Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[1] www.abinit.org.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Background: The novel technology of laser particle acceleration, which promises ion radiotherapy accelerators of compact size and reasonable costs, generates ultra-short pulsed particle beams (~ 100 fs) with very high pulse dose rate (more than 1012 Gy/min). The development of this new technology for radiotherapy application is the aim of the joint research project onCOOPtics – High intensity lasers for radiooncology. One important step before potential medical application is the radiobiological characterization of this new radiation quality starting with in vitro cell experiments.

Material and Methods: Cell irradiations have been performed with protons generated at the 150 TW laser system Draco installed at the FZD. Before starting irradiation experiments the laser particle accelerator had to be optimized with respect to intensity, energy distribution, spot size, stability and reliability of the proton beam. Furthermore, beam filtering and transport to an in-air irradiation site and a dosimetry system were developed and realised. For a precise dose measurement, low energy protons were filtered out by a permanent magnet system. At cell irradiation site the proton beam possessed an energy spectrum of 6 to 18 MeV with a maximum at 7 MeV resulting in a minimal penetration depth in water of approximately 500 µm. To avoid stopping of protons within the bottom of the cell culture vessel or the cell monolayer, dedicated material for cell cultivation and irradiation had to be established to minimize material on the proton path. Cells of the radiosensitive tumour cell line SKX were seeded at thin biofilm (50 µm thickness) in place of conventional cultivation vessels. To quantify the irradiation damage, residual DNA double strand breaks were detected using the immunofluorescence H2AX/53BP1 staining technique 24 h after irradiation, optimized for the special cell carrier material. Cell samples were irradiated with three different doses applied by different proton pulse numbers and controlled by online dose measurement. As online dosimetry system an ionization chamber was used, cross-calibrated against Gafchromic EBT radiochromic films and a Faraday cup to provide precise dose determination at the cell site.

Results: The successful in vitro cell irradiation by laser-accelerated protons represents an important milestone on the long term development of laser ion acceleration for clinical radiotherapy. The laser accelerator generated a stable and reproducible proton beam over the whole experiment time. The measurement of the ionization chamber as online dosimeter showed a stable mean dose per pulse of (0.1370.039) Gy during all irradiations. The EBT films verified a homogeneous dose distribution at the cell location. The irradiated tumour cells demonstrated a clear trend in the number of DNA double-strand breaks in accordance with delivered dose.

Conclusion: Systematic cell irradiation experiments with laser-accelerated protons has been started determining dose-effect curves for both tumour and normal tissue cell lines and also including the cell surviving assay as second biological endpoint. In addition to the experiments with laser-accelerated proton pulses reference cell irradiations are performed using a continuous proton beam at a conventional tandem accelerator.

Funding: This work was supported by the BMBF (no. 03ZIK445).

Results on the experimental and numerical modelling of the melt flow typically observed in Vertical Gradient Freeze (VGF) crystal growth with a Travelling Magnetic Field (TMF) are presented. Particular attention is paid on the transition from a laminar to a time-dependent flow, which represents a crucial problem in VGF growth. Low-temperature model experiments at around 80°C were performed using a GaInSn melt in a resistance furnace with concentric, separately adjustable heating zones. The TMF was created by an external coil system, and the flow velocity was measured by means of the Ultrasonic Doppler Velocimetry (UDV). The melt flow was simulated numerically using a finite volume code based on the open source code library OpenFOAM. As a criterion for the stability of the flow the turbulent kinetic energy was calculated under the influence of the TMF and thermal buoyancy. The results obtained are compared to isothermal TMF flow modelling at ambient temperature. The stability limit of the melt flow is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. Both experimental and numerical results show the stabilizing effect of a natural, VGF-type buoyancy on the TMF-induced flow.

