Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The rate of the hydrogen-burning CNO cycle is controlled by the slowest reaction, 14N(p,gamma)15O. 15-30% of the total cross section are contributed by radiative capture to the ground state in 15O. Previous extrapolated S-factors for this ground state contribution disagree by a factor 2. The precision of those previous studies had been limited by a sizable true coincidence summing correction. In a new experiment using a segmented Clover detector deep underground at LUNA, the summing correction has been reduced by a factor 30, so existing R-matrix fits can now be precisely tested. The present data enable a direct measurement of the metallicity at the center of the Sun by detecting solar CNO neutrinos, for example at Borexino.

Electromagnetic dipole absorption cross sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of instantaneous-shape sampling, which is based on slow shape dynamics as compared with fast dipole vibrations. The dipole strength is calculated by means of the quasiparticle random-phase approximation (QRPA) for the instantaneous shapes, the probability of which is obtained by means of the interacting boson approximation. The calculations agree well with the experimental photoabsorption cross sections near the nucleon emission threshold, but they underestimate it at low energies. The cumulative cross sections for the region below the threshold are a factor of 2 too low.

Fe60Al40 (at. %) alloys show an interesting combination of magnetic and structural properties, where atomically ordered Fe60Al40 (B2-structure) is paramagnetic at room temperature, whereas disorder Fe60Al40 (i.e., atomically intermixed, A2-structure) becomes ferromagnetic [1]. The transformation from paramagnetic B2-phase to the ferromagnetic A2-phase can be accomplished by means of homogeneous ion irradiation procedures. The irradiation induced transformation depends on the irradiation dose and the type of ions [2]. Furthermore, local ion irradiation procedures (i.e., focused ion beam or ion irradiation through masks) have been also used in order to fabricate periodic arrays of ferromagnetic structures embedded in a paramagnetic matrix [3]. Patterned polymer layers defined by electron beam lithography and porous alumina templates were used as masks. While the e-beam lithography allows for a careful design of the patterns, alumina templates lead to fast processing of very large areas. Importantly, due to the low fluences used, this method does not induce any roughening of the surface, leading to topographically featureless magnetic dots. The fabricated entities exhibit a range of magnetic properties depending on the size and shape, which were investigated by means of magneto-optical Kerr effect magnetometry, while the local character of the induced ferromagnetism was examined by magnetic force microscopy. The smallest dots (sub-50 nm in size) exhibit coercivities in the range of HC  500 Oe and a large squareness, MR/MS  1 (see Fig. 1). Interestingly, when the patterned sheets are annealed at sufficiently high temperatures, the ferromagnetic properties are removed due to the annealing-induced atomic reordering. Hence, these methods may lead to a novel type of patterned recording media free from tribological and exchange coupling effects. Moreover, these approaches can be easily extrapolated to a variety of other systems exhibiting disorder-induced magnetism.

[1] J. Nogués et al., Phys. Rev. B 74, 024407 (2006)
[2] J. Fassbender et al., Phys. Rev. B 77, 174430 (2008)
[3] E. Menéndez, (2008) submitted

Nach 1990 erlebte die Wasserkraftnutzung in Thüringen und Sachsen-Anhalt eine Renaissance. 20 neue WKA mit einer Leistung von mehr als 20 MW entstanden bisher an den vorhandenen Wehren mit teilweise interessanten technischen Lösungen. Die mögliche jährliche Stromerzeugung dieser Anlagen liegt bei 70 GWh. Die Kaplan-Turbine dominiert bei den Neubauten eindeutig, wobei sowohl Schacht- als auch Rohrturbinen zum Einsatz kommen. Technisch bemerkenswert sind die überströmten WKA in Jena sowie die PIT-Turbine in der mit 2 MW größten neu errichteten Anlage in Calbe. Nur an wenigen Anlagen ist noch Bedienungspersonal erforderlich, an einigen Standorten ist die Zukunft teils denkmalgeschützter, heute nicht mehr genutzte Gebäude offen.

