Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33403 Publications

The Exchange bias in oxygen-implanted Co/Au thin film heterostructures

Perzanowski, M.; Gregor-Pawłowski, J.; Zarzycki, A.; Böttger, R.; Hübner, R.; Potzger, K.; Marszałek, M.
Magnetic systems exhibiting exchange bias effect are being considered as functional parts of modern data storage devices. A model system for the investigation of this effect is an antiferromagnetic-ferromagnetic CoO/Co interface. In this paper we present the studies of magnetic properties of Co-CoO/Au multilayers where the cobalt oxide was formed by oxygen ion beam implantation. Special emphasis is given to the role of the oxygen concentration profile in the magnetic properties. By properly designed the implantation conditions (ion beam energy and fluence) it is possible to fabricate a system revealing controlled stepwise magnetization reversal process. This underlines the great potential of this approach to tailor the magnetic properties through modification of implantation profiles.

This work was supported by DAAD Service with contract No. PPP-PL 57214850 „Magnetic anisotropies in cobalt heterostructures induced by oxidation”.
Keywords: Ion Implantation Magnetic multilayers
  • Poster
    The European Conference Physics of Magnetism 2017, PM’17, 26.-30.06.2017, Poznan, Polen

Permalink: https://www.hzdr.de/publications/Publ-26607
Publ.-Id: 26607


Metallurgy key enabler of the Circular Economy

Reuter, M. A.
Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated.
Keywords: Circular Economy, Circular Economy Engineering, Fairphone, Recycling
  • Lecture (others)
    Workshop, 30.11.2017, Madrid, Spanien

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Permalink: https://www.hzdr.de/publications/Publ-26606
Publ.-Id: 26606


The Akademii Nauk ice core and solar activity

Fritzsche, D.; von Albedyll, L.; Merchel, S.; Opel, T.; Rugel, G.; Scharf, A.
Ice cores are well-established archives for paleo-environmental studies, but this requires a reliable ice core chronology. The concentration of cosmogenic radionuclides in ice cores reflects the solar activity in the past and, thus, can be used as a dating tool for ice cores. Accelerator mass spectrometry (AMS) allows the determination of nuclides in high resolution. Here, we present results of a 10Be study in an ice core from Akademii Nauk (Severnaya Zemlya, Russian Arctic). AMS analyses of more than 500 samples were carried out using the 6 MV accelerator facility of the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf. For the time period 400 to 2000 CE the temporal variations of 10Be reflect the centennial variations of solar activity known from similar studies of Greenlandic ice cores and from 14C production reconstructions. The 10Be peak of 775 CE, today understood as result of the strongest known solar particle storm, was found by high-resolution core analysis. This peak is used as a tie point (additionally to volcanic reference horizons) for the development of the depth-age relationship of the Akademii Nauk ice core. Indications of the so called “Carrington Event” of 1859 CE, 20 to 30 times weaker than 775 CE, could also be detected in the core.
Keywords: AMS, climate, ice core
  • Lecture (Conference)
    27th International Polar Conference, 25.-29.03.2018, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26603
Publ.-Id: 26603


Search for Recent 60Fe Deposition in Antarctic Snow via AMS

Koll, D.; Busser, C.; Faestermann, T.; Fimiani, L.; Gomez-Guzman, J. M.; Kinast, A.; Korschinek, G.; Krieg, D.; Lebert, M.; Merchel, S.; Sterba, J.; Welch, J.; Kipfstuhl, S.
60Fe with a half-life of 2.6 Myr [1] is produced in stellar Environments and ejected into space mainly by core-collapse supernovae. Due to its long half-life, traces of 60Fe were deposited and incorporated on Earth and on the Moon and have been detected there [2,3,4,5].
Here, a new possible reservoir will be presented: Antarctic snow.
This time, in contrast to former investigations, any signal detected would be recent material which might origin from the local interstellar cloud. 500 kg of Antarctic snow were chemically processed and are going to be analyzed by AMS in Munich at the 14 MV tandem. First results for 60Fe measurements will be presented as well as chemical extraction methods applied.
[1] Rugel et. al. ; Phys. Rev. Lett. 103, 072502 (2009)
[2] Knie et. al. ; Phys. Rev. Lett. 93, 171103 (2004)
[3] Ludwig et. al. ; PNAS 113 (33), 9232-9237 (2016)
[4] Wallner et. al. ; Nature 532, 69-72 (2016)
[5] Fimiani et. al. ; Phys. Rev. Lett. 116, 151104 (2016)
Keywords: supernovae, AMS
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26602
Publ.-Id: 26602


The Flux of Interplanetary Dust on Earth: Status

Krieg, D.; Busser, C.; Faestermann, T.; Fimiani, L.; Gomez-Guzman, J. M.; Kinast, A.; Koll, D.; Korschinek, G.; Lebert, M.; Merchel, S.; Welch, J.; Kipfstuhl, S.
Earth’s accumulation rate of Interplanetary Dust Particles (IDPs) is a matter of discussion, ranging from 5 (middle atmosphere measurements) up to 300 (space borne dust detection) tons per day. A new approach for a more precise measurement of this accumulation rate is made by extracting manganese from 500 kg of Antarctic snow collected near the Kohnen station, and measuring the concentration of 53Mn with AMS at the MLL in Munich.
This 53Mn (t1/2 = 3.7 Ma) is mostly produced by nuclear reactions of cosmic rays on the iron of the IDPs. Relating the amount of 53Mn to the precipitation rate, a meridional transport and deposition model based on 10Be measurements, and to a chemical model of meteoritic ablation will help to reduce the uncertainty of the IDP input on Earth. The method of our measurement and the status of this study will be discussed.
Keywords: IDP, AMS
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26601
Publ.-Id: 26601


Phase Formation and Selectivity on Cr (co-)Doped TiOU+2082 through Interface Engineering and Post-Deposition Flash Lamp Annealing

Gago, R.; Prucnal, S.; Palomares, J.; Jiménez, I.; Hübner, R.
Many applications of TiO2 partially rely on its good performance as solvent for numerous impurities [1]. In particular, metal (cation) dopants have been used to functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. One of the most interesting properties of TiO2 relies on its photoactivity, exploited in many applications from catalysis, hydrogen production, pigments or solar cells [2]. However, TiO2 is mostly active in the ultraviolet (UV) region of the solar spectrum (band-gap > 3 eV) and there is a great interest in band-gap narrowing of TiO2 to achieve visible-light (VISL) response [2]. Metal doping do so and increases VISL absorption significantly but, unfortunately, introduces structural distortions in the host matrix that result in carrier recombination centers [5]. Apart from the structural quality, another relevant consideration on the production of doped TiO2 relies on the particular oxide matrix phase (anatase/rutile) [6]. For example, anatase has superior photoactivity than rutile although phase mixtures with high anatase content may present even higher photoactivity [7]. Therefore, special attention should also be devoted to the phase selectivity. Moreover, (heavily) doped TiO2 may display a completely different electronic structure that the pristine oxide material.
The aim of this study is to promote customized phase formation in Cr (co-)doped TiO2 films produced by magnetron co-sputtering. Special attention is paid to the structural arrangements around host and dopant sites from the X-ray absorption near-edge structure. We report the conditions driving to single- or mixed-phase formation with the novelty of exploring film architectures based on interface engineering and/or post-deposition flash-lamp annealing (FLA) [8]. The latter is a non-contact rapid thermal processing extensively used in Microelectronics but yet to be explored in the present context. Hence, FLA can be attractive for many industrial applications dealing with the synthesis of band-gap engineered TiO2-based materials.
REFERENCES:
[1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Furubayashi et al., Appl. Phys. Lett. 86, 252101 (2005); [5] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [6] Yang, et al., Phys. Rev. B 76, 195201 (2007); [7] Scanlon et al., Nat. Mater. 12, 798 (2013); [8] D. Reichel et al., Phys. Status Solidi C 9, 2045 (2012)
  • Invited lecture (Conferences)
    2017 MRS Fall Meeting & Exhibit, 26.11.-01.12.2017, Boston, MA, USA

Permalink: https://www.hzdr.de/publications/Publ-26600
Publ.-Id: 26600


Energy-filtered TEM studies on silicon nanoparticles acting as quantum dots in single electron transistors