At the bremsstrahlung facility of the ELBE accelerator there exists the possibility to investigate dipole strength distributions up to the neutronseparation energies with photon energies up to 18 MeV. The facility and various results for nuclides measured during recent years will be presented. One example is the study of 86Kr that complements a systematic study of stable isotones at the shell closure of neutron number N = 50. As a special feature, a high-pressure gas target was used in this experiment. The other presented example is an experiment on 136Ba. GEANT4 simulations were performed to detremine the non-nuclear background that has to be removed from the measured spectra. This opens up the possibility to take into account also the strength of unresolved transitions. Simulations of gamma-ray cascades were carried out that consider the transitions from states in the quasicontinuum and allow us to estimate their branching ratios. As a result, the photoabsorption cross sections obtained from corrected intensities of ground-state transitions are combined with existing data from (gamma,n) experiments and are compared with theoretical predictions.

The dipole strength function of 78Se and 196Pt are investigated by two different experimental methods, capture of cold neutrons in 77Se and 195Pt, and photon scattering experiments on 78Se and 196Pt. Considering the different ways of excitation, the strength function deduced from the results are expected to agree. The report shows the status of the data analysis and presents first preliminary results.

The aim of this paper is to present the validation of a new methodology implemented in ANSYS CFX (ANSYS, 2009), that extends the standard capabilities of the inhomogeneous MUltiple-SIze Group model (MUSIG) by additionally accounting for bubble size changes due to heat and mass transfer. Bubble condensation plays an important role in sub-cooled boiling or steam injection into pools among many other applications of interest in the Nuclear Reactor Safety (NRS) area and other engineering areas. Since the mass transfer rate between phases is proportional to the interfacial area density, a polydisperse modelling approach considering different bubble sizes is of main importance, because an accurate prediction of the bubble diameter distribution is required.
The standard MUSIG approach is an inhomogeneous one with respect to bubble velocities, which combines the size classes into different so-called velocity groups to precisely capture the different behaviour of the bubbles depending on their size. In the framework of collaboration between ANSYS and the Forschungszentrum Dresden-Rossendorf (FZD) an extension of the MUSIG model was developed, which allows to take into account the effect of mass transfer due to evaporation and condensation on the bubble size distribution changes in addition to breakup and coalescence effects.
After the successful verification of the model, the next step was the validation of the new developed model against experimental data. For this purpose an experiment was chosen, which was investigated in detail at the TOPFLOW test facility at FZD. It consists of a steam bubble condensation case at 2MPa pressure in 3.9K sub-cooled water at a large diameter (DN200) vertical pipe. Sub-cooled water flows into the 195.3 mm wide and 8 m height pipe, were steam is injected at z=0.0 m and is recondensing. The experimental results are published in (Lucas, et al., 2007). Using a wire-mesh sensor technique the main characteristics of the two-phase flow were measured, i.e. radial steam volume fraction distribution and bubble diameter distribution at different heights and cross-sections.
ANSYS CFX 12.0 was used for the numerical prediction. A 60 degrees pipe sector was modelled in order to save computational time, discretized into a mesh containing about 260.000 elements refined towards the pipe wall and towards the location of the steam injection nozzles. Interfacial forces due to drag, lift, turbulent dispersion and wall lubrication force were considered. The numerical results were compared to the experimental data. The agreement is highly satisfactory, proving the capability of the new MUSIG model extension to accurately predict such complex two-phase flow.

The dipole-strength distribution of 136Ba has been investigated at the bremsstrahlung facility at the ELBE accelerator of the Forschungszentrum Dresden-Rossendorf. The photon-scattering experiment was carried out at an electron beam energy of 10.9 MeV in order to study the energy region up to the neutron separation. GEANT4 simulations were performed to subtract the atomic background from the measured spectrum and deduce the intensity of the resonantly scattered gammarays. Considering the transitions from states in the quasicontinuum, simulations of gammaray cascades were carried out to estimate branching ratios. As a result the photoabsorption cross section obtained from transitions to the ground state are combined with existing data from photoneutron experiments.