Mit dem erreichten beachtlichen Stand ist das technische Wasserkraftpotenzial der Saale noch nicht erschöpft. Unterhalb der Saalekaskade hat die Saale in Thüringen insgesamt ein Gefälle von 110 m, und in Sachsen-Anhalt zwischen Bad Kösen und Calbe beträgt das Gefälle etwa 63 m. Die bisher genutzten Fallhöhen in den genannten Bereichen liegen bei 33 m in Thüringen und bei knapp 29 m in Sachsen-Anhalt. In Sachsen-Anhalt laufen derzeit Vorbereitungen zum Bau von weiteren WKA (etwa 4-5 MW) an bisher nicht bzw. nur zum Teil genutzten Wehren, wodurch sich die genutzte Fallhöhe um etwa 10 m erhöhen kann. Im Zusammenhang mit dem geplanten Bau des Tornitz-Kanals an der Saalemündung ist keine weitere Wasserkraftnutzung vorgesehen. In Thüringen ist die Perspektive wegen des erfolgten Rückbaus von 2 Wehren (Saalfeld und Kunitz) weniger günstig. Nur an 2 noch bestehenden Wehren ist eine Wasserkraftnutzung denkbar (etwa 0,5 MW).

Insgesamt sind die Rahmenbedingungen für den Wasserkraftausbau in Deutschland in den letzen Jahren deutlich ungünstiger geworden. Die EU-WRRL und ihre Untersetzung in nationalen Gesetzen bzw. Vorschriften führten praktisch zu einem Baustopp für neue Wehre sowie zu hohen Anforderungen an die Restwassermenge bei Ausleitungskraftwerken. Unter diesen Bedingungen ist ein weiterer Ausbau der Wasserkraftnutzung trotz ihrer unbestreitbaren Vorteile und der jüngsten Modifizierungen im EEG kaum realisierbar.

Between 1973 and 1990 4 units of the Russian NPP type WWER-440/230 were operated in Greifswald (former East Germany). Material probes from the pressure vessels were gained in the frame of the ongoing decommissioning procedure. The investigations of this material started with material from the circumferential core weld of unit 1.
Firstly this paper presents results of the RPV fluence calculations depending on different loading schemes and on the axial weld position based on the Monte Carlo code TRAMO. The results show, that the use of the dummy assemblies reduces the flux by a factor of 2 – 5 depending on the azimuthal position. The circumferential core weld (SN0.1.4) received a fluence of 2.4•1019 neutrons/cm² at the inner surface, it decreases to 0.8•1019 neutrons/cm² at the outer surface.
The material investigations were done using a trepan from the circumferential core weld. The reference temperature T0 was calculated with the measured fracture toughness values, KJc, at brittle failure of the specimen. The KJc values show a remarkable scatter The highest T0 was about 50°C at a distance of 22 mm from the inner surface of the weld The Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
The VERLIFE procedure prepared for the integrity assessment of WWER RPV was applied on the measured results. The VERLIFE lower bound curve indexed with the SINTAP reference temperature RTT0SINTAP envelops the KJc values. Therefore for a conservative integrity assessment the fracture toughness curve indexed with a RT representing the brittle fraction of a dataset of measured KJc values has to be applied.

The occurrence of strong negative phases at 7,5s Ps delay, may indicate body of partial melt at ca. 65km depth beneath
western Bohemian Massif (see Figure below). To test the hypothesis, we studied 2 suites of lithospheric
mantle xenoliths, different in age (P-T-fO2, petrophysical, geochemical and isotope [Sr, Nd, Pb] constraints). The
xenoliths from 25 Ma old volcanics are spinel lherzolithes. The suite from 0.3 Ma old volcanics represent cumulates,
porous fragments of magmatic veins or porous wehrlites. These samples are strongly altered by mantle metasomatism
(changes of fO2, geochemical constraints, density/porosity).