Wolf, D.; Xu, X.; Prüfer, T.; Hlawacek, G.; Bischoff, L.; Möller, W.; Engelmann, H.-J.; Facsko, S.; von Borany, J.; Heinig, K.-H.; Hübner, R.
The miniaturization of computing devices and the introduction of the internet of things generate an increasing demand for the development of low-power devices. Single electron transistors (SETs) are ideally suited for this demand, because they are promising very low power dissipation devices. For roomtemperature operation of an SET it is necessary to create a single quantum dot (QD) with a diameter below 5 nm exactly positioned between source and drain at a tunnel distance of only a few nanometers. Within the IONS4SET project [1], we aim to achieve this goal by ion irradiation induced Si-SiO2 mixing and subsequent thermally activated self-assembly of single Si nanocrystals surrounded by a thin SiO2 layer. This process is illustrated in Fig. 1 by means of simulations results.
Here, we present energy-filtered (EF)TEM studies in order to monitor the influence of process parameters, such as stack geometry, ion fluence for irradiation, annealing temperature and annealing time, on the self-assembly of Si QDs. Fig. 2 shows representative EFTEM micrographs of a Si-SiO2-Si layer stack imaged using different electron energy-loss (EEL) windows. The Si plasmon-loss filtered images yield thereby the best signal-to-noise for detection of Si nanodots, because the Si plasmon peak is the most intense peak with a relatively small FWHM of 4 eV in the EEL spectrum.
Moreover, since the obtained (raw) EFTEM images provide only qualitative information about the Si concentration in the oxide layer, they cannot give a clear answer if for example the observed contrast corresponds to one or more Si nanodots (NDs) in projection. Therefore, EFTEM images are quantified further by converting them into so-called thickness over mean free path length (MFPL) t/λSi maps, in which λSi is the MFPL corresponding to the chosen energy range. The experimental t/λSi maps are then compared with simulated t/λSi maps of a single Si ND. Fig. 3 depicts that our approach enables us not only to detect single Si nanodots (Fig. 3c,e) but also to count them if they are arranged in projection direction of the electron beam (Fig. 3d,f). For these experiments, the layer stacks were irradiated with Ne+ ions within an Orion NanoFab (Zeiss). This allows controlled line or point irradiation and ensures Si QD formation within a confined region. In a next step, confined regions will be established by fabricated nanopillars that enhances reproducibility as the volume relevant for the self-assembly of the nanocluster will be better defined.
[1] We thank for financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).
  • Lecture (Conference)
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 12-14

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Permalink: https://www.hzdr.de/publications/Publ-26599
Publ.-Id: 26599


Insights into the 3D electric potential structure of III-V semiconductor core-multishell nanowires through combined STEM and holographic tomography

Wolf, D.; Hübner, R.; Sturm, S.; Lubk, A.
Off-axis electron holographic tomography (EHT) has been successfully applied to reveal the 3D structure of III-V semiconductor core-shell nanowires (NWs) [1,2]. The technique probes the phase shift of an electron wave transmitted through such a NW that is proportional to the NWs projected electrostatic potential. Thus, a tilt series of phase images (projected potentials) can be used as input to compute a 3D tomogram of the electrostatic potential by tomographic reconstruction algorithms. Typically, the recovered 3D potential is dominated by the mean inner potential (MIP), which is related to the materials composition. Consequently, space charge potentials determining for example the electric properties, e.g., at interfaces or pn-junctions in semiconductors [2] may be superimposed by MIP variations caused by compositional changes within the heterostructures.
Here, we show on the example of a GaAs/AlGaAs core-multishell NW, how the space charge potentials can be uncovered from materials contrast (MIP) by determining the latter independently: To this end, high-angle annular dark-field (HAADF) STEM tomography was applied in addition to EHT on the same NW. STEM tomograms provide solely materials contrast that depends exponentially on the atomic number. Fig. 1 compares both methods in terms of the relation between reconstructed signal and projected property, exemplary for three different tomogram regions identified as pure Au, GaAs and AlGaAs: In case of EHT between the reconstructed potential and the MIP, and in case of STEM tomography between the reconstructed intensity and the atomic number. The latter relation enables converting the STEM tomogram in units of (mean) atomic numbers.
Tilt series were acquired from -70° to +71° with 3° tilt steps in holography mode, and from -68° to +68° with 2° tilt steps in STEM mode. Since phase images of axially scattered electrons are used for EHT, it suffers much more from diffraction contrast than STEM tomography (high-angle scattering). Consequently, only 39 projections could be used for tomographic reconstruction in the case of EHT compared to 68 in the case of STEM tomography. For this reason, resolution and contrast in the 3D potential are slightly lower than in the STEM tomogram, which can be seen on the cross-section of the NW in Fig. 2. Nevertheless, the core-shell structure, the ca. (5-10) nm thick GaAs shell acting as quantum well tube (QWT), and unintended Al segregations are clearly resolved in both cases. Last but not least, longitudinal slices (Fig.3) exhibit clear differences of both tomograms that strongly suggest additional local space-charge related potentials to be investigated in greater detail in a next step.
References:
[1] A Lubk, D Wolf, P Prete, N Lovergine, T Niermann, S Sturm and H Lichte, Phys. Rev. B 90 (2014) p. 125404.
[2] D Wolf, A Lubk, P Prete, N Lovergine and H Lichte, J. Phys. D: Appl. Phys. 49 (2016) p. 364004
[3] We thank N Lovergine of University of Salento, Lecce for provision of the samples.
[4] We thank the group of Michael Lehmann at TU Berlin for access to the TEM FEI Titan 80-300 Berlin Holography Special.
[5] DW acknowledges financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET). AL has received funding from the European Research Council (ERC) under the European Union"s Horizon 2020 research and innovation programme (grant agreement No 715620).
  • Poster
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 753-755

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Permalink: https://www.hzdr.de/publications/Publ-26598
Publ.-Id: 26598


Subsurface Engineering of Silicon for 3D Devices

Tokel, O.; Turnali, A.; Makey, G.; Elahi, P.; Ilday, S.; Colakoglu, T.; Yavuz, O.; Hübner, R.; Zolfaghari, M.; Pavlov, I.; Bek, A.; Turan, R.; Ilday, O.
Recently we have demonstrated a new 3D-laser-fabrication method which enabled, for the first time, creating highly-controlled subsurface structural modifications (structural imperfections, or defects) buried deep inside Silicon (Si) wafers [1]. Characterizing the material properties of these subsurface Si structures are very critical towards enabling new optical and micro-mechanical applications inside chips [2,3]. Here, we present optical, chemical and microscopic analysis of these buried structures. Specifically, Transmission Electron Microscopy (TEM) studies, Optical Birefringence Analysis and Selective Chemical Etching analysis of the modifications will be presented. Infrared Transmission Microscopy will be shown to be applicable for subsurface imaging, providing a diagnostic tool without damaging the samples.

Material properties of the disruptions in the crystal lattice are then exploited for fabricating various micro-devices. For instance, oxidation-reduction chemistry on laser-induced modifications enables the creation of highly-controllable, uniform and large-area micropillar arrays for solar cell applications, embedded microfludic channels for chip cooling and thru-Si vias for electrical interconnects in Si. These elements, which are challenging to form with conventional methods, can find use in various MEMS and electronics applications. The optical properties (refractive index change) of the structures are used to fabricate functional components such as lenses and gratings buried in chips. Further, the birefringence effect induced in Si may lead to holograms and other photonic applications, such as creating wave plates and polarizers. These functional optical and MEMS elements created inside Si, may find use in imaging and sensing in the near- and mid-infrared wavelength range, as well as in micro-devices towards micro-surgical tools, micro-motors, and micro-resonators. Thus, these capabilities are leading to a new fabrication approach in Si, which is fully CMOS compatible, rapid and mechanically robust, and builds on the optical,electrical and chemical properties of the modified volumes in Si.

[1] Tokel et. al., arxiv.org/abs/1409.2827
[2] Tokel et. al, Direct Laser Writing of Volume Fresnel Zone Plates in Silicon., CLEO/Europe - EQEC, Munich, Germany, 2015.
[3] Tokel et. al., 3D Functional Elements Deep Inside Silicon with Nonlinear Laser Lithography, APS March Meeting, Baltimore, USA, 2016.
  • Poster
    2017 MRS Spring Meeting & Exhibit, 17.-21.04.2017, Phoenix, AZ, USA

Permalink: https://www.hzdr.de/publications/Publ-26597
Publ.-Id: 26597


Application of Ion Beams to Fabricate and Modify Properties of Dilute Ferromagnetic Semiconductors

Yuan, Y.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.
Dilute ferromagnetic semiconductors (DFS) have been investigated for more than two decades due to their potentials for spintronics. Mn doped III-V semiconductors have been regarded as the prototype of the type. In this contribution, we will show how ion beams can be utilized in fabricating and modifying DFS. First, ion implantation followed by pulsed laser melting (II-PLM) provides an alternative to low-temperature molecular beam epitaxy (LTMBE) to prepare diverse DFS. The prepared DFSs exhibit pronounced magnetic anisotropy, large X-ray magnetic circular dichroism, anomalous Hall effect and magnetoresistance [1-9]. Going beyond LTMBE, II-PLM is successful to bring two new members, GaMnP and InMnP, into the family of III-Mn-V. Both GaMnP and InMnP show clear signatures of ferromagnetism and an insulating behavior. Second, helium ions can be used to precisely compensate the holes while keeping the Mn concentration constant [10-12].
For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC over a wide temperature range with carrier compensation while the conduction is changed from metallic to insulating. We can tune the uniaxial magnetic easy axis of (Ga,Mn)(As,P) from out-of-plane to in-plane with an isotropic-like intermediate state. These materials synthesized or modified by ion beams provide an alternative avenue to understand how carrier-mediated ferromagnetism is influenced by localization.
  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-26596
Publ.-Id: 26596


