Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The generation of high magnetic fields for scientific and industrial applications, in particular those techniques which meet critical limits of field strength, coil heating, and mechanical stress as well, require a careful design and modelling. In order to describe the mutual dependences of the electrical, thermodynamical, and mechanical processes in such systems in a reasonable way, the use of multi-physics modules of finite-element software packages becomes more and more relevant. Here, the designs based on finite-element simulations of pulsed magnetic-field coils for industrial applications as well as of their pulsed-power supplies for the generation of electrical-current pulses are presented.

In the talk, results of experimental investigations of terahertz and infrared electrodynamics of different families of superconductors will be reviewed. In the conventional BCS-superconductors, a pronounced gap feature dominates the terahertz response below T_c. In the cuprates, entering into the superconducting state is accompanied by developing of a narrow zero-frequency centered mode in the real part of the in-plane complex conductivity. In the multi-gap superconductors (such as MgB₂), opening of the gap on each sheet of the Fermi surface contributes to the changes of dynamic complex conductivity.
A particular stress will be given on electron-doped cuprates, the electrodynamical response of which was found to have a remarkable dependence on the doping level. Significant changes in the gap anisotropy or even in the gap symmetry may account for this dependence.
The majority of the experiments have been performed on a home-made spectrometer, which utilizes backward-wave oscillators as sources of coherent and frequency-tunable terahertz radiation. An interferometer arrangement of the spectrometer has allowed both, amplitude and phase shift measurements, thus permitting direct (without using the Kramers-Kronig relations) determination of the optical constants.

To simultaneously perform magnetization and magnetostriction measurements in high magnetic fields, a miniaturized device was developed that combines an inductive magnetometer with a capacitive dilatometer and, therefore, it is called “dilamagmeter.” This combination of magnetic and magnetoelastic investigations is a new step to a complex understanding of solid state properties. The whole system can be mounted in a 12 mm clear bore of any cryostat usually used in nondestructive pulsed high field magnets. The sensitivity of both methods is about 10⁻⁵ Am² for magnetization and 10⁻⁵ relative changes in length for striction measurements. Measurements on a GdSi single crystal, which are corrected by the background signal of the experimental setup, agree well with the results of steady field experiments. All test measurements, which are up until now performed in the temperature range of 4–100 K, confirm the perfect usability and high stability in pulsed fields up to 50 T with a pulse duration of 10 ms. © 2008 American Institute of Physics.

NiCl₂-4SC(NH₂)₂ (known as DTN) is an S = 1 chain system with the easy-plane anisotropy dominating over the exchange interaction (so-called large-D system) and a new candidate for studying the fieldinduced Bose-Einstein condensation of magnons. The excitation spectrum of DTN has been investigated by means of tunable-frequency ESR technique in fields up to 25 T. Based on analysis of the magnon excitation spectrum, a revised set of spin-Hamiltonian parameters was obtained. These values were used to calculate the AFM phase boundary, low-temperature magnetization and the frequency-field dependence of two-magnon bound-state excitations, predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data was obtained. Published in Phys. Rev. Lett. 98, 047205 (2007).

CeRu₂Si₂ is a well-known prototypical heavy fermion system and shows a sudden strong increase in the magnetization M and the sample length ΔL for magnetic fields parallel to the crystallographic c-direction at around 7.8 T. These anomalies occur below 4K and sharpen with decreasing temperatures, but no features for a first order phase transition are observed down to 15mK. We report new thermal expansion α, magnetostriction λ and specific heat C/T measurements, which have been made in mT magnetic field steps around the metamagnetic crossover down to 15mK on very pure single crystals. The results show hints for the existence of a quantum critical endpoint in CeRu₂Si₂ and were compared with an extended model of metamagnetic quantum criticality, which was first introduced by Millis et al. in 2002.

In modern designs of nuclear reactors often natural circulation is used as a passive mechanism for heat removal. In the concepts the heat is removed from the reactor and transported into a large pool. Examples are the pressure suppression pool (wet-well) of the ESBWR, the in-containment refuelling water storage tank of the AP-1000, the pool of the emergency condenser of the SWR-1000 and the gravity driven water pool of the AHWR.
In large pools temperature stratification can compromise the heat transfer process. Generation of steam might lead to an increase of the flow velocities, to a mixing of liquids having different temperatures and to a disappearance of temperature stratification. At the corresponding temperatures steam is released from the pool into the containment and influences the increase of the containment pressure. Under conditions of strong temperature stratification compared to a homogeneous temperature distribution, the fluid at the top of the pool much earlier reaches the saturation temperature. The evaporation starts much earlier resulting in an earlier the pressure increase in the containment.
In the presentation both experiments and numerical CFD simulations are reported to investigate the capability of actual CFD modeling this task.

es hat kein Abstract vorgelegen

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the presentation the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

es hat kein Abstrakt vorgelegen

In modern designs of nuclear reactors often natural circulation is used as a passive mechanism for heat removal. In the concepts the heat is removed from the reactor and transported into a large pool. Examples are the pressure suppression pool (wet-well) of the ESBWR, the in-containment refuelling water storage tank of the AP-1000, the pool of the emergency condenser of the SWR-1000 and the gravity driven water pool of the AHWR.

In large pools temperature stratification can compromise the heat transfer process. Generation of steam might lead to an increase of the flow velocities, to a mixing of liquids having different temperatures and to a disappearance of temperature stratification. At the corresponding temperatures steam is released from the pool into the containment and influences the increase of the containment pressure. Under conditions of strong temperature stratification compared to a homogeneous temperature distribution, the fluid at the top of the pool much earlier reaches the saturation temperature. The evaporation starts much earlier resulting in an earlier the pressure increase in the containment.

In the presentation both experiments and numerical CFD simulations are reported to investigate the capability of actual CFD modeling this task.

Most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources require electron beams with an unprecedented combination of high brightness, low emittance, and high average current. In all projects photoguns will be applied: DC-photoguns, normal conducting RF-photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF-gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high average power into the gun, and, finally, the risk of beam excitation of higher-order cavity modes. In combination with SRF linacs, the SRF-guns seem to be the best solution for high average currents. Several R&D projects of SRF-gun have been launched. In this paper, we will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, the performance and the status of the Dresden Rossendorf SRF-gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. The main design parameters of this SRF-gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three TESLA-shaped cells, a specially designed half-cell where the photocathode is placed and a choke filter in order to prevent RF losses at the cathode side. The normal-conducting photocathode with a Cs2Te photoemission layer is cooled by liquid nitrogen. The SRF-gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen-cooled thermal shield and a titanium He tank with a two-phase supply tube. The 10 kW fundamental power coupler is adopted from the ELBE cryomodule. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF-gun. In a final step, the gun will be connected to the ELBE superconducting linear accelerator to deliver an improved electron beam to the user labs.

We test the quark mass dependence implemented in the quasiparticle dispersion relations of our quasiparticle model for the QCD equation of state by comparing with recently available lattice QCD data near Tc employing almost physical quark masses. In addition, we emphasize the capability of our model to successfully describe lattice QCD results for imaginary chemical potential and to analytically continue the latter to real chemical potential.

From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it appears that reversing dynamos are a quite common phenomenon.
Long time series of mean field simulations adopting Earth-like parameters yield reversal sequences whose statistical behavior is comparable to the Earth.
Recent hints for a reversing experimental dynamo give reason for the examination of a cylindrical dynamo with simulations that are especially suited to the experimental conditions.
This requires a numerical scheme that is able to treat insulating boundary conditions and material properties like permeability and/or conductivity jumps.
Preliminary calculations including a high permeability zone show a slight reduction of the critical Reynolds number.
In future simulations permeability jumps will be increased and an alpha-effect describing the inductive action of turbulence will be included.

