cm-2.μm2) and a solid or dense target through the use of proton emission imaging. We used targets of different material (Cu, Al, Au) with a regularly modulated rear target surface in order to compare the electron transport in different conditions. As result, we see that the electron transport depends on the target material and on the interaction conditions.

Permalink: https://www.hzdr.de/publications/Publ-14540


Bioaccumulation of U(VI) by Sulfolobus acidocaldarius at moderate acidic conditions.

Reitz, T.; Merroun, M. L.; Rossberg, A.; Steudtner, R.; Selenska-Pobell, S.

Abstract

U(VI) accumulation by the acidothermophilic archaeon Sulfolobus acidocaldarius at pH 4.5 and 6 was investigated. These pH values are relevant for some heavy metal and uranium polluted environments where populations of S. acidocaldarius were found to persist. We demonstrate that at these pH values U(VI) is rapidly complexed by the archaeal cells. A combination of X-ray absorption spectroscopy and time-resolved laser induced fluorescence spectroscopy revealed that at pH 4.5 both, organic phosphate and carboxylic groups are involved in the U(VI) complexation. In addition, at this pH, part of the added U(VI) was precipitated in inorganic uranyl phosphate mineral phases. These mineral phases were the most predominant uranium complexes found after the treatment of the cells with U(VI) at pH 6. Transmission electron microscopic analysis of the cells treated at pH 4.5 showed extracellular and intracellular U(VI) accumulates. The extracellular complexes represented mainly inorganic uranyl phosphate complexes. The formation of the intracellular uranyl phosphate deposits is attributed to uncontrolled uptake of U(VI) as a result of the increased cell permeability, most likely due to the stress of the non-optimal pH and uranium toxicity. Our results demonstrate that at moderate acidic conditions S. acidocaldarius immobilizes U(VI) via biosorption and biomineralization processes.

Keywords: Sulfolobus acidocaldarius DSM 639; Interactions with U(VI); X-ray absorption spectroscopy; Time-resolved laser-induced fluorescence spectroscopy; Transmission electron microscopy

Permalink: https://www.hzdr.de/publications/Publ-14538


Studying Hadron Properties in Baryonic Matter with HADES

Kugler, A.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Díaz, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A. P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Kraza, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kurepin, A.; Kählitz, P. K.; Lamsa-Verde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roskoss, J.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Simon, R.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Weber, M.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.

Abstract

The HADES spectrometer installed at GSI Darmstadt is a second generation experiment to study production of lepton pairs from proton, pion and nucleus induced reactions at the SIS/BEVALAC energy regime. The HADES study of the light C+C system at 1 and 2 AGeV confirms former finding of the DLS collaboration. Further studies of the reaction p+p and d+p allowed to reveal contribution to the above mentioned data of di-leptons produced during first chance collision. Finally, the results of the study of heavier system Ar+KCl indicates possible nonlinear dependence of the observed excess over the known long lived sources of di-leptons on the number of participants.

Permalink: https://www.hzdr.de/publications/Publ-14537


Hydrogen evolution under the influence of a magnetic field

Koza, J. A.; Mühlenhoff, S.; Zabinski, P.; Nikrityuk, P.; Eckert, K.; Uhlemann, M.; Gebert, A.; Weier, T.; Schultz, L.; Odenbach, S.

Abstract

The effect of a uniform magnetic field on the hydrogen evolution reaction (HER) during water electrolysis in 0.1 M Na2SO4 solution was investigated. Irrespective of the magnetic field orientation with respect to the electrode surface, the desorption of hydrogen is enhanced by the presence of the magnetic field. This effect is displayed by a reduction of the mean bubble size as well as a narrower bubble size distribution in a magnetic field. Moreover, it is shown that in the presence of an external magnetic field the fractional bubble coverage is strongly retarded. As a consequence the current density is increased since more active sitesare available for the reduction processes. These effects are discussed with respect to the Lorentz force driven convection induced by a magnetic field. In order to resolve further the influence of a magnetic field applied in the perpendicular-to-electrode configuration, where the bulk Lorentz force is negligible, a numerical study has been performed. This revealed the mechanism of the improved desorption of a hydrogen bubble from the electrode surface. The numerical study has been validated by a model experiment. Most importantly, it is clearly demonstrated that a magnetic field superposed during water decomposition is a very effective method to intensify hydrogen evolution processes, and it should be possible to significantly improve the energetic efficiency of the hydrogen production via water electrolysis in a magnetic field.

Keywords: Lorentz force; Water electrolysis; MHD effect; micro-MHD; Desorption of hydrogen

Permalink: https://www.hzdr.de/publications/Publ-14536


Geogas transport in fractured hard rock - correlations with mining seismicity at 3.54 km depth, TauTona gold mine, South Africa

Lippmann-Pipke, J.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M.; van Heerden, E.; Bester, A.; Moller, H.; Stroncik, N. A.; Reches, Z.

Abstract

An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (the international NELSAM-DAFGAS projects) at the TauTona Gold mine, South Africa. Extensive underground activities began in 2004 with the establishment of a 25 m² cubby and the drilling of five boreholes up to 60 m apart within the Pretorius Fault zone at 3.54 km depth. Instruments for chemical and seismic monitoring were then installed within the cubby and boreholes. Since 2007 sensitive gas monitoring devices have been continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N2, 21% O2, 1% Ar, while the geogas components CO2, CH4, He and H2 show most interesting trends and variations on the minute-by-minute basis. Time series and cross correlation analysis with meteorologic and seismic data allow the identification of two different gas components (geogas and tunnel air) and the identification of the two most significant processes influencing the borehole gas composition: 1) pumping-induced tunnel air breakthrough events through networks of initially water-saturated fault fractures; and 2) blasting induced permeability enhancement of the fault fractures to above ~5*10-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ≤ 1*109 Nm, located within 1000 m of the cubby) – and, we suggest, also during induced earthquakes – a final goal of the project.

Keywords: Gas transport; gas permeability of faults; gas breakthrough; mining; seismicity; DAFSAM; NELSAM

Permalink: https://www.hzdr.de/publications/Publ-14535


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