Modelling of turbulence modulation in bubbly flows with the aid of DNS

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
Modelling of turbulence modulation in bubbly flows with the aid of DNS data
  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-26595
Publ.-Id: 26595


new model for bubble-induced turbulence based on direct numerical simulation data

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
Three main issues are addressed in the present study. First, an appropriate time scale is selected with the aid of the energy spectra determined on the basis of the DNS data. Then, links between the unclosed terms in the transport equations of the turbulence quantities and the DNS data for small bubbles are established. Third, a suitably chosen iterative procedure employing the full Reynolds-averaged model provides suitable coefficients for the closure of the terms resulting from BIT while largely removing the influence of others. Here, using DNS data with iterations to obtain term-by-term match (Figure 1b) in the model equations avoids pitfalls of ad hoc models targeting the TKE only. At the same time these results validate the closure, exhibiting very good agreement with the DNS and better performance than the standard closures. Beyond the resulting model itself the study also furnishes a systematic procedure which is of general use. The model is now ready for use and can be employed in practical Euler-Euler simulations.
  • Lecture (Conference)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, 26.-29.06.2017, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-26594
Publ.-Id: 26594


DNS-based RANS closure for bubble-induced turbulence

Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
DNS-based RANS closure for bubble-induced turbulence
Keywords: DNS, RANS, bubble-induced turbulence
  • Lecture (Conference)
    ProcessNet Jahrestreffen Dresden, 14.-17.03.2017, Dresden, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-26593
Publ.-Id: 26593


A contribution to turbulence modelling in bubbly flows

Ma, T.
Modelling turbulence in bubbly flows that arise in the engineering and environment is of great challenges for multiphase Computational Fluid Dynamics. In the present book various turbulence modelling approaches are investigated in bubble columns and bubbly channel flows. The considered approaches contain Scale Resolving Simulations and the traditional Reynolds-averaged Navier-Stokes closure. The focus is set on the representation of the so-called bubble-induced turbulence in the modelling framework. A major chapter addresses a complete route to construct such a model embedded in Euler-Euler approach with the aid of Direct Numerical Simulation data. This procedure is employed to propose an improved model for bubble-induced turbulence.
Keywords: Scale Resolving Simulation, Direct Numerical Simulation data, bubble-induced turbulence
  • Book (Authorship)
    Dresden: TUDpress, 2017

Permalink: https://www.hzdr.de/publications/Publ-26592
Publ.-Id: 26592


Simulation of Reconfigurable Field-effect Transistors: Impact of the NiSi2-Si Interfaces, Strain, and Crystal Orientation

Fuchs, F.; Schuster, J.; Gemming, S.
Reconfigurable transistors (RFETs) can be switched between electron and hole current by changing the polarity of the gate potential. The device performance of such a transistor is strongly dominated by the contact physics.
In this work, the electron transport across the NiSi2-Si interface is studied using the NEGF formalism and density functional theory. A new model is presented which relates the electron transport through the interface to the transfer characteristic of an RFET. The model is compared to experimental data showing good agreement.
Based on the model, the influence of strain and the choice of the crystal orientation is discussed. It is demonstrated that best symmetry between electron and hole current is achieved for the <110> orientation. Furthermore, this symmetry can be tuned by strain, which is not possible for the <100> and <112> orientations. A discussion of these differences based on band structure analysis will be given, too.
Keywords: Reconfigurable field-effect transistor, silicon, interface
  • Lecture (Conference)
    IHRS NanoNet Annual Workshop 2017, 16.-18.08.2017, Neuklingenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26591
Publ.-Id: 26591


Injection locking of constriction based spin Hall nano-oscillators

Hache, T.; Weinhold, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Schultheiss, H.
Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs under the forcing influence of an added alternating current. We show the possibility of injection locking between the applied external signal and the auto-oscillations driven by a direct current. Within the locking range the frequency of the auto-oscillations is forced to the external stimulus. In addition the intensity of the oscillations is increased strongly and the linewidth decreases. Due to the controllability of the auto-oscillations of the magnetization, injection locking can be used to influence the properties of future communication technologies, i.e. based on synchronized constriction based spin Hall nano-oscillators arrays.
Keywords: spin Hall, spin Hall nano-oscillators, auto-oscillations, injection locking, phase locking, Auto-Oszillationen, Spin-Hall Nanooszillatoren
  • Poster
    2017 European School on Magnetism: Condensed Matter Magnetism : bulk meets nano, 09.-20.10.2017, Cargese, France
  • Poster
    Nano-Magnonics Workshop 2018, 19.-21.02.2018, Diemerstein, Kaiserslautern, Deutschland
  • Poster
    Intermag 2018, 23.-27.04.2018, Marina Bay Sands Convetion Center, Singapore
  • Poster
    IEEE Magnetics Society Summer school, 03.-08.06.2018, Universidas San Francisco de Quito, Equador
  • Poster
    The Joint European Magnetic Symposia 2018, 03.-07.09.2018, Rheingoldhalle, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26590
Publ.-Id: 26590


Möglichkeiten der Kreislaufwirtschaft

Reuter, M. A.
Knapp 780.000 Tonnen Elektro-Altgeräte wurden laut Umweltbundesamt im Jahr 2010 in Deutschland gesammelt. Das entspricht 8,8 Kilogramm pro Einwohner und Jahr. Viele wertvolle Metalle, Legierungen, funktionale Materialien sowie Kunststoffe sind darin enthalten. Wie kann man die Wertstoffe im Sinne einer Kreislaufwirtschaft (Circular Economy) bestmöglich zurückgewinnen, um neue Güter herzustellen? Was leistet Recycling schon heute? Was müsste getan werden, um es weiter zu verbessern? Und wie energetisch sinnvoll ist es überhaupt?
Prof. Markus Reuter, Direktor am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) des HZDR, widmet sich diesen Fragen. Der Metallurge und Recyclingexperte beschäftigt sich mit der Wiederverwertbarkeit von Produkten und erforscht innovative, digitale Systeme und Prozesse für optimales Recycling.
Keywords: Kreislaufwirtschaft
  • Lecture (others)
    Möglichkeiten der Kreislaufwirtschaft / Wintersemester der Seniorenakademie, 06.11.2017, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-26589
Publ.-Id: 26589


Auto-oscillations in double constriction spin Hall nano-oscillators

Hache, T.; Wagner, K.; Arekapudi, S. S. P. K.; Hellwig, O.; Lindner, J.; Schultheiss, H.
Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs. These are devices where the current density is increased locally due to lateral confinement. Hence, the spin current generated by the spin Hall effect can create well defined hot-spots for auto-oscillations.
We present BLS measurements of auto-oscillations in Co60Fe20B20(5 nm)/Pt(7 nm) based samples with two interacting, neighbouring nanoconstrictions.
The precession amplitude in these samples can be driven far from equilibrium, resulting in clear nonlinear signatures in the spinwave spectra. The spatial distributions of the observed modes and current dependencies are shown.
Keywords: spin Hall, spin Hall nano-oscillators, Spin-Hall Nanooszillatoren, spin current, auto-oscillations, Autooszillationen
  • Poster
    DPG-Frühjahrstagung SKM, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26588
Publ.-Id: 26588


Circular Economy within and beyond manufacturing processes

Reuter, M. A.
This workshop will gather around 30 representatives of business support organisations, including established and prospective providers of resource efficiency advisory and consulting services from European countries and regions in the process of setting up resource efficiency services for small and medium-sized enterprises (SMEs).
  • Invited lecture (Conferences)
    Resource Efficiency in the Manufacturing Industry - Workshop, 24.11.2017, Berlin, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-26586
Publ.-Id: 26586