The HADES spectrometer at GSI (Darmstadt) is investigating the e⁺e^- pair production in p+p, p+A and A+A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming form ¹²C+¹²C collisions at 1 and 2 AGeV, and on preliminary results from p+p/d+p collisions at 1.25 AGeV.

The K0 meson production by pi- mesons of 1.15 GeV/c momentum on various nuclear targets was measured with the FOPI spectrometer at the SIS accelerator of GSI. Inclusive production cross-sections and the momentum distributions of K0 mesons are compared to the elementary production cross-sections and to QMC and HSD model predictions. The results point to modifications of the elementary reactions amplitudes inside nuclei and to the existence of a repulsive KN potential of about 20 MeV at normal nuclear matter density.

Nanogranular materials will play an important role in future technologies due to their exciting magnetic and superconducting properties that differ strongly from their bulk counterparts. In this study, we have focused on metal and oxide nanoclusters that have been deposited on a biological template, a self-assembling surface layer (S-layer) of Bacillus sphaericus JG-A12 which is composed of identical monomers. We present data of Pd, Pb, and Fe₃O4 nanograins with sizes of 2, 19, and 13 nm respectively. The magnetization data obtained for the palladium clusters demonstrate that the Stoner enhancement factor of the d conduction-electron susceptibility is clearly reduced compared to the one of bulk Pd. For the Pb nanograins we have investigated the superconducting B-T phase diagram and encountered a superconducting critical field of the size of several Tesla which is strongly enhanced in comparison to the corresponding critical magnetic field of 0.09 T for bulk Pb. Last but not least we investigated the superparamagnetic properties of Fe₃O4 nanograins and have found a magnetic anomaly at 30 K. Here, we present magnetization data taken by SQUID magnetometry as well as experimental results of dielectric measurements.

We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl₂-4SC(NH₂)₂, in magnetic fields up to 18 T. This material is discussed in the context of Bose-Einstein condensation of magnons. The longitudinal c33 acoustic mode, which has a propagation direction along the spin chains, shows pronounced spin-lattice effects. This mode demonstrates a softening in the vicinity of the field-induced antiferromagnetic ordering (below T = 1.2 K), accompanied by an energy dissipation in the acoustic wave. A broad maximum has been observed in the temperature dependence of the sound velocity at 44 K. The low-temperature sound-velocity and sound-attenuation behavior is subject to fluctuations of Ni spin degrees of freedom resulting in frequency-dependent effects. The B − T phase diagram obtained from the ultrasonic measurements is compared with results extracted from other experimental investigations. The ultrasonic results are analyzed with a theory based on exchange-striction spin-phonon coupling.

Yttrium hydride demonstrates a remarkable transition of its electronic and optical properties upon change of hydrogen concentration: a thin YHx film can be continuously and reversibly brought from a shiny metal at x = 2 to a transparent dielectric at x = 3, by changing pressure of the surrounding hydrogen gas [1]. It has been showed that the metal-insulator transition (MIT) could be neatly passed under constant hydrogen pressure by changing the carrier doping via ultraviolet illumination at low temperatures [2]. Pronounced electron-electron interactions are posited to lead to the opening of a large optical gap. The established scaling laws of the conductivity with temperature and doping [2] are strong indications for the quantum nature of the metalinsulator transition in YHx. To shed more light on the quantum nature of the MIT, the frequency dependence of conductivity is very informative. In an extensive frequency range, frequency ! and temperature T will influence the conductivity in a similar way, which will lead to a so-called !/T -scaling behaviour. In this talk results on the optical conductivity in the sub-terahertz regime will be presented.

Recently, low-dimensional spin systems have received a considerable amount of attention due to their relevance to numerous quantum phenomena such as quantum criticality problems, spin-Peierls transitions, etc. Here we report on magnetization, electron paramagnetic resonance (EPR) and specific-heat measurements of the spin-1/2 Heisenberg antiferromagnetic chain material (6MAP)CuCl₃. Magnetization data measured at 0.1 T exhibit a maximum at about 70 K, indicating the low-dimensional character of the magnetic interactions. The data are in a good agreement with the temperature dependence of the resonance peak intensity measured at 73 GHz. At low temperatures (T < 25 K) the EPR linewidth drastically increases, indicating a possible enhancement of 3D short-range-order correlations. Such behavior is consistent with a broad maximum in the specific heat observed at about 1.5 K, which can be interpreted in terms of 3D magnetic ordering. In addition, we present results of room-temperature X-band EPR measurements of (6MAP)CuCl₃, including angular dependence of the g-factor and of the resonance linewidth.

The magnetic properties of metalorganic compounds attract much attention as their structural and electronic exchange dimensionality can vary between one and three. Here, we present data of representatives which exhibit magnetic ordering and have been recently investigated by means of magnetometry and calorimetry. In the quasi-cubic compound [Cu(HF₂)(pyz)₂]BF₄, we have observed an antiferromagnetic (AF) ordered phase occurring at T_N = 1.6K and a rich magnetic phase diagram up to 14 T as well. Above T_N, the specific heat of that compound is in reasonable agreement with the predictions of the model for a s = 1/2 2D square lattice quantum Heisenberg AF describing the in-plane exchange via the Cu−F −H−F −Cu bonds. In the quasi- 1D compound Mn(glycine)(H₂O)₂Cl₂ which is structurally arranged in helical chains, we have observed an unexpected 3D AF ordering at T_N = 0.84 K, both in the results of the heat capacity and ac susceptibility. Probably, the 3D exchange is mediated by hydrogen bonds between the chains in addition to Mn−O−Mn bonds along the chains.

Results of magnetization and high-field ESR studies of the new spin- 1 Haldane-chain material Ni(C₂H₈N₂)₂NO₂ are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were cal-
culated, yielding Δ/k_B = 17.4 K, gk = 2.14, D/k_B = 7.5 K, and |E/k_B| = 0.7 K for the Haldane gap, g factor. and the crystal-field anisotropy, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass-freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, whose origin is discussed.

Die in dieser Arbeit vorgestellten Simulationen aufsteigender fluider Partikel wurden mit dem CFD-Programm FS3D durchgeführt, welches auf der Volume-of-Fluid (VoF) Methode basiert. Die Validierung des Codes erfolgt durch Vergleich der numerischen Lösungen für schleichende Strömungen mit analytischen Lösungen, wobei eine gute Übereinstimmung festgestellt wird.
Im ersten Teil der Dissertation werden Simulationen für den freien Aufstieg von Öltropfen in Wasser mit experimentellen Beobachtungen hinsichtlich der Aufstiegsgeschwindigkeit, der Tropfenform und der Bewegungsbahn verglichen. Die Aufstiegsgeschwindigkeiten und Widerstandsbeiwerte sind vergleichbar, die simulierten Tropfen sind jedoch deutlich flacher. Dieser Unterschied kann durch Verunreinigungen der Grenzfläche im Experiment verursacht sein. Der Übergang von einem gradlinigen Aufstieg zu zickzack-förmigen Aufstiegsbahnen kann mit Hilfe der Simulationen auf Instabilitäten im Nachlauf der Blasen zurückgeführt werden, die zu einer periodischen Wirbelablösung führen.
Im zweiten Teil der Dissertation wird der Aufstieg von Blasen in linearen Scherströmungen untersucht. Steigen die Blasen in einer vertikalen Scherströmung auf, so beobachtet man eine seitliche Migration. Diese seitliche Migration der Blasen wird durch die sogenannte Liftkraft verursacht, deren Vorzeichen und Betrag von der Blasengröße und den Stoffeigenschaften der Flüssigkeit abhängt. Die Simulationen zeigen, daß das Vorzeichen der Liftkraft für eher sphärische Blasen durch den Bernoulli-Effekt erklärt werden kann. An stark deformierten Blasen hingegen wirkt die Liftkraft in umgekehrter Richtung. Dieses Phänomen tritt auch in den Simulationen auf.
Verschiedene Hypothesen für die Ursache dieses Phänomens werden überprüft. Die bekannteste experimentelle Korrelation für die Liftkraft von Tomiyama u. a. (2002) wird durch Simulation von realen Flüssigkeiten mit bekannten Stoffeigenschaften wie auch von Modellfluiden mit willkürlichen Stoffeigenschaften validiert und weitgehend bestätigt. Die Lift-Korrelation hat demnach hinsichtlich der Stoffeigenschaften der Flüssigkeit einen größeren Geltungsbereich, als bisher experimentell überprüft wurde.