Es wird das Verhalten von Carbon Nanotubes in Umweltwässern analysiert. Insbesondere werden die Mobilität in wässriger Suspension und die Adsorption von Schwermetallen (Uran) diskutiert.

Purpose: The novel technology of laser based particle acceleration promises accelerators of compact size and reasonable costs that may significantly contribute to a widespread use of ion radiotherapy. Although some basic properties of laser acceleration are reasonably well known from theory, simulations and fundamental experiments, several demands have to be fulfilled for its medical application. Moreover, the ultra-short pulsed particle beams with resulting high pulse dose-rate have to be characterized with regard to their radiobiological properties. Therefore, a precise dosimetry is necessary that considers the special characteristics of the laser accelerated protons. Special attention has to be drawn on the low energy (<10 MeV), the exponential energy spectrum, the low repetition rate and the pulse-to-pulse fluctuations of the available laser accelerated proton beams.

Material & Methods: An Integrated Dosimetry and Cell Irradiation Device (IDCID) for systematic in vitro and in vivo experiments with laser accelerated protons was developed and characterized. The IDCID (Fig. 1) consists of a kapton vacuum window, an ionisation chamber consisting of ultra-thin foils (22.5 µm) for online dose information and a Faraday cup inset for absolute dosimetry that can be replaced by an inset for cell or even mouse model irradiation. Radiochromic films, i.e. GafChromic EBT, or CR-39 solid state track detectors can be included matching the plane of the cell monolayer. For the use of the Faraday Cup (FC) for absolute dosimetry and cross-calibration of the ionisation chamber, an accurate FC calibration is necessary. Therefore, three independent ways were chosen: (1) electronic calibration by applying a defined charge to the FC amplifier, (2) dose calibration against a clinical established absolute dosimetry and (3) calibration with CR-39 solid state track detectors. The dose calibration was performed at the proton therapy facility at the Helmholtz Zentrum Berlin, where also EBT and EBT2 films were calibrated for determination of 2D dose distribution. Moreover, the FC calibration with the help of CR-39 was carried out at the Tandem accelerator of the Forschungszentrum Dresden-Rossendorf.

Results: Successfully, the functional capability of the IDCID was thoroughly tested and precisely calibrated with three independent methods. EBT / EBT2 films were calibrated for several proton beam qualities with mean energies between 5 - 62 MeV. As next step, first systematic in vitro cell irradiations were performed for a human squamous cell carcinoma (FaDu) cell line irradiated with 7 MeV monoenergetic protons.

Conclusion: Both the dosimetric and radiobiological requirements for systematic cell irradiations with laser accelerated protons have been fulfilled.

Supported by the BMBF, grant 03ZIK445

Fig. 1: Integrated dosimetry and cell irradiation device (a) with Faraday cup inset, (b) with cell holder inset

The conversion of ZnO into a p-type semiconductor remains a major challenge for its application in optoelectronic devices, since up to now neither the suitable type of defects nor the possible role of secondary phase formation during doping has been clarified. Here, the implantation of arsenic into epitaxial ZnO thin films on Alpha-Al₂O₃ (0001) and subsequent isothermal annealing in high vacuum are studied by particle induced X-ray emission, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-implanted ZnO:As films are single phase and exhibit a locally disordered ZnO lattice structure. Zn₃As₂ nanocrystals segregate at 700°C. Due to annealing at 800°C, Alpha-As and Alpha-As₂O₃ are formed. The study demonstrates the role of solid state reactions and secondary phase formation for group V element doping of ZnO that is a promising route to convert this material into a p-type semiconductor.