Dual energy CT: Benefits for proton therapy planning and beyond

Richter, C.; Wohlfahrt, P.; Möhler, C.; Greilich, S.
For about a decade, dual-energy CT (DECT) has been clinically available, mainly for radiology applications. In contrast, in the field of radiotherapy DECT has gained relevant interest over the last few years and here clinical use is still far away from being clinical standard. In this lecture benefits of DECT for radiotherapy applications will be discussed.
The focus will be on application for treatment planning in proton therapy, namely the individual prediction of tissue’s stopping power relative to water (SPR) as an alternative to the standard approach using a generic look-up table (HLUT). The manifold information gathered by two CT scans with different X-ray spectra allow for a patient-specific and direct calculation of relative electron density and SPR [1,2]. This enables the consideration of intra- and inter-patient variabilities in CT-based SPR prediction and ultimately a more accurate range prediction. The talk will cover the validation of the SPR prediction accuracy in realistic ground-truth scenarios [3,4], the investigation of clinical relevant differences between the DECT-based and the standard HLUT-based SPR prediction in clinical patient data [5] as well as the status of its clinical implementation [6].
Furthermore, additional applications in radiotherapy, e.g. for photon treatment planning, delineating and material differentiating will be briefly discussed.
  • Invited lecture (Conferences)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S289-S290
    DOI: 10.1016/S0167-8140(18)30854-5

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Permalink: https://www.hzdr.de/publications/Publ-26585
Publ.-Id: 26585


Dual energy CT for range prediction in proton therapy: Validation, clinical benefit & status of implementation

Richter, C.
Overview of DECT project + outlook
  • Invited lecture (Conferences)
    33rd Conference on Clinical and Experimental Research in Radiation Oncology (C.E.R.R.O.), 13.-20.01.2018, Les Menuires, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26584
Publ.-Id: 26584


Inter-centre variability of CT-based range prediction in particle therapy: Survey-based evaluation

Taasti, V.; Bäumer, C.; Dahlgren, C.; Deisher, A.; Ellerbrock, M.; Free, J.; Gora, J.; Kozera, A.; Lomax, T.; de Marzi, L.; Molinelli, S.; Teo, K.; Wohlfahrt, P.; Petersen, J.; Muren, L.; Hansen, D.; Richter, C.
Purpose: To assess the inter-center variability of the conversion between CT number and particle stopping power ratio (SPR), a survey-based evaluation was carried out in the framework of the European Particle Therapy Network (EPTN). The CT-to-SPR conversion (Hounsfield look-up table, HLUT) is applied to treatment planning CT scans to finally derive the particle range in patients. Currently, CT scan protocols for treatment planning are not standardized regarding image acquisition and reconstruction parameters. Hence, the HLUT depends on the selected scan settings and must be defined by each center individually. Aiming to access the current inter-center differences, this investigation is a first step towards better standardization of CT-based SPR derivation.
Methods: A questionnaire was sent to particle therapy centers involved in the EPTN and two centers in the United States. The questionnaire asked for details on CT scanners, acquisition and reconstruction parameters, the calibration and definition of the HLUT, as well as body-region specific HLUT selection. It was also assessed whether the influence of beam hardening was investigated and if an experimental validation of the HLUT was performed. Furthermore, different future techniques were rated regarding their potential to improve range prediction accuracy.
Results: Twelve centers completed the survey (ten in Europe, two in the US). Scan parameters, in particular reconstruction kernel and beam hardening correction, as well as the HLUT generation showed a large variation between centers. Eight of twelve centers applied a stoichiometric calibration method, three defined the HLUT entirely based on tissue substitutes while one center used a combination of both. All facilities performed a piecewise linear fit to convert CT numbers into SPRs, yet the number of line segments used varied from two to eleven. Nine centers had investigated the influence of beam hardening, and seven of them had evaluated the object size dependence of their HLUT. All except two centers had validated their HLUT experimentally, but the validation schemes varied widely. Most centers acquired CT scans at 120 kVp, all centers individually customized their HLUT, and dual-energy CT was seen as a promising technique to improve SPR calculation.
Conclusions: In general, a large inter-center variability was found in implementation of CT scans, image reconstruction and especially in specification of the CT-to-SPR conversion. A future standardization would reduce time-intensive institution-specific efforts and variations in treatment quality. Due to the interdependency of multiple parameters, no conclusion can be drawn on the derived SPR accuracy and its inter-center variability. As a next step within the EPTN, an inter-center comparison of CT-based SPR prediction accuracy will be performed with a ground-truth phantom.
Keywords: proton therapy, particle therapy, range prediction, stopping-power ratio, Hounsfield look-up-table, inter-center comparison

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Permalink: https://www.hzdr.de/publications/Publ-26583
Publ.-Id: 26583


Inherited control of crystal surface reactivity

Fischer, C.; Kurganskaya, I.; Lüttge, A.
Material and environmental sciences have a keen interest in the correct prediction of material release as a result of fluid-solid interaction. For crystalline materials, surface reactivity exerts fundamental control on dissolution reactions; however, it is continuously changing during reactions and governs the dynamics of porosity evolution. Thus, surface area and topography data are required as input parameters in reactive transport models that deal with challenges such as corrosion, CO2 sequestration, and extraction of thermal energy. Consequently, the analysis of surface reaction kinetics and material release is a key to understanding the evolution of dissolution-driven surface roughness and topography. Kinetic Monte Carlo (KMC) methods simulate such dynamic systems. Here we apply these techniques to study the evolution of reaction rates and surface topography in crystalline materials. The model system consists of domains with alternating reactivity, implemented by low vs. high defect densities.
Our results indicate complex and dynamic feedbacks between domains of high versus low defect density, with the latter apparently limiting the overall dissolution rate of the former - a limitation that prevails even after their disappearance. We introduce the concept of “inherited” control, consistent with our observation that maximum dissolution rates in high defect density domains are lower than they would be in the absence of low defect density neighboring domains.
The controlling factor is the spatial pattern of surface accessibility of fluids. Thus, the distribution of large etch pits centers is inherited almost independently of spatial contrasts in crystal defect density during ongoing reactions. As a critical consequence, the prediction of both the material flux from the reacting surface and the evolution of topography patterns in crystalline material is constrained by the reaction history. Important applications include the controlled inhibition of reactivity of crystalline materials as well as the quantitative evaluation and prediction of material failure in corrosive environments.
Keywords: Kinetic Monte Carlo simulation, rate spectra, crystal dissolution, surface reactivity, surface topography and roughness patterns

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Permalink: https://www.hzdr.de/publications/Publ-26582
Publ.-Id: 26582


Pulsating dissolution of crystalline matter

Fischer, C.; Lüttge, A.
Fluid-solid reactions result in material flux from or to the solid surface. The prediction of the flux, its variations and changes with time are of interest to a wide array of disciplines, ranging from the material and earth sciences to pharmaceutical sciences. Reaction rate maps that are derived from sequences of topography maps illustrate the spatial distribution of reaction rates across the crystal surface. Here we present highly spatially-resolved rate maps that reveal the existence of rhythmic pulses of the material flux from the crystal surface. This observation leads to a change in our understanding of the way crystalline matter dissolves. Rhythmic fluctuations of the reactive surface site density and potentially concomitant oscillations in the fluid saturation imply spatial and temporal variability in surface reaction rates. Knowledge of such variability could aid attempts to upscale microscopic rates and predict reactive transport through changing porous media.
Keywords: surface reactivity | kinetics | dissolution | fluid-solid interaction | rate spectra
  • Open Access Logo Proceedings of the National Academy of Sciences of the United States of America 115(2018)5, 897-902
    DOI: 10.1073/pnas.1711254115

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Permalink: https://www.hzdr.de/publications/Publ-26581
Publ.-Id: 26581


Vibrational properties of metal phosphorus trichalcogenides from first principles

Hashemi, A.; Komsa, H.-P.; Puska, M.; Krasheninnikov, A. V.ORC
Two-dimensional (2D) sheets of transition metal phosphorus trichalcogenides (TMPTs) offer unique magnetic and optical properties that can complement those found in other 2D materials. Insights into the structure and properties of these materials can be obtained by a juxtaposition of the experimental and calculated Raman spectra, but there is very little theoretical knowledge of the vibrational properties of TMPTs. Using first-principles calculations, we study mechanical and vibrational properties of a large set of monolayer TMPTs. From the phonon dispersion curves, we assess the dynamical stabilities and general trends on the atomic character of the vibrational modes. We determine Raman active modes from group theory, calculate Raman intensities, and analyze them with the help of the corresponding atomic displacements. We evaluate how the mode frequencies shift in response to a biaxial strain. We also determine elastic properties, which show that these systems are softer than many other layered materials. In addition to shedding light on the general features of vibrational properties of these materials, our results should also prove useful for interpreting experimental Raman spectra.
Keywords: 2D materials, transition metal phosphorus trichalcogenides, first-principles calculations, Raman spectra

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Permalink: https://www.hzdr.de/publications/Publ-26580
Publ.-Id: 26580