The simulations presented in this thesis were performed with the CFD code FS3D which is based on the Volume of Fluid method. The code is validated using analytical solutions for creeping flows and a good agreement is observed between simulation and analytical solution.
In the first part of the thesis, the free rise of oil drops in water is simulated and compared with experimental observations. The results show that the rising velocities and the drag coefficients are similar in both cases, but the simulated drops are flatter (more oblate). This difference may be caused by impurities of the particle surface (surfactants) in the experiments. The simulations show that the transition from rectilinear to periodic trajectories is caused by instabilities in the wake, which lead to a periodic vortex shedding.
In the second part of the thesis, the rise of bubbles in linear shear flows is investigated. If bubbles rise in a vertical shear flow, a lateral migration can be observed. This migration is caused by the so called lift force. Sign and magnitude of the lift force depend on the size of the bubble and the material properties of the liquid. The simulation results show that the sign of the lift force on spherical bubbles can be explained by the Bernoulli effect. However, the lift force on more distorted bubbles acts in the opposite direction. This phenomenon can also be observed in the simulation. In this work several hypotheses for the reason of this phenomenon are checked. Furthermore, most common correlation for the lift force (developed by Tomiyama et al. in 2002) is validated for fluids of known material and model fluids with arbitrary material data. The correlation is valid in a wider range of fluid material properties than proved experimentally up to now.

Since the beginning of 2007 the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD) has opened as a user facility offering access to world-unique experimental infrastructure in pulsed-field magnets. Some of the available user magnets, reaching up to 70 T, and experimental techniques are reported. The brilliant light of a next-door free-electron-laser source allows dedicated high-field infrared spectroscopy. First scientific results obtained in pulsed magnetic fields are highlighted.

The recent progress made at and the status quo of the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD) is reported. This laboratory, pres-ently under construction at the research center (Forschungszentrum) Dresden-Rossendorf, is planned to open as user facility in 2007 offering access to various pulsed-field magnets. Besides introducing the installed capacitive energy supply at the HLD, the pulsed-magnet designs are discussed in some detail. The experimental techniques that are routinely running at the HLD and the additional ones being set up, are summarized. First scientific results are highlighted.

Leitermaterialien mit besonderen mechanischen Eigenschaften werden in vielen wissenschafts- und anwendungsorientierten Bereichen eingesetzt. Diese Leiter werden gezielt auf ihre Eigenschaften optimiert, um eine bestmögliche Funktionalität der Werkstoffe zu erreichen. Daher stellen diese auf ihre Anwendung zugeschnittenen Leiter oft eine Schlüsselkomponente des Systems, in dem sie eingesetzt sind, dar. Dieser Beitrag zeigt gegenwärtige und zukünftige Anwendungen der am IFW Dresden entwickelten hochfesten Leitermaterialien auf Kupfer-Basis auf.

We present a comprehensive de Haas–van Alphen study on the nonmagnetic borocarbide superconductor LuNi₂B₂C. The analysis of the angular-dependent effective masses for different bands in combination with full-potential density functional calculations allowed us to determine the massenhancement factors, λ, for the different electronic bands and their wave-vector dependences. Our data clearly show the anisotropic multiband character of the superconductivity in LuNi₂B₂C.

The critical parameters of a first-order magnetization process, H_cr and m_cr, are used to determine the anisotropy constants K₁ and K₂ of Tb₂Fe₁₇ in the temperature range between 5 and 300 K. Both anisotropy constants are proportional to the critical field H_cr (times spontaneous magnetization), whereas their ratio is independent of H_cr and depends solely on the dimensionless reduced critical magnetization mcr. The employed method of determining K₁ and K₂ is complementary to the classical Sucksmith–Thompson technique, which is inapplicable in the case of a first-order magnetization process.

This paper presents a literature review on mechanisms and models for the breakage of bubbles and drops (fluid particles) in turbulent dispersions. For the mechanisms, four categories are summarized, namely, turbulence fluctuation, viscous shear stress, shearing-off process and interfacial instability. The models for breakup frequency and daughter size distribution available in literature are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.

The design of a high-energy pulsed magnet is a challenging task and usually implies substantial calculation efforts. As the maximum stress is located in the mid-plane of the magnet, this region is usually the only focus of analysis. For that a number of well-established algorithms are available. However, the coil performance is governed not exclusively by the mid-plane. Therefore, it is important to simulate the whole coil behavior. Here we report on a simulation approach used among others at the Hochfeld-Magnetlabor Dresden (HLD). Assuming axial symmetry of the coil, the cross section of the magnet is modeled by finite elements. We illustrate this simulation technique for an 8.5 MJ 70 Tesla mono-coil and a 46 MJ double-coil magnet designed at the HLD.

This contribution presents different approaches for the modeling of air entrainment under water by plunging jets in CFD codes. In simulations which include the full length of the jet and its environment, the process of bubble generation can not be resolved due to computational limitations. This is why the air entrainment has to be modeled in meso-scale simulations. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. In the impinging jet configuration, the air is a continuous phase above the water level but bubbly below the water level. Various drag models are implemented in the CFD solver CFX11 and their influence on the gas void fraction below the water level is discussed. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g. correlations) for the gas entrainment.

Pulsed magnets are generally evaluated and compared in terms of the magnetic field they can achieve in combination with a bore size. However, in practice another criterion is equally important: the waiting time for a researcher in between two consecutive shots. The cooling time of pulsed magnets can range from a few minutes up to several hours, depending on coil size and desired field. Using simulations and measurements several options to reduce the cool down time are compared in this paper. One of the discussed methods is now routinely in use at the Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse.

The presentation summarizes the activities regarding the simulation of Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. Some Loss of Coolant Accident (LOCA) scenarios for Pressurized Water Reactors (PWR) may lead to PTS situations. They imply the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. Current generation PWR (including the Russian VVER types), are primarily affected by the phenomenon which is investigated within three broad areas: material damage originated by irradiation, thermal-hydraulics (including single and two-phase flow conditions in the region of the ‘shock’) and structural mechanics with main reference to fracture mechanics. The present paper, in the area of thermal-hydraulics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. Within the above context, the paper summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase mechanisms (or sub-phenomena) are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance (case of two phase flow) is presently not available.

Es wird eine Übersicht über den aktuellen Status der vom BMWi gefördeten Projekte "TOPFLOW-Experimente, Modellentwicklung und Validierung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang " und "Entwicklung und Validierung von Modellen für Blasenkoaleszenz und –zerfall " gegeben.

The quantum mechanical brachistochrone system with PT-symmetric Hamiltonian is Naimark dilated and reinterpreted as subsystem of a Hermitian system in a higher-dimensional Hilbert space. This opens a way to a direct experimental implementation of the recently hypothesized PT-symmetric ultra-fast brachistochrone regime of [C. M. Bender et al, Phys. Rev. Lett. {\bf 98}, 040403 (2007)] in an entangled two-spin system.

