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34118 Publications

Research activities of photocathodes for HZDR SRF gun

Xiang, R.; Arnold, A.; Freitag, M.; Michel, P.; Murcek, P.; Teichert, J.

Since 2005 the photocathode laboratory has been in operation at HZDR. The main goal is to prepare Cs2Te photocathodes for the SRF gun. A vacuum transport system with UHV is used to move the cathodes from preparation lab to accelerator hall. Up to now 34 Cs2Te photocathodes have been deposited and eight of them have been used in the SRF gun. Quantum efficiency (QE) of 1% and life time of months can be maintained during the gun operation. At the same time activities are directed towards new photocathode materials with high Q.E. for high current electron sources. Cs3Sb and GaN(Cs) photocathodes have been tested as new candidates, and the design of a preparation system for GaAs(Cs, O) is ongoing

Keywords: SRF-gun; Photocathode; Quantum efficiency

  • Open Access Logo Contribution to proceedings
    International Particle Accelerator Conference 2012 (IPAC2012), 20.-25.05.2012, New Orleans, USA
    Proceedings of IPAC2012, 978-3-95450-115-1, 1524
  • Poster
    International Particle Accelerator Conference 2012 (IPAC2012), 20.-25.05.2012, New Orleans, USA

Publ.-Id: 17268

Coupling Schemes and Measurements for Multiple Eigenmode Application in Superconducting RF Guns

Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.

Superconducting electron sources are a promising candidate to meet the challenges of future electron accelerator, such as high average beam current and high peak brilliance at the same time. Compared to their normal conducting rf equivalent and due to the Meissner-Ochsenfeld effect, the solenoid for emittance compensation has to be placed far in front of the cathode. To solve this problem the use of transverse electric (TE) modes in parallel to the accelerating mode was proposed*. This contribution presents two suitable coupling schemes and first rf measurements at the warm and cold HZDR SRF gun cavity.
* V. Volkov, D. Janssen, Phys. Rev. ST Accel. Beams 11, 061302 (2008)

Keywords: TE mode; emittance compensation; SRF gun; coupling scheme

  • Poster
    International Particle Accelerator Conference IPAC12, 20.-25.05.2012, New Orleans, LA, USA

Publ.-Id: 17267

Monopol HOM Analysis for the 3.5 Cell SRF Gun Cavity

Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.

Superconducting radio frequency photoinjectors (SRF gun) seems to be a promising candidate to achieve the required brightness and the high average current for future light sources. In contrast to normal conducting DC and RF guns, higher order modes (HOM) and their influence on beam quality are of particular interest. For this reason, a method is presented that considers the accelerated motion of nonrelativistic electrons to calculate the longitudinal coupling impedances. The results are compared with first beam-based measurements and used to determine the required HOM damping. Additionally, a selective detuning of the eigenmode spectra is discussed.

Keywords: higher order mode; HOM; SRF gun

  • Invited lecture (Conferences)
    EuCARD SRF Annual Review, 29.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17266

RF power upgrade at the superconducting 1.3 GHz CW LINAC “ELBE” with solid state amplifiers

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.

The RF power for the superconducting CW LINAC has been doubled from 10 to 20 kW per cavity. In January 2012 the four 10 kW klystrons used to drive the four superconducting cavities of the LINAC have been replaced by a pair of 10 kW solid state power amplifiers. ELBE is now worldwide the first 1.3 GHz CW LINAC equipped with Solid State RF Power Amplifiers. This technical note details on this project.

Keywords: Solid state RF power amplifiers; Superconducting CW RF; 1.3 GHz Solid state RF-power amplifiers; ELBE-RF; Superconducting LINAC RF

Publ.-Id: 17265

Core-core interaction in spin-torque double-vortex oscillators

Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Hertel, R.; Schneider, C. M.

Owing to their ability of narrow bandwidth operation, magnetic vortex based spin-torque nano-oscillators (STNOs) are promising candidates for future on-chip microwave sources. Typically, these oscillators are nanopillars containing two stacked ferromagnetic disks, one in a vortex state, the other with quasi-homogeneous magnetization. Devices of that kind have been investigated extensively over the past years [1-3]. Only recently, a different type of vortex oscillators has attracted much interest. In these “double vortex oscillators”, both ferromagnetic disks are in a vortex state. Depending on the relative vorticity, the local alignment of the magnetic layers can be either parallel or antiparallel. Thus, the system constitutes an analogue to single domain spin valves, while also retaining the good oscillator properties of magnetic vortices, which makes this type of STNO particularly interesting for studying fundamental aspects of spin-transfer torque. However, only few studies of double-vortex oscillators exist to-date [5,6].
Here we present our results on Fe/Ag/Fe double vortex oscillators. Combining experimental and numerical methods, we address the yet open question of how the magnetostatic interaction of the vortices – their separation is typically in the order of a few nanometers –affects the spin-torque induced dynamics. Our samples are all-metallic nanopillars 150 nm in diameter, containing a Fe(30)/Ag(6)/Fe(15) pseudo spin valve (layer thicknesses given in nm). By applying d.c. currents perpendicular to the plane of the layers, we excite magnetization dynamics corresponding to gyrotropic vortex motion. The sample geometry stabilizes the magnetic vortex state in each Fe disk even if the strong Oersted fields and the vortex magnetization have opposite sense of rotations. This high degree of stability provides a yet unprecedented opportunity to investigate a more exotic class of double vortex states – those with opposed vorticities – under the high current densities necessary to enter the spin-torque precession regime.
Figure 1 displays a typical combined magnetoresistance and high frequency measurement. The magnetic field, which has an angle of 30° with the sample plane, is swept from positive values to negative saturation. For each field value, in addition to the d.c. voltage, a spectrum is also recorded. In a field interval about 100 mT wide, the sample is in a double vortex state where the vorticities of the top and bottom vortices are opposed to each other. According to the top panel of Fig. 1, this state exhibits magnetization dynamics. We vary our state preparation procedure in order to create the various vorticity and core polarity combinations. The obtained states are characterized with respect to their d.c. and high frequency behavior using the above described measuring technique where in all measurements, the electron flow is directed from the bottom to the top Fe disk. We obtain a fine structure in the modes, where the frequency splittings are in the order of hundreds of MHz.
The micromagnetic simulations are performed with our code TetraMag [7]. The simulations include the Oersted field corresponding to a sample current of 10 mA in magnitude. For a given vorticity and core polarity combination, we find the eigenmodes and frequencies of the system. Comparing the experimentally found set of frequencies to the simulated cases, we find that each measured peak matches the lowest mode of a corresponding computed spectrum in frequency. This suggests that the observed fine structure is caused by two effects. First, the Oersted field lifts the degeneracy of states with the top vortex vorticity parallel or antiparallel to the field’s sense of rotation. On top of this Zeemann-type frequency alteration, the resulting modes are split further depending on the relative alignment of the top and bottom vortex cores. This suggests that the second splitting is due to the magnetostatic interaction of the vortex cores. This remarkable result sheds light on the subtle interplay of forces governing the dynamics of double vortex oscillators, while on the other hand it allows measuring changes in relative core alignment.
[1] V. S. Pribiag et al., Nature Phys. 3, 498 (2007).
[2] A. Dussaux et al., Nat. Commun. 1:8 DOI:10.1038 / ncomms1006 (2010).
[3] X. W. Yu et al., Phys. Rev. Lett. 106, 167202 (2011).
[5] A. V. Khvalkovskiy et al., Appl. Phys. Lett. 96, 212507 (2010).
[6] N. Locatelli et al., Appl. Phys. Lett. 98, 062501 (2011).
[7] A. Kákay, E. Westphal, R. Hertel, IEEE Trans. Magn. 46, 2303 (2010).

Keywords: magnetic vortex; magnetization dynamics; spin-transfer torque; spin-torque nano-oscillators

  • Lecture (Conference)
    Intermag 2012, 07.05.2012, Vancouver, Canada

Publ.-Id: 17264

Quenched Slonczewski-windmill in spin-torque vortex-oscillators

Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Hertel, R.; Schneider, C. M.

Spin-torque nano-oscillators (STNOs) typically consist of two single domain ferromagnetic layers separated by a metallic spacer or a tunnel barrier, one with its magnetization fixed (polarizing layer), the other one susceptible to torques (free layer). An electric current traversing the system perpendicular to the layers becomes spin-polarized and exerts torques on the magnetic moments [1-3], thereby inducing switching or steady-state dynamics. The pinning of the polarizing layer can be achieved by exchange coupling to an antiferromagnet [4] or by extending its thickness and lateral dimension [5]. In the absence of pinning, both ferromagnetic layers can be excited. For increasingly symmetric STNOs, this can lead to a dynamic equilibrium state called the Slonczewski-windmill [1,6], with the magnetic moments of both layers rotating in the same direction with a constant relative angle, resulting in a vanishing magnetoresistance (MR) time-dependence.
Here we investigate STNOs containing two stacked magnetic vortices, i.e., a system consisting of two ferromagnetic disks, each in a vortex state and separated by a metallic, nonmagnetic spacer. Employing analytical and numerical methods, we study the coupled spin torque-driven motion of the magnetizations in the two disks, which are not pinned by any of the above mentioned mechanisms. The theoretical findings are supported by our experimental data obtained from double-vortex Fe/Ag/Fe STNOs.
The motion of the magnetic vortex in each of the disks is governed by the Thiele equation [7] with an additional force expression arising from the transfer of spin angular momentum from the polarised current to the vortex. Assuming that in the double vortex system, each vortex is free to move while at the same time it serves as a polarizing layer for the other, we solve the system of Thiele equations coupled by the spin-polarized current. We use parabolic approximations to the magnetostatic potentials for each vortex, which are chosen to represent our Fe/Ag/Fe nanopillars with ferromagnetic layers with a thickness ratio of 5/3; the uncoupled top and bottom vortices’ eigenfrequencies are set to 1.0 and 1.7 GHz, respectively.
The solutions are obtained numerically using Maple's rkf45 implementation. The results can be summarized as follows: While the spin torque induces large orbit vortex gyration in one of the layers, the vortex motion in the other disk is strongly reduced, resulting in a quenching of the Slonczewski-windmill mode. Which of the two layers contributes dominantly to the magnetization dynamics is determined by the direction of the applied current. This effect results from an adaption of the motion of the constricted vortex according to the dominant one. The former acquires a stable phase to the dominant vortex, while the latter determines the frequency and sense of gyration of the whole system: If its core polarity is positive (negative), the system gyrates in the counterclockwise (clockwise) direction. If the dominating vortex is in the top disk, the gyration frequency is 1.0 GHz while for large orbit gyration in the bottom disk, we obtain 1.7 GHz. Figure 1 displays the relations between the phase, frequency and gyration radius of the bottom vortex in the case, where the top vortex is dominant. For an experimental confirmation of the frequency and phase adaption mechanism and the related quenching of the windmill modes, we study the current-induced magnetization dynamics of a Fe/Ag/Fe nanopillar with a Fe layer thickness ratio of 5/3. We apply current densities of 6.1x107 A/cm2 and investigate the resulting double vortex dynamics depending on the current polarity. At low external field, the ratio between the obtained frequencies is close to the ratio of the disk aspect ratios, which strongly supports our numerical findings.

[1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996).
[2] L. Berger, Phys. Rev. B 54, 9353 (1996).
[3] J. C. Slonczewski, J. Magn. Magn. Mater. 247, 324 (2002).
[4] I. N. Krivorotov et al., Science 307, 228 (2005).
[5] I. Kiselev et al., Nature 425, 380 (2003).
[6] Y. B. Bazaliy, D. Olaosebikan, and B. A. Jones, J. Nanosci. Nanotechnol. 8, 2891 (2008).
[7] A. A. Thiele, Phys. Rev. Lett. 30, 230 (1973).

Keywords: Spin-transfer torque; spin-torque nano-oscillators; magnetic vortex; magnetization dynamics

  • Poster
    Intermag 2012, 07.-11.05.2012, Vancouver, Canada

Publ.-Id: 17263

Use of cold liquid metal models for investigations of the fluid flow in the continuous casting process

Timmel, K.; Wondrak, T.; Röder, M.; Stefani, F.; Eckert, S.; Gerbeth, G.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. Water model experiments are of limited value, particularly in the cases of strong temperature gradients, two-phase flows or flows exposed to electromagnetic fields. We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. A selection of results from LIMMCAST and mini-LIMMCAST will be presented in this paper covering various phenomena occurring in single-phase and two-phase flows.
Main emphasis of the experimental programme is put on the effect of diverse magnetic fields on the fluid flow in the mould. Although magnetic fields have already been adopted for industrial use since more than 20 years, the impact of electromagnetic brakes or stirrers on complex and highly turbulent flows appears to be very complex and has not been fully understood until now. The flow measurements performed at the liquid metal model experiments deliver a valuable experimental data base being suitable for validation of numerical simulations.

Keywords: continuous casting; liquid metal models; electromagnetic brake; ultrasonic flow measurement; contactless inductive flow tomography

  • Lecture (Conference)
    5th International Congress on the Science and Technology of Steelmaking, 01.-03.10.2012, Dresden, Deutschland
  • Contribution to proceedings
    5th International Congress on the Science and Technology of Steelmaking, 01.-03.10.2012, Dresden, Deutschland
  • Steel Research International 85(2014)8, 1283-1290
    DOI: 10.1002/srin.201300034

Publ.-Id: 17262

Ultrafast electron beam X-ray computed tomography for 2D and 3D two-phase flow imaging

Bieberle, M.; Barthel, F.; Hoppe, D.; Banowski, M.; Wagner, M.; Lucas, D.; Stürzel, T.; Hampel, U.

Imaging of complex and dynamic processes such as two- or multiphase flows with high structural as well as temporal resolution has always been a challenging task. In recent years, the electron beam X-ray computed tomography technique has been developed towards a powerful imaging tool, which reaches frame rates of 8000 fps in 2D and 1000 fps in 3D. In this paper, the latest developments as well as selected applications of ultrafast electron beam X-ray CT are presented.

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

  • Lecture (Conference)
    2012 IEEE International Conference on Imaging Systems and Techniques, 16.-17.07.2012, Manchester, United Kingdom
  • Contribution to proceedings
    2012 IEEE International Conference on Imaging Systems and Techniques, 16.-17.07.2012, Manchester, United Kingdom
    Proceedings 2012 IEEE International Conference on Imaging Systems and Techniques: IEEE, 978-4577-1774-1, 1569596631

Publ.-Id: 17261

Grundlagen und Anwendungen der kontaktlosen induktiven Strömungstomographie

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

The contactless inductive flow tomography (CIFT) aims at the determination of flow structures in metal and semiconductor melts. It relies on the induction of electric currents in moving conductors exposed to magnetic fields. The flow induced deformations of the magnetic fields can be measured in the exteriour of the melt and utilized for the reconstruction of the velocity field. After a presentation of the principles, first applications and possible extensions of the method are discussed.

Publ.-Id: 17260

Combining contactless inductive flow tomography and mutual inductance tomography for two-phase flow measurements at a continuous casting model

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

The flow structure in the mould of a continuous caster is of key importance for the quality of the final product. The use of most conventional flow measurement techniques is prevented by the high temperature of the liquid steel. For a downscaled physical model of the continuous casting process, we present combined measurements of the flow in the mould by Contactless Inductive Flow Tomography (CIFT), and of the conductivity distribution in the submerged entry nozzle by Mutual Inductance Tomography (MIT). In addition, we summarize an experiment with a magnetic stirrer around the submerged entry nozzle and its effects on the flow in the mould. Some new developments towards a robust implementation of CIFT at a real caster, including the use of pickup coils and gradiometric probes, are also discussed.

  • Lecture (Conference)
    7th International Conference on Electromagnetic Processing of Materials (EPM2012), 22.10.-26.12.2012, Bejing, China
  • Journal of Iron and Steel Research International 19(2012)Suppl. 1-1, 479-482

Publ.-Id: 17259

Temperature impact on the sorption of selenium(VI) onto anatase

Jordan, N.; Müller, K.; Franzen, C.; Brendler, V.

The impact of temperature (298 K, 313 K and 333 K) on the sorption of selenium(VI) onto anatase was investigated for the first time. At a macroscopic level, batch experiments showed a decrease of selenium(VI) retention with both increasing pH (3.5-7.0) and temperature. The thermodynamic parameters of the sorption reaction, i.e. the enthalpy ΔRH, entropy ΔRS and the Gibbs free energy ΔRG were determined from the temperature dependence sorption data using the van´t Hoff equation. The sorption process was found to be exothermic. Neither significant phase transformation nor a significant increase of anatase solubility could be detected with increasing temperature by XRD and ICP-MS. However, electrophoretic mobility measurements showed that both the zeta potential as well as the isoelectric point (pHIEP) of anatase were shifted to lower values with increasing temperature, decreasing selenium(VI) sorption. At a microscopic level, the sorption mechanism of selenium(VI) onto anatase was elucidated at the three investigated temperatures by means of in situ Attenuated Total Reflection Fourier-Transform Infrared spectroscopy (ATR FT-IR). Results evidenced the formation of outer-sphere surface complexes, with no significant structural changes within the investigated temperature range.

Keywords: selenate; titanium dioxide; anatase; infrared spectroscopy; ATR FT-IR

Publ.-Id: 17258

Superconducting layers in semiconductors – Ready for the quantum interference?

Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Skorupa, W.; Gobsch, G.; Helm, M.

Superconductivity is a fascinating ground state of matter and has been discovered one century ago. A new debate about the fundamental physical background and technological potential of superconducting group-IV semiconductors occurred, since superconductivity at ambient pressure conditions was shown for boron doped diamond [1] and silicon [2]. These unusual superconductors open the way towards new microelectronic devices and applications.
In our previous work, we used Ga-ion implantation and subsequent short-time annealing for creating highly Ga doped layers in Ge. [3] These layers show an intrinsic superconducting transition at temperatures below 1 K because of the high doping level. [4] In a next step we could show the feasibility to stabilize Ga-rich layers at SiO2/Si [5,6] and SiO2/Ge [7] interfaces by using a 30 nm SiO2 cover layer during implantation and annealing.
The presented structural investigations by means of Rutherford Backscattering Spectrometry (RBS) and cross-sectional Transmission Electron Microscopy (XTEM) reveal the presence of a 10 nm thin, superconducting layer at the interfaces containing Ga-rich precipitates. In both cases the critical temperature increases to 7 K which is comparable to amorphous Ga and therefore enables the detailed investigation of the influence of superconducting precipitates on the superconducting properties of doped semiconductor layers.
However, the previous investigations were done on 1 x 1 cm2 size samples. The possibility of fabricating superconducting microstructures in Si with standard microelectronic lithography will be shown. Theses microstructures still undergo a superconducting transition below 7 K. High critical magnetic fields in the range of 10 T and high critical current densities of 50 kA/cm2 were achieved. For applications in superconducting microelectronics a Josephson-Junction has to be implemented. [8] We plan to use a Focused Ion Beam (FIB) for this task. Details about the sample processing, layer microstructure and processing of superconducting microstructures will be presented.