Revealing the Atomic Defects of WS2 Governing Its Distinct Optical Emissions

Lin, Y.-C.; Li, S.; Komsa, H.-P.; Chang, L.-J.; Krasheninnikov, A. V.ORC; Eda, G.; Suenaga, K.
Defects and their spatial distribution are crucial factors in controlling the electronic and optical properties of semiconductors. By using scanning transmission electron microscopy and electron energy loss spectroscopy, the type of impurities/defects in WS2 subdomains with different optical properties is successfully assigned. A higher population of Cr impurities is found in the W-terminated edge domain, while the S-terminated domain contains more Fe impurities, in accordance with the luminescence characteristics of chemical-vapor-grown WS2 of a hexagonal shape. In agreement with the first-principles calculations, the domains with Cr substitutional dopants exhibit strong trion emission. Fe atoms tend to gather into trimer configuration and introduce deep acceptor levels which compensate the n-type doping and suppress trion emission. It is also discovered that the domain with higher luminescence but smaller defect concentration tends to get oxidized more rapidly and degrade the 2D structure with many triangular holes. Excitons tend to accumulate at the edges of the oxidized triangular holes and results in enhanced PL emission. The findings indicate that choosing stable elements as dopant and controlling the number of specific edge structures within a crystal domain of 2D transitional metal dichalcogenides can be a new route to improve the optical properties of these materials.
Keywords: Defects, 2D materials, transition metal dichalcogenides, transmission electron microscopy, first-principles calculations

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Permalink: https://www.hzdr.de/publications/Publ-26579
Publ.-Id: 26579


Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses The PENELOPE Laser System

Loeser, M.
The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10²¹ W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb³⁺:CaF₂) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb³⁺:CaF₂ matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb³⁺:CaF₂. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.
Keywords: laser, CPA, diode-pumped, PENELOPE, high-intensity laser, ultrashort pulse laser
  • Doctoral thesis
    HZDR, TU Dresden, 2017
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-083 2018

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Permalink: https://www.hzdr.de/publications/Publ-26578
Publ.-Id: 26578


Shedding light on LWFA plasma dynamics - in-situ radiation diagnostics in PIConGPU

Pausch, R.; Debus, A.; Garten, M.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.
We present recent results from the in-situ radiation diagnostics available in the particle-in-cell code PIConGPU and illustrate its power to provide insight into LWFA experiments when linked to experimental measurements.

PIConGPU is currently one of the fastest 3D3V PIC codes. Its speed allows including an in-situ radiation diagnostic based on Liénard-Wiechert potentials. This synthetic diagnostic is capable of computing the spectrally resolved far field radiation of billions of macro-particles for numerous observation directions. It allows resolving the intensity and polarization of the emitted radiation both temporally and spatially for frequencies extending from infrared to x-rays. Its use of form-factors and its capability of phase tracking each individual macro-particle enable quantitative predictions in both the coherent and incoherent regime. Applications for this synthetic radiation diagnostics have already been demonstrated in astrophysical simulations to identify and quantify the Kelvin-Helmholtz instability.

After a brief introduction of the techniques for computing the radiation in-situ, we focus on the characteristic radiation of LWFA, which allows identifying the various stages of the laser-plasma dynamics. We demonstrate the correlation between emitted radiation and particle dynamics and discuss application of these signatures in laboratory experiments
Keywords: radiation, PIConGPU, in-situ, LWFA, spectra
  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 24.-29.09.2017, La Biodola, Isola d'Elba, Italien

Permalink: https://www.hzdr.de/publications/Publ-26577
Publ.-Id: 26577


Platinum-Group Elements and Minerals in the Lower and Middle Group Chromitites of the Bushveld Complex, South Africa

Junge, M.; Oberthür, T.; Osbahr, I.
The 2,050 Ma old Bushveld Complex in South Africa is the largest layered mafic-ultramafic intrusion on Earth and contains the largest resources of platinum-group elements (PGE) as well as economically important reserves of chromium and vanadium. The correlation between chromite and PGE is remarkably well expressed as even the thinnest chromitite stringers in the Bushveld Complex contain elevated concentrations of PGE. The UG-2 chromitite has been investigated in great detail, however, studies on the distribution of PGE and the mineralogical character of the PGM in the LG and MG chromitites are scarce and the knowledge of the distribution and the mineralogical siting of the PGE in the chromitite seams of the Lower Group (LG) and Middle Group (MG) of the Bushveld Complex is limited.
In the present study, concentrates from the LG-6 and MG-2 chromitites of the Bushveld Complex are studied to determine the distribution of the PGE and the nature of the platinum-group mineral (PGM) in these chromitite seams. Quantitative mineralogical analysis using the Mineral Liberation Analyser (MLA) software was carried out in order to determine the PGM proportions in these concentrates. The dominant PGM are sulfides, namely cooperite-braggite, malanite-cuprorhodosite, and laurite, followed by PGE-sulfarsenides, sperrylite, and Pt-Fe alloys. The additional information of PGM area percentages compared to frequency data obtained by the MLA data, show that in LG and MG chromitites of the western Bushveld Complex laurite grains make up the largest area amount of PGM. The matching sets of PGM present in the LG and MG chromitites of both the western and the eastern Bushveld Complex, and the UG-2 chromitite show far-reaching similarities which support the indication of a characteristic, general chromitite-related PGM assemblage. These PGM in the LG and MHR are mostly associated with silicates (54 and 60% in the LG-6 and MG-2, respectively), followed by sulfides (32 and 37% in the MG-2 and LG-6, respectively). Rarer associations are with chromite (2%) or other PGM (5 to 7%). Palladium and Rh contents in sulfides (mainly pentlandite) may range up to thousands of ppm in ores associated with mafic-ultramafic intrusions. Palladium and Rh contents in pentlandite of the LG and MG chromitites of this study are low and erratic although maximum contents of 7731 ppm Pd and 6023 ppm Rh were detected. Rare thiospinels of the polydymite-linnaeite-greigite series achieve PGE contents of 1428 ppm Pt, 5370 ppm Rh and 1460 ppm Pd.
Keywords: Bushveld Complex, platinum-group-minerals, chromitites
  • Contribution to proceedings
    EMC 2016, 11.-15.09.2016, Rimini, Italy

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Permalink: https://www.hzdr.de/publications/Publ-26576
Publ.-Id: 26576


Elektrostatische Kontrolle des Stofftransports in mikro- und nanoskaligen Elektrolytsystemen

Kubeil, C.ORC
Viele Produktions- und Analyseverfahren profitieren zunehmend von neuesten nanotechnologischen Entwicklungen zur Erweiterung bzw. Optimierung des jeweiligen Anwendungsgebietes. Häufig sind die systemtypischen Eigenschaften jedoch nur unvollständig verstanden, da sie verstärkt durch Oberflächeneigenschaften und Größenquantifizierungseffekte dominiert werden. Auch in der Elektrochemie und Galvanotechnik besteht großes Interesse die notwendigen und grundlegenden Erkenntnisse über Mikro- und Nanosysteme zu gewinnen und entsprechend für eine Anwendung nutzbringend bereitzustellen.
Insbesondere in nanoskaligen Elektrolytsystemen, z.B. an porösen Oberflächen, in Membranen oder bei der Kompositabscheidung, spielt die elektrochemische Doppelschicht an geladenen Oberflächen eine entscheidende Rolle. Aufgrund der begrenzten Ausdehnung des
Elektrolyten wird die Ionenverteilung maßgeblich durch die Oberflächenladung bestimmt. Dies hat unmittelbar Auswirkungen auf den ionischen und molekularen Stofftransport und somit auch auf die Potential- und Stromdichteverteilung. Für die galvanische Abscheidung von Metallen in solch kleinen Bereichen bedeutet dies, dass die elektrische Ladungsdichte der Matrix an kritischem Einfluss gewinnt: Je nach Vorzeichen kann sie eine inhibierende oder verstärkende Wirkung auf den Transport der Metallionen ausüben.
Der Vortrag zeigt anhand numerischer Simulationen und ausgewählten Experimenten, welche Doppelschicht-Effekte in nanoskaligen System auftreten und wie sich diese gezielt nutzen lassen, um beispielsweise galvanisch abgeschiedene Strukturen vorteilhaft zu beeinflussen.
Keywords: Nanoporen, elektrochemische Doppelschicht, Elektrolyt, Galvanotechnik, Metallabscheidung
  • Lecture (Conference)
    ZVO Oberflächentage 2017, 13.-15.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26575
Publ.-Id: 26575


Effizienzsteigerung von Kläranlagen - Vorstellung von Mess- und Simulationstechnischen Methoden