Nanocomposites are heterogeneous materials wherein the lateral extension of at least one component is lower than 100 nm.[1] They represent a new class of functional materials, whose properties cannot be predicted from those of their constituents alone. Among the various classes of nanocomposites, metal-containing nano-particles embedded in a carbon matrix have recently attracted considerable interest regarding their structure and properties.[2,3]
This study focuses on the structure and the mechanical properties of C:V nanocomposites. A series of C:V films with a varying vanadium concentration of 2 at.% ≤ xv ≤ 50 at.% was grown on silicon by DC dual magnetron sputtering. Depending on the metal concentration, significant structural variations were observed within both phases (dispersed phase and matrix) of the nanocomposite. At low vanadium concentrations, an amorphous metal rich and an amorphous carbon phase are formed. An increasing metal content promotes the formation of cubic VC and a graphitic carbon phase. With optimized deposition parameters, the hardness of the C:V nanocomposite films is higher then 10 GPa, and the elastic modulus achieves values of about 130 GPa. The friction coefficients for sliding conditions are as good as 0.1.

[1] P. M. Ajayan, L.S. Schadler, P.V. Braun, Nanocomposites Science and Technology, Wiley, 2005
[2] T. Hayashi, S. Hirono, M. Tomita, S. Umemura, Nature 381, 772-774 (1996)
[3] M. Krause et al., Phys. Stat. Sol. (B), 244, 4236-4239 (2007); G. Abrasonis et al. Carbon, 45, 2995-3006 (2007); M. Berndt et al., Plasma Process. Polym. 6, S902–S906 (2009); C. Adelhelm et al., J. Appl. Phys. 105, 033522 (2009); M. Magnuson et al. Phys. Rev. B, 80, 235108 (2009).

Control over surface roughness (σ) is a critical issue in many physical, chemical, biological and technological processes. Regarding relevant systems, silicon is a model material that finds a wide range of applications in microelectronic and photovoltaic devices. Further, the growth of amorphous silicon (a-Si) could yield ultrasmoothness, a keystone for the production of ultrathin films, in analogy to amorphous diamond-like carbon [1]. Based on this motivation, we have studied the roughness evolution of a-Si films prepared by DC magnetron sputtering at low (LP) and high (HP) plasma pressures (10-3 and 3×10-3 mbar, respectively). The morphological analysis was carried out by atomic force microscopy and interpreted in the framework of dynamic scaling concepts [2]. The film thickness evolution was analyzed by ex-situ spectroscopic ellipsometry, providing also information on the disorder character of the films. Smooth (σ<0.2nm) films were produced at LP whereas rougher surfaces were grown at HP. The growth exponent [σ(t)~tβ] was close to 0.25 at LP, compatible with a morphology controlled by surface diffusion relaxation processes, whereas HP yielded considerably higher β characteristic of unstable growth. The distinct evolution should be related to the lower mean free path in the gas phase at HP, which alters the incidence angle and/or size of the particles condensing at the substrate and can result in shadowing effectsduring growth [3]. Finally, a negative DC bias voltage (-400V) applied to the substrate at HP changes drastically the surface morphology to ultrasmooth (σ~0.12 nm) during the whole temporal window sampled, resulting in β~0 (i.e. suppressing surface roughening). The latter could be consistent with the Edwards-Wilkinson interface equation [2]. This evident surface smoothing could be ascribed to ion-induced downhill currents that preferentially erode prominent features [1].
REFs.: [1] M. Moseler, P. Gumbsch, C. Casiraghi, A.C. Ferrari, and J. Robertson, Science 309, 1545 (2005); [2] A.L. Barabasi, and H.E. Stanley, Fractal Concepts in Surface Growth (Cambridge Univ. Press, 1995); [3] J.T. Drotar et al., Phys. Rev. B 62, 2118 (2000).