[1] E. A. Ekimov et al., Nature (London) 428 (2004) 542.
[2] E. Bustarret et al., Nature 444 (2006) 465.
[3] V. Heera et al., J. Appl. Phys. 107 (2010) 053508.
[4] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003.
[5] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505.
[6] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.
[7] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530.
[8] J. Q. You et al., Nature 474 (2011) 589.

  • Poster
    18th International Conference on Ion Beam Modifications of Materials (IBMM 2012) - Ausgezeichnet mit einem "Best Poster Award", 02.-07.09.2012, Qingdao, China

Publ.-Id: 17257

Superconductivity in Ga-implanted group-IV semiconductors

Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Facsko, S.; Reuther, H.; Perego, M.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.

Beginning in 2004, the interest in superconductivity of elemental group-IV semiconductors has been renewed because Ekimov et al. [1] showed that boron doped diamond could become superconducting at ambient pressure conditions. Besides fundamental physical background of driving a semiconductor into a superconducting state, the high potential for applications in new microelectronic devices is in the main focus.
High doping levels are needed to observe superconductivity at ambient pressure conditions in elemental group-IV semiconductors. Gas immersion laser doping is used to fabricate superconducting boron doped silicon [2]. The possibility to use Ga-ion implantation and short-time annealing for creating superconducting Ga-doped Ge layers was shown in our previous work [3, 4]. These highly doped Ge-layers show an onset of superconductivity below 1 K. All doping techniques mentioned above exceed the equilibrium solid solubility limit by far and the question arises, whether the observed superconductivity is a doping effect or related to dopant clusters [5].
Especially if the doping element itself is a superconductor, like Ga in Ge, it was not clear how superconducting precipitates influence the low-temperature transport properties. To investigate these effects, we stabilized superconducting Ga-rich layers at SiO2/Si interfaces [6, 7]. Again, we have used ion implantation through a 30 nm thick SiO2 cover layer and rapid thermal annealing. The critical temperature of 7 K is comparable to the values obtained for amorphous Ga. Furthermore, high critical magnetic fields of 14 T and critical current densities of 50 kA/cm2 were achieved.
With the results of the investigations discussed above, we could go one step further and fabricate similar Ga-rich layers at SiO2/Ge interfaces. Now it is possible to investigate selectively the influence of superconducting Ga-rich areas on the normal- and superconducting properties of Ga-doped Ge. It will be shown that the critical temperature changes dramatically while the critical magnetic field stays rather constant. The results of detailed microstructural investigations by means of XTEM and time-of-flight SIMS will be correlated with electrical properties. Finally, the presented results indicate that superconductivity with critical temperatures around 1 K can clearly be attributed to a doping effect.

[1] E. A. Ekimov et al., Nature (London) 428 (2004) 542.
[2] E. Bustarret et al., Nature 444 (2006) 465.
[3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003.
[4] V. Heera et al., J. Appl. Phys. 107 (2010) 053508.
[5] N. Dubrovinskaia et al., PNAS 105 (2008) 11619.
[6] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505.
[7] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.

  • Lecture (Conference)
    18th International Conference on Ion Beam Modifications of Materials (IBMM 2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17256

Nanoteilchen in biologischen Systemen

Bergmann, R.

kein Abstract verfügbar

  • Lecture (others)
    Akademisches Donnerstagkolloquium der Dresdner Seniorenakademie, 24.05.2012, Dresden, Deutschland

Publ.-Id: 17255

From sponge to dot arrays on (100) Ge by increasing the energy of ion impacts

Böttger, R.; Bischoff, L.; Heinig, K.-H.; Pilz, W.; Schmidt, B.

Ge surfaces were subjected to normal incidence Bi+ irradiation with ion energies from 10 to 30 keV. The Ge substrate was irradiated with fluences up to 1 x10^17 / cm² and substrate temperatures up to 780 K. Surface modification was investigated using scanning electron microscopy. While at room temperature porous networks are obtained, increase of temperature during irradiation leads to formation of hexagonal dot arrays at the surface, which vanish at very high temperatures. Extensive experimental studies of energy and temperature ranges and limits for dot formation are presented. Formation of dot arrays is governed by the vacancy diffusion mechanism via different energy densities deposited in the cascade volume, as well as by substrate heating. An energy-temperature phase diagram of the obtained surface morphology is composed with respect to varying order of dot-like patterns.

Keywords: Ge; FIB; sponge; ordered dots; self-organization; vacancy; ion beam

Publ.-Id: 17254

Probing Graded Perpendicular Anisotropy with Polarized Neutron Reflectometry

Greene, P.; Gilbert, D.; Kirby, B.; Borchers, J.; Lau, J.; Shull, R.; Chih-Huang, L.; Osten, J.; Fassbender, J.; Davies, J.; Fitzsimmons, M.; Zimanyi, G.; Liu, K.

Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. However, it is challenging to probe and tune the depth-dependent anisotropy gradient, as conventional magnetometry approaches only give convoluted response from the entire layer. In this work, we have investigated magnetization reversal in Co/Pd and Co/Pt films and patterned structures with perpendicular anisotropy using polarized neutron reflectometry (PNR), along with magnetometry and structural characterizations. Perpendicular magnetic anisotropy is varied by changing the growth conditions during synthesis (Co layer thickness, sputtering pressure, or multilayer deposition order), or post-deposition ion irradiation. PNR directly reveals depth-dependent magnetization profiles along the in-plane magnetic hard axis, which reflect the magnetic anisotropy gradient as different amounts of magnetic moment come into alignment with the in-plane field. Effects of lateral patterning have also been investigated in patterned nanostructures (networks and nanodots). An increase in coercivity and a modified switching field distribution are observed in patterned structures. This is due to the reduced lateral dimensions which limit the domain nucleation and propagation commonly found in unpatterned films. These results demonstrate attractive features of nanostructures with graded anisotropy towards future magnetic recording applications.
Work supported by the US NSF (DMR-1008791 & ECCS-0925626).

  • Invited lecture (Conferences)
    ACNS American Conference on Neutron Scattering, 24.-28.06.2012, Washington, DC, USA

Publ.-Id: 17253

Tuning Perpendicular Anisotropy Gradients in Co/Pd Multilayers by Ar Ion Irradiation

Greene, P.; Osten, J.; Fassbender, J.; Endo, T.; Iwata, N.; Liu, K.

Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. Typically, the anisotropy gradient has been achieved by changing the sample growth conditions [3-5]. In this work we report an alternative approach of using Ar ion irradiation to create an anisotropy gradient in Co/Pd multilayer films.

  • Lecture (Conference)
    INTERMAG 2012, IEEE International Magnetics Conference, 07.-11.05.2012, Vancover, Kanada

Publ.-Id: 17252

Microscopic magnetic structuring of a spin-wave waveguide by ion implantation in a Ni81Fe19 layer

Obry, B.; Meyer, T.; Pirro, P.; Brächer, T.; Lägel, B.; Neb, R.; Osten, J.; Strache, T.; Fassbender, J.; Hillebrands, B.

Ion implantation of ferromagnetic films has proven to be a promising tool for the fabrication of fully planar samples with a microscopic magnetic substructure. A waveguide-like propagation of spin waves in a Ni81Fe19 film which was locally patterned by ion implantation could be observed. The investigations have been performed using Brillouin light scattering microscopy on samples patterned with varying ion fluences. Further investigations on the coupling behavior of two parallel stripes in this fully planar structures have been performed. The presented fabrication technique of spin-wave waveguides provides much lower stray fields and better heat conduction. Especially the latter is a matter of interest when the objects are exposed to intense microwave fields (excitation of spin waves) or investigated by laser spectroscopy like Brillouin light scattering. Financial support by the DFG (GRK 792) is gratefully acknowledged.

  • Poster
    Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland
  • Poster
    INTERMAG 2012, 07.-11.05.2012, Vancover, Kanada
  • Applied Physics Letters 102(2013)2, 022409
    DOI: 10.1063/1.4775759

Publ.-Id: 17251

Shell model for REOx nanoclusters in amorphous SiO2: charge trapping and electroluminescence quenching

Tiagulskyi, S.; Nazarov, A.; Tyagulskii, I.; Lysenko, V.; Rebohle, L.; Lehmann, J.; Skorupa, W.

In this work charge trapping and electroluminescence (EL) quenching in rare-earth (RE) implanted SiO2 on Si as a function of injected charge into the dielectric were studied. The blocking of the luminescent REOX nanoclusters from the hot exciting electrons by negative charge trapping in a defect region (shell) located in the vicinity of the REOX nanocluster/SiO2 interface is considered as the main mechanism of EL quenching for small size (up to 10 nm) REOX nanoclusters. It is suggested that the increase of the nanoclusters size results in disordering of the SiO2 matrix but in a decrease of local blocking for excitation of the luminescent centers.

Keywords: MOSLEDs; rare earth implanted oxide; electroluminescence; charge trapping; clustering

Publ.-Id: 17250

Thermal Effect on Electroluminescence Quenching in SiO2 with Ge and ReOX Nanoclusters

Tiagulskyi, S. I.; Tyagulskiy, I. P.; Nazarov, А. N.; Nazarova, T. M.; Rymarenko, N. L.; Lysenko, V. S.; Rebohle, L.; Lehmann, J.; Skorupa, W.

Thermal quenching and thermal dependences of the electrical quenching of electroluminescence in metal-oxide-silicon lightemitting devices implanted by Ge and Tb ions containing Ge and TbOx nanoclusters after annealing are studied. Light thermal quenching of the main green line (541 nm) in the EL spectrum of Tb implanted structures is observed. The strong temperature dependence of the electrical quenching of EL both for Ge and Tb implanted structures is explained by the participation of mobile ions in negative and positive charge generation in the bulk of SiO2 and near the SiO2-Si interface, correspondingly.

Keywords: MOSLEDs; rare earth implanted oxide; electroluminescence; charge trapping; clustering

Publ.-Id: 17249

Nd-implanted MOS light emitting devices for smart biosensor applications

Rebohle, L.; Wutzler, R.; Germer, S.; Lehmann, J.; Helm, M.; Skorupa, W.

Electrically driven, Si-based light emitters are of great interest for integrated photonic applications, especially for smart biosensors. Among the possible candidates Nd-implanted MOS devices are of special interest because of the emission wavelength of 900 nm of Nd3+ which have the potential to integrate a complete SPR (surface plasmon resonance) measurement in one chip.
In this study we explore the influence of the Nd-concentration and the annealing parameters on the electrical and optoelectronic properties. The focus is on the electroluminescence and the electrical properties of the devices which will be compared to those of Er-implanted devices.

Keywords: Electroluminescence; Erbium; Neodymium; Rare Earth; Optoelectronic Device; Si-based light emission

  • Poster
    E-MRS 2012 Spring Meeting, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17248

Er- and Nd-implanted MOS light emitting devices and their use for integrated photonic applications

Rebohle, L.; Wutzler, R.; Germer, S.; Lehmann, J.; Helm, M.; Skorupa, W.

In the past, the suitability of Er for Si-based light emission was already investigated in detail. However, much less attention has been paid to Nd with its main electroluminescence (EL) line around 900 nm. In this study we compare the electrical and EL properties of Er- and Nd-implanted metal-oxide-semiconductor (MOS) structures where the dielectric stack is composed of the implanted SiO2 layer and a SiON buffer layer. Regarding the EL, the EL spectrum, the EL decay time and the EL efficiency were measured. The electrical characterization comprises current-voltage and capacitance-voltage measurements. Although the EL efficiency of Nd-implanted devices is by a factor of 5 to 10 lower than that of Er-based, the emission wavelength of Nd has some advantages compared to that of Er. Finally, based on these results the suitability of these two types of light emitters for integrated photonic devices is discussed.

Keywords: Electroluminescence; Erbium; Neodymium; Rare Earth; Optoelectronic Device; Si-based light emission

  • Lecture (Conference)
    SPIE Photonics Europe, 16.-19.04.2012, Brussel, Belgium
  • Contribution to proceedings
    SPIE Photonics Europe, 16.-19.04.2012, Brussel, Belgium
    Proceedings of SPIE, 978-0-8194-9123-7, 843116
    DOI: 10.1117/12.921755

Publ.-Id: 17247

Formation of dendritic structures in thin silicon films on amorphous substrates by high intensity flash lamp annealing

Endler, R.; Voelskow, M.; Schumann, T.; Gebel, T.; Liepack, H.; Kolitsch, A.; Skorupa, W.

Grain enlargement of the poly silicon is a key process to improve the electronic properties of microelectronic and photovoltaic devices. We report on lateral dendritic crystal growth in thin silicon films during liquid phase crystallization (LPC) induced by high intensity flash lamp irradiation (FLA). In a series of experiments first a 140 nm SiO2 film and then amorphous silicon of 100 nm thickness were deposited on 500µm thick (100) Si wafers. After that the top silicon film was ion implanted with carbon, first, with the aim to improve the wetting properties of the underlying silicon dioxide by the liquid silicon film during the LPC process. Secondly, due its different solubility in solid and liquid silicon, carbon is responsible for the formation of a laterally depending melting temperature inducing a lateral dendritic growth process. To prove in particular this influence of carbon on the wetting and crystallization process, the flash lamp irradiated structures were studied using XTEM analysis. The pulse annealing process was carried out using the commercial flash lamp annealing tool FLA-50RD of DTF-Technology. The installed set of standard Xenon flash lamps guarantees irradiation densities up to 150 J/cm2 at a pulse length of 20 ms on preheated substrates. As expected, depending on the carbon implantation conditions and the FLA energy densities, the films show, as a result, up to several hundred micrometers extended grains having the characteristic dendritic shape.

Keywords: Large grain silicon; Silicon layers on SiO2; Flash Lamp Annealing; Pulse melting; Dendritic crystal growth

  • Poster
    E-MRS 2012 SPRING MEETING, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17246

Evidence for a novel superconducting state in quasi-two-dimensional organic superconductors at high magnetic fields

Wosnitza, J.

In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the super-conducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good can-didates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 32 T for such 2D organic superconductors. Besides an upturn of the upper critical field towards lowest temperatures, we observe a second thermodynamic transition within the superconducting phase signaling the existence of an additional superconducting phase. These features appear only in a very narrow angular region close to parallel-field orientation as evi-denced by comprehensive angular- and field-dependent specific-heat measurements for one organic superconductor. Our results give strong evidence for the realization of the FFLO state in organic superconductors.

  • Invited lecture (Conferences)
    Workshop on "Novel States in Quantum Matter", 03.-04.02.2012, Braunschweig, Deutschland

Publ.-Id: 17245

EPR Study of the Two-Dimensional Quantum System Cu(en)(H2O)2SO4

Tarasenko, R.; Orendácová, A.; Cizmár, E.; Orendác, M.; Zvyagin, S.; Wosnitza, J.

The angular dependence of electron paramagnetic resonance spectra of Cu(en)(H2O)2SO4 single crystals was studied in the X-band frequency range at temperatures 4 and 300 K. Analysis of the linewidth at 300 K revealed nice agreement with the angular variation of the g-factor. This coincidence is the manifestation of the symmetric and antisymmetric exchange coupling, as main broadening mechanisms in Cu(en)(H2O)2SO4 at high temperatures. The radical change of the angular dependence of the linewidth observed at 4 K can be ascribed to dipolar coupling.

  • Open Access Logo Acta Physica Polonica A 121(2012), 1095-1097

Publ.-Id: 17244

Magnetotransport through graphene nanoribbons at high magnetic fields

Minke, S.; Jhang, S. H.; Wurm, J.; Skourski, Y.; Wosnitza, J.; Strunk, C.; Weiss, D.; Richter, K.; Eroms, J.

We have investigated the magnetoresistance of lithographically prepared single-layer graphene nanoribbons in pulsed, perpendicular magnetic fields up to 60 T and performed corresponding transport simulations using a tight-binding model and several types of disorder. In experiment, at high carrier densitieswe observe Shubnikov-de Haas oscillations and the quantum Hall effect, while at low densities the oscillations disappear and an initially negative magnetoresistance becomes strongly positive at high magnetic fields. The strong resistance increase at very high fields and low-carrier densities is tentatively ascribed to a field-induced insulating state in the bulk graphene leads. Comparing numerical results and experiment, we demonstrate that at least edge disorder andbulk short-range impurities are important in our samples.

Publ.-Id: 17243

High-field electron spin resonance in a spin-1/2 ladder with strong leg interactions

Ozerov, M.

es hat kein Abstract vorgelegen.

  • Poster
    International Workshop on Strongly Correlated Electron systems in high magnetic Fields (SCEF), 20.-25.05.2012, Les Houches, France

Publ.-Id: 17242

Magnetic excitations in the distorted diamond chain system Cu3(CO3)2(OH)2

Kamenskyi, D.

  • Poster
    International Workshop on Strongly Correlated Electron systems in high magnetic Fields (SCEF), 20.-25.05.2012, Les Houches, France

Publ.-Id: 17241

In vitro and in vivo evaluation of yttrium-90 labelled cetuximab in combination with external X-ray irradiation – radiooncology and nuclear medicine shake hands

Heldt, J.-M.; Saki, M.; Saker, J.; Zenker, M.; Koi, L.; Ingargiola, M.; Reichelt, U.; Sommer, D.; Bergmann, R.; Sihver, W.; Mosch, B.; Dikomey, E.; Kunz-Schughardt, L.; Cordes, N.; Pietzsch, H.-J.; Pietzsch, J.; Zips, D.; Henniger, J.; Rodemann, H. P.; Baumann, M.; Steinbach, J.