Reinecke, S. F.; Höffmann, A. K.; Stachowske, M.; Hampel, U.; Ehrhard, P.
Für den Großteil der in Deutschland betriebenen Kläranlagen übersteigt die aufgewendete Energie zur Durchmischung und Belüftung des Abwassers oftmals den tatsächlich notwendigen Energiebedarf. Zwischen 50% und 80% des Gesamtenergiebedarfs einer Kläranlage fällt auf die Belüftung des Belebungsbeckens (Fricke, 2009; Haberkern et al., 2008). Unabhängig von der Ausbaugröße der Kläranlage ist dementsprechend dort das mit Abstand größte Energieeinsparpotenzial zu finden. Dies wird oft durch eine nicht-optimale Auslegung bzw. Anordnung der Begasungs- und Dispergierorgane im Belebtschlammbecken hervorgerufen.
Ziel dieses Vorhabens ist die Entwicklung einer Methodik, mit welcher basierend auf numerischen Simulationen die Optimierungspotenziale der jeweiligen Anlage aufgedeckt werden, optimierte Anlagenkonfigurationen und Betriebsweisen bestimmt bzw. bewertet werden. Dies entspricht einer virtuellen Anlagenoptimierung durch numerische Experimente. Weiterhin werden die Maßnahmen nach ihrer Umsetzung der an der konkreten Anlage mit Hilfe innovativer Sensorik messtechnisch validiert.
Damit soll eine grundlegende Verbesserung der Hydrodynamik und des Stofftransportes in Belebungsbecken in Verbindung mit der Effizienzsteigerung der Anlage basierend auf numerischen Simulationen und innovativen Sensortechnologien möglich werden.
  • Open Access Logo GIT Labor-Fachzeitschrift 62(2018)4, 53-56

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Permalink: https://www.hzdr.de/publications/Publ-26574
Publ.-Id: 26574


Severe Accident Management Measures for a Generic German PWR. Part II: Small-break loss-of-coolant accident

Jobst, M.ORC; Wilhelm, P.; Kozmenkov, Y.; Kliem, S.
This series of two papers focuses on the analysis of severe accident management measures for a generic German PWR of type Konvoi. A nuclear power plant model based on the severe accident code ATHLET-CD was developed in order to assess the code applicability for simulation of accident scenarios with core degradation. It was applied for investigation of two main groups of accident scenarios: station blackout and small-break loss-of-coolant accidents.
Part I presented the analyses of a station blackout accident. Part II is focused on the analysis of the plant response in case of a hypothetical small-break loss-of-coolant accident (SBLOCA with 50 cm² leak in cold leg of pressurizer loop). Due to failure of components of the emergency core cooling system and assumed unavailability of several preventive and mitigative accident management measures (AMM), the accident develops into a severe accident scenario with core melt and reactor pressure vessel failure. An alternative AMM, which is not implemented in German PWRs, is investigated in the current paper: late coolant injection to the primary circuit with a mobile equipment (bleed and feed with low pressure pump). The analysis is performed on the basis of ATHLET-CD simulations (code version Mod 3.0 Cycle A). Two injection points are investigated: injection to cold leg and injection to hot leg. As in SBLOCA scenarios the primary pressure might remain high that injection by low pressure systems is not effective, the influence of additional primary side depressurization (PSD) is investigated.
The simulations show, that mobile pump injection significantly reduces the amount of the released fission products and hydrogen, if it is started within 75 min after the core exit temperature (CET) exceeded 400 °C. Without PSD, melting of the fuel can be prevented if the mobile pump is started immediately when CET > 650 °C, but release of fission products can only be prevented if early pump injection is combined with PSD. Cases with a delay of mobile pump injection in combination with a delay of PSD (e.g. due to temporary malfunction) are also investigated: until 50 min after CET > 400 °C a lower release of fission products and longer grace times to prevent melt relocation to the lower head are observed (compared to immediate PSD at CET > 400 °C).
Keywords: Severe accident analysis; SBLOCA; PWR; Accident management measures

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Publ.-Id: 26573


Magnetic properties of Co/Ni multilayer structures for use in STT-RAM

Arora, M.; Lee-Hone, N. R.; Mckinnon, T.; Coutts, C.; Hübner, R.; Heinrich, B.; Broun, D. M.; Girt, E.
Magnetic properties of (111)-textured SAF/Cu/FL multilayer film structures have been optimized by varying individual layer thickness and sputtering conditions. The SAF is a synthetic antiferromagnet consisting of Co/Ni multilayers coupled antiferromagnetically across a Ru spacer layer, and the FL is a free layer consisting of a single Co/Ni multilayer. The Co thickness was varied from 0.16 nm to 0.26 nm and the Ni thickness from 0.47 nm to 0.57 nm at two different deposition rates to obtain a perpendicular magnetic anisotropy of the 8 × [Co/Ni] multilayers ranging from 4×105 to 4.6×105 Jm-3. The perpendicular magnetic anisotropy, saturation magnetization, damping and zero-frequency line broadening of the Co/Ni multilayers strongly depend on the number of bilayers, N1, for N1<10. With increasing Cu seed-layer thickness, the texture of the Co/Ni multilayers improves while the grain size and film roughness increase. The increase in grain size results in the reduction of the direct exchange coupling between magnetic grains, which enhances the coercivity of the SAF and the FL. Experimentally measured coercivities of the SAF and FL are compared with calculations obtained from a coherent rotation model. The effect of the Co/Ru interface in the SAF on the exchange coupling, and the role of the Co/Cu interface in the magnetoresistance, is also discussed. This study provides an important step towards the realization of STT-RAM devices consisting of only Co/Ni multilayers.
Keywords: magnetic multilayers, perpendicular magnetic anisotropy, giant magneto-resistance, spin transfer torque, magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-26572
Publ.-Id: 26572


Study of Defects in High Energy Ion Implanted ZnO Crystals

Melikhova, O.; Čížek, J.; Procházka, I.; Hruška, P.; Anwand, W.; Havránek, V.; Skuratov, V. A.; Strukova, T. S.
Positron annihilation spectroscopy (PAS) was employed for characterization of defects in the hydrothermally (HT) grown zinc oxide single crystals irradiated by high energy ions. Defects created in ZnO crystals by 2.5 MeV protons, 7.5 MeV N3+ and 167 MeV Xe26+ ions were compared. The virgin ZnO crystals contain Zn-vacancies associated with hydrogen. Ion implantation introduced additional defects, namely Zn+O di-vacancies in crystals irradiated by protons and small vacancy clusters in samples implanted by N and Xe ions.

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Permalink: https://www.hzdr.de/publications/Publ-26571
Publ.-Id: 26571


"SE-FLECX"-Project: Development of new extractants for Rare Earths

Balinski, A.; Bauer, A.; Schmeide, K.; Mansel, A.; Jäschke, A.; Glasneck, F.; Kersting, B.; Krause, J.; Atanasova, P.; Scharf, C.
The extraction of rare earth elements (REEs) from ores with simple mineralogy has been largely optimized over the past years. However, because of the dwindling of ore, which are easy to concentrate, it is necessary to develop new processes which are more effective and transferable to the ores with complex mineralogy. The SE-FLECX-Project, which is coordinated at the Helmholtz Institute Freiberg in Germany, is dealing with the extraction process. To determine an optimal leaching method and to provide leach solutions for the extraction experiments two ores are processed in different ways. The main focus is to develop new extractants based on calix[4]arene molecules for separation of radioactive elements and single REEs, for example uranium.
Keywords: Calix[4]arene, extraction of rare earth elements and uranium, ore processing
  • Lecture (Conference)
    The 21st International Solvent Extraction Conference, 05.-09.11.2017, Miyazaki, Japan

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Permalink: https://www.hzdr.de/publications/Publ-26570
Publ.-Id: 26570


Platinum-group elements and platinum-group minerals in the weathered chromitities of the Lower and Middle Group chromitites of the Bushveld Complex

Junge, M.; Bachmann, K.; Kotzé, E.; Oeser-Rabe, M.
The mineralization of economically important platinum group elements (PGE) mainly occurs in mafic-ultramafic intrusions such as the Bushveld Complex. PGE are currently mined from the Merensky Reef, the Platreef and the UG-2 chromitite, which is the only chromitite layer mined for PGE, however, the Lower Group (LG) and Middle Group (MG) chromitites also contain significant PGE concentrations ranging from 0.5 to 9 g/t. In the pristine ores, PGE occur both as discrete platinum-group minerals (PGM) and included within sulfides. Previous studies showed that in the LG-6 and MG-1/2, PGE-sulfides (cooperite-braggite, malanite, laurite) are the dominant PGM, followed by PGE-sulfarsenides, sperrylite and Pt-Fe alloys. The rocks in the Bushveld Complex are strongly weathered down to 10 to 40 m below the surface. Near-surface chromitite seams of the LG and MG of the western Bushveld Complex at the Thaba Mine are studied by electron microprobe and LA-ICP-MS for the distribution of PGE. The analytical conditions employed for silicates were: 20 kV acceleration voltage, 120 nA beam current, focused beam, and up to 360 s measuring time. LA-ICP-MS measurements were carried out on a ThermoScientific Element XR (HR-ICP-MS) coupled with a femtosecond laser ablation system. During weathering, sulfides and PGM are largely destroyed and PGE are mobilized and redistributed in the near-surface ores. Within the near-surface weathered chromitite seams, only relict PGM can be observed, which are observed within silicates or as inclusions in chromite. Former grains of PGM are observed in secondary silicates showing larger shapes but are locally redistributed along small cracks and Pt-Fe-(oxides) are observed as well, arguing for the neoformation of PGM. Secondary silicate minerals in weathered ores show concentrations of Pt and Pd in the 100s-ppm range. A good correlation can be observed with Ni and Pd, arguing for the weathering of pentlandite, which hosts Pd in the pristine PGE ore. Palladium and Ni partly remained and were incorporated into secondary silicates while S is largely lost.
  • Contribution to proceedings
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland
    Proceedings of the GeoBremen 2017