Segregation of Al2O3 or ZnAl2O4 in Al-doped ZnO (AZO) is often discussed as a reason for deterioration of the film electrical properties during growth at temperatures above a certain optimum value (150-300 °C). However, conclusive evidence of these phase segregation in AZO is lacking since electrical properties and crystallinity of the films deteriorate simultaneously and, the disordered structure precludes a proper analysis using conventional methods. The present work overcomes these limitations using characterization techniques based on synchrotron radiation, such as X-ray diffraction and X-ray absorption near edge structures. These studies were combined with investigations by spectroscopic ellipsometry, Hall effect measurements and elastic recoil detection analysis. The AZO films grown by reactive pulsed magnetron sputtering at substrate temperatures, Ts, ranging from RT to 550 °C, were investigated. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above an optimum Ts value (200-400 °C), which depends on the metal/oxygen flux ratio. Energy deposition during growth due to the elevated TS and from the flux of energetic particles incident on the substrate causes preferential Zn desorption. Thus, increasing TS above the optimum value leads to a higher Al concentration (cFAl) in the films, as compared with that of the sputter targets. It exceeds the solubility limit and triggers the formation of this phase, whose volume fraction scales with increasing cFAl. This impedes crystal growth, causes a significant increase of free electron scattering, and results in an increase of the film electrical resistivity. It is shown that one can grow low-resistivity AZO films in a wider range of TS using lower metal/oxygen flux ratios during deposition. This may be suggested as an approach to minimizing the effect of such undesirable phase formation on AZO film electrical properties.

Abstract not available.

Abstract not available

Magnetic fields allow to study distinct magnetic effects in various electrochemical systems. Lorentz forces can be utilized to tailor convection and mass transfer in electrolytic cells, thereby influencing for example the morphology and the structure of the electrodeposits [1]. Recently, the influence of magnetic gradient forces on the preparation of microstructured metal deposits on field-gradient electrodes has been discussed in the literature [2]. The presentation summarizes new experimental results, analytical findings and numerical simulations in order to discuss the influence of different magnetic forces involved and the prospects towards smaller deposition structures.

[1] G. Mutschke, A. Hess, A. Bund, J. Fröhlich,
On the origin of horizontal counter-rotating electrolyte flow during
copper magnetoelectrolysis.
Electrochimica Acta 55 (2010) 1543-1547.

[2] K. Tschulik, J. Koza, M. Uhlemann, A. Gebert, L. Schultz,
Effects of well-defined magnetic field gradients on the electrodeposition
of copper and bismuth.
Electrochemistry Communications 11 (2009) 2241-2244.

Surface tension and density measurements of liquid Bi-Pb, Bi-Sn and Bi-Pb-Sn eutectic alloys were carried out by the large drop method in the temperature range 350 - 750 K. The regular solution model is used in conjunction with Butler's equation to calculate the surface tension of binary and ternary alloys of the Bi-Pb-Sn system, while the surface tension of ternary alloys is also predicted by geometric models. The new experimental results were compared with the calculated values of the surface tension as well as with the data available in literature.

This presentation considers various situations where the flow inside a liquid metal column is driven by different configurations of AC magnetic fields. The ultrasonic Doppler method has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both a swirling flow in the horizontal planes and the flow pattern in the radial-meridional plane. In particular, we consider here transient liquid metal flows generated inside a cylindrical container by the superposition of a rotating magnetic field (RMF) and a travelling magnetic field (TMF). The application of the magnetic body forces can be used to create a tornado-like vortex in a closed volume of liquid metal. Moreover, the case of an RMF-driven flow will be discussed which is influenced by an oxide layer at the free surface of the metallic melt. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if the both forces are in the same order of magnitude. In that case, our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow.

Single-phase vanadium dioxide films grown on (0001) sapphire and (001) silicon substrates show very different insulator-metal electronic transition. A detailed description of the growth mechanisms and the substrate-film interaction is given, and the characteristics of the electronic transition are described by the morphology and grain boundary structure. (Tri-)epitaxy-stabilized columnar growth of VO2 takes place on the sapphire substrate, while on silicon the expected Zone II growth is identified. We have found that in the case of the Si substrate the reasons for the broader hysteresis and the lower switching amplitude are the higher average oxygen vacancy concentration and the VxSiyO built up in the grain boundaries. These phenomena are the result of the material transport between the silicon substrate and the growing film.

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