Results from preclinical and clinical trials indicate that combination of the Epidermal Growth Factor Receptor (EGFR) specific antibody Cetuximab (C225) with classical radiotherapy improves local tumor control and overall survival of patients with head and neck cancers1-4. First results of Meller et al. showed a synergistic effect of 131I-labelled C225 in combination with external irradiation in vitro5. These data indicate that the combination of internal radiation dose delivered by radiolabelled C225 plus the therapeutic effect of C225 in combination with radiotherapy might significantly lower the overall external dose applied to patients, reducing undesired side effects on healthy tissue. Thus, bimodal cancer therapy seems a promising approach. This encouraged us to investigate the combined effect of 90Y[Y]-CHX-A"-DTPA-Cetuximab (90Y-C225) and radiation dose delivered by external beam irradiation in vitro and in vivo in our joint project.

Materials and Methods
CHX-A´´-DTPA was conjugated to C225 via thiourea bridging. Radiolabelling was performed under mild conditions using [90Y]YCl3. Binding affinity of 90Y-C225 was studied by flow cytometric analysis as well as by competitive binding assays using cells in 2D and 3D culture or cell membrane preparations. Distribution in spheroids (FaDu) was studied in a concentration- and time-dependent manner. Cellular uptake, EGFR binding specificity and kinetics, retention of 90Y-C225 as well as clonogenic activity of 90Y-C225 treated cells in combination with external irradiation were studied. The capacity of 90Y-C225 to induce DNA double-strand breaks (DSBs) was assessed through the Gamma-H2AX/53BP1 foci technique and cell survival by colony formation. Ex vivo autoradiography was performed with 90Y-C225. Biodistribution and in vivo kinetics were measured with PET using 86Y as radiolabel. FaDu tumour bearing nude mice were treated with 90Y-C225 (2.8 MBq 13 μg C225 / mouse, i.v.) and external beam irradiation (20 Gy single dose, 1.1 Gy/min). Experimental endpoints are the tumour growth delay and the local tumour control after 180 d.

Radiolabelling of the conjugate resulted in specific activities up to 9 GBq/mg. For the present study, a labelling protocol to achieve a reproducible specific activity of 1.2 GBq/mg was established.

in vitro: Flow cytometric analysis showed that affinity of 90Y-C225 is not significantly reduced compared to native C225. A Ki of 0.4 nM vs 0.22 nM for native C225 was determined by a competitive binding assay. Saturation of FaDu spheroids with 90Y-C225 was achieved after 24 h of incubation at 5 μg/ml. A saturation test showed that the optimal concentration to block all EGFR (SAS and UT5 cells) by C225 in monolayer culture is about 3-5 nM. No unspecific binding on an EGFR-negative CHO cell line was observed. Binding 90Y-C225 to EGFR in HNSCC cells occurred time dependently with a maximum after 24 h. 24 h after treatment approximately 10% of bound activity was found in the supernatant. Conjugation of CHX-A"-DTPA to C225 does not alter the cellular and biological function of C225. Combination of single doses of 2 or 4 Gy with 90Y-C225 reduced clonogenic survival in the UT5 and SAS cell lines. For UT5 cells the D37 value for non-treated control cells was 3.7 Gy with X-rays. Treatment with C225 reduced D37 of UT5 cells to 2.7 Gy. When 90Y-C225 was combined with X-rays, the D37 of UT5 cells dropped to 1.8 Gy. Thus, in comparison to C225, a decrease of D37 by about 33 % was observed in cells treated with 90Y-C225. D37 of untreated cells was only reduced from 3.9 Gy to 3.7 Gy after incubation with native C225. A D37 of 3.3 Gy resulted upon treatment with 90Y-C225 which reflects only a reduction of about 11%, compared to C225.
Induction of DNA DSBs by 90Y-C225 in cell lines with varying EGFR expression showed that the amount of 90Y-C225 binding and the number of induced DSBs is proportional to the EGFR on the cell membrane and that the cytotoxicity is dependent on the number of residual DSB (clonogenic survival).

in vivo: Autoradiography revealed high tumour accumulation 48 h p.i., also PET showed an increasing accumulation of activity in the tumour, which was abundant after 24 h p.i.
The combined treatment was well tolerated by all mice and no histological alterations in organs were found. A clear dose-dependent effect of the external irradiation was observed. A significant improvement of the local tumour control after X-ray irradiation with 20 Gy was achieved after application of 13 μg of 90Y-C225 compared to native C225 or to the treatment by external irradiation alone.

The results from in depth investigations of the effects of 90Y-C225 on various EGFR expressing cell lines validate it as a powerful tool for in vivo studies. The combined treatment of tumours in our experimental mouse model permits a reduction of the external radiation dose of 12 Gy. Our in-vivo data support the concept that bimodal cancer treatment results in a potentially relevant improvement of local tumour control. This encourages us to follow this promising scientific concept.

Research Support: The Bundesministerium für Bildung und Forschung (grant 02NUK006, framework “Kompetenzverbund Strahlenforschung” (KVSF)) is gratefully acknowledged for the financial support.

1 Bonner JA, Harari PM, Giralt J et al. [2010] Lancet Oncol.; 11: 21-8.
2 Bonner JA, Harari PM, Giralt J et al. [2006] N Engl J Med.; 354: 567-78.
3 Curran D, Giralt J, Harari PM et al. [2007] J Clin Oncol.; 25: 2191-7.
4 Zhang N, Erjala K, Kulmala J et al. [2009] Radiother Oncol.; 92: 388-92.
5 Meller B, Rades D, Wolff C et al. [2009] IJROBP 75: 1226-1231.

  • Lecture (Conference)
    ESRR'12 - 16th European Symposium on Radiopharmacy and Radiopharmaceuticals, 26.-29.04.2012, Nantes, France
  • Abstract in refereed journal
    Quarterly Journal of Nuclear Medicine and Molecular Imaging 56(2012), 7

Publ.-Id: 17240

Ultrasound investigations of spin-ice materials

Erfanifam, S.; Zherlitsyn, S.; Wosnitza, J.; Moessner, R.; Petrenko, O. A.; Balakrishnan, G.; Zvyagin, A. A.

The elastic properties of spin-ice materials Dy2Ti2O7 and Ho2Ti2O7 have been studied for different longitudinal and transverse acoustic modes in a temperature range from 20 mK to 300 K and magnetic fields applied along various crystallographic directions up to 17.5 T. The sound velocity and the sound attenuation exhibit a number of anomalies versus applied magnetic field at temperatures below the “freezing” temperature. In Dy2Ti2O7 compound, most notable are peaks in the sound velocity, which exhibit two distinct regimes: an intrinsic (extrinsic) one in which the data collapse for different field sweep rates when plotted as function of field strength (time). The intrinsic regime involves the release of Zeeman energy from spins, the extrinsic one, transfer of energy out of the sample. At B = 1.25 T additionally a sharp drop in the sound velocity can be seen. This can indicate a 1st-order phase transition from a low-density monopole state to the highdensity monopole state. We discuss our observations in context of the emergent quasiparticles which govern the low-temperature dynamics of the spin ice.

  • Poster
    International Workshop on Strongly Correlated Electron systems in high magnetic Fields (SCEF), 20.-25.05.2012, Les Houches, France
  • Poster
    Quantum Criticality & Novel Phases 2012 (QNCP12), 26.-29.08.2012, Dresden, Deutschland

Publ.-Id: 17239

Magnetization and magneto-acoustics studies on UCo2Si2 single crystal

Yasin, S.; Andreev, A. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.

We report results of magnetization and magneto-acoustic studies on a UCo2Si2 single crystal in high magnetic fields. This compound has a tetragonal crystal structure and orders antiferromagnetically at TN = 83 K. At low temperatures, it shows a first-order metamagnetic transition (MT) at 45 T with very small hysteresis (μ0ΔHcr = 0.16 T) to a ferrimagnetic state. This transition is seen as a sharp jump in the magnetization when the magnetic field is applied along the c direction. The acoustic properties exhibit drastic anomalies in the vicinity of both magnetic phase transitions; the spontaneous and the field-induced one. At TN, a pronounced change in the sound velocity Δv/v accompanied with a peak in the attenuation Δα has been observed. Whereas only Δα shows a very sharp peak at the MT, Δv/v displays a more complicated behavior. In addition the sound-velocity anomaly exhibits a non-monotonous temperature evolution with maximum effects at 30 K, which can be due to the transition change from the first to the second order. Our results enabled us to map the phase diagram of UCo2Si2 in fields applied along the c axis. We discuss our observations in relation to the magnetism on the U site and the magneto-elastic interaction in this material.

  • Poster
    International Workshop on Strongly Correlated Electron systems in high magnetic Fields (SCEF), 20.-25.05.2012, Les Houches, France

Publ.-Id: 17238

Spin Dynamics in Quantum Spin Chains

Zvyagin, S.

Quantum fluctuations, significantly enhanced in spin systems with reduced dimensionality, give rise to a variety of strongly correlated spin states, making low-dimensional magnets an ideal ground for testing various theoretical concepts. The way a magnetic field changes the ground-state properties and, correspondingly, the low-energy excitation spectrum of such systems is one of the fundamental aspects in quantum magnetism. Here, we report on experimental studies of the spin dynamics in copper pyrimidine dinitrate (hereafter Cu-PM), a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions, by means of high-field electron spin resonance (ESR) spectroscopy in magnetic fields up to 64 T. Due to the presence of the field-induced staggered moment, this material exhibits a field-induced gap. We show that the spin dynamics of Cu-PM can be effectively described using the quantum-field-theory sine-Gordon formalism (with soliton and breather modes forming the excitation spectrum). Furthermore, we show that in the fully spin-polarized state (Hsat = 48.5 T) the spectrum is formed by ordinary magnons. The soliton-magnon crossover is characterized by a minimum of the spin gap, predicted using DMRG calculations and clearly observed by us. The temperature and field evolution of the ESR parameters approaching the sine-Gordon regime is studied as well. Excellent agreement with the theory in all cases is found.

  • Invited lecture (Conferences)
    III International Conference for Young Scientists, Low Temperauture Physics (ICYS-LTP-2012), 14.-18.05.2012, Kharkov, Ukraine
  • Invited lecture (Conferences)
    International WORKSHOP on Strongly Correlated Electron systems in high magnetic Fields (S C E F), 20.-25.05.2012, Les Houches, France

Publ.-Id: 17237

Dresden High Magnetic Field Laboratory: Towards 100 T and Higher

Zvyagin, S.

As a high-field user facility, the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, hereafter HLD) at the Helmholtz-Zentrum Dresden-Rossendorf is open since 2007. In this presentation I will give some details of the instrumentation and research infrastructure of HLD. The talk will be illustrated by some recent examples of the high-field applications in solid state physics and material science.

  • Invited lecture (Conferences)
    III International Conference for Young Scientists Low Temperature Physics (ICYS-LTP-2012), 14.-18.05.2012, Kharkov, Ukraine

Publ.-Id: 17236

Production of 85Sr at a 18 MeV-cyclotron and purification for geochemical investigations

Mansel, A.; Gruhne, S.; Franke, K.; Fischer, S.

The production of 85Sr by irradiation of a Rb-target at a cyclotron was investigated. The purification of the radionuclide was performed by a Sr-selective resin. 85Sr was separated in no-carrier-added aqueous solution with a recovery of 98% and a concentration up to 5 MBq in 200 µl.

Keywords: Strontium-85; Rubidium target; Proton induced nuclear reaction; Chemical separation; Sr-SpecTM

Publ.-Id: 17235

Improved anatomic visualization of a glomus caroticum tumour within the carotic bifurcation with combined 68Ga-DOTATATE PET/MRI

Beuthien-Baumann, B.; Platzek, I.; Lauterbach, I.; van den Hoff, J.; Schramm, G.; Zöphel, K.; Laniado, M.; Kotzerke, J.

kein Abstract verfügbar

Publ.-Id: 17234

Ion beams for application in science and industry: Activities in Germany and the European infrastructure project SPIRIT

Möller, W.

On the grounds of largely mature methodologies of ion beam modification, ion irradiation and ion beam materials analysis, ion beams have established as a powerful and indispensable tool in front-line research and present-day industrial production, with special impact in fields of high socio-economic relevance such as new functional materials, information technology, health, environment and cultural heritage.
The present lecture will first give an overview of corresponding activities in Germany. The availability of ion facilities is concentrating at a few Universities and public research infrastructures such as the Helmholtz association. Prominent research includes the ion-beam assisted generation and modification of nanostructures at ion energies ranging from eV/amu to MeV/amu, damage of materials in the electronic stopping regime, low-fluence ion implantation for single photon emission, and radiation-biology studies with living cells. A significant amount of device capacity is also available for industrial services. For this purpose, associated transfer companies have been created in some cases.
The second part of the lecture will briefly report on the performance of the European Integrated Infrastructure Activity SPIRIT ( 9 of the 11 beneficiaries of the project offer their ion beam facilities transnational European users, with about 8000 user hours having been delivered so far. The areas of user interest will be discussed at the hand of selected results. Finally, the lecture will address new instrumental and methodological developments within SPIRIT, such as the development and employment of new detectors and the use of ion beams for chemical analysis of solid surfaces.

Keywords: Ion technologies; EU Project SPIRIT

  • Invited lecture (Conferences)
    Ion Beams '12: Multidisciplinary Applications of Nuclear Physics with Ion Beams, 06.-08.06.2012, Legnaro, Italia

Publ.-Id: 17233

Taming Nanostructures: From Sponge to Dot Pattern on Ge Controlled by Heavy-Ion-Deposited Energy

Böttger, R.; Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Anders, C.; Urbassek, H.

The self-organization of highly ordered patterns on surfaces, induced by ion beam irradiation, has attracted attention as potential nanostructured templates for magnetic and plasmonic applications. The origin of the high spatial order and its dependence on ion irradiation parameters are still under discussion. In agreement with former studies we found that ion irradiation of Ge with heavy ions (here: Bi) leads to a strong change in surface morphology in terms of roughness and formation of amorphous porous layers (sponge) with a thickness of about six times the projected ion range.
Here, we present our finding that the surface morphology on Ge, caused by irradiation with focused Bi monomer and cluster ions, can be controlled by the deposited energy density as well as the substrate temperature. While, at room temperature, the irradiation with Bi cluster ions can lead to highly ordered dot pattern having high aspect ratios, irradiation with Bi monomers results in the well-known porous surface patterns ranging from holes via columns to sponge. At elevated substrate temperatures, highly ordered dot structures can be achieved by monomer irradiation too. The pair correlation of these SEM images reveals that dot formation occurs in a temperature range which depends on the energy density deposited by a single ion. At very high temperatures, surface diffusion leads to smoothing.
A cellular defect structure model based on ion beam induced strong defect creation and high vacancy mobility in Ge explains the formation of holes, columns and sponge-like structures at low atomic energies in the cascade, i.e. Bi monomer irradiation at room temperature. This defect formation is incapacitated by thermal spikes, which form at elevated temperatures or by cluster ion impacts.
The dependence of the observed dot formation on the deposited energy density and the substrate temperature under normal ion beam irradiation cannot be explained by any model published up to now.

Keywords: Germanium; Bi; monomer; cluster; ions; surface patterns; self-organized; void formation

  • Lecture (Conference)
    56th International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication, 29.05.-01.06.2012, Waikoloa, USA

Publ.-Id: 17232

Quasi-temperature Stable Luminescence at 1.3 μm from Flash Lamp Annealed GaAs

Gao, K.; Prucnal, S.; Anwand, W.; Skorupa, W.; Helm, M.; Zhou, S.

GaAs is being widely used in optical communication devices in virtue of its outstanding luminescent and electronic performances. Many approaches have been applied to GaAs based materials, to realize the luminescence in fiber-optic transmission windows.

In this contribution, we present a novel method to achieve the 1.3 μm light emission by defect-induced luminescent centers. N, Bi and Mn were doped into GaAs wafers by ion-implantation and then their incorporation into GaAs lattice was carried out by flash lamp annealing (FLA). The optical and structural properties of the samples were investigated by micro-Raman spectroscopy, temperature dependent photoluminescence and positron annihilation spectroscopy. For the intrinsic and the N or Bi incorporated GaAs, a strong luminescence peak occurs at 1.3 μm. On the other hand, Mn-doping had suppressed this luminescence. Results have shown that for the 1.3 μm emission the donor and acceptor pairs are responsible. Furthermore, it is noticeable that the 1.3 μm light emission exhibited outstanding thermal stability (e.g., 20nm red-shift and 58% intensity decline as temperature rose from 20 K to room temperature). Our investigation suggests that GaAs treated by flash lamp annealing (i.e. a chip-relevant technology) exhibits a promising prospect on applications of light emitters and detectors for optical communication devices.

  • Lecture (Conference)
    European Materials Research Society Spring Meeting, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17231

Millisecond flash lamp annealed GaAs: a promising light emitter material at 1.3 um

Gao, K.; Prucnal, S.; Jiang, Z.; Skorupa, W.; Helm, M.; Yastrubchak, O.; Gluba, L.; Zhou, S.

Gallium arsenide based materials have outstanding performances in light-emitting devices and are being widely used in optical communication devices in virtue of their remarkable efficiency and thermal stability.
We present a novel method to achieve the 1.3 um light emitting by defect-induced luminescent centers. Mn-implanted and N-implanted GaAs as well as un-doped GaAs wafers were treated by millisecond flash lamp annealing techniques. The optical properties of the samples were investigated. Results have shown the successful incorporation of Mn and N into GaAs lattice. For the intrinsic and the N-incorporated GaAs, a strong luminescence peak occurs at 1.3 um. On the other hand, Mn-doping has suppressed this luminescence. It is still noticeable that the 1.3 um light emitting only have a slight redshift (about 20 nm) and 58% intensity decline as the temperature rises from 20 K to room temperature. Our investigation suggests that after flash lamp annealing GaAs based materials exhibit a promising prospect on applications of light emitters and detectors for optical communication devices.

Keywords: GaAs; ion-implantation; flash lamp annealing; 1.3 um luminescence

  • Lecture (Conference)
    76. Jahrestagung der DPG und DPG-Frühjahrstagung, 25.-30.03.2012, Berlin, Germany

Publ.-Id: 17230

Ion Beams in Materials Processing and Analysis

Schmidt, B.; Wetzig, K.