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Publ.-Id: 26569


Hydrothermal formation of HREE-xenotime deposits at 100 °C in a sedimentary basin

Richter, L.; Diamond, L. W.; Atanasova, P.; Banks, D. A.; Gutzmer, J.
Most rare-earth element deposits form from magmatic fluids but there have also been discoveries of heavy rare-earth element (HREE)-enriched hydrothermal xenotime deposits within sedimentary basins. As xenotime is notoriously insoluble, the question arises as to whether these lesser known deposits form at typical basin temperatures or by influx of much hotter magmatic-hydrothermal fluids. The Browns Range District in northern Australia hosts deposits of xenotime that is enriched in HREE and also uranium. The ore bodies consist of fault-controlled hydrothermal quartz–xenotime breccias that crosscut Archean basement rocks and overlying Paleoproterozoic sandstones. Analyses of fluid inclusions show that the xenotime precipitated at remarkably low temperatures between 100 and 120 °C, in response to decompression boiling. The inclusions contain high excess REE concentrations (10−6 to 10−5 molal) and high U concentrations (5 × 10−5 molal) in equilibrium with xenotime at these low temperatures, showing that availability of phosphate limited the amount of xenotime precipitated. The analyses further identify SO42– and Cl- as the ligands that facilitated the elevated REE and U solubilities. These findings establish that significant REE transport and deposition is feasible at basin temperatures and hence they raise the potential of unconformity settings for REE exploration. Moreover, the aqueous metal contents support a genetic link between this type of ore fluid and world-class Proterozoic unconformity-related uranium deposits elsewhere.

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Publ.-Id: 26568


Platinum-group element and minerals in the Lower and Middle Group chromitites of the western Bushveld Complex, South Africa

Junge, M.; Oberthür, T.; Osbahr, I.; Gutter, P.
The chromitites of the Bushveld Complex in South Africa contain vast resources of platinum-group elements (PGE). However, knowledge of the distribution and the mineralogical siting of the PGE in the lower group (LG) and middle group (MG) chromitite seams of the Bushveld Complex is limited. We studied concentrates from the LG-6 and MG-2 chromitites of the western Bushveld Complex by a variety of microanalytical techniques. The dominant PGM are sulfides, namely laurite, cooperite-braggite, and malanite-cuprorhodsite, followed by PGE-sulfarsenides, sperrylite, and Pt-Fe alloys. Laurite is the most abundant PGM (vol%). The matching sets of PGM present in the LG and MG chromitites of both the western and the eastern Bushveld Complex, and in the UG-2 chromitite, show strong similarities which support the assumption of a characteristic and general chromitite-related PGM assemblage. Palladium and Rh contents in pentlandite are low and erratic although maximum contents of 7730 ppm Pd and 6020 ppm Rh were detected. Rare thiospinels of the polydymite-linnaeite-greigite series have PGE contents of 1430 ppm Pt, 5370 ppm Rh, and 1460 ppm Pd. The various PGE occur in different deportment: Platinum is generally present in the form of discrete PGM (sulfides, arsenides, alloys). Palladium is present as a large variety of discrete PGM and also incorporated in pentlandite. Rhodium forms discrete PGM and is occasionally present in pentlandite. The IPGE (Os, Ir, and Ru) are dominantly incorporated in laurite (often as inclusions in chromite) and also occur as sulfarsenides.

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Publ.-Id: 26567


Cryogenic jet targets for high power laser experiments

Rehwald, M.; Göde, S.; Obst, L.; Zeil, K.; Metzkes-Ng, J.; Schlenvoigt, H.; Kraft, S. D.; Brack, F.; Wolter, S.; Kazak, L.; Gauthier, M.; Roedel, C.; Kluge, T.; Fiuza, F.; Mishra, R.; Ruyer, C.; Sommer, P.; Loeser, M.; Ziegler, T.; Curry, C.; Macdonald, M.; Schumaker, W.; Glenzer, S.; Cowan, T.; Schramm, U.
We present a pure condensed hydrogen jet as a renewable and debris-free target for high power laser experiments. The jet's nominal electron density is approximately 30 times the critical density and its diameter can be varied to be 2µm, 5µm or 10µm and thus allowing to study the regime of relativistic transparency. Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target. Radiochromic film stacks in forward direction display signatures of filament-like structures, stemming from a Weibel-like instability generated at the rear side of the target in the underdense plasma region.
  • Lecture (Conference)
    MoU HZDR-ILE and HZDR-KPSI, 07.-08.12.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26566
Publ.-Id: 26566


Using optical probing to study laser-proton acceleration from a condensed hydrogen jet

Rehwald, M.; Goede, S.; Obst, L.; Zeil, K.; Metzkes, J.; Schlenvoigt, H.; Kraft, S. D.; Brack, F.; Wolter, S.; Kazak, L.; Gauthier, M.; Roedel, C.; Kluge, T.; Fiuza, F.; Mishra, R.; Ruyer, C.; Sommer, P.; Loeser, M.; Ziegler, T.; Curry, C.; Macdonald, M.; Schumaker, W.; Glenzer, S.; Cowan, T.; Schramm, U.
The presentation will give an overview of the recent experiments for laser driven proton acceleration with high contrast at the high power laser system Draco at HZDR. We present results of an experimental campaign employing a pure condensed hydrogen jet as a renewable and debris free target.
Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target, reaching cut-off energies of up to 20 MeV and exceeding 109 protons per MeV per steradian. Evaluation of two different target geometries (cylindrical with a diameter of 2µm, 5µm or 10µm and planar with 2x20 µm²) demonstrating more optimized acceleration conditions from the planar hydrogen jet.
We report on modulations of laser accelerated protons by strong filamentary electromagnetic fields. Such modulations are related to the appearance of electron Weibel instability in the preplasma at the rear side of the target and impose important constraints on the preplasma level for high-quality proton acceleration [1].
Furthermore we present the usage of optical probing to study the laser plasma interaction providing plasma density measurements at the time of the interaction and to precisely determine the jet position. Recorded probe images taken up to 100 ps after the laser pulse arrived at the target, indicating plasma density modulations from pinching effects along the jet axis.
  • Lecture (Conference)
    Laser Plasma Accelerator Workshop 2017, 27.08.-01.09.2017, Jeju island, Korea
  • Lecture (Conference)
    SPIE – Laser Acceleration of Electrons, Protons, and Ions, 24.-27.04.2017, Prag, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-26565
Publ.-Id: 26565


Investigation of pinching effects in intense laser plasma interactions

Rehwald, M.; Zeil, K.; Obst, L.; Goede, S.; Metzkes, J.; Schlenvoigt, H.; Kraft, S. D.; Brack, F.; Wolter, S.; Kazak, L.; Gauthier, M.; Roedel, C.; Kluge, T.; Fiuza, F.; Mishra, R.; Ruyer, C.; Sommer, P.; Loeser, M.; Ziegler, T.; Curry, C.; Macdonald, M.; Schumaker, W.; Glenzer, S.; Cowan, T.; Schramm, U.
Developments in the field of laser plasma accelerators have been pushed by applications like radiation therapy in the past years. The acceleration of particle to higher energies is one of the key questions for such applications. Probing methods offer the capability for investigating the laser target interaction and thus allow for studying the acceleration process. In this talk results obtained by optical probing in recent experiments for laser driven proton acceleration with high contrast at the high power laser Draco at HZDR are presented. Draco delivers pulses of 30 fs and 5 J at 800 nm, focused to a 3 µm spot by a F/2.5 off-axis parabolic mirror. We present results of an experimental campaign using a cryogenic hydrogen jet as a renewable debris free target.
The hydrogen jet’s nominal electron density is approximately 30 times the critical density for 800 nm and its shape and size can be varied. For instance cylindrical geometries with diameters of 2µm, 5µm or 10µm were used. The laser plasma interaction could be monitored on-shot with two temporally synchronized optical probe beams perpendicular and longitudinal to the Draco laser axis. Recorded probe images taken up to 100 ps after the laser pulse arrived at the target indicate plasma density modulations from pinching effects along the jet axis. A possible driver for those density modulations is a strong surface current which has been studied with 2D-PIC simulations. Such density modulations may modify the shape of the electron sheath and thereby alter the beam profile of the laser accelerated protons.
Keywords: MHD instabilities, laser plasma interaction
  • Poster
    European Physical Society Conference June 2017, 26.-30.06.2017, Belfast, Vereinigtes Königreich