At present, in-beam positron emission tomography (PET) is the only method for in vivo and in situ range verification in ion therapy. At the GSI Helmholtzzentrum f¨ur Schwerionenforschung GmbH (GSI) Darmstadt, Germany, a unique in-beam PET installation has been operated from 1997 until the shut down of the carbon ion therapy facility in 2008. Therapeutic irradiation by means of 12C ion beams of more than 400 patients have been monitored. In this paper a first quantitative study on the accuracy of the inbeam PET method to detect range deviations between planned and applied treatment in clinically relevant situations using simulations based on clinical data is presented. Patient treatment plans were used for performing simulations of positron emitter distributions. For each patient a range difference of ±6mm in water was applied and compared to simulations without any changes. The comparisons were performed manually by six experienced evaluators for data of 81 patients. The number of patients required for the study was calculated using the outcome of a pilot study. The results indicate a sensitivity of (91±3)% and a specificity of (96 ± 2)% for detecting an overrange, a reduced range is recognized with a sensitivity of (92±3)% and a specificity of (96±2)%. The positive and the negative predictive value of this method are 94% and 87%, respectively. The interobserver coefficient of variation is between 3 and 8%. The in-beam PET method demonstrated a high sensitivity and specificity forthe detection of range deviations. As the range is a most indicative factor of deviations in the dose delivery, the promising results shown in this paper confirm the in-beam PET method as an appropriate tool for monitoring ion therapy.

Coupled code systems consisting of 3D neutron kinetics in combination with advanced thermal hydraulic plant models have been developed for an improved analysis of the whole reactor system. At Forschungszentrum Dresden-Rossendorf, the 3D neutron kinetic core model DYN3D, developed in house, was coupled with the advanced thermal hydraulic system code ATHLET of the German Gesellschaft für Anlagen- und Reaktorsicherheit.
Analyses of a hypothetical boron dilution event were carried out using that coupled code system. For that purpose a validated coolant mixing model was implemented into the code. Transient calculations for the bounding scenario of the start-up of one main coolant pump with the maximum size of a deborated slug showed a significant reactivity insertion and over-criticality. However, according to the calculations, even an over-criticality of about 2 $ did not lead to safety-relevant consequences. The power excursion is mitigated and stopped by fuel temperature feedback.
Anticipated transients without SCRAM are a second application area of the coupled code systems. In such transients with a postulated failure of the control rod insertion, the core power behavior is determined exclusively by the neutron kinetic feedback of the fuel and the moderator. The DYN3D/ATHLET code was used to investigate the influence of the core loading on the safety parameters during the transient: “Loss of main feedwater at running main coolant pumps”. It was shown that the variation of the number of mixed oxide (MOX) fuel elements in the reactor core has a remarkable influence on the fuel temperature and the moderator density feedback, which influences through the core power the primary coolant pressure. Increasing the number of MOX fuel elements decreases the calculated pressure maximum.

Reduced activation ferritic-martensitic (RAFM) Cr-steels are candidate materials for future applications in fusion and generation IV fission research and technology. Previous SANS experiments for this class of materials indicated defects on the nanometer size scale to be formed as a result of neutron irradiation. The experiment was devoted to the investigation of Eurofer97, which is in the focus of current coordinated European research activities, and related Fe-Cr model alloys. The investigation of binary Fe-Cr alloys will significantly contribute to the understanding of the behaviour of more complex alloys.

Positron emission tomography (PET) is used for independent monitoring of dose delivery in ion therapy. An in-beam PET scanner registers the annihilation γ-rays following the decay of minor amounts of β+ radioactive nuclei, which are produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. In-beam PET, therefore, allows to verify the physical beam model used in the treatment planning, to detect patient dislocations and density changes in the irradiated tissue. Treatment of more than 400 patients has been monitored by means of in-beam PET at Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The in-beam PET method demonstrated a positive clinical impact as in vivo, in situ, non-invasive technique for independent monitoring of dose application.