The main purpose of this book is two-fold. On the one hand, it is meant as a compendium for the physical fundamentals of ion-solid interactions, which are important for the understanding of ion implantation, ion beam sputtering, ion channeling, ion-induced damage formation and ion-beam mixing, but also for the comprehension of ion beam synthesis, ion-induced phase transformation and nano-patterning. Therefore, the book addresses both scientists and research engineers. The principles of ion-solid interactions are not only of fundamental importance, but ion beam irradiation of solids is becoming an increasingly important technique for modifying surface and thin film properties. Therefore, this book is also intended to bridge the gap between fundamental phenomena and their technological applications in modern materials research, development and analysis. The book demonstrates the possibilities for optimisation of solid state properties related to modern functional materials such as doped semiconductors and metal based layers for micro- and nanoelectronics, to metal alloys, nanopatterned surfaces and to new ion beam synthesized materials. A thematic rounding of the book is realized by special ion beam applications in selected materials fields. To these belong the use of ion beam analysis in magnetoelectronic layers, in art and archeometry and also in life sciences. The present book is organized into several chapters covering the range from principal aspects and phenomena over actual technological and device concepts to contemporary challenges in materials science. It thereby mainly concentrates on the relevant fields of semiconductors, nanomaterials, metals and polymers, interfaces and thin layers.

  • Book (Authorship)
    Wien, Austria: Springer-Verlag, 2013
    418 Seiten

Publ.-Id: 17229

Synthesis, microstructure, and mechanical properties of YPd3B thin films

Takahashi, T.; Iskandar, R.; Munnik, F.; Music, D.; Mayer, J.; Schneider, J. M.

Ternary Y-Pd-B thin films have been synthesized by magnetron sputtering from elemental targets to investigate the mechanical properties of the perovskite YPd3B phase. The as-deposited YPd2.73B1.18 film is identified as a single phase fcc-type structure with the measured lattice parameter of 0.415(5) nm. The film microstructure consists of dense columnar grains. The elastic modulus of the YPd2.73B1.18 film is determined to be 137 GPa by nanoindentation, which is in good agreement with ab initio calculations reported previously. The measurement of the critical shear stress for the onset of plasticity suggests that YPd3B can be classified as ductile material.

Keywords: Thin films; Transition metal alloys and compounds; Vapor deposition; Mechanical properties

Publ.-Id: 17228

Electron microscopic imaging of an ion beam mixed SiO2/Si interface correlated with photo- and cathodoluminescence

Fitting, H.-J.; Fitting-Kourkoutis, L.; Schmidt, B.; Liedke, B.; Ivanova, E. V.; Zamoryanskaya, M. V.; Pustovarov, V. A.; Zatsepin, A. F.

Energy filtered transmission electron microscopy (EFTEM), scanning transmission electron microscopy (STEM) imaging, and electron energy loss spectroscopy (EELS) of a thin 28 nm SiO2 layer on Si substrate implanted by Si+ ions with an energy of 12 keV are reported. The maximum concentration of implanted Si+ ions is located near the SiO2–Si interface region leading there to an ion beam mixed gradual SiOX (2>x>0) buffer region, which is even extended into the Si substrate by atomic collisions (knocking-off and knocking-on processes) during ion implantation. Thus, the width of this SiOX buffer layer amounts to about 30 nm extended from 10 to 40 nm depth. The SiOX profile is demonstrated by the above given electron microscopic and spectroscopic methods. Thermal annealing leads to partial phase separation from SiOX1 to SiOX2 with x2>x1 and silicon precipitates (partially nc-Si) changing the photo- (PL) and cathodoluminescence (CL) spectra especially in the near IR-region, probably, due to the formation of Si nanoclusters and associated quantum confinement effects.

Keywords: cathodoluminescence; energy-filtered TEM; ion beam mixing; silicon suboxides

Publ.-Id: 17227

Update on the laser facility at HZDR

Kraft, S.

  • Lecture (Conference)
    Ion instrumentation workshop, 07.-08.06.2012, Palaiseau, Frankreich

Publ.-Id: 17226

Scintillator-based online detectors for laser-accelerated protons – Concepts and realizations at the DRACO lab

Metzkes, J.; Zeil, K.; Kraft, S. D.; Stiller, N.; Schramm, U.; Karsch, L.; Richter, C.; Pawelke, J.; Sobiella, M.

Es werden zwei am HZDR entwickelte Online-Detektoren für laserbeschleunigte Protonen basiert auf Plastikszintillatoren vorgestellt.

Keywords: online detectors for laser-accelerated protons; plastic scintillators

  • Lecture (Conference)
    Instrumentation for Diagnostics and Control of Laser-Accelerated Proton (Ion) Beams: Second Workshop, 07.-08.06.2012, Paris, Frankreich
  • Invited lecture (Conferences)
    NAUUL 2013 - 2nd Workshop Operation of PW-class lasers, 13.-14.06.2013, Dornburg, Deutschland

Publ.-Id: 17225

The impact of climate transitions on the radionuclide transport through a sedimentary aquifer

Flügge, J.; Stockmann, M.; Schneider, A.; Noseck, U.

In long-term safety assessments for nuclear waste repositories in deep formations, geological time scales have to be considered. Possible future climatic changes are expected to alter the boundary conditions, the flow regime and the geochemical environment in the aquifers. The codes d³f (distributed density-driven flow) and r³t (radionuclides, reaction, retardation, and transport) are being developed to simulate contaminant transport in large heterogeneous areas over long periods in time, considering hydrogeochemical interactions and radioactive decay. A new methodology to use temporally and spatially variant sorption coefficients depending on the geochemical environment is being developed by introducing the transport of relevant components in solution and a pre-computed matrix of sorption coefficients with values being dependent on these components. In Germany, the Gorleben salt dome is being investigated as a potential site for a nuclear waste repository. A sea water inundation will lead to a decrease of the flow velocities and a horizontal salinity-dependent stratification of the groundwater, while permafrost formation in the upper aquifer and an inflow of glacial meltwater into the lower aquifer will lead to low salinities and high flow velocities in unfrozen zones. Transport simulations employing conventional sorption coefficients are the basis for future analyses employing the new methodology.

Keywords: Climate transitions; nuclear waste disposal; radionuclide transport; numerical modeling; smart Kd-concept; Northern Germany

  • Book chapter
    Jude Cobbing; Shafick Adams; Ingrid Dennis; Kornelius Riemann: Assessing and Managing Groundwater in Different Environments, Netherlands: CRC Press, 2013, 9781138001008, Kapitel 11


Publ.-Id: 17224

Approaching physical limits of ZnO:Al film performance for application in photovoltaics

Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Möller, W.

ZnO:Al films which combine high optical transmittance in the visible, maximum carrier mobility (mu), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells.
Present work focuses on systematic investigation of ZnO:Al films grown by reactive magnetron sputtering, a cost-efficient deposition method, using metal Zn-Al alloy targets with a wide range of Al target concentrations (c_Al). The observed dependence of the mobility on Ne is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of mu. Precise control of growth parameters results in high quality polycrystalline and epitaxial ZnO:Al films exhibiting optimum mobility values (>45 and >55 cmK/Vs, respectively) approaching the upper limit set by ionized impurity scattering. A combination of ion beam analysis for Al quantification in the film with Hall effect measurements shows that above a critical Al concentration (~2.5 at.%) further Al enrichment in the films with increasing substrate temperature leads to deterioration of electrical properties. This approach also enables estimation of the fraction of electrically active Al in the ZnO matrix, which is rarely reported in a quantitative and systematic manner. It is shown that the Al donor activation in the ZnO:Al films does not exceed 40%.

Keywords: transparent conductive oxide; zinc oxide; dopant activation; ion beam analysis; mobility

  • Poster
    EMRS Spring Meeting 2012, 14.-18.05.2012, Strasbourg, France

Publ.-Id: 17223

Nature and origin of the protolith succession to the Paleoproterozoic Serra do Navio manganese deposit, Amapa Province, Brazil

Chisonga, B. C.; Gutzmer, J.; Beukes, N. J.; Huizenga, J. M.

Until its closure in 1997, the Serra do Navio deposit, located in Amapá Province, Brazil, was one of the most important sources of high-grade manganese ore to the North American market. The high-grade manganese oxide ores were derived by lateritic weathering from metasedimentary manganese protoliths of the Serra do Navio Formation. The local geological context and nature of this protolith succession are not well understood, due to poor surface outcrop conditions, and intense deformation. However, based on similar age, regional tectonic setting and lithology the Paleoproterozoic volcanosedimentary succession that includes the Serra do Navio Formation is widely believed to be similar in origin and laterally equivalent to the Birimian Supergroup in West Africa. For the present investigation several diamond drill cores intersecting the protolith succession were studied. Detailed petrographic and whole rock geochemical studies permit distinction of two fundamental lithological groups comprising of a total of five lithotypes. Biotite schist and graphitic schist lithotypes are interpreted as former metapelites. A greywacke or pyroclastic protolith cannot be excluded for the biotite schist, whereas the graphitic schist certainly originated as a sulfide-rich carbonaceous mudstone. Rhodochrosite marble, Mn-calcite marble and Mn-silicate rock are grouped together as manganiferous carbonate rocks. Manganese lutite constitutes the most probable protolith for rhodochrosite marble, whereas Mn-calcite marble was derived from Mn-rich marl and Mn-silicate rock from variable mixtures of Mn-rich marl and chert.

The sedimentary succession at the Serra do Navio deposit is similar to that encountered at many other black shale and chert-hosted Mn carbonate deposits. A metallogenetic model is proposed, predicting deposition of manganese and closely associated chert in intra-arc basins, in environments that were bypassed by distal siliciclastic (carbonaceous mud) and proximal pyroclastic/siliciclastic detritus. Positive Ce anomalies and δ13CVPDB values of − 4.3 to − 9.4 per mill suggest that manganiferous carbonates derived during suboxic diagenesis from sedimentary Mn4+ oxyhydroxide precipitates. Metamorphic alteration of manganese carbonate–chert assemblages resulted in the formation of Mn-silicates, most importantly rhodonite and tephroite; porphyroblastic spessartine formed where Mn-carbonate reacted with aluminous clay minerals. Microthermometric studies of fluid inclusions in spessartine porphyroblasts suggests that peak metamorphic conditions reached the upper greenschist facies (1–2 kbars and 400–500 °C). Retrograde metamorphism is marked by partial re-carbonation, expressed by the formation of small volumes of rhodochrosite, and Mn-calcite that are closely associated with quartz, chlorite and minor amounts of sulfides related to post-metamorphic veinlets. It is this metamorphosed succession that sourced the high-grade manganese oxide ores during prolonged lateritic weathering.

Keywords: Serra do Navio manganese deposit; Brazil; Lithogeochemistry; Metamorphic petrology; Fluid inclusion microthermometry; Metallogenesis

Publ.-Id: 17222

Manganese metallogenesis: Introduction to the special issue

Polgari, M.; Gutzmer, J.

Research into the origin and distribution of manganese deposits has always occupied a small but important niche in economic geology. Of particular value for the progress achieved in manganese deposit research was a succession of programs funded by the International Geological Correlation Programmes (IGCP). Through six of these IGCP projects international research collaboration was effectively supported from 1975 until 2002 (Table 1). These programs enabled a large number of scientists and postgraduate students from various continents and countries to interact with one another. Manganese ore deposits worldwide were investigated during field workshops and results were presented at numerous international conferences.

Keywords: Manganese; metallogenesis

Publ.-Id: 17221

Master equation approach of classical noise in intersubband detectors

Delga, A.; Carras, M.; Trinité, V.; Guériaux, V.; Doyennette, L.; Nedelcu, A.; Schneider, H.; Berger, V.

Electronic transport in intersubband detectors is investigated theoretically and experimentally. Within the framework of inter–Wannier-Stark level electron scattering, consistent dark current and low-frequency noise expressions are obtained through the resolution of the two first moments of a master equation for classical particles. In particular, the formulation of noise bridges over the vision of uncorrelated Johnson and shot contributions. Theoretical predictions are compared to measurements for five quantum well detectors, either photovoltaic or photoconductive, whose detection wavelength span from 8 μmto17 μm. Quantitative agreement with experiment is found for a broad range of biases and temperatures. Correlation effects are discussed and proven to either reduce or enhance the noise.

Keywords: quantum well infrared photodetector; intersubband transition; noise

Publ.-Id: 17220

REE redistribution during hydrothermal alteration of ores of the Kalahari Manganese Deposit

Chetty, D.; Gutzmer, J.

The Kalahari Manganese Deposit (KMD) is the largest land-based manganese deposit, hosting approximately 80% of the world's known, mineable manganese resources. The deposit, located near Kuruman in the Northern Cape Province of South Africa, is one of five erosional relics of the Paleoproterozoic (ca. 2.2 Ga) Hotazel Formation, with sedimentary manganese ores occurring as up to 50 m thick beds interbedded with banded iron-formation (BIF) and hematite lutite.

The study focuses on the manganese ores of the Nchwaning–Gloria mining area of the northern KMD. In this area, pronounced mineralogical and major element alteration was imparted on the sedimentary manganese ores by a structurally-controlled hydrothermal fluid flow event. Most notable effects of hydrothermal alteration are the decomposition and leaching of Ca- and Mg-carbonate, and marked residual enrichment of manganese. On the basis of mineral assemblage, grade, texture and geochemical characteristics, three ore types were distinguished in the studied sample set, classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. Advanced altered ores may be further classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. The rare earth element (REE) geochemistry of these fundamental ore types was studied in detail, to document REE mobility during hydrothermal alteration.

Total REE concentrations in LA ores were found to be very low (14–22 ppm) and remarkably uniform, within the range typically observed for BIF. Hydrothermal alteration results in residual enrichment and a much larger scatter in REE contents. A small Ce anomaly observed in the protolith remains similar in magnitude when observed in PAAS-normalised REE plots. The data define, however, a power trend in the (Ce/Ce*) vs (Pr/Pr*) diagram. Such behaviour is interpreted in terms of a conservative system that was predominantly protolith-buffered. Local remobilisation of REE during hydrothermal alteration is attributed to the dissolution of diagenetic apatite and redistribution of hydrothermal trace minerals, including neoformed apatite, monazite and cerianite.

Keywords: REE; Kalahari; Manganese; Hydrothermal alteration; Cerium anomaly

Publ.-Id: 17219

Timing of supergene enrichment of low-grade sedimentary manganese ores in the Kalahari Manganese Field, South Africa

Gutzmer, J.; Du Plooy, A. P.; Beukes, N. J.

Low-grade carbonate-rich manganese ore of sedimentary origin in the giant Kalahari Manganese Field, South Africa, is upgraded to high-grade todorokite–manganomelane manganese ore by supergene alteration below the unconformity at the base of the Cenozoic Kalahari Formation. Incremental laser-heating 40Ar/39Ar dating of samples from the supergene altered manganese ore suggest that chemical weathering processes below the Kalahari unconformity peaked at around 27.8 Ma, 10.1 Ma and 5.2 Ma ago. Older ages are dominant in the upper part of the weathering profile, while younger ages are characteristic of the deeper part of the profile. Younger ages partially overprint older ages in the upper part of the weathering profile and demonstrate the downward progression of the weathering front by as little as 10 cm per million years. The oldest age obtained in the weathering profile, namely 42 Ma, is considered a minimum estimate for the onset of the post African I cycle of weathering and erosion that followed the break up of Gondwanaland and formation of the Cretaceous to early Cenozoic African land surface. The youngest ages, recorded at around 5 Ma, in turn, correspond well to the Pliocene transition from humid to arid climatic conditions in Southern Africa.

Keywords: Ar geochronology; Rate of chemical weathering; Supergene alteration; Kalahari Manganese Field; South Africa

Publ.-Id: 17218

Fluorine-18-Radiolabeling and Radiopharmacological Characterization of a Benzodioxolylpyrimidine as a Radiotracer Targeting the Receptor Tyrosine Kinase EphB4

Mamat, C.; Mosch, B.; Neuber, C.; Köckerling, M.; Bergmann, R.; Pietzsch, J.

Members of the Eph receptor tyrosine kinase family play essential roles in the pathogenesis of cancer and, therefore, are promising candidates for molecular imaging purposes, e.g. by positron emission tomography (PET). In this regard, radiochemical access to novel PET radiotracers derived from potent inhibitors targeting EphB4 kinase domain and bearing the benzodioxolylpyrimidine structural motif was developed. In order to obtain a fluorine-18-radiolabeled tracer, the respective tosylated precursor was prepared. Due to the implication of EphB4, particularly, in melanoma progression, angiogenesis, and metastasis, EphB4 overexpressing human melanoma cells were used as an in vitro model for radiopharmacological evaluation of the radiotracer. Furthermore, NMRI nu/nu mice bearing both EphB4 overexpressing tumors and control tumors were used for radiopharmacological characterization by biodistribution studies ex vivo and dynamic small animal PET experiments in vivo.

Publ.-Id: 17217

DRESDYN - a new facility for MHD experiments with liquid sodium

Stefani, F.; Eckert, S.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Steglich, C.; Weier, T.; Wustmann, B.

The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is intended as a platform both for large-scale experiments related to geo- and astrophysics as well as for experiments related to thermohydraulic and safety aspects of liquid metal batteries and liquid metal fast reactors. The most ambitious projects in the framework of DRESDYN are a homogeneous hydromagnetic dynamo driven solely by precession and a large Taylor--Couette type experiment for the combined investigation of the magnetorotational instability and the Tayler instability. In this paper, we give a short summary about the ongoing preparations and delineate the next steps for the realization of DRESDYN.

  • Magnetohydrodynamics 48(2012)1, 103-113

Publ.-Id: 17216

Comparison of different fluorine-treatments for improved high temperature oxidation resistance of TiAI-alloys

Donchev, A.; Schiitze, M.; Kolitsch, A.; Yankov, R.