Permalink: https://www.hzdr.de/publications/Publ-26564
Publ.-Id: 26564


Flow Regime Transitions in a Bubble Column with Internals Based On a Novel Approach

Nedeltchev, S.; Möller, F.; Hampel, U.; Schubert, M.ORC
In this work the main flow regime boundaries in a bubble column with internals were investigated based on a novel statistical-chaotic method. The latter was applied to gas holdup fluctuations recorded by means of a wire-mesh sensor (8 x 8 wires). The bubble column (0.1 m in ID) was operated with an air-deionized water system at ambient conditions. 37 vertical tubes (arranged in a square pitch with a diameter of 8 x 10-3 m) were installed as internals. Based on an original combination of statistical and chaotic parameters was found that in the core of the bubble column with internals, the first transition velocity Utrans-1 (end of homogeneous regime) occurred at superficial gas velocity UG of 0.06 m/s, whereas the second transition velocity Utrans-2 (end of heterogeneous regime) appeared at UG = 0.13 m/s. At these critical velocities the new parameters exhibited well pronounced minima. In the core of the column the existence of transition flow regime was not identified. In the annulus of the bubble column with internals, three transition velocities (at UG = 0.03, 0.06 and 0.10 m/s) were identified. The first transition velocity identified the end of the gas maldistribution regime. The second and third critical velocities distinguished the ends of the homogeneous and heterogeneous regimes, respectively. The processing of the gas holdup data in the entire cross-section of the column revealed that the Utrans-1 and Utrans-2 values occurred at somewhat lower UG values (0.05 and 0.08 m/s). These critical gas velocities identified both the lower and upper boundaries of the transition regime.
Keywords: Bubble Column, Internals, New Statistical-Chaotic Method, Flow Regime Identification, Wire-Mesh Sensor

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Publ.-Id: 26563


Laser-proton acceleration from a condensed hydrogen jet

Rehwald, M.; Zeil, K.; Obst, L.; Metzkes, J.; Schlenvoigt, H.; Goede, S.; Kraft, S. D.; Brack, F.; Wolter, S.; Kazak, L.; Gauthier, M.; Roedel, C.; Kluge, T.; Fiuza, F.; Mishra, R.; Ruyer, C.; Sommer, P.; Loeser, M.; Ziegler, T.; Curry, C.; Macdonald, M.; Schumaker, W.; Glenzer, S.; Cowan, T.; Schramm, U.
Applications like radiation therapy of cancer have pushed the development of laser plasma accelerators and defined levels of control and necessary particle beam stability in laser plasma experiments. The poster will give an overview of a recent experiment for laser driven particle acceleration with high contrast at the high power laser Draco at HZDR, delivering pulses of 30fs and 5J. We present results of an experimental campaign employing a cryogenic hydrogen jet as a renewable target. The jet's nominal plasma density is approximately 30 times the critical density and its diameter can be varied to be 2µm, 5µm or 10µm and thus allowing to study the regime of relativistic transparency. In addition a planar aperture was commissioned, providing a different geometry of the hydrogen jet. Different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane around the wire-like target. Radiochromic film stacks in laser forward direction display filament-like structures, stemming from a Weibel-like instability generated at the rear side of the target. Furthermore the micro-jet target could be monitored on-shot with a temporally synchronized optical probe beam perpendicular and almost parallel to the pump laser axis. Recorded probe images taken on a timescale of several 10’s of picoseconds indicating plasma density modulations from pinching effects along the jet axis.
Keywords: laser particle acceleration, optical probing, plasma instabilities
  • Poster
    3. Annual MT Meeting, 31.01.-02.02.2017, GSI Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26562
Publ.-Id: 26562


PENELOPE main amplifier performance and development status

Albach, D.; Loeser, M.; Siebold, M.; Bernert, C.; Schramm, U.
We present an update on the development of the PENELOPE laser system currently under construction at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Pulses from an oscillator are stretched to the nanosecond scale before several amplification stages will boost the energy up to the 150 J level after compression. About 150 fs are foreseen at repetition rates of up to 1 Hz, ultimately yielding a peak power of 1 PW.
Current development focusses on the energetic performance of the last two main amplifier stages, especially the second to last amplifier. We will present the performance at the 10 J level, while simulating both amplifiers by double-passing the 12-pass setup. A small signal gain of more than 900 was achieved with these 24 passes using 4 Yb3+:CaF2 gain medium disks being pumped at up to 120 kW within 4 ms. Single-shot operation at room temperature is shown with a thorough discussion of the impact of temperature on the future operation below room temperature.
Keywords: PENELOPE, laser, diode-pumping, petawatt, ytterbium, CaF2
  • Lecture (Conference)
    The 10th International Workshop of High Energy Class Diode Pumped Solid State Lasers (HEC-DPSSL), 23.-26.05.2017, Noboribetsu, Japan

Permalink: https://www.hzdr.de/publications/Publ-26561
Publ.-Id: 26561


PENELOPE – amplifier benchmarks and 10 J performance

Albach, D.; Siebold, M.; Loeser, M.; Schramm, U.
We present the status of the PENELOPE laser system currently under construction at the Helmholtz-Zentrum Dresden-Rossendorf. We show the first energetic activation of the second to last major amplification stage boosting available energies to the 10 Joule-level, while benchmarking the performance of the whole last two amplifier sections. The expected small-signal gain at the full bandwidth of 20 nm was cross-checked with the front-end amplifier at 100 mJ.
Keywords: PENELOPE, Laser, Ytterbium, diode-pumping, CaF2
  • Invited lecture (Conferences)
    The 6th Advanced Lasers and Photon Sources (ALPS’17), 18.-21.04.2017, Yokohama, Japan

Permalink: https://www.hzdr.de/publications/Publ-26560
Publ.-Id: 26560


Recovery of Copper through Bioleaching from Copperslags in Kazakhstan

Kutschke, S.; Möckel, R.; Dirlich, S.; Pollmann, K.
Kazakhstan is one of the large copper producers world wide. Copper is mostly produced by pyrometallurgy and copper slags deposited on site at steppe. The slag contains high amounts of valuable metals, e.g. zinc, iron, and silver. Material samples from a heap near Ust Kamenogorsk were analyzed with chemical and mineralogical methods. Some minerals detected are ferrosilite, andradite, chalcopyrite, charmosite, and tetrahedrite. The material was leached with A. ferroxidans, A. thiooxidans, Y. lipolytica, B. licheniformis and the fungus Kombucha. Copper is leached by B. licheniformis, iron and silver by Kombucha. Leaching success was detected using biochemical chelators. However, these results are based only on the very first experiments with the sample material.
Keywords: Bioleaching, copperslags
  • Lecture (Conference)
    5th International Symposium on Sustainable Minerals, 14.-15.06.2018, Windhoek, Namibia

Permalink: https://www.hzdr.de/publications/Publ-26559
Publ.-Id: 26559


New biodegradable leaching agents for recovery of rare earth elements (REE) from ion adsorption clay deposit (IAC) in north west Madagascar

Kutschke, S.; Möckel, R.; Bachman, S.; Pollmann, K.
IAC’s are the world's main source of heavy rare earth elements. In situ leaching is the most common extraction technology for REE from IAC's but it is responsible for tremendous environmental damages. New biodegradable leaching agents were tested to extract REEs from an IAC from Madagascar. They are culture broths of S. urea, Y. lipolytica, and B. licheniformis. The culture broth of Y. lipolytica, containing tricarboxylic acids, revealed a generally low recovery except for Gd. Pr and Dy were selectively leached by the broth of S. urea. The highest recovery of REE was achieved by the B. licheniformis culture.
Keywords: Bioleaching, Rare Earth Elements
  • Lecture (Conference)
    9th International Symposium on Biohydrometallurgy, 11.-13.06.2018, Windhoek, Namibia

Permalink: https://www.hzdr.de/publications/Publ-26558
Publ.-Id: 26558


Local structural analyses of the mixed uranium-zirconium oxides in fuel debris simulated for the Fukushima Daiichi NPP accident

Uehara, A.; Akiyama, D.; Numako, C.; Takeda, S.; Ikeda-Ohno, A.ORC; Terada, Y.; Nitta, K.; Ina, T.; Kirishima, A.; Sato, N.
A series of the mixed uranium-zirconium oxides was prepared at high temperature to simulate the nuclear fuel debris remaining in the nuclear reactor(s) of Fukushima Daiichi Nuclear