In this presentation I will talk about recent developments of the high-field Electron Spin Resonance facility at the Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden–Rossendorf. A unique feature of the facility is a combination of an extraordinary broad frequency range, 9 GHz – 100 THz (achieved by use of a number of tunable-frequency radiation sources, including MVNA, BWOs and FEL) and high magnetic fields (70 T and 16 T, produced by pulsed and superconducting magnets, respectively). The talk will be illustrated by recent results obtained in-house (including the study of the excitation spectrum in the spin-1/2 chain system (6MAP)CuCl₃, the spin-ladder material BPCB, and others), as well as by results of international collaborations (including the collaboration with the National Institute of Chemical Physics and Biophysics, Tallinn, Estonia)

Here, I present results of our recent tunable-frequency high-field Electron Spin Resonance (ESR) studies of two low-dimensional quantum spin systems. The first one, copper pyrimidine dinitrate, is an S=1/2 antiferromagnetic chain material with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, which exhibits a field-induced gap Δ. Employing ESR technique, the gap was observed directly.1 Experimental data are sufficiently detailed to make an accurate comparison with predictions based on the sine-Gordon quantum-field theory. Signatures of three breather branches and a soliton are identified. In addition, the temperature and field dependences of ESR parameters in the perturbative spinon regime (T > Δ/k_B) are studied.2 Excellent agreement with theory is found. The second material, NiCl₂-4SC(NH₂)₂ (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the field-induced Bose-Einstein condensation (BEC) of spin degrees of freedom. Employing ESR, we were able to accurately estimate parameters of the spin-Hamiltonian, to study the frequency-field dependence of two-magnon bound-state excitations 3 (predicted by theory and observed in DTN for the first time), and to investigate the magnetic excitation spectrum in DTN in the field-induced ordered phase.4 Supported in part by NHFMF (through NSF and DOE) and DFG.

We present de Haas{van Alphen measurements of the nonmagnetic borocarbide superconductors LuNi₂B₂C and YNi₂B₂C. The measurements have been performed by use of the torque method in high magnetic fields up to 32 T and at temperatures down to 50 mK. The Fermi-surface cross sections are extracted from the magnetic quantum oscillations in the normal state. In accordance with previous investigations we find a complex band structure with dfferent open and closed Fermi-surface sheets. From the temperature dependence of the oscillations amplitude the effective mass of the single bands can be determined. We observe sizeable and anisotropic enhancements of the effective masses compared to full-potential-localorbital calculations which is due to anisotropic many-body interactions.

We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using Ga as dopant, we have produced a series of GeGa_x samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 14%, i.e. a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with T_c up to 0.39 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field re ecting the two-dimensional character of the superconducting state in the thin GeGa_x layer having an effective depth of only 20 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors.

NiCl₂-4SC(NH₂)₂ (known as DTN) is a quantum S = 1 system with an easy-plane anisotropy dominating over the exchange interaction and exhibiting a field-induced low-temperature ordering with critical fields B_c1=2.1 T and B_c2=12.6 T. A systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase at temperatures down to 0.45 K and frequencies down to 25 GHz is presented. It is argued that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a weak isotropic corner-center interaction of magnetic ions in the body-centered tetragonal lattice with unbroken axial symmetry.1 The latter is of particular importance, being a necessary prerequisite for the interpretion of the antiferromagnetic ordering in DTN in terms of the Bose-Einstein condensation of the spin degrees of freedom

Experimental studies of magnetic susceptibility and electron-spin resonance (ESR) properties of the spin-1 Haldane-chain material Ni(C₂H₈N₂)₂NO₂ doped with non-magnetic Zn-ions in a range up to 5% are reported. The presence of fractional S = 1/2 chain-end states, revealed by ESR and susceptibility measurements in nominally pure single crystals of NENB, is found to be responsible for spin-glass freezing effects. Higher doping ratio of Zn-ions suppresses the spin-glass behaviour by creating shorter and isolated chain fragments. The effect of non-magnetic doping on the lineshape of ESR spectra of fractional S = 1/2 chain-end states is discussed.