Intermetallic TiAI-alloys can replace the heavier Ni-based superalloys in several high temperature applications with regards to their mechanical properties, however they can not be used at temperatures above 800DC in oxidizing environments for longer times because of insufficient oxidation resistance. Despite an AI-content of about 45 at. % in technical alloys, no protective alumina layer is formed because the thermodynamic stabilities of titanium oxide and aluminum oxide are of the same order of magnitude. Therefore a mixed Ti02/Ah03-scale is formed which is fast growing so that the metal consumption rate is quite high. On the other hand the formation of a slow growing alumina layer is promoted by a fluorine treatment. This so called fluorine effect leads to the preferential intermediate formation of gaseous aluminium fluorides at elevated temperatures if the fluorine content at the surface stays within a defined concentration range. These fluorides are converted into solid Ah03 due to the high oxygen partial pressure of the high temperature service environment forming a protective pure Ah03 surface scale. In this paper results of high temperature oxidations tests of several technical TiAIalloys will be presented. Different F -treatments e.g. dipping or spaying which are easy to apply have been used and their results will be compared. The mass change data of the F –treated specimens are always lower than those of the untreated ones. Post experimental investigations such as light microscopy, scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of a thin alumina layer on the F-treated samples after optimization of the process while a thick mixed scale is found on the untreated samples. The results will be discussed in view of an optimized procedure and the future use of TiAI-components in high temperature environments.

Keywords: TiAI-alloys; F-treatment; alumina protective layer

  • Contribution to proceedings
    2011 MRS Fall Meeting & Exhibit, 28.11.-02.12.2011, Boston, USA
    Materials Research Society Symp. Proc. Vol. 1295

Publ.-Id: 17214

Investigation of vortex dynamics in coupled trilayer systems

Banholzer, A.; Wintz, S.; Osten, J.; Raabe, J.; Quitmann, C.; Lenz, K.; Fassbender, J.

Magnetic vortices are of great interest for storage media since quite some time. Different control methods are used to manipulate them [1]. We now use scanning transmission X-ray microscopy (STXM) to image the magnetic configurations within the different layers of a trilayer system of a Co/Cu/FeNi disc. Inside the hard and soft magnetic layers with a thickness of 25 nm vortices are formed. They couple depending on the interlayer. The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling [2]. The setup allows to drive a current perpendicularly through the disc. The corresponding behaviors of the magnetization configurations with a DC-current, in a static magnetic field, as well as in an oscillating magnetic field, are investigated. The emerging movement of the core can be tuned with the amplitude and frequency of the field. The interactions of the two cores and their individually movements are studied. This implies the corresponding resistance changes within different configurations at different magnetic fields and currents as well as the shifting of the core.
[1] N. Locatelli et al., Appl. Phys. Lett. 98, 062501 (2011)
[2] S. Wintz et al., Appl. Phys. Lett. 98, 232511 (2011)

Keywords: magnetic vortex; STXM

  • Poster
    JEMS 2012 - Joint European Magnetic Symposia, 09.-14.09.2012, Parma, Italy

Publ.-Id: 17213

Improvement of the resistance of titanium aluminides to environmental embrittlement

Masset, P.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R.

Titanium aluminide alloys have recently been applied for first time as structural alloys in low-pressure turbine blades by an engine manufacturer. Indeed, they exhibit equivalent mechanical properties under service conditions as nickel-based superalloys but for half of their density. This enables an increase of the performances of the engine and/or a fuel consumption reduction. However, for engine applications requiring a higher thermal resistance, e.g. above 750°C, TiAl alloys possess an insufficient oxidation resistance and suffer from environmental embrittlement. In this interdisciplinary work, focus has been made from the surface preparation of alloys, development of coatings against environmental embrittlement up to the testing of mechanical properties after high temperature oxidation. The GE alloy (Ti-48Al-2Cr-2Nb) was used for the investigations as it exhibits a relative high ductility at room temperature (εR ~ 1.5 %) and has been already extensively investigated. Surface engineering showed that the surface temperature during the machining of the alloy increases significantly leading to embrittlement and ductility loss. Therefore, post polishing steps were achieved to obtain suitable surface roughness for the coating process without local embrittlement. Aluminum enriched coatings (between 50 and 60 at.%) combined with alloying elements, i.e. Cr, Nb, Si, Y, to improve the oxidation behavior and the corrosion resistance were produced by metal oxide chemical vapour deposition (MO-CVD), physical vapor deposition (PVD) and thermal spraying techniques (HVOF, APS). In addition, fluorine treatment (halogen effect [1]) either by plasma-immersion-ion-implantation (PI³) or by fluorine based polymer spraying was applied to the coating to enhance the growth of a dense and protective alumina layer on the top of the coating. The adhesion properties of thin coating (CVD, PVD) were investigated by applying repeated impacts of 2 to 15 mJ (Mercedes test [2]). All tests highlight the good impact resistance of the asdeposited coatings and no significant damage has been detected even after 105 impacts using a force of 800N.
After oxidation, the CVD deposited coatings exhibit very good behavior under repeated impacts. Thin (CVD, PVD) as well as thick (thermal sprayed) coatings were obtained and were tested for oxidation and corrosion resistance. CVD and PVD coatings exhibit thicknesses between 3 and 10 μm whereas the thickness of thermal sprayed coatings ranges between 150 and 300 μm (Fig. 1). Figure 1. SEM images of produced coatings. (a) MO-CVD, (b) PVD, (c) HVOF with ethene, (d) HVOF with kerosene, (e) HVOF with kerosene + Al addition in the powder, (f) APS. The produced coatings were tested for oxidation and corrosion. After pre-oxidation, the samples exhibit a better corrosion resistance in presence of salts (75-25 NaCl-NaSO4 mixture) at 850 °C after 350 h in air compared to literature data obtained at 650 °C [3]. The mechanical properties were investigated by means of 4-point bending and tensile tests on coated samples after 100 h oxidation at 900 °C in laboratory air. Results of mechanical testing are shown in Fig. 2. The CVD process combined with fluorine implantation (PI³) offers the best combination to remedy environmental embrittlement.
Using this process, after 100h of oxidation, it has been shown that 90% of the initial fracture strain and fracture stress can be maintained. For long term service (thousands of hours) coating thickness should be increased to offer an aluminium reservoir for the oxidation and to provide an efficient physical barrier to hot gas and corrosion agents. Figure 2. Fracture stress vs. fracture strain for the investigated coated samples.

Keywords: TiAl-alloy; fluorine implantation (PI³); metal oxide chemical vapour deposition; oxidation resistance

  • Lecture (Conference)
    Pacific Rim Meeting on Electrochemical and Solid-State Science (PRIME 2012), 07.-12.10.2012, Honolulu, Hawaii, USA

Publ.-Id: 17212

Efficient oxidation protection of Ti- and TiAl-alloys by fluorine treatments

Donchev, A.; Schütze, M.; Yankov, R. A.; Kolitsch, A.

Ti-alloys suffer from high oxidation rates and oxygen uptake during exposure in oxidizing environments at elevated temperatures above approximately 600°C. TiAl-alloys have the same problem due to the insufficient oxidation resistance at temperatures above 850°C. The use of these alloys is hence limited. The fluorine effect is a very promising way to improve the oxidation resistance of TiAl-alloys. Defined amounts of fluorine in the surface zone of TiAl-components change the oxidation mechanism. A protective alumina layer is formed which prevents further oxidation and subsequently allows the use of this new alloy family in several high temperature applications. The Al-content of standard Ti-alloys is not enough to get the fluorine effect to operate but after Al-enrichment of the surface zone a subsequent fluorination leads to the same results. In this paper results of oxidation tests of untreated and treated Ti- and TiAl-alloys will be presented and their behavior compared.

Keywords: TiAl-alloys; oxidation resistance; Al-enrichment

  • Lecture (Conference)
    TMS Annual Meeting 2012, 11.-15.03.2012, Orlando, Florida, USA

Publ.-Id: 17211

Combination of a chemical vapor deposition coating and plasma immersion ion implantation of fluorine for oxidation protection and suppression of oxygen embrittlement in titanium aluminide alloys

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Bortolotto, L.; Schütze, M.

The ongoing gradual replacement of heavy nickel-based superalloys with lightweight titanium aluminide (TiAl) intermetallic alloys is a long-term development objective in demanding applications such as the manufacture of aerospace and automotive engine components. TiAl alloys, however, are prone to destructive oxidation and oxygen embrittlement when exposed to oxidizing gases at temperatures above 700°C. Therefore, the successful use of this class of advanced structural materials in components operating under conditions of environmental oxidation at elevated temperatures will ultimately depend on their oxidation resistance. We have developed a method of oxidation protection of TiAl alloys, which solves satisfactorily the above-mentioned problems. The method involves two steps, namely formation of an aluminum-rich coating by chemical vapor deposition (CVD) followed by plasma immersion ion implantation (PIII) of fluorine to provide conditions necessary for activating the so-called halogen effect. The aim of combining a CVD coating and a fluorine PIII treatment is to prevent oxygen diffusion and dissolution into the Ti-rich α2-phase substrate material, which is an integral part of most of the technical alloys being used at present. Preliminary mechanical testing performed on an unprotected reference alloy of a composition of Ti-48Al-2Cr-2Nb has shown drastic degradation in its mechanical properties after exposure in hot air at 900°C for 100 h, namely 23% loss in strength and 38% reduction in ductility. In contrast, the application of a CVD coating in conjunction with surface fluorination by PIII has been shown to enhance the environmental durability of the TiAl alloy after long-term oxidation at 900°C in that the alloy is capable of maintaining up to 90% of its initial mechanical properties (strength and ductility). We present here experimental results detailing both the CVD and the PIII processing steps.

Keywords: titanium aluminides; oxidation protection; fluorine plasma immersion ion implantation

  • Poster
    13th International Conference on Plasma Surface Engineering, 10.-14.09.2012, Garmisch-Partenkirchen, Germany

Publ.-Id: 17210

Fluorine-implanted titanium aluminide alloys for use in high-temperature oxidizing environments

Yankov, R.; von Borany, J.; Kolitsch, A.; Munnik, F.; Friedle, S.; Donchev, A.; Schütze, M.; Nießen, N.; Braun, R.

Plasma immersion ion implantation (PI3) of fluorine has been used to enhance the oxidation resistance of several commercial TiAl alloys (γ-MET, TNB and TNM) with the aim of expanding their high-temperature (750°-1050°C) structural potential for advanced aerospace, power generation and automotive applications. The mechanism that operates in the F-implanted TiAl alloys, enabling one to achieve oxidation protection up to 1050°C, is the so-called halogen effect.
Two types of F-containing precursor gases, namely a mixture of difluoromethane and argon (CH2F2+25% Ar), and a mixture of silicon tetrafluoride and argon (SiF4+25% Ar) have been employed for implanting F. A variety of analytical techniques such as X-ray diffraction (XRD), elastic recoil detection (ERD), Rutherford backscattering spectrometry (RBS) and cross-sectional electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) have been used for material characterization. The degree of oxidation protection has been evaluated by testing F-implanted samples under conditions of both isothermal and thermocyclic oxidation in air employing thermal gravimetric analysis (TGA). The formation of a protective scale has been studied by metallography, EDXS, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).
For the CH2F2/Ar-based PI3 process, ERD analyses have revealed in the F-implanted γ-MET and TNB alloy samples anomalously broad, high-concentration (up to 70 at. %) F profiles of either Gaussian or plateau-like shape extending to much larger depths than those predicted by theory. It has been found that the broad F implant profiles are not associated with F diffusion, but rather result from a complex amorphization/phase transition process, which occurs via the implant zone/substrate interface progressing toward the bulk. As distinct from the implanted fluorine, the co-implanted carbon forms a shallow surface peak of a concentration of about 15 at. %, much in accordance with the theoretical predictions. Optimized PI3 of F into γ-MET and TNB alloys in this case leads to a dramatic improvement in their environmental durability due to the formation of a stable, adherent and highly protective α-Al2O3 scale on the alloy surface upon subsequent high- temperature oxidation. On the basis of the results obtained, components of complex geometry (turbine blades and turbochargers) made of TiAl alloys have been successfully implanted with F for times as short as 22 min, and a commercially viable PI3 technique has been developed.
Furthermore, we have demonstrated for the first time the possibility of fabricating yttria- stabilized-zirconia thermal barrier coatings (YSZ-TBCs) on PI3-treated γ-TiAl to improve turbine efficiency, thereby enabling turbines made of γ-TiAl to be used for longer times at higher service temperatures. TBCs have been deposited by electron-beam physical vapor deposition (EB-PVD) at 900° and 1000°C on γ-TiAl that had been pre-implanted with F and then subjected to oxidation. Excellent adhesion of the TBCs to the Al2O3 scale present on the alloy surface has been observed, with the coatings retaining adherence and the halogen effect still lasting under cyclic oxidation at 900°C in air. Another aspect of our research has been to investigate the halogen effect resulting from the PI3 of F in a new class of TiAl materials containing a β-phase, namely TNM-B1. The preliminary results have been positive, strongly indicating that further work is warranted.
The SiF4/Ar-based PI3 process is still being optimized. Under certain implantation conditions, adequate oxidation protection has been achieved in both γ-MET and TNB alloys for an implant time twice as short (11 min) compared with that used in the CH2F2/Ar process. This can be explained by the combined effect of F and Si. The latter element is believed to reduce the rate of oxygen diffusion into the incipient protective scale. A non-linear time dependence of the retained F dose has been observed, presumably due to enhanced ion etching and material removal for longer implant times. These phenomena are currently under study.

Keywords: TiAl alloys; PIII of F; oxydation protection; thermal barrier coatings

  • Poster
    19th International Conference on Ion Implantation Technology, 25.-29.06.2012, Valladolid, Spain

Publ.-Id: 17209

Efficient oxidation protection of Ti- and TiAl-alloys by F-treatments

Donchev, A.; Schütze, M.; Yankov, R.; Kolitsch, A.

Ti-alloys suffer from high oxidation rates and oxygen uptake during exposure in oxidizing environments at temperatures above approximately 600°C. Technical TiAl-alloys have the same problem due to the insufficient oxidation resistance at temperatures above 750°C. The use of these lightweight alloys is hence limited. The fluorine effect is a very promising way to improve the oxidation resistance of TiAl-alloys. Defined amounts of fluorine in the surface zone of TiAl-components change the oxidation mechanism. A protective alumina layer is formed which prevents further oxidation and subsequently allows the use of this new alloy family in several high temperature applications. The Al content of standard Ti-alloys is not enough to get the fluorine effect to operate but after Al-enrichment of the surface zone a subsequent fluorination leads to the same results. In this paper results of oxidation tests of untreated and treated Ti- and TiAl-alloys will be presented and their behavior compared.

Keywords: Ti-alloys; fluorine effect; Al-enrichment; oxydation protection

  • Contribution to proceedings
    TMS (The Minerals, Metals & Materials Society) Annual Meeting 2011, 27.02.-03.03.2011, San Diego, California, USA
    TMS 2011 Proceedings, CD-ROM

Publ.-Id: 17208

Optimization of the fluorine effect for improving the oxidation resistance of TiAl alloys

Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.

The oxidation resistance of TiAl-alloys can be improved drastically by treating the surface of the components with small amounts of fluorine. The oxidation mechanism is changed. Hence, the formation of a fast growing mixed oxide scale on untreated alloys is suppressed. Instead a thin protective alumina scale is formed on samples after fluorine treatment. The different methods only influence the surface region of the components so that the bulk properties are not affected. Recent results achieved with F-containing inorganic compounds showed that the fluorine effect can be improved even further. TiAl-specimens were treated only with fluorine and with F-containing compounds in several ways and their performance during high temperature oxidation tests in air was investigated. Results of isothermal and thermocyclic oxidation tests are presented. The results are discussed in terms of a later use of the fluorine effect for technical applications.

Keywords: TiAl; fluorine treatment; oxydation resistance

Publ.-Id: 17207

Sputter deposition of TiO2-based transparent conductive thin films

Neubert, M.; Vinnichenko, M.; Gebel, T.; Liepack, H.; Kolitsch, A.

Transparent electrodes are widely used in photovoltaic cells which drives the need for novel cost-efficient transparent conductive materials. The epitaxially grown TiO2 films doped with Nb or Ta show electrical resistivity values comparable to those of the best In2O3:Sn and ZnO:Al films. However, for the most applications the growth of low electrical resistivity polycrystalline TiO2 films is required. In order to address this challenge, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2:Ta ceramic targets followed by vacuum annealing. We present a systematic study of the effect of the process total pressure (Ar+O2) during the deposition on electrical and structural properties of the films after annealing. The optimum total pressure in combination with O2 fine tuning yielded the films with the best free electron mobility of 8 cm²/Vs. Our approach delivered films with an electrical resistivity in the range of 10-3  cm, optical transmittance above 80% for 400nm thick films and electrical activation of Ta dopants up to 80% that is substantially higher than that of Al in ZnO.

Keywords: TCO; transparent conductive oxides; TiO2; Ta; tantalum; polycrystalline; thin film

  • Poster
    E-MRS 2012 Spring Meeting, 13.-18.05.2012, Strasbourg, France

Publ.-Id: 17206

Characterisation of permanent magnetic quadrupoles for focussing proton beams

Melone, J. J.; Mccanny, T.; Schramm, U.; Akhmadaliev, S.; Spohr, M.; Cowan, T.; Mitchell, M. R.; Ledingham, K. W. D.; Burris-Mog, T.; Groetzschel, R.; Hanf, D.; Bussmann, M.; Wiggins, S. M.

High intensity laser driven proton beams are at present receiving much attention. The reasons for this are many but high on the list is the potential to produce compact accelerators. However, two of the limitations of this technology is that unlike conventional nuclear RF accelerators lasers produce diverging beams with an exponential energy distribution. A number of different approaches have been attempted to monochromise these beams but it has become obvious that magnetic spectrometer technology developed over many years by accelerator physicists to transport and focus proton beams could play an important role for this purpose. This paper deals with the design and characterisation of a magnetic quadrupole system which is intended to focus and transport laser-accelerated proton beams.

Keywords: ion beam focusing

Publ.-Id: 17205

Section Reports: 2012 Annual Meeting on Nuclear Technology - Part 5

Stieglitz, R.; Mull, T.; Höhne, T.; Rieger, U.; Buettner, K.