The analysis of the UV range spectral characteristics can supply additional
information on the formed sub-surface buried layer with implanted dopants. The near-surface
layer (50÷150 nm) of bulk polymer samples have been implanted with silicon (Si+) ions at low
energies (E=30 keV) and a wide range of ion doses (D=1.1013 ÷ 1,2.1017 cm-2). The studied
polymer materials were: ultra-high-molecular-weight polyethylene (UHMWPE), poly-methylmetacrylate
(PMMA) and poly-tetra-fluor-ethylene (PTFE). The diffuse optical reflectivity
spectra Rd = f(λ) of the ion implanted samples have been measured in the UV range (λ =
220÷350 nm). In this paper the dose dependences of the size and sign of the diffuse optical
reflectivity changes ΔRd = f(D) have been analysed.

Detailed insight into the near-surface area of the ion beam modified polymer is supplied by the measured diffuse reflectivity spectra. The near-surface layer (50÷150 nm) of bulk polymer samples have been implanted with silicon (Si+) and carbon (C+) ions at low energies (E=30 keV) and a wide range of ion doses (D=5.1012-2.1017 cm-2). The polymer materials studied were: ultra-high-molecular-weight polyethylene (UHMWPE), poly-propylene (PP), and poly-tetra-fluor-ethylene (PTFE). The diffuse optical reflectivity spectra Rd = f(λ) of the implanted samples have been measured in the visible range (λ=400÷830 nm). In this paper the dose dependences of the size and sign of the diffuse reflectivity changes ΔRd=f(D) have been analyzed.

Presentation about the application of in-beam PET for high-energy photons

Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittelpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren. Im FZD angwendete Methoden zur experimentellen Mikrostrukturanalyse, zur Modellierung von strahleninduzierten Defekten mit Ratentheorie und zur bruchmechanischen Analyse werden erläutert.

The last decade has seen an increasing use of three-dimensional Computational Fluid Dynamics (CFD) codes to predict steady state and transient flows in industrial applications because a number of important phenomena such as slugging, pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution. CFD codes contain models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in industrial applications. The necessary validation is performed by comparing model results against measured data. The multipurpose thermalhydraulic test facility TOPFLOW was designed at FZD to investigate stationary and transient phenomena in two-phase flows with the purpose of development and validation of models used in CFD codes. In addition, for the experimental investigation of horizontal two phase flows, different non pressurized channels and the Hot Leg Model in a pressure chamber were built and the experimental results compared with numerical simulations. Our partner for CFD code qualification is ANSYS CFX. Based on this partnership physical models which are developed are implemented into the code and thus contribute to the code qualification.

This work presents the development of an analytical approximation solution for a space-time-dependent neutron transport problem in a one-dimensional system consisting of a homogenized medium with a central external source with Green functions. The delayed neutron production is implemented with the multiple-scale expansion method. Qualitative results for a given system are analyzed and an example of the use for the analysis of accelerator-driven systems is given.

Plant measured data from VVER-1000 coolant mixing experiments were used within the OECD/NEA and AER coupled code benchmarks for light water reactors to test and validate CFD codes. The task is to compare the various calculations with measured data, using specified boundary conditions and core power distributions. The experiments, which are provided for CFD validation, include single loop cooling down or heating-up by disturbing the heat transfer in the steam generator (SG) through the steam valves at low reactor power in the range of 5-14% and with all main coolant pumps (MCP) in operation. They were conducted during the plant commissioning phase at Kozloduy-6, Bulgaria and Kalinin-1, 2, Russia. CFD calculations have been performed for the thermal hydraulic benchmark V1000CT-2 using ANSYS CFX. The numerical grid model was generated with the grid generator ICEM-CFD and contains 4.7 Mio. tetrahedral elements. The Best Practice Guidelines (BPG) in using CFD in Nuclear Reactor Safety Applications has been used. Different advanced turbulence models were utilized in the numerical simulation. The best agreement with the Kozloduy heating-up experiment at the core inlet shows the Detached Eddy Simulation (DES). The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%. Uncertainties are still the estimation and interpolation of experimental values at the core outlet to the core inlet.

extrapolation of lattice QCD to large baryon densities, e.g. CBM@FAIR; QPM with ImΠi ≠ 0, plasmons and plasminos from HTL; Is the small -T region accessible? Improvement of previous models?

In-Medium Modification of Hadrons: w, N, D
QCD Sum Rules
Four-Quark Condensates

A superconducting Electron Linac with high Brilliance and low Emittance (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. The technical setup of the accelerator and secondary beam generation will be explained and some representative application examples will be demonstrated. ELBE runs in routine user operation since 2004 with stepwise commissioning of the secondary radiation targets.

In der Reaktorsicherheitsforschung sind auftriebsgetriebene Strömungen von Relevanz für Störfall-szenarien mit Verdünnung der Borkonzentration und für thermische Schockbelastungen des Reak-tordruckbehälters. In der numerischen Simulation der Strömungen werden neben der Berücksichtigung der Auftriebskräfte Quell- und Korrekturterme in die Bilanzgleichungen für die turbulente Energie und die turbulente Dissipation eingeführt. Es wurden erweiterte Modelle entwickelt, in die zusätzliche Gleichungen für die Turbulenzgrößen „turbulenter Massenstrom“ und „Dichtevarianz“ eingehen. Die Modelle wurden in den CFD-Code ANSYS-CFX implementiert.
Die Validierung der Modelle erfolgte an einem speziellen Versuchsaufbau (VeMix-Versuchsanlage), mit Einspeisung von Fluid höherer Dichte in eine Vorlage. Als Kriterien für die Validierung wurde der Umschlag zwischen impulsdominiertem Strömungsregime mit vertikalem Jet oder ein vertikales Absinken bei Dominanz von Dichteeffekten herangezogen sowie lokale Konzentrationsmessungen mit Hilfe eines speziell entwickelten Leitfähigkeits-Gittersensors. Eine Verbesserung der Simulation dichtedominierter Vermischungsprozesse mit den erweiterten Turbulenzmodellen konnte allerdings nicht nachgewiesen werden, da die Unterschiede zwischen den Rechnungen mit verschiedenen Turbulenzmodellen zu gering sind. Andererseits konnte jedoch die Simulation der Stratifikation von Fluiden unterschiedlicher Dichte im kalten Strang einer Reaktoranlage deutlich verbessert werden. Anhand der Nachrechnung von Ver-suchen am geometrisch ähnlichen Reaktor-Strömungsmodell ROCOM wurde gezeigt, dass diese Stratifikation von bedeutendem Einfluss auf die Vermischung und somit letztendlich auch auf die Temperatur- bzw. Borkonzentrationsverteilung innerhalb des Reaktordruckbehälters ist. Sie lässt sich nur korrekt simulieren, wenn ausreichend große Abschnitte des kalten Stranges mit modelliert werden. Somit konnte doch eine bessere Vorhersagegenauigkeit der Simulation der Vermischung erreicht werden.

In reactor safety research, buoyancy driven flows are of relevance for boron dilution accidents or pressurised thermal shock scenarios. Concerning the numerical simulation of these flows, besides of the consideration of buoyancy forces, source and correction terms are introduced into the balance equations for the turbulent energy and its dissipation rate. Within the project, extended turbulence models have been developed by introducing additional balance equations for the turbulent quantities “turbulent mass flow” and “density variance”. The models have been implemented into the computati-onal fluid dynamics code ANSYS-CFX.
The validation of the models was performed against tests at a special experimental set-up, the VeMix facility, were fluid of higher density was injected into a vertical test section filled with lighter fluid. As validation criteria the switching-over between a momentum controlled mixing pattern with a horizontal jet and buoyancy driven mixing with vertical sinking down of the heavier fluid was used. Additionally, measurement data gained from an especially developed conductivity wire mesh sensor were used. However, an improvement of the modelling of buoyancy driven mixing by use of the extended models could not be shown, because the differences between calculations with the different models were not relevant. On the other hand, the modelling of the stratification of fluids with different density in the cold leg of a reactor primary circuit could be significantly improved. It has been shown on calculations of experi-ments at the ROCOM mixing test facility, a scaled model of a real reactor plant, that this stratification is relevant as a boundary condition for the mixing process inside the reactor pressure vessel. It can be correctly simulated only if sufficient large parts of the cold legs are included in the modelling. On this way, an improvement of the accuracy of the prediction of mixing processes was achieved.