We report results of ultrasonic investigations of the quantum S = 1 spin-chain magnet NiCl₂-4SC(NH₂)₂ (DTN), in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the c axis induces a transition into an antiferromagnetic phase with Tmax N ≈ 1:2 K. Accordingly, at T = 0 there are two quantum critical points at ~ 2:1 T and at ~ 12:6 T. The acoustic c33 mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound-wave. The H - T phase diagram obtained from our measurements is compared with results from other experimental investigations, and the low temperature acoustic anomalies are traced up to T > TN. We suggest a model where the main contribution to the spin-lattice interactions arises from the exchange- striction coupling within one-dimensional spin chains, and find a good qualitative agreement with the experimental data from the disordered phase.

We report on the magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl₃. The magnetic susceptibility exhibits a pronounced maximum at T ≈ 70 K, which is a signature of low-dimensional magnetic interactions in (6MAP)CuCl₃, following by a pronounced Curie-like behavior at low temperatures. In order to understand the nature of low-temperature magnetic interactions, the excitation spectrum of (6MAP)CuCl₃ is probed using the electron spin resonance (ESR) technique. The angular dependence of the g-factor clearly indicates the existence of two magnetically non-equivalent sites of Cu-ions in neighboring chains. The ESR signal exhibits a significant linebroadening with decreasing temperature (starting at approximately 30 K), accompanied by a pronounced shift of the g-factor. The observed features can be explained by enhanced short-range-order spin correlations when approaching the long-range ordering at low temperature. Our suggestion is confirmed by the observation of a lowtemperature (T ~ 2.3 K) anomaly in the specific heat. The anomaly measured in field up to 14 T does not exhibit any significant dependence on the applied magnetic field.

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Among hexagonal magnanites, the largest magnetoelectric effect was found in HoMnO₃, which is ferroelectric below T_c = 875 K and antiferromagnetically ordered below TMn N = 75 K (Mn-subsystem). In addition, at THo N ~ 5 K the Ho-subsystem undergoes a transition into antiferromagnetically ordered state. The coupling between ferroelectric and antiferromagnetic order parameters in HoMnO₃ has not been yet unambiguously explained, revealing the importance of geometrical frustrations and a complex interplay between Ho and Mn magnetic subsystems. Here, the magnetic excitation spectrum in high-quality single-crystalline samples of HoMnO₃ was probed by means of X-band (9.3 GHz) electron spin resonance spectroscopy. A relatively strong absorption was found below 5 K, which corresponds to the temperature of the magnetic ordering of the Ho-subsystem. The observed mode exhibits very pronounced anisotropic behavior and can be interpreted as excitations within the antiferromagnetically ordered Ho-subsystem.

A population balance model (the Inhomogeneous MUSIG model) has recently been developed in close cooperation between ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into the CFD-Code CFX (Krepper et al. 2005, Frank et al. 2005, Krepper et al. 2007). The current paper presents a brief description of the model principles. The capabilities of this model are discussed via the example of a bubbly flow around a half-moon shaped obstacle arranged in a 200 mm pipe. In applying the Inhomogeneous MUSIG approach, a deeper understanding of the flow structures is possible and the model allows effects of poly-dispersion to be investigated. For the complex flow around the obstacle, the general structure of the flow was well reproduced in the simulations. This test case demonstrates the complicated interplay between size dependent bubble migration and the effects of bubble coalescence and break-up on real flows. The closure models that characterize the bubble forces responsible for the simulation of bubble migration show agreement with the experimental observations. However, clear deviations occur for bubble coalescence and fragmentation. The models applied here, which describe bubble fragmentation and coalescence could be proved as a weakness in the validity of numerous CFD analyses of vertical upward two-phase pipe flow. Further work on this topic is under way.

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.