The session Testing Plants was chaired by Thomas Höhne (Helmholtz-Zentrum Dresden-Rossendorf e.V.). The first presentation from S. Schollenberger (Co-authors: K. Umminger, B. Schoen, all Areva NP GmbH) was about „PKL-Experiments on failure of RHRS under 3/4-loop operation for closed primary circuit – Phenomena and operational aspects“. At first, S. Schollenberger gave a few introducing remarks on the PKL test facility, he explicated that the PKL (German acronym for Primärkreislauf, primary circuit) is a scaled down replication (1:1 heights, volumes, power input and mass flows of safety and operational systems 1:145) of the nuclear steam supply system of a 1300 MW KWU type pressurized water reactor (PWR). It is operated at AREVA NP Germany to experimentally investigate the thermal hydraulic behavior of PWRs under accident conditions for design and beyond-design basis accidents (e.g. efficiency of accident management measures). He then stated the motivation for the adoption of the topic “failure of RHRS under cold shut-down states in the PKL experiments to be founded in the significant contribution to the integral core damage frequency (CDF) of 1.1∙10-5 p.a. and plant implied by failure of RHRS: broken down to 24 h, a day under shut-down conditions implies a much higher risk than a full load day. He further stressed, that in the long run, a stationary state (stationary boiling) with constant primary pressure and assured heat transport to secondary side (core cooling) becomes always established as long as at least 1 of 4 SGs is operable (MS/ FW available), even without intervention of the operating personnel. He then summarized, that additional coolant injections result in a deterioration of heat transport to secondary and give rise to the RCS pressure level. He concluded that additional coolant injections should therefore only be considered as a preparative measure for the immediate re-connection of the RHRS (operability assumed). S. Schollenbegrer added that heat transfer mechanisms with prospect of a continuous boron dilution in below SG outlet (due to condensate transport across the SGs) may be excluded for the operation of 2 active SGs (out of 4). S. Schollenberger then focused on the operational aspects, he presented recommendations for the reconnection of the RHRS (re-availability assumed): The PKL tests proved the deployment of a single LPSI/RHRS pump in flooding mode (simultaneous hot and cold side injection with maximum flow rate) to be an adequate preparative measure to re-establish operating conditions of the RHRS from boiling condition in the RCS (i.e. quick and enduring subcooling of core, downcomer and hot sides). If only one RHRS line is operational, the flooding (simultaneous hot/cold leg injection) of large amounts of ECC with the available line and the following re-start of RHRS operation after switchover in the same line may allow a safe reconnection of the RHRS.

J. Dumond (AREVA NP GmbH, Offenbach, co-authors: F. Maisberger, AREVA NP GmbH, A. Class, Karlsruhe Institute of Technology, Karlsruhe) presented the “Development and first experimental results of the KERENA Passive Outflow Reducer”. Increased safety and reduced costs are achieved in the boiling water reactor KERENA with a smart combination of active and passive safety systems. One of these passive systems is the Passive Outflow Reducer (POR). It is positioned in the reactor nozzle to passively limit without moving parts the loss of coolant (LOC) following the break of a large pipe connected to the reactor pressure vessel at a low elevation in one flow direction; while it minimizes the flow resistance in the other flow direction. An innovative design consisting of 37 parallel profiled channels where each channel is composed of two Venturi-nozzles was introduced. The development of this design with numerical tools was explained and the experimental validation in the LOC flow direction was described. The experiments were performed for single Venturi-nozzle and double Venturi-nozzle designs under realistic plant conditions. One profiled channel was tested at a time. Experimental results indicated that double-nozzle designs do reduce loss of coolant in comparison to single-nozzle designs (50% for the LOC considered here in the KERENA reactor) and that the innovative POR design meets KERENA requirements. Finally, computational fluid dynamic is developed to further optimize the geometry. In the summary, it was emphasized that this simple innovative passive fluidic diode without moving part is ready for similar applications.
Further Mr. M. Majed (Co-authors: S. Andersson, F. Waldemarsson, all Westinghouse Electric Sweden) showed the presentation „Westinghouse Critical Heat Flux Test Facility – ODEN“. The ODEN test facility is a replacement to (and improvement upon) the well known former Heat Transfer Research Facility (HTRF) of Columbia University in New York City. The ODEN loop shares the laboratory infrastructure (power supply, heat sink and control room) with the well-known FRIGG Boiling Water Reactor (BWR) test loop. The ODEN loop is designed to cover DNB (Departure of Nuclear Boiling) testing needs for all types of PWR lattices in 5x5 or 6x6 rectangular geometry or in hexagonal test sections. The loop installation was completed in 2006, shakedown testing in 2009, and qualification / benchmark testing versus HTRF data was completed in 2010. The ODEN critical heat flux test loop has been utilized recently to perform DNB measurements on Westinghouse fuel design for VVER 1000 type reactors. The test bundle configuration is a 19 rod hexagonal array. The fuel has been tested in an extensive thermal-hydraulic verification program with axially uniform test (typical cell) and two axially cosine tests (typical and thimble cells). The DNB measurements have been performed at low to high pressures (10 to 17 MPa), low to high mass flows, (0.8 to 7.8 kg/s) and include very high mass steam quality conditions, up to and exceeding 50 %. Mr. Majed closed his presentation with the statement that the ODEN loop has again showed the high DNB data quality, and excellent consistency and repeatability of the DNB data were achieved.
The last presentation was given by A. Onea (Co-authors: M. Lux, W. Hering, all Karlsruher Institut für Technologie – KIT) and about „Optimization of the cold trap design for the KASOLA sodium facility“. The authors envisaged the employment of the new sodium facility for research of transmutation, accelerator target development, as well as an innovative assignment of sodium for solar applications. It is reported that the sodium purification will be performed by cooling it below its saturation temperature in a cold trap that integrates in the upper part a Na-air heat exchanger and a Na-Na heat recuperator, while the bottom part integrates a wire mesh, where the main impurities NaH and Na2O can deposit on its “cold” surface. The talk was focused on the optimization and layout of the wire mesh and of the Na-air heat exchanger and Na-Na heat recuperator, for which two design proposals are compared, namely a simple design, in which the sodium exists through a straight vertical pipe that serves as a heat recuperator and an optimized design, in which the sodium exists through an optimized helical coil that serves also as a heat recuperator. The authors discussed the optimal wire mesh capacity for capturing of the impurities, their residence time distribution in the wire mesh, the pressure loss in the wire mesh and the planned operating range of the cold trap. The optimized design offers increased heat transfer surface for both the air cooling circuit and the recuperation side, while the disadvantages of this design are moderate increase in the pressure loss and an increased manufacturing cost. Analyses with ANSYS CFX 13 for the flow dynamics and heat transfer, using a conjugate heat transfer approach and modeling the wire mesh as a porous domain confirmed the expected results: in the optimized design the wire mesh is cooled at least 15°C more than in the simple design, at the same air cooling capacity and furthermore, quasi the entire heat of the sodium is recuperated, denoting a heat recuperation efficiency of ~99% for the entire range of the air flow rate. Due to the enhanced cooling capacity it is reported that the optimized design offers an increased temperature operation range for sodium, while the safe operation is still warranted and although the manufacturing costs are higher as for the simple design, the operating costs will be smaller due to the enhanced cooling.

Keywords: Jahrestagung Kerntechnik; Sektion 2; Technische SItzung

  • atw - International Journal for Nuclear Power 58(2013)1, 43-44

Publ.-Id: 17204

Dose Controlled Radiobiological Experiments with Ultra-short Pulse Laser Accelerated Proton Pulses

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

Over the last decade laser particle acceleration has made such progress that first applications in special fields can be envisioned. Prominent examples are radiation therapy with laser accelerated ion beams as well as the generation of pulsed X-ray sources. Here the demonstration of laser acceleration of proton pulses to maximum energies in the range of up to 20 MeV making use of the 100 TW table-top laser Draco installed at HZDR Dresden will be reported. Reproducible conditions over thousands of shots allowed for the first dose controlled irradiation of in vitro tumor cell samples, representing the first step towards radiobiological applications. A detailed description of experimental requirements as sufficiently high proton energies providing applicable doses of a few Gy within minutes, a beam transport and filtering system, an in-air irradiation site, a dedicated dosimetry system providing both online dose monitoring and a precise absolute dose information applied to the cell sample will be given.

Keywords: Laser ion acceleration; cancer therapy

  • Poster
    IPAC 2012, 21.-25.05.2012, New Orleans, LA, USA

Publ.-Id: 17203

Picosecond Narrow Bandwidth X-ray Pulses from a Laser-Thomson-Backscattering Source

Jochmann, A.; Cowan, T.; Kuntzsch, M.; Lehnert, U.; Sauerbrey, R.; Wagner, A.; Trotsenko, S.; Couperus, J. P.; Debus, A.; Irman, A.; Schlenvoigt, H.-P.; Schramm, U.; Ledingham, K.

Intense, ultimately coherent, ultrashort hard X-ray pulses can serve as a novel tool for structural analysis of complex systems with unprecedented temporal and spatial resolution. With the simultaneous availability of a high power short-pulse laser system it provides unique opportunities for a number of subsequent research steps at the forefront of relativistic light-matter interactions. At HZDR we demonstrated the generation of such a light source (PHOENIX) by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating femtosecond laser pulses from the 150 TW Draco Ti:Sapphire laser system. The generated narrowband X-rays are highly collimated and can be reliable adjusted from 5.5 to 23.5 keV by tuning the electron energy (24 MeV to 30 MeV) and the laser intensity. Ensuring the spatiotemporal overlap and suppressing the bremsstrahlung background we have achieved a signal-to-noise ratio greater than 300:1. Together with the use of an X-ray camera (resolution of 250 eV(FWHM)) to record the spectrum, we were able to resolve the angular-energy correlation and to study the influence of the beam emittance on the observed bandwidth.

Keywords: X-ray light sources; Thomson scattering

  • Poster
    IPAC 2012, 21.-25.05.2012, New Orleans, LA, USA

Publ.-Id: 17202

Extension and application of the reactor dynamics code DYN3D for Block-type High Temperature Reactors

Baier, S.; Fridman, E.; Kliem, S.; Rohde, U.

The reactor dynamics code DYN3D was developed at the Helmholtz-Zentrum Dresden-Rossendorf to study steady state and transient behavior of Light Water Reactors. Concerning the neutronics part, the multigroup diffusion or SP3 transport equation based on nodal expansion methods is solved both for hexagonal and square fuel element geometry. To deal with Block-type High Temperature Reactor cores DYN3D was extended to a version DYN3D-HTR. A 3D heat conduction model was introduced to include 3D effects of heat transfer and heat conduction and the detailed structure of the fuel element. Results of coupled steady state and transient calculations with 12 energy groups are presented. Transient case studies are control rod insertion a change of the inlet coolant temperature and a change of the coolant gas mass flow rate. It is shown that DYN3D-HTR is an appropriate code system to simulate steady states and short time transients. Furthermore the necessity of the 3D heat conduction model is demonstrated.

Keywords: high temperature gas cooled reactor; heat conduction model; transient analysis; computer code; temperature reactivity feedback

  • Contribution to proceedings
    6th International Topical Meeting on High Temperature Reactor Technology HTR2012, 28.10.-01.11.2012, Tokyo, Japan
  • Nuclear Engineering and Design 271(2014), 431-436
    DOI: 10.1016/j.nucengdes.2013.12.013

Publ.-Id: 17201

Precise millisecond annealing for advanced material processing

Reichel, D.; Skorupa, W.

Flash Lamp Annealing (FLA) reduces the thermal budget on the bulk and thus hinders undesired thermal diffusion. For reliable process control, however, a temperature measurement concept is needed that is capable of facing the high radiation background of the flash lamps and the millisecond detection regime at the same time [1]. A new concept has been developed for precise in-situ temperature measurement during flash-lamp Millisecond Annealing. There has been taking advantage of FLA for various applications. Implantation and subsequent FLA were used to obtain III-V semiconductor quantum dots on silicon pillars [2]. The same procedure was applied to achieve superconductivity with conventional silicon technolog [3]. FLA was further used for advanced doping of “dirty-silicon” solar cells. The short annealing cycles allow for successful dopant activation while undesired metal impurities remain electrically inactive [4]. These examples show that in-situ process control is required to make sure the major advantage of Millisecond Annealing is not narrowed by unreliable temperature measurement. In this contribution, a method will be presented that satisfies this issue by in-situ distinction between thermal and flash lamp radiation.

Keywords: annealing; millisecond; flash lamps; temperature measurement

  • Contribution to proceedings
    EMRS Spring Meeting 2012, 14.-18.05.2012, Strasbourg, France
    Advanced Silicon Materials Research for Electronic and Photovoltaic Applications III
  • Poster
    EMRS Spring Meeting 2012, 14.-18.05.2012, Strasbourg, France
  • Physica Status Solidi (C) 9(2012)10-11, 2045-2049
    DOI: 10.1002/pssc.201200277

Publ.-Id: 17200

The Factor Cloud Computing in IT Risk Management

Penzina, V. J.; Konrad, U.; Yusupova, N. I.

Der Artikel beschreibt eine Definition und den Prozess des IT Risiko-Managements mit dem besonderen Einfluss von Cloud-Computing, insbesondere die Identifikation von Schwachstellen, Steuermöglichkeiten und Maßnahmen.
Today Risk Management plays a crucial role in protecting information. Effective Risk Management is one of the most important parts of a security program in IT organizations.
This paper represents a definition of Risk Management, first steps of the process and the influence of cloud computing according to vulnerability identification and controls and measures analysis subprocesses.

  • Contribution to proceedings
    The 14th International Workshop on Computer Science and Information Technologies, CSIT’2012, 20.-26.09.2012, MSC Lirica, Norway
    Proceedings of the 14th International workshop on computer science and information technologies, CSIT’2012, Ufa – Hamburg – Norwegian Fjords, 2012

Publ.-Id: 17199

Development and implementation of a 3D heat conduction model for (very) High Temperature Reactors into the reactor dynamics code DYN3D

Baier, S.; Rohde, U.; Kliem, S.; Fridman, E.

The reactor dynamics code DYN3D was extended to treat phenomena in Block-type High Temperature Reactors (HTR). Therefor, a new heat conduction model was implemented into the code to tackle 3D effects of heat conduction and heat transfer. The first part of the paper describes the details of the heat conduction model. In the second part results of coupled neutron-kinetics/thermal-hydraulics calculations of steady state and short-time transients in block-type HTRs are discussed.

Keywords: high temperature gas cooled reactor; heat conduction model; transient analysis; computer code; temperature reactivity feedback

  • Contribution to proceedings
    20th International conference on Nuclear Engineering - ICONE20, 30.07.-03.08.2012, Anaheim, USA
    Proceedings of ICONE20
  • Lecture (Conference)
    20th International conference on Nuclear Engineering - ICONE20, 30.07.-03.08.2012, Anaheim, USA

Publ.-Id: 17198

Investigation on the structural and magnetic properties of Co+ implanted rutile TiO2

Cheng, F.; Ding, B.; Pan, F.; Yao, S.; Potzger, K.; Zhou, S.

Crystalline Co nanoparticles in rutile TiO2 were synthesized by 180 keV Co+ ion implantation at 623 K with the fluence of Φ = 4 × 1016 cm−2. The structural and magnetic properties of samples after thermal annealing at different temperatures were characterized by synchrotron radiation X-ray diffraction (SR-XRD), Rutherford backscattering/channeling (RBS/C) and superconducting quantum interference device (SQUID) magnetometer. The SR-XRD results reveal the formation of hcp Co nanoparticles in the as-implanted samples. With increasing annealing temperature, the transition of Co nanoparticles from hcp to fcc is observed. After annealing at 1073 K, the lattice damage is significantly repaired compared with the as-implanted one. The Co nanoparticles forming inside TiO2 are the major contribution of the measured ferromagnetism.

Keywords: Rutherford backscattering and channeling; X-ray diffraction; SQUID magnetometers; Magnetic nanoparticles; Ion implantation

Publ.-Id: 17197

CFD analysis on the NUPEC PWR Subchannel and Bundle Test (PSBT) - model calibration and influence of turbulence modelling

Krepper, E.; Rzehak, R.

The presentation shows CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns. Furthermore the influence of bubble forces on the void distribution cross sections was shown.

Keywords: CFD; wall boiling; CFX; PSBT benchmark; rod bundle; two phase flow; turbulence; bubble forces

  • Lecture (Conference)
    AER WG C and D Meeting, 31.05.-01.06.2012, Paks, Ungarn

Publ.-Id: 17196

Numerical calculations for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg

Kinoshita, I.; Murase, M.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.

In reflux condensation, steam generated in the reactor core and water condensed in a steam generator (SG) form countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. Both countercurrent air–water and steam–water tests were previously carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) using the 1/3 scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, the steam–water CCFL (countercurrent flow limitation) tests at HZDR were simulated using the CFD software, FLUENT 6.3.26. The computational domain included the reactor vessel simulator, hot leg and SG inlet chamber in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) method and two-fluid (2F) model were used. In the 2F model, the combination of three correlations on the interfacial friction coefficients, which had been validated for the 1/15 and 1/5 scale tests at Kobe University, was used as a function of local void fractions. The CCFL characteristics predicted by the 2F and VOF agreed relatively well with the steam–water CCFL data at HZDR but overestimated the effects of fluid properties on CCFL. The VOF simulations were better able to reproduce the fluid properties than the 2F simulations.

Keywords: CCFL; PWR; hot leg; simulation; experiment

Publ.-Id: 17195

Nanoscale TiO2 particles: relationship between surface properties and toxicity measurements

Hurel, C.; Clement, L.; Jordan, N.; Weiß, S.; Marmier, N.

Titanium oxides nanoparticles have been widely used in industrial applications such as cosmetics, food industries, environment, paints and surface coatings…Face to their growing use in various domains and the difficulties to separate them from the aqueous phase during wastewaters treatment due to their nanometric size, one can expect that the final host for these particles should be environmental compartments (soil, air and water).
Nanometric-sized particles are known to cause pulmonary damages and to be toxic for mammals (mice, rats). Nevertheless, few studies dealt with the toxic impact of nanoparticles with ecosystems. Previous studies have shown that the toxic effect was dependent (i) on the size of the particles and (ii) on the allotropic form of TiO2 (anatase or rutile). But a lack of information remains concerning the relationship between the surface properties of TiO2 nanoparticles (surface site density, surface charge) and the observed toxicity.
In this study we were interested in anatase (15 nm, 32 nm, 44 μm) and rutile (1 μm) commercial particles. Their toxic effect (acute or chronic) versus microcrustaceans, algae and plants was measured and compared to the particles size. Surface properties of each TiO2 particles were determined by acid-base titration, and electrokinetics measurements, in order to complete data concerning the relationship between nanoparticles toxicity, size and allotropic form.