Es wurde eine SP3-Transportmethode entwickelt, die neutronenkinetische Rechnungen für die Kerne von Leichtwasserreaktoren mit höherer Genauigkeit als die gegenwärtig in der Kernauslegung angewandten Standardmethoden auf Basis der Zweigruppendiffusionsnäherung er-laubt. Eine Verbesserung der Genauigkeit von Abbrandrechnungen und der Berechnung von Tran-sienten ist für heterogene Kerne notwendig, in denen neben UO2-Brennelementen auch Mischoxyd – Brennelemente eingesetzt werden.
In einem ersten Schritt wird die in dem Rechenprogramm DYN3D verwendete Zweigruppendiffusi-onsmethode auf viele Energiegruppen erweitert. Auf der Basis von Untersuchungen zu einer optima-len Gruppenstruktur wird die Verwendung von 8-10 Energiegruppen der Neutronen als optimal erach-tet. Das Verfahren wurde anhand von stationären und transienten Rechnungen für das OECD/NEA und US NRC PWR MOX/UO2 Core Transient Benchmark verifiziert.
In den nächsten Schritten erfolgte die Entwicklung und Implementierung einer SP3-Näherung in DYN3D. Dabei besteht die Möglichkeit, ein feineres Gitter im BE zu benutzen. Das Verfahren wurde zunächst durch pinweise Berechnung stationärer Zustände des obigen Benchmarks verifiziert.
Untersuchungen für das Benchmarkproblem zeigen, dass das Verhältniss des 2-ten Momentes zum 0-ten Moment des Flusses klein ist. Die beiden SP3-Gleichungen können deshalb separat in iterativer Weise gelöst werden. Dies reduziert den benötigten Speicherplatz und erfordert weniger CPU-Zeit. Dieses vereinfachte Verfahren wurde deshalb ebenfalls in das Programm implementiert. Es wird ge-zeigt, dass mit diesem Verfahren eine vergleichbare Genauigkeit erreicht wird. Stabweise Rechnun-gen mit 4, 8 und 16 Energiegrupppen wurden für einen stationären Zustand des Benchmarks durch-geführt. Eine 3-dimensionale Aufgabe des Benchmarks mit Rückkopplung und Vollleistung wurde mit dem optimierten SP3-Verfahren gerechnet.

A SP3 transport approximation was developed for neutron kinetic calculations of cores of light water reactors with a higher accuracy than the present standard methods of core design based on the two group diffusion approximation. An improvement of accuracy for burnup and transient calculations is required for cores loaded with UO2 and MOX fuel assemblies.
In the first step, the two group diffusion method applied in the computer code DYN3D was extended to an arbitrary number of groups. Investigations for an optimal group structure have shown that a number of 8 to 10 energy groups of neutrons seems to be reasonable. The multi-group technique was verified for steady states and transients of the OECD/NEA und US NRC PWR MOX/UO2 Core Tran-sient Benchmark.
In the next steps, a SP3-approximation was developed and implemented into DYN3D. The possibility of using finer meshes inside the fuel assemblies is involved in this method. The technique was veri-fied by pinwise calculations for steady states of the above mentioned benchmark.
The investigations to the benchmark problem have shown that ratio of the 2nd moment of flux to the 0th moment is small. Therefore the two coupled SP3 equations can be solved separately in an iterative way. The required computer memory and the CPU time can be reduced by this technique. This sim-pler method was also implemented in the code. It is shown that the reached accuracy is comparable to accuracy of the original technique. Pinwise calculations with 4, 8 and 16 energy groups were per-formed for a steady state of this benchmark. A three-dimensional problem of the benchmark at full power and with feedback was calculated with the optimized SP3 technique. The optimized method was used for the time integration of the transient SP3 equations. The pinwise calculation of a control rod ejection was tested for a simple system and the results were compared with the diffusion solution.

The mixing ratios for M1 and E2 radiation for transitions in 11B have been determined by measuring the azimuthal asymmetry of the radiation emitted from levels populated by resonant absorption of polarized photons. The photon-scattering experiments were carried out at the FreeElectron Laser Laboratory at Duke University using nearly monoenergetic and linearly polarized photon beams. The mixing ratios were deduced from a comparison of the measured azimuthal asymmetries with calculations for the angular distribution of mixed transitions.

The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors.

The reason for the increased use of multidimensional CFD methods is that a number of important phenomena such as pressurized thermal shocks, boron mixing and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

CFD codes contain empirical models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in NRS (Nuclear Reactor Safety) applications.
CFD simulations are shown with an emphasis on validation in areas such as: heat transfer, buoyancy, multi-phase flows, natural circulation, turbulent mixing, and complex geometries. These topics are related to NRS-relevant issues such as: pressurized thermal shocks, boron dilution, hydrogen distribution, sub-cooled boiling etc.

Deep sub-threshold production of Xi(1321) hyperons in collisions of Ar+KCl at 1.76 AGeV

The HADES Eventdisplay

Parametrization of pp and pn bremsstrahlung for PLUTO

Activities towards the mounting of the MDC DAQ upgrade parts

Current status regarding MDC FEE and how to equip the plane I chambers

Status of MDC-I ...

We discuss the open charm production in peripheral reactions pp → YcYc and pp → McMc, where Yc and Mc stand for Lambda^+_c, Sigma^+_c and D,D∗, respectively, at √s <~ 15 GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams which allows to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependance is determined by the effective interaction of lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in pp → YY and pp → KK reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a non-trivial t and s dependence which is sensitive to details of the open charm production mechanism.

The physics of the PT-symmetric two-mode Bose-Hubbard model is discussed in detail. Special emphasis is laid on the unfolding of higher-order exceptional points (EPs) and on a detailed presentation of the Newton polygon technique. It is shown that the latter can be considered as a highly efficient tool for the unfolding analysis of higher-order roots in any polynomial equation.

The basics of the theory of generalized quantum measurements is briefly discussed. Starting from positive operator valued measures (POVMs) (as generalization of decompositions of unity in terms of orthogonal projectors) it is demonstrated how to associate the POVMs in a natural way with the nonorthogonal eigenvectors of non-Hermitian operators with non-degenerate real spectrum. This approach allows for a self-consistent treatment of the non-Hermitian operators connected with a state discrimination technique for their non-orthogonal eigenvectors and the definition of a probabilistic content of corresponding generalized measurement procedures. The technique is applied to the brachistochrone problem of PT-symmetric quantum mechanics (PTSQM) in a measurement frame with Hermitian Hamiltonian and non-Hermitian generalized spin-type observables. The Naimark dilation (extension) technique for POVMs is briefly sketched.

Der Vortrag dient der Vorstellung abgeschlossener, laufender und geplanter Forschungsarbeiten zum Thema bakterielle S-Layer-Proteine. Insbesondere werden dabei aktuelle Arbeiten zur Herstellung fotokatalytisch aktiver Nanopartikel zur Eliminierung von Arzneimittelrückständen aus Wasser vorgestellt.

wird nachgereicht

Nach der Verabreichung von Arzneimitteln werden vom menschlichen Körper bis zu 95% des wirkstoffs unverändert ausgeschieden und können über das Abwasser in den Wasserkreislauf gelangen. In den weitaus meisten Fällen werden die Wirkstoffe jedoch schnell abgebaut oder die Wirkstoffkonzentrationen sind derart gering, dass keine akute Gefährdung für die Umwelt und die menschliche Gesundheit besteht. Dennoch weisen einige wenige Stoffe in umweltrelevanten Konzentrationen negative Langzeiteffekte auf. Dazu gehört zum Beispiel das schwer abbaubare und in der Umwelt nachweisbare Schmerzmittel Diclofenac. Aufgrund der niedrigen Konzentrationen ist es mit konventionellen Verfahren sehr aufwendig, derartige Stoffe aus dem Wasser zu entfernen. Abhilfe können hier alternative Verfahren schaffen. Mittels hoch geordnetet bakterieller Hüllproteine können in enfacher Art und Weise verschiedenste nanostrukturierte fotokatalytisch aktive Schichten auf der Basis von ZnO und TiO2-Nanocluster hergestellt werden und durch Bindung an oder Einbettung in silikatische Träger immobilisiert werden...

Projektvorstellung

Ferromagnetic Mn5Si3C0.8 and Mn5Ge3C0.8 films with Curie temperatures TC well above room temperature are obtained by 12C+-ion implantation in antiferromagnetic Mn5Si3 or ferromagnetic Mn5Ge3. Patterning of the films with a gold mesh serving as a stencil mask during implantation allows a lateral modification of magnetic order creating ferromagnetic regions of high-TC Mn5Ge3C0.8 which are embedded in low-TC Mn5Ge3. This provides a procedure for the fabrication of magnetoelectronic hybrid-devices comprised of different magnetic phases.

We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can easily be confused with the formation of a ferromagnetic diluted magnetic semiconductor (DMS). We will focus on metallic as well as oxide precipitates and the difficulties of their identification. Moreover, we will try to clarify the role of lattice disorder or point defects upon development of ferromagnetic properties.

Recent studies of the magnetic properties of Sr2FeMoO6, a half metallic double perovskite showing large magneto resistance effects at room temperature, by means of site specific x-ray absorption spectroscopy (XAS) have led to very different results concerning the Fe valence state. We present a detailed study of a Sr2FeMoO6 polycrystalline sample, which has been probed by means of XAS and XMCD over several years. We find a mixed valent Fe2+, Fe3+ state, which shifts towards Fe3+ with time. An understanding of such a chemical change is of importance for potential applications of Sr2FeMoO6 and related transition metal oxides.

We develop a formalism for studying vector meson (V ) photo-production at the proton (p) with polarized photons, ~γp ! V p, through an analysis of the decay distribution in the channel V ! π0γ. We show that this decay distribution differs noticeably from the distributions of purely hadronic decays, like φ ! K+K−, ω ! π0π+π−. Formulas for the decay distributions are presented which are suitable for data analysis and interpretation.

A full size prototype of the new inner HADES-TOF wall based on Resistive Plate Chambers (RPCs) was mounted and exposed to secondaries from C reactions on Be and Nb targets at 2 AGeV kinetic energy and typical HADES particle fluxes. The tested sextant is constituted by 187 individual 4-gap glass-aluminium shielded RPC cells distributed in three columns and two layers, covering an area of 1.26 m2.
An average timing resolution of 73 ps σ was measured with 99% intrinsic efficiency, on a random location, and moderate timing tails, along with an average longitudinal position resolution of 7.7 mmσ, in the range from a few Hz/cm2 up to 80 Hz/cm2 without noticeable degradation of performance. Aditionally, the atching efficiency was estimated using the tracking system of HADES, yielding an average value of 97.5%.

Electroproduction of phi mesons

Strangeness Electroproduction

The image quality in a conventional positron emission tomography (PET)/computed tomography (CT) scanner is degraded by respiratory motion because of erroneous attenuation correction when three-dimensional image acquisition is used. To overcome this problem, time-resolved data acquisition (4D) is required. For this, a Siemens Biograph 16 PET/CT scanner has been modified and its normal capability has been extended to a true 4D-PET/4D-CT imaging device including phase-correlated attenuation correction. To verify the correct functionality of this device, experiments on a respiratory motion phantom that allowed movement in two dimensions have been performed. The measurements showed good spatial correlation as well as good time synchronization between the PET and CT data. Furthermore, the motion pattern of the phantom and the shape of the activity distribution have been examined, and the volume of the reconstructed PET images has been analyzed. The results demonstrate the feasibility of such a procedure, and we therefore recommend that 4D-PET data should be reconstructed using 4D-CT data, which can be acquired on the same machine.

Diagonal and Off-Diagonal Susceptibilities as Diagnostics of the QCD Phase Diagram: A Quasiparticle Perspective

Diagonal and Off-Diagonal Susceptibilities in a Quasiparticle Model of the Quark-Gluon Plasma

QCD Equation of State

Motivation für neue Therapiestrahlen etc.

Die Wechselwirkung ionisierender Strahlung mit (belebter) Materie etc.

Umsetzung biologisch adaptierter Bestrahlungspläne

Laser-Beschleuniger für die Strahlentherapie etc.

Strahlentherapie - Einführung, Tumortherapie mit Ionenstrahlen, Beschleuniger und Therapiestrahlführung, Laserbeschleuniger für die Krebtherapie

Konventionelle Partikel-Strahlführungen,, Strahführungen für Laser-Beschleuniger, Strahlungs-Quelltherme (DAP 3.1), Konzeption der Therapie-Strahlführung (DAP 3.2), Sekundäre Untergrundstrahlung (DAP 3.3)

Medical Radiation Sciences

Lase particle acceleration, the irradiation device, dosimetry, cell irradiation, direct effects of ultrashortly pulsed beams, conclusions

Im Vortrag wird der aktuelle Stand der experimentellen Arbeiten, die im Rahmen des TOPFLOW-II Projektes notwendig sind, ausführlich erläutert. Hauptaufgabe dieses wissenschaftlichen Projektes ist die Bereitstellung von qualitativ hochwertigen Daten zur Modellierung von Strömungsphänomenen im CFD Code und deren Validierung.
Nach einer kurzen Vorstellung der TOPFLOW Versuchsanlage werden die erzielten Ergebnisse der Dampf/Wasser-Experimente im Modell eines heißen Stranges eines Konvoi Druckwasserreaktors erörtert. Danach folgt die Beschreibung der zur Vorbereitung der Kondensations- und Druckentlastungsexperimente in einer vertikalen Teststrecke durchgeführten Arbeiten. Hierbei wird besonders auf den Versuchsaufbau und die Spezialmesstechnik (Thermoelementlanze, Doppel-Thermonadelsonden, Hochtemperatur-Gittersensoren) eingegangen. Des Weiteren wird der schnelle Röntgentomograph als nichtinvasives Messverfahren zur Erfassung der Strömungsformen in einem vertikalen DN50 Ti-Rohr vorgestellt und die Anwendung dieses Scanners bei der Durchführung von Experimenten mit auf- bzw. abwärtsgerichteten Strömungen beschrieben.
Zusätzlich zu diesen Arbeiten beinhaltet das TOPFLOW-II Projekt Kondensationsversuche an freien Oberflächen und an einem Wasserstrahl sowie Experimente zum Blasenmitriss beim Auftreffen eines Wasserstrahls auf eine freie Wasseroberfläche. Zu diesem Thema werden Aufbau und Ziele eines kleinskaligen Vorversuches sowie die anlagentechnischen Erweiterungen zum Durchführen derartiger Experimente im TOPFLOW-Drucktank vorgestellt. Abschließend werden kurz die Ergebnisse einer umfangreichen Luft/Wasser-Versuchsserie mit optimierten Randbedingungen zur Validierung der Blasenkoaleszenz- und fragmentationsmodelle im CFD-Code erläutert.

It is well known that oblique low and medium energy (typically 0.1 - 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [1].

The formation of the ripple patterns can be qualitatively explained by continuum models like the Bradley-Harper model [2] which attributes the formation of regular patterns as resulting from the interplay between roughening due to sputter erosion and smoothing by surface diffusion. A surface instability is induced by the curvature dependence of the sputter yield, as the local erosion rate is higher in depressions than on elevations. This leads to an amplification of initial surface modulations and, therefore, to roughening of the surface. The resulting linear continuum equation is able to reproduce the formation and early evolution of the ripple patterns [2]. However, at longer times nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation [3].

In this work, Grazing Incidence Small Angle X-ray Scattering (GISAXS) has been used to study the evolution of Si(100) surfaces in-situ during oblique sub-keV ion sputtering. The sputtering has been performed with 500 eV Ar ions at incident angles ranging from 65° to 70°. The observed surface morphologies are dominated by nanoscale ripple patterns at short lateral distances but exhibit kinetic roughening at larger scales. The dynamic scaling properties of the surfaces have been analyzed by evaluating the one-dimensional power spectral density (PSD) functions in the direction normal and parallel to the ripples, respectively, which are extracted from the recorded scattering diagrams. A transition from anisotropic to isotropic scaling is observed with increasing incident angle. In addition, the ripples exhibit wavelength coarsening which is only slightly affected by the angle of incidence.

REFERENCES

[1] Chan, W.L. and Chason, E. Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering, J. Appl. Phys. 101, 121301 (2007).
[2] Bradley, R.M. and Harper, J.M.E. Theory of ripple topography induced by ion bombardment, J. Vac. Sci. Technol. A 5, 2390 (1988).
[3] Makeev, M.A., Cuerno, R. and Barabási, A.-L. Morphology of ion-sputtered surfaces, Nucl. Inst. Meth. Phys. Res. B 197, 185 (2002).

Stratified two-phase flow regimes can occur
-in the main cooling lines of Pressurized Water Reactors (PWR)
-Chemical plants
-Oil pipelines
The slug flow regime is characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry a significant amount of liquid with high kinetic energy. It is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs.
State of the art:
1D system codes validated, but:
geometry and scale dependent
no access to local parameters

CFD codes for application in multiphase flows:

the investigation of the feasibility of numerical prediction of stratified two phase flow with existing multiphase flow models in ANSYS CFX
to prove the understanding of the general fluid dynamic mechanism
to identify the critical parameters (like e.g. slug length, frequency and propagation velocity, pressure drop, CCFL)
to improve the multiphase flow modeling (interfacial momentum transfer, turbulence at the free surface et.)
experimental data required for the validation

A superconducting radio frequency photo-electron injector (SRF injector)is currently under construction by a collaboration of BESSY, DESY, FZD and MBI. The project aims at the design and setup of a continuous-wave SRF injector including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings. In this paper the layout and the rationale of the diagnostics beamline is described. Furthermore detailed information on specific components is given, together with results from laboratory tests and data taking.

Beitrag zum 10. Sächsischen Landeswettbewerb zur Umsetzung der Agenda21 in der beruflichen Ausbildung, 2007/2008

Das Ziel dieser Arbeit besteht in der Auswahl geeigneter Trennverfahren, Abtrennung und Rückgewinnung des Neptuniums aus einer Vielzahl verschiedener nicht charakterisierbarer Lösungen und Feststoffe unter Beachtung strahlenschutz-technischer Aspekte, der Charakterisierung der zurückgewonnenen Neptuniumlösung sowie der Erstellung einer Vorschrift für die Rückgewinnung.

Batch sorption studies show strong retention of U(VI) by C-S-H phases
U(VI) retention by C-S-H phases may be controlled by the formation of a Ca-U(VI) solid-solution
TRLFS studies indicate the presence of sorbed U(VI) species in an uranate-like coordination environment at high loadings and sorbed U(VI) species in an Ca-UO2-silicate-like coordination environment at low loadings.

A superconducting radio frequency photo electron injector (SRF injector) has been developed by a collaboration of BESSY, DESY, FZD and MBI and is in operation since late 2007. After the initial commissioning in late 2007 with a Copper photocathode a Caesium-Telluride cathode was installed early 2008 to allow for high charge production. The longitudinal and transverse electron beam parameters are measured in a compact diagnostics beamline. This paper describes results from beam commissioning of the main diagnostic tools. Special emphasis is given on the bunch length measurement system for the 15 ps FWHM electron bunches. The system is based on the conversion of the electron pulses into radiation pulses by Cherenkov radiation. These radiation pulses are transported in a novel fully-reflective, relay imaging optical beamline to a streak camera, where the temporal properties of the pulses are measured. Results from beam measurements at 2pC (Copper cathode) and 1nC (Cesium-Telluride cathode) bunch charge are presented and discussed.

In November 2007 the first electron beam was generated from the superconducting RF photo electron gun installed at the ELBE linear accelerator facility. The injector together with a sophisticated laser system and a diagnostic beam line were developed and constructed within a collaboration of BESSY, DESY, MBI and FZD. Delivering a CW beam with up to 1 mA average current, a significant improvement of the beam quality like an increase of the bunch charge up to 1 nC and a reduced transverse emittance will be obtained. After the cool-down of the cryostat the RF properties of the 3½-cell niobium cavity like pass band mode frequencies, unloaded quality factor versus accelerating gradient, Lorentz force detuning, and He pressure influence were measured. The first beam was extracted of a Cu photo cathode using a 262 nm UV laser system with a repetition rate of 100 kHz and about 0.4 W laser power. Later, caesium telluride photo cathodes will be applied. The installed diagnostics allow beam current, energy, energy spread, transverse emittance and bunch length measurements of the beam. The results of these measurements and the operational experiences with the gun will be presented.

Nanowires, nanocantilevers and nanobridges will be important components for future micro- and nanoelectronic devices as well as for nano-electro-mechanical systems (NEMS).
A modern technique to fabricate three-dimensional (3D) nanostructures is the combination of high-concentration p-type doping of silicon by writing implantation using a focused ion beam (FIB) with subsequent wet chemical anisotropic and selective etching. Free-standing FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated on 4 inch Silicon-On-Insulator (SOI) substrates using 30 keV Ga+ ion implantation and subsequent anisotropic etching in KOH/H2O solution. This technology is combined with classical microelectronic processing steps of photolithographic patterning and broad beam ion implantation to position and integrate 3D nanostructures into current technological platforms and therefore to increase the fabrication efficiency. Design, performance and fabrication considerations to achieve free-standing Si structures, like wires, bridges and cantilevers are discussed and some typical examples are shown. Static and dynamic electrical measurements are presented, including I-V characteristics and displacements after AC excitation.
The temperature dependence of the electrical resistance of nanostructures is demonstrated, which reveal, for example, the applications as nanowire thermal sensors.

Sicherheitsventile schützen druckbeaufschlagte Räume oder Druckbehälter (z. B. Dampfkessel, Druckbehälter, Rohrleitungen, Transportbehälter) vor einem unzulässigen Druckanstieg, der zu einer Schädigung des angeschlossenen Druckgerätes führen kann. Sicherheitsventile leiten bei Überschreiten des Ansprechdruckes Gase, Dämpfe oder Flüssigkeiten in die Atmosphäre ab. Das Sicherheitsventil wird verwendet, wenn der Druck in einem Druckbehälter den zulässigen Betriebsdruck bei vorhersehbaren Störungen um mehr als 10 % übersteigen kann. Bei richtiger Dimensionierung des Sicherheitsventils bleibt der Druckaufbau beherrschbar. Nach dem Ansprechen des Sicherheitsventils und Abbau des zu hohen Druckes durch Abblasen in die Umgebung oder über eine Rohrleitung schließt das Ventil wieder; und die Anlage kann weiter betrieben werden.
Numerische Strömungs-berechnungsprogramme (CFD-Codes) können bei Auslegungsberechnungen, Optimierungen und Sicherheitsanalysen von Sicherheitsventilen helfen. Um Leistungsparameter zu studieren, wurden Experi-mente am Institut für Strömungsmechanik der Technischen Universität Hamburg-Harburg (TUHH) für die CFD-Code-Validierung genutzt. Durch die konstante Weiterentwicklung der Numerik bzw. der physikalischen Modelle ist es nun möglich, die relativ komplexen Strömungsvorgänge in einem Sicherheitsventil (Jets, Umströmung von Hindernissen, Strömungsseparation, Stagnationsgebiete, Zonen mit hohen Ma-Zahlen) zu simulieren.
Mit dem ANSYS CFX-Code erfolgten Nachrechnungen von Durchsatzparametern eines LESER-Sicherheitsventils auf einem numerischen Gitter von einer Million Hexaederzellen (Abb. 1). Am Ein- bzw. Austritt des Strömungsgebietes wurden Druckrandbedingungen definiert. Die Turbulenzmodellierung erfolgte unter Nutzung des k-ε und k-ω basierten SST-Modellansatzes. Eine sehr gute Übereinstimmung zwischen Messung und CFD-Rechnung ist für die Durchsatzkennlinien der Charakteristiken für die Medien Luft bzw. Wasser bis 5 bar Stagnationsdruck erreicht worden, es existierte jedoch eine systematische Abweichung bei Luft im Falle hoher Ansprechdrücke (über 20 bar) durch Realgasverhalten und das Auftreten hoher Ma-Zahlen. CFD-Rechnungen mit Luft/Wasser-Zweiphasengemischen bei 5 - 9 bar Überdruck und 79 - 93 % Gasanteil ergaben realistische Durchsatzraten. Hierbei wurde das monodisperse Modell des homogenen Euler-Euler-Ansatzes für Zweiphasengemische genutzt. Weitere numerische Untersuchungen, insbesondere das Verhalten von Stoffgemischen (Glukoselösung) bzw. der Einfluss des Hubs des Sicherheitsventils (Stellung des Ventiltellers zwischen Sitz und maximaler Öffnung) auf den Durchsatz im Vergleich mit Experimenten werden vorgestellt.

In a screen for flavonoid target proteins we identified actin as a quercetin-binding protein. This interaction was studied using fluorescence and infrared spectroscopy and compared with the binding parameters of related flavonoids. The biological relevance of the flavonoid/actin interaction in the cytoplasm and the nucleus was assayed using an actin polymerization and a transcription assay, respectively. While some flavonols inhibit actin functions, the structurally related epigallocatechin tends to promote actin functions in the chosen in vitro assays. Furthermore, cellular test systems were used to evaluate the biological consequences of the flavonoid/actin interaction. The flavonoid – induced conformational changes of actin were analyzed by infrared spectroscopy. The obtained data and in silico docking studies gave further insights into possible modes of protein-ligand interactions and helped to understand the molecular basis of the observed biological effects.

A commercial CFD code was applied, for validation purposes, to the simulation of a slug mixing experiment carried out at OKB “Gidropress” scaled facility in the framework of a TACIS project: “Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”. Such experimental model reproduces a VVER-1000 nuclear reactor and is aimed at investigating the in-vessel mixing phenomena. The addressed experiment involves the start-up of one of the four reactor coolant pumps (the other three remaining idle), and the presence of a tracer slug on the starting loop, which is thus transported to the reactor pressure vessel where it mixes with the clear water. Such conditions may occur in a boron dilution scenario, hence the relevance of the addressed phenomena for the nuclear reactor safety.
Both a pre-test and a post-test CFD simulation of the mentioned experiment were performed, which differ in the definition of the boundary conditions (based either on nominal quantities or on measured quantities, respectively). The numerical results are qualitatively and quantitatively analyzed and compared against the measured data in terms of space and time tracer distribution at the core inlet. The improvement of the results due to the optimization of the boundary conditions is evidenced, and a quantification of the simulation accuracy is proposed.

Nitrogen ions were implanted into undoped melt grown ZnO single crystals. A light-emitting p-n junction was subsequently formed by postimplantation annealing in air. Deep level transient spectroscopy was used to investigate deep level defects induced by N+ implantation and the effect of air annealing. The N+ implantation enhanced the electron trap at E-C-(0.31 +/- 0.01) eV (E3) and introduced another one at E-C-(0.95 +/- 0.02) eV (D1), which were removed after annealing at 900 and 750 degrees C, respectively. Another trap D2 (E-a = 0.17 +/- 0.01 eV) was formed after the 750 degrees C annealing and persisted at 1200 degrees C.

Stratified two-phase flow regimes can occur
-in the main cooling lines of Pressurized Water Reactors (PWR)
-Chemical plants
-Oil pipelines
The slug flow regime is characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry a significant amount of liquid with high kinetic energy. It is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs.
State of the art:
1D system codes validated, but:
geometry and scale dependant
no access to local parameters

CFD codes for application in multiphase flows:

the investigation of the feasibility of numerical prediction of stratified two phase flow with existing multiphase flow models in ANSYS CFX
to prove the understanding of the general fluid dynamic mechanism
to identify the critical parameters (like e.g. slug length, frequency and propagation velocity, pressure drop, CCFL)
to improve the multiphase flow modeling (interfacial momentum transfer, turbulence at the free surface et.)
experimental data required for the validation

The production of e+e− pairs in 12C + 12C collisions at 1 GeV/u was investigated with the HADES experiment at GSI, Darmstadt. In the invariant-mass region 0.15GeV/c2 Mee 0.5GeV/c2 the measured pair yield shows a strong excess above the contribution expected from hadron decays after freeze-out. The data are in good agreement with the results of the former DLS experiment for the same system and energy.

In this chapter we review our findings on the bonding structure and growth mechanisms of carbon-based thin solid films with fullerene-like (FL) microstructure. The so-called FL arrangements arise from the curvature and cross-linking of basal planes in graphitic-like structures, partially resembling that of molecular fullerenes. This three-dimensional superstructure takes advantage of the strength of planar pi bonds in sp2 hybrids and confers the material interesting mechanical properties, such as high hardness, high elastic recovery, low-friction and wear-resistance. These properties can be tailored by controlling the curvature, size and connectivity of the FL arrangements, making these materials promising coatings for tribological applications. We have focused our interest mostly on carbon nitride (CNx) since nitrogen promotes the formation of FL arrangements at low substrate temperatures and they are emerging over pure carbon coatings in tribological applications such as protective overcoats in magnetic hard disks. We address structural issues such as origin of plane curvature, nature of the cross-linking sites and sp2 clustering, together with growth mechanisms based on the role of film-forming precursors, chemical re-sputtering or concurrent ion assistance during growth.

57Fe doped titanium oxide monocrystals, prepared by ion implantation at different temperatures and subsequent thermal treatment, were characterized by conversion electron Mössbauer spectroscopy, synchrotron radiation x-ray diffraction and superconducting quantum interference device magnetometry. After implantation at 240 K and room temperature Fe is present in divalent state. Upon annealing in high vacuum Fe2+ is reduced to metallic Fe, while during annealing on air Fe2+ is oxidized to Fe3+. After implantation at 623 K most iron is in metallic state. During annealing on air Fe is gradually oxidized from Fe2+ to Fe3+.
Depending on preparation conditions and thermal treatment the role of different nanosized secondary phases is discussed in terms of their influence on the magnetic properties of Fe:TiO2. α-Fe nanoparticles are found to be responsible for ferromagnetism observed in TiO2.