Keywords: TiO2; nanoparticles; toxicity

  • Lecture (Conference)
    Interfaces Against Pollution, 11.-14.06.2012, Nancy, France

Publ.-Id: 17194

Focused Ion Beams - Status and New Trends

Bischoff, L.

In the last decade focused ion beams (FIB) became an irrecoverable instrument in research and industry. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium liquid metal ion source (LMIS). But, modern trends in nanotechnology require more extended properties like variable ion species, non-contaminating milling at higher rates or higher lateral resolution in the field of ion microscopy [1].
In this presentation the implementation of an alloy LMIS in a mass separated FIB system is introduced. Fabrication and characterization of such sources will be briefly shown and prospective applications like self-organized surface modification with focused heavy cluster ions on a germanium surface or local ion beam syntheses of CoSi2 nanostructures are demonstrated.
Furthermore the status and application of new source concepts including prototypes will be reviewed in particular high current gas sources (ECR, ICP) for effective high rate milling, ion trap sources providing highly charged ions or used for SIMS applications as well as gas field ion sources for high resolution ion microscopy in the sub-nm range. Additionally, the use of alloy liquid metal ion sources and its characterization for mass separated FIB systems and ToF-SIMS applications will be presented. New trends and possibilities in FIB employment will be discussed.

Keywords: FIB; LMIS; Mass sparation; alternative FIB Sources; SIMS

  • Invited lecture (Conferences)
    ITG WORKSHOP: Vacuum Electronics 2012, 20.-21.08.2012, Bad Honnef, Germany

Publ.-Id: 17193

Modern Trends in FIB Development

Bischoff, L.

In the last decade focused ion beams (FIB) became an irrecoverable instrument in research and industry. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium liquid metal ion source (LMIS). But, modern trends in nanotechnology require more extended properties like variable ion species, non-contaminating milling at higher rates or higher lateral resolution in the field of ion microscopy.
In this presentation the application of alloy LMIS in a mass separated FIB system is introduced as well as new source concepts will be reviewed including high current gas sources for effective milling, ion trap sources for highly charged ions or SIMS applications and high resolution gas field ion sources for ion microscopy in the sub-nm range.
New trends and possibilities in FIB employment will be discussed.

Keywords: focused ion beams; liquid metal ion source; mass separated FIB system; new source concepts

  • Invited lecture (Conferences)
    7. FIB-Workshop Focused Ion Beams in Research, Science and Technology, 25.-27.06.2012, Dresden, Germany

Publ.-Id: 17192

Cyclotron resonance spectroscopy

Drachenko, O.; Helm, M.

We give an overview of the basic theory of cyclotron resonance, discuss some experimental aspects of cyclotron resonance spectroscopy in high, mostly pulsed magnetic fields, and finally discuss some recent cyclotron resonance experiments on various semiconductor materials.

Keywords: cyclotron resonance; high magnetic field; infrared

  • Book chapter
    Amalia Patane, Naci Balkan: Semiconductor Research, Berlin-Heidelberg: Springer-Verlag, 2012, 978-3-642-23350-0, 283-307

Publ.-Id: 17191

German SFR research and european sodium fast reactor project

Merk, B.

In the first part an overview on the fast reactor related work at HZDR is given with the focus on liquid metal technology for sodium cooled fast reactors, on a method to created enhanced feedback effects in sodium cooled fast reactors, and on the development of DYN3D for fast reactor applications. A short insight into the german contributions to the IAEA EBR-II benchmark and on the SFR work at KIT is presented. The second part consists of an overview on the safety related work packages of the 7. Framework Program project ESFR.

Keywords: enhanced feedback effects; liquid metal technologies; DYN3D for fast reactors; ESFR

  • Invited lecture (Conferences)
    International Workshop on Prevention and Mitigation of Severe Accidents in Sodium-cooled Fast Reactors, 12.-13.06.2012, Tsuruga, Japan

Publ.-Id: 17190

First Experience at ELBE with the new 1.3 GHz CW RF-System based on 10kW Solid State Amplifiers

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.

With the expansion of the radiation source ELBE, a centre for high power radiation sources is being built between 2009 and 2014 at the Helmholtz Zentrum Dresden Rossendorf. One part of this program is to increase the beam current of the ELBE LINAC. In January 2012 each of the 10kW CW klystrons used to operate the superconducting cavities of ELBE since 2001 had been replaced by a pair of 10kW solid state amplifiers.The talk gives an overview on the new RF-system of ELBE and its performance.

Keywords: ELBE RF; Solid State Power Amplifier 10 kW 1300MHz; 10kW SSPA 1300MHz; Superconducting Linac RF SSPA; SSPA 10 kW

  • Lecture (Conference)
    CWRF2012,The Seventh CW and High Average Power RF Workshop, 07.-11.05.2012, Port Jefferson, NY, USA

Publ.-Id: 17189

Verminderung des Verblockungspotentials von Sumpfansaugsieben durch Korrosionsprodukte nach Kühlmittelverluststörfällen

Hoffmann, W.; Kryk, H.

Bei einem postulierten Kühlmittelverluststörfall (Loss of Coolant Accident LOCA) eines Druckwasserreaktors (DWR) kann die thermische Isolation (Mineralwolle) durch das austretende Dampf-Kühlmittelgemisch zerstört werden und das freigesetzte Material durch Ablagerung auf den Sumpfansaugsieben einen Druckverlust verursachen, der die Notkühlung beeinträchtigt. Im weiteren Verlauf bewirkt das borsäurehaltige Primärkühlmittel eine Korrosion von feuerverzinktem Stahleinbauten im Containment (überwiegend Gitterroste), deren feste Produkte bei Anlagerung an den Mineralwolleablagerungen zu einen kritischen Anstieg des Differenzdrucks über den Sumpfansaugsieben bis hin zur Blockade und dem Ausfall der Notkühlung führen können.
In der Laborversuchsanlage (KorrVA) wurde die Korrosion verzinkter Materialproben unterschiedlicher Größe und Geometrie bei verschiedenen Anströmbedingungen des borsäurehaltigen Kühlmittels unter störfallähnlichen Bedingungen untersucht. Der in der Nachkühlphase durch die Fallhöhe des Leckstrahls verursachte Impact auf die Materialprobe wurde mittels Flachstrahldüse nachgebildet. Für diese generischen Untersuchungen wurden die Prozesse Faseablagerung auf einem Sieb von dem der Bildung und Einlagerung der Korrosionsprodukte getrennt, indem Kühlmittelstrom erst nach Ausbildung des Faserbetts auf die Korrosionsprobe gerichtet wurde.
Ausgehend von dem festgestellten Mechanismus einer strömungsinduzierten Korrosion des Zinks im Leckstrahl, die verbunden ist mit der Änderung wasserchemischer Parameter wie einem Anstieg des pH-Werts und der Bildung von gelöstem Zink, kann nach schneller Freilegung des Stahls im unmittelbaren Leckstrahlbereich als Korrosionsprodukt Rost entstehen und bis hin zu einer Verblockung des Faserbetts führen. Ausgehend von den Experimenten ergaben sich zwei grundsätzliche Möglichkeiten diese Gefahr zu vermindern, indem die Freilegung der blanken Stahloberfläche zeitlich zu verzögert oder möglichst verhindert wird. In zwei Versuchsreihen mit verzinkten Flachstahlproben wurde gezeigt, dass sowohl ein zusätzliches Angebot an im Kühlmedium getauchter Oberfläche als auch eine Anhebung des pH-Werts den Anstieg des Differenzdrucks und speziell die Ablagerung von Korrosionsprodukten des Eisens am Faserbett vermindern. Als bester Weg erwies sich die Anhebung des pH-Werts durch eine ausreichende Menge an Borax. Weil im Leckstrahl die Korrosionsbeanspruchung von Gitterrosten, bedingt durch deren Geometrie, sich von der einer Flachstahlprobe unterscheidet, wurden die Ergebnisse an reellen Proben verzinkter Gitterroste in der Versuchsanlage überprüft.

Keywords: LOCA; corrosion products; zinc; sump screen clogging

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2012, 22.-25.05.2012, Stuttgart, Deutschland

Publ.-Id: 17188

Physics of spectral and geometric singularities on the WKB thresholds of Standard and Helical MRI

Kirillov, O.; Stefani, F.

The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in accretion disks. What laws of differential rotation are susceptible to the destabilization by axial, azimuthal, or helical magnetic field? How the standard, helical and azimuthal versions of MRI are related to each other? The answer to these questions, which is vital for astrophysical and experimental applications, inevitably leads to the study of spectral and geometrical singularities on the instability threshold. These singularities provide a connection between seemingly discontinuous stability criteria and thus explain several paradoxes in the theory of MRI that were poorly understood since the 1950s. On the other hand, the singular geometry of the instability threshold is a powerful tool for parametric optimization that predicts, e.g., how close to the Kepler or solid body rotation profiles the instability threshold can be moved by varying the magnetic field configuration, velocity, and material properties of the liquid. Using the local WKB approximation we study the thresholds of standard and helical MRI for axi- and non-axisymmetric perturbations, their extrema and the links between them in the fully viscous and resistive setting. We discuss the connection between standard and helical MRI via a spectral exceptional point as well as the behavior of the helical MRI threshold both in the inductionless approximation when the magnetic Prandtl number (Pm) tends to zero and in case when it is small but finite. We demonstrate that the Liu limit for the Rossby number at the onset of HMRI slightly increases when Pm is not vanishing and find its ultimate value.

Keywords: Magnetorotational instability; WKB; azimuthal magnetic field; non-axisymmetric perturbations; Rossby number; Liu limit

  • Invited lecture (Conferences)
    Rotational dynamics for planetary and stellar applications, 29.-30.05.2012, Marseille, France

Publ.-Id: 17187

Exceptional and diabolical points in stability questions

Kirillov, O.

“I never satisfy myself until I can make a mechanical model of a thing” - guided by this motto of Lord Kelvin we would like to invite a reader to look at some modern concepts such as a non-Hermitian Hamiltonian, exceptional points, the geometric phase, and PT -symmetry, through the prism of the classical mechanics and stability theory. Mathematical and historical parallels discussed in the paper evidence that positions occupied by the non-Hermitian physics and non-conservative mechanics are closer to each other than one might expect.

Keywords: Non-Hermitian Hamiltonian; exceptional point; stability; non-conservative system; modulational instability

Publ.-Id: 17186

Experimental Studies On Sub-Cooled Boiling In A 3x3 Rod Bundle

Barthel, F.; Franz, R.; Krepper, E.; Hampel, U.

With the continuing interest in modeling of boiling heat transfer in complex geometries, such as rod bundles, dedicated experiments with advanced instrumentation are essential. Within a larger cooperative project on boiling flow and heat transfer in rod bundle geometries HZDR has developed and setup an experimental rod bundle facility where first experiments were conducted. The facility is a flow loop with a vertical rod bundle test section operated with a refrigerant coolant (RC318). The test section is 1078 mm long and equipped with an electrically heated 3 × 3 rod bundle. The heating pattern is constant along the height and heating is concentrated in the central rod with 98.5% of total heating power. Experiments can be conducted with variable liquid flow rates, heating power and sub-cooling. Single phase flow in the bundle was studied with DPIV measurements. For void fraction measurement we operate both a gamma ray densitometer as well as high-speed X-ray tomography. In this paper we present first experimental studies with both void measurement techniques.

Keywords: sub-cooled boiling; electron beam X-ray CT; rod bundle experiment

  • Lecture (Conference)
    CFD4NRS-4, 10.-12.09.2012, Daejeon, Korea
  • Contribution to proceedings
    CFD4NRS-4, 10.-12.09.2012, Daejeon, Korea
    Proceedings of the CFD for Nuclear Reactor Safety Applications (CFD4NRS-4) Workshop

Publ.-Id: 17185

First Experience at Elbe with the new 1.3 GHz CWRF-Power System equipped with 10 kW Solid State Amplifiers

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.

With the expansion of the radiation source ELBE, a centre for high power radiation sources is being built until 2014 at the Helmholtz Zentrum Dresden Rossendorf. One part of this program is to double the beam current of the ELBE LINAC. In January 2012 each of the 10 kW CW klystrons, used to operate the superconducting cavities of ELBE since 2001, had been replaced by a pair of 10 kW solid state amplifiers. The paper gives an overview on the activities around this project and the first experience with the new RF-system.

Keywords: ELBE RF; 1.3 GHz Solid State Power Amplifier; 10kW, 1.3 GHz SSPA; LDMOS PA 10kW at 1300MHz; ELBE RF Upgrade; BRUKER SSPA 10kW at 1300MHz

  • Open Access Logo Contribution to proceedings
    IPAC2012 - International Particle Accelerator Conference 2012, 20.-25.05.2012, New Orleans, USA
    Proceedings of IPAC2012, THPPC053: Joint Accelerator Conference Website (JACoW)., 978-3-95450-115-1, 3407

Publ.-Id: 17183

Modelling and esxperimental databases on poly-dispersed bubbly flows

Lucas, D.; Krepper, E.; Beyer, M.; Szalinski, L.

In dispersed flows particle sizes play an important role on the evolution of the flow along the flow path. Flow situations where the dispersed phase is liquid or gas as e.g. in dispersed oil-water or in bubbly flows can frequently be found. Coalescence and breakup become important as soon as the dispersed phase volume fraction exceeds several percent. In the result a spectrum of bubble or drop sizes occurs. The momentum exchange between the continuous and dispersed phase strongly depend on the bubble respective drop size, i.e. the resulting velocity fields differ for particles with different sizes. In following the discussion is focused on poly-dispersed bubbly flows, but the phenomena are similar for dispersed oil-water flows in which oil or water may be the dispersed phase, respectively.

The momentum transfer between bubbles and the continuous liquid phase is usually considered by so-called bubble forces. The most important ones are drag, virtual mass, lift, turbulent dispersion and wall forces. All of them depend on the bubble size and the lateral lift force even may change its sign depending on the bubble size. This was found experimentally for single bubbles rising in a laminar linear shear flow [1] and confirmed by several DNS simulations. Lucas & Tomiyama showed that the change of the sign of the lift force predicted by the correlation obtained by Tomiyama et al. even holds turbulent poly-dispersed for air-water and steam flows with high gas volume fraction. In case of air-water flows at ambient conditions the critical bubble diameter for the change is 5.8 mm. In consequence for modeling poly-dispersed flows in a liquid shear flow, e.g. in a vertical tube a spatial separation of large and small bubbles occur and local bubble size distributions differ clearly from tube cross section averaged ones. For this reason the evolution of poly-dispersed flows is characterized by a complex interaction between local and bubble size effects.
To consider the different behavior of particles with different sizes the so-called Inhomogeneous MUSIG-Model was developed jointly by HZDR and ANSYS. It is implemented in the CFX-code and allows the representation of the dispersed phase by a (small) number of velocity groups (phases) and larger number of bubbles size classes (MUSIG groups).

For the validation of the model concept and appropriate closure models experimental data in high resolution in space and time are required. Vertical pipe flow is a suitable configuration to investigate such flows. Detailed data were obtained in several experiments at HZDR using the wire-mesh sensor technique. A high quality data base was established from experiments in a 8 m long pipe with an inner diameter of 195.3 mm. Measurements were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for liquid and 0.0025 m/s to 3.2 m/s for air. Data were obtained for 12 different L/D in case of gas injection via 1 mm orifices in the pipe wall and for 6 different L/D in case of 4 mm orifices. From the raw data three-dimensional matrices of the instantaneous void fraction were obtained by calibration. These matrices were used for the calculation of time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size, interfacial area density and from a cross correlation between two sensors also the radial profiles of the gas velocity. All data are checked regarding their consistency. An estimation of errors was done by comparing the gas volume flow rates obtained from the measured radial profiles of void fraction and gas velocity with the setting values.

Within the same experimental setup also databases for condensing and evaporation steam-water flows were generated. They allow to validate the transferability of the models for different combinations of fluids. All these data bases are used in house and by different groups worldwide to develop, test and validate closure models for bubble forces and coalescence and break-up. At HZDR a standard model combining the closure models most suitable for wide range of flow conditions was developed. It will now be improved step by step.

Keywords: bubbly flow; model; CFD; poly-dispersed; pipe flow

  • Contribution to proceedings
    5th Latin American Workshop Applied to the Oil and Gas Industry, 10.-11.07.2012, Rio de Janeiro, Brasilien
  • Lecture (Conference)
    5th Latin American Workshop Applied to the Oil and Gas Industry, 10.-11.07.2012, Rio de Janeiro, Brasilien

Publ.-Id: 17182

Quantitative data from ultra-fast electron beam X-ray computer tomography measurements

Lucas, D.; Hoppe, D.; Banowski, M.; Hampel, U.; Barthel, F.; Sprewitz, U.; Beyer, M.

The ultra-fast electron beam X-ray computer tomography was developed during last years at HZDR and turned out to be a suitable measuring technique to get new insights into two-phase flow structures. The aim of new experiments done at a vertical pipe with an inner diameter of about 54 mm and a length of 4 m (usable for experiments) was to obtain quantitative data suitable for CFD-code development and validation. The pipe was built up using Titanium. This allows a wall thickness of only 1.6 mm which is enough for steam-water experi¬ments which will be carried out at a pressure up to 6.5 MPa. To generate the X-rays an electron beam is focused on a circular two-step target. This electron beam is deflected very fast and moves over the target resulting in a fast moving X-ray source. The X-rays pass through the object to be investigated and are registered by an arc of detectors. A tomographic reconstruction algorithm provides images of the attenuation distribution in the cross section of the object which is interpreted as density distribution. This allows the determination of the gas- liquid interfacial structure inside the considered object. Measurements were done with a measuring frequency of 2500 images/s and measuring time was 10 s. Air-water and steam-water flows were investigated for different combinations of gas and liquid flow rates and different distances from the gas injection.
The tomographic reconstruction provides 2 3D matrices of gray-scale values since the two-step target allows measurement in two planes with an axial distance of about 11 mm. Cross-correlation algorithms are applied to obtain the information on local gas velocities. Due to noise and artifacts a binarisation of the data seems to be necessary. Using a simple threshold method may cause small bubble to go missing. For this reason another method basing on gradients was developed. The presentations discusses this method and the present status of this new measuring technology in respect to quality and uncertainties of the quantitative data obtained as e.g. local void fraction and bubbles sizes.

Keywords: two-phase; measuring technique; X-ray; tomogrphy; pipe flow; bubble

  • Lecture (Conference)
    50th European Two-Phase Flows Group Meeting 2012, 16.-18.05.2012, Udine, Italy

Publ.-Id: 17181

Geology and architecture of the Norra Kärr Zr-REE deposit, Southern Sweden

Atanasova, P.; Leijd, M.; Gutzmer, J.

The Norra Kärr rare metal deposit in Southern Sweden represents one of the largest resources of rare earth elements (REE) in Europe. The deposit is hosted by a metamorphosed and deformed peralkaline nepheline syenite intrusion, which covers an area of 350m by 1100m. This intrusion is situated within a suite of Proterozoic gneisses and granites referred to as the Växjö Granite. The Växjö Granite belongs to the Trans-Scandinavian Igneous belt (1.85-1.65 Ga); the age of the peralkaline intrusion is rather poorly constrained at about 1545 ± 61 Ma (Blaxland 1977, recalculated by Welin 1980). Gross magmatic layering and orientation of early deformation fabrics suggest the intrusion was emplaced as a sill within the granitic basement (Rankin 2011). The granitoid rocks close to the contact to the peralkaline intrusion exhibit signs of fenitization (Adamson 1944, Eckermann 1968).

The Norra Kärr nepheline syenite and the surrounding basement have been deformed by weak to moderate N-S directed compression (Rankin 2011). This late-stage fold event has produced rhombic bulging and necking of the intrusion. The body is preserved within an overturned synformal hinge suggesting potential for other nepheline syenite bodies within the region. The intrusion has undergone not only modification of its shape by 3 phases of folding, but also possible transport of the body from its original emplacement locus by both N-S movement and E-vergent movement. In addition, the overprinting of the regional NNE-trending structural corridor by later episodes of extensional faulting also obscures the original geometry.

The Norra Kärr REE mineralization is notably enriched in the coveted heavy REE (HREE) and has been granted by the Geological Survey of Sweden a “national interest” status. The intrusion was first discovered by the Swedish Geological Survey in the earlier year of the 20th century and first described by A. E. Törnebohm in 1906. Since its discovery it has been explored – and on a small scale exploited - for nepheline, Zr and Hf. Since August 2009 Tasman Metals pursues an aggressive exploration program that focuses on rare metals mineralization, in particular HREE, in the intrusion. Currently, resources in the deposit are 41.6 Mt @ 0.57 % TREO with 51 % HREO/TREO and 1.7 % ZrO2 (indicated) and 16.5 Mt @ 0.64 % TREO with 49% HREO/TREO and 1.7 % Zr2O (inferred).

The lithotypes that comprise the intrusion are mostly identified by local names only; they share an agpaitic composition but their spatial and genetic relationship of the lithotypes remains unclear at present. The most common lithotype present is referred to as grennaite, best described as a fine to medium grained meta-syenite consisting of alkali feldspar, nepheline, aegirine, natrolite, eudialyte and catapleiite (Adamson 1944, Blaxland 1977). Less common lithotypes include lakarpite (arfvedsonite-albite nepheline meta-syenite), pulaskite (microcline-arfvedsonite-albite nepheline meta-syenite) and kaxtorpite (eckermannite-microcline-aegirine-pectolite nepheline meta-syenite). Exploration has revealed that much of the rare metal mineralization is associated with pegmatitic and migmatitic intervals within the complexly zoned intrusion, suggesting an important influence of (fluid-induced?) recrystallization and remobilization on the character and distribution of rare metal mineralization. Mineralogical studies have shown REE bearing minerals to include eudialyte group minerals and very minor mosandrite and cerite. The Zr-silicates catapleiite and eudialyte host the majority of the zirconium.

Keywords: REE; rare earth elements; zirconium; deposit; alkaline; rare metals

  • Poster
    Geochemistry of mineral deposits, 15.-20.07.2012, Andover, NH, United States

Publ.-Id: 17180

Numerical Simulation of Horizontal Two-Phase Flow Experiments Using an Morphology Detection Model

Höhne, T.; Darlianto, D.; Lucas, D.

Eine geschichtete Zweiphasenströmung liegt z.B. im Heißstrang eines Kernreaktors bei einem Kühlmittelverluststörfall vor. Ein Problem der Simulation von Zweiphasenströmungen mit CFD-Codes besteht darin, dass lokal unterschiedliche Morphologien der Phasengrenzen auftreten können. Die disperse und die kontinuierliche Form der Gas- und Fluidphase werden in der Modellierung jeweils als separate Phasen behandelt. Die disperse Phase liegt in Form von Wassertröpfchen oder Gasblasen vor. An der Phasengrenze zwischen kontinuierlichen Phasen (d.h. in der Simulation wird die Phasengrenze aufgelöst) müssen andere Schließungsmodelle, z.B. für den Impulsaustausch, angewendet werden als an einer Grenze zwischen kontinuierlicher und disperser Phase. Bisher war das nicht möglich, da die Information über die jeweils vorliegende Strömungsmorpholgie im CFD-Code nicht vorlag. Deshalb wurde in enger Zusammenarbeit mit dem Codeentwickler ANSYS ein Modell zur besseren Beschreibung der wirkenden physikalischen Gesetze bei Zweiphasenströmungen in Abhängigkeit der Strömungsmorphologie (AIAD= Algebraic Interfacial Area Density Modell) entwickelt, erprobt und in den CFD-Code CFX implementiert. Validierungsrechnungen für das AIAD-Modell wurden für Experimente am Heißstrangmodell an TOPFLOW bzw. dem TOPFLOW_PTS Versuchsstand sowie für Schwallströmungen und dem stationären hydraulischen Sprung im horizontalen Strömungskanal HAWAC durchgeführt und zeigten durchweg gute Ergebnisse. Für die Zukunft ist eine verbesserte Beschreibung der Turbulenz an der Phasengrenzfläche geplant.


  • Invited lecture (Conferences)
    ANSYS Conference & dem 30. CADFEM Users´ Meeting, 24.-26.10.2012, Kassel, Deutschland
  • Contribution to proceedings
    ANSYS Conference & dem 30. CADFEM Users´ Meeting, 24.-26.10.2012, Kassel, Deutschland

Publ.-Id: 17179

Development and validation of a morphology detection algorithm (AIAD) for horizontal two phase flows

Höhne, T.

In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi Pressurized Water Reactor (PWR) with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler-Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a SST turbulence model for each phase.

In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. To validate the model and to study scaling effects CFD simulations of the CCFL phenomenon in a full scale PWR hot leg of the UPTF test facility were performed. Also these results indicated a good agreement between the calculation and experimental data. The final goal is to provide an easy usable AIAD framework for all ANSYS CFX users, with the possibility of the implementation of their own correlations.


  • Lecture (Conference)
    5th Latin American CFD Workshop Applied to the Oil and Gas Industry, 10.-11.07.2012, Rio de Janeiro, Brasilien
  • Contribution to proceedings
    5th Latin American CFD Workshop Applied to the Oil and Gas Industry, 10.-11.07.2012, Rio de Janeiro, Brasilien
  • Open Access Logo Petrobras Technical Bulletin (2016)

Publ.-Id: 17178

High energy CPA-free picosecond Yb:YAG amplifier

Loeser, M.; Siebold, M.; Roeser, F.; Schramm, U.

We report on a CPA free picosecond MOPA system consisting of a fs Yb:KGW oscillator and 2 subsequent amplifiers using Yb:YAG active mirrors. A maximum pulse energy of 35mJ at 10Hz repetition rate was achieved.

Keywords: Lasers, diode-pumped; Lasers Ytterbium; Laser amplifiers

  • Poster
    Advanced Solid-State Photonics (ASSP), 29.01.-03.02.2012, San Diego, USA
  • Lecture (others)
    Disk Laser Workshop, 14.-15.05.2012, Stuttgart, Germany

Publ.-Id: 17177

High-energy laser amplifiers using ultra-broad emitting Yb-doped materials

Siebold, M.; Loeser, M.; Roeser, F.; Uecker, R.; Koerner, J.; Hein, J.; Hornung, M.; Keppler, S.; Kaluza, M.; Schramm, U.

High-energy laser amplifiers using Yb-doped gain media often show reduced efficiencies especially when operating at ultra-short pulses. We summarize techniques to improve storage and extraction efficiencies of Yb-based laser amplifiers.

Keywords: Lasers diode-pumped; Lasers Ytterbium; Laser amplifiers

  • Invited lecture (Conferences)
    Advances in Optical Materials (AIOM), 01.-03.02.2012, San Diego, USA

Publ.-Id: 17176

New Aspects in Modelling Counter-Current Flow Phenomena Using a Morphology Detection Algorithm

Höhne, T.

Counter current flow was successfully simulated in the Hot Leg Channel.
A new surface drag model inside the morphology detection algorithm AIAD was introduced, it further improves the physics.
The qualitative structure of the flow morphology is similar to the one observed in the experiment (slug flow regime).
The calculated quantitative CCFL characteristics & water levels inside the hot leg channel were in an agreement with the experiments.
CFD calculations of 1:1 scaled UPTF CCFL experiments show very promizing results.
The effect of turbulence parameters near the free surface has to be studied in future.
Validation of the AIAD model is going on – Official release of the AIAD framework in CFX is on the way.

Keywords: CCFL AIAD CFX Hot Leg Channel

  • Lecture (Conference)
    Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 13.-14.06.2012, Dresden, Deutschland
  • Contribution to proceedings
    Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 13.-14.06.2012, Dresden, Deutschland

Publ.-Id: 17175

Development and validation of a morphology detection algorithm (AIAD)

Höhne, T.

Counter current flow was successfully simulated in the Hot Leg Channel.
A new surface drag model inside the morphology detection algorithm AIAD was introduced, it further improves the physics.
The qualitative structure of the flow morphology is similar to the one observed in the experiment (slug flow regime).
The calculated quantitative CCFL characteristics & water levels inside the hot leg channel were in an agreement with the experiments.
CFD calculations of 1:1 scaled UPTF CCFL experiments show very promizing results .
The effect of turbulence parameters near the free surface has to be studied in future.
Validation of the AIAD model is going on – Official release of the AIAD framework in CFX is on the way.

Keywords: UPTF CCFL CFD Hot Leg Channel AIAD CFX

  • Lecture (Conference)
    AER Working Group C and G, 31.05.-01.06.2012, Paks, Ungarn

Publ.-Id: 17174

Ultrasonic flow measurements in a model of a Czochralski puller

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

An experimental study of the buoyancy-induced flow in a model of a Czochralski crystal growth system was conducted. Ultrasonic velocimetry was used to measure fluid velocities. To have similar thermal boundary conditions as in an industrial growth facility, a double-walled glass crucible flown through by a heating fluid was chosen to hold the fluid. Similarity of the heat transfer conditions was achieved by selecting a liquid metal as the fluid under investigation, which was the ternary alloy GaInSn having a Prandtl number of 0.021. Because of the double-walled crucible, measurements through the container wall are difficult if ever possible. Since the availability of relatively short ultrasonic transducers it is practicable to have the sensor immersed into the fluid. Measurements of the radial velocity component shortly below the melt surface across the entire diameter of the crucible at various azimuthal angles reveal the complex flow structure of natural convection in a Czochralski crucible. As it is not to be expected to grow high quality mono-crystalline crystals from such a non-axisymmetric flow, rotating magnetic fields (RMF) are often proposed to render the flow more axisymmetric. This paper also addresses the question what happens to the buoyancy-driven flow when such an RMF is applied.

Keywords: Czochralski crystal growth; Rayleigh-Benard convection; ultrasonic flow measurement; electromagnetic stirring

Publ.-Id: 17173

Numerical simulation and experimental verification of the DC magnetic field effect on the fluid flow in a continuous casting mould

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

This paper presents numerical and experimental investigations with respect to the fluid flow in the continuous casting process under the influence of an external DC magnetic field. According to the concept of the electromagnetic brake (EMBR) the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied up to Hartmann numbers of about 400. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements carried out in a small-scale mockup using the eutectic alloy GaInSn. The comparison between our numerical calculations and the experimental results displays a very well agreement. The magnetic field causes a deflection of the jet and decreases its exit angle from the nozzle ports. An elongation of the jet cross section can be observed along the magnetic field direction. A significant return flow occurs in the adjacent regions of the jet. Specific vortices are formed with axes being aligned with the magnetic field direction, which is typical for quasi-two-dimensional magneto-hydrodynamic flows. Likewise, the results did not confirm the expectation that the use of the DC magnetic field induces a general reduction of the velocity fluctuations all over the mould region. Actually, under certain conditions the application of a horizontal magnetic field may cause intense, non-steady and non-isotropic flow structures. Another important result of our study is the feature that the electrical boundary conditions have a serious influence on the mould flow just as it is exposed to an external magnetic field.

Keywords: continuous casting; liquid metal model; electromagnetic brake; MHD-turbulence; RANS-SST turbulence model

  • Lecture (Conference)
    5th International Congress on the Science and Technology of Steelmaking 2012, 01.-03.10.2012, Dresden, Deutschland
  • Contribution to proceedings
    5th International Congress on the Science and Technology of Steelmaking 2012, 01.-03.10.2012, Dresden, Deutschland

Publ.-Id: 17172

Flow following sensor particles – validation and macro-mixing analysis in a stirred fermentation vessel with a highly viscous substrate

Reinecke, S.; Kryk, H.; Hampel, U.; Deutschmann, A.; Jobst, K.; Friedrich, E.

A group of flow following sensor particles was validated under real flow conditions in a highly viscous substrate in a 1000 L model fermenter vessel, equipped with a pitched blade impeller, which was operated at two different axial positions in an intermittent mixing regime. The neutrally buoyant sensor particles track basic hydrodynamic and process parameters, namely hydrostatic pressure (giving the axial position), temperature and acceleration. The sensors are connected to a measurement electronics, which is enclosed in a robust capsule that can resist the harsh conditions in an industrial mixing process. The results show that the sensor particles still reflect the flow conditions in the vessel qualitatively. Moreover, the sensor particle data allow estimation of macro-mixing parameters, such as circulation time distributions and average circulation times.

Keywords: Flow Follower; Sensor Particle; Autonomous Sensor; Macro-Mixing; Circulation Time; Parameter Tracking; Bio-substrate; Biogas; Bioreactor

Publ.-Id: 17171

Intelligente Sensorpartikel zur Prozessdiagnose in Mischbehältern

Reinecke, S.; Kryk, H.; Hampel, U.

Der Betrieb großer Anlagen und Behälter wird von dem Problem begleitet, dass darin ablaufende verfahrens- und energietechnische Prozesse aufgrund erschwerter oder unmöglicher messtechnischer Zugänglichkeit nicht genügend beschrieben und überwacht werden können. Die Installation von lokal installierten Sonden mit Kabelverbindungen ist in großen Behältern, wie Chemie- und Bioreaktoren, Fermentern oder Schüttgutbehältern, oft nicht realisierbar oder unerwünscht. Zudem sind bildgebende Messverfahren, wie Kameras oder Tomografiesysteme, auf Grund der trüben Medien und der Behälterabmessungen von mehreren Metern meist nicht anwendbar.
Der Einsatz intelligenter Strömungsfolger und autonomer Sensortechnologien ermöglicht die messtechnische Erfassung verteilter Parameter und gewinnt deshalb zunehmend an Bedeutung für Anwendungen in der Prozessindustrie [1].
Aus diesem Grund wurde am HZDR das Konzept autonomer Sensorpartikel entwickelt, welche als auftriebsneutrale Strömungsfolger in großen Behältern, wie Biogasfermentern, eingesetzt werden können und dabei kontinuierlich Prozessparameter erfassen, speichern und diese nach Rückgewinnung der Partikel aus dem Prozess einem computergestützten Analysesystem zur Verfügung stellen [2].

  • Poster
    15. Köthener Rührer-Kolloquium, 14.06.2012, Köthen, Deutschland

Publ.-Id: 17170

Autonome Sensorik

Reinecke, S.; Hampel, U.

Für eine effiziente Steuerung von Prozessen in verfahrenstechnischen Anlagen ist eine detaillierte räumliche und zeitliche Erfassung von Prozessparametern erforderlich, die jedoch mit herkömmlichen Messverfahren nicht realisiert werden kann. Als vollkommen neuen Lösungsansatz dazu wurde am HZDR ein autonomes Sensorpartikel entwickelt, welches als Strömungsfolger in großen Behältern, wie Biogasfermentern, eingesetzt werden könnte und somit kontinuierlich Prozessparameter erfasst, speichert und diese nach Wiedergewinnung des Partikels am Behälterauslass einem Analysesystem zur Verfügung stellt.

  • Industrielle Automation 1(2012)3, 43-43

Publ.-Id: 17169

Autonome Sensorik für große Prozessbehälter (AUTOSENS)

Reinecke, S.; Kryk, H.; Tschofen, M.

Für eine effiziente Steuerung von Prozessen in verfahrenstechnischen Anlagen ist eine detaillierte räumliche und zeitliche Erfassung von Prozessparametern erforderlich, die jedoch mit herkömmlichen Messverfahren nicht realisiert werden kann. Als vollkommen neuen Lösungsansatz dazu wurde am HZDR ein autonomes Sensorpartikel entwickelt, welches als Strömungsfolger in großen Behältern, wie Biogasfermentern, eingesetzt werden könnte und somit kontinuierlich Prozessparameter erfasst, speichert und diese nach Wiedergewinnung des Partikels am Behälterauslass einem Analysesystem zur Verfügung stellt.

Publ.-Id: 17168

Grain refinement by electromagnetic stirring and the impact on the mechanical properties of alsi-alloys

Räbiger, D.; Krößig, C.; Eckert, S.; Gerbeth, G.

This present study examines the directional solidification of AlSi7 alloys from a water cooled copper chill. A rotating magnetic field was used for melt agitation. Different magnetic field configurations were considered to demonstrate the impact of diverse flow conditions on the resulting microstructure and the mechanical properties. The solidified structure was evaluated in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were performed. Our results reveal the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields demonstrated their capability to homogenize both the grain size distribution and to improve the mechanical properties.

Keywords: rotating magnetic field; solidification; grain refinement; mechanical properties; AlSi alloys

  • Journal of Iron and Steel Research International 19(2012)Suppl. 1-1, 341-344
  • Poster
    7th International Conference on Electromagnetic Processing of Materials, 22.-26.10.2012, Beijing, China

Publ.-Id: 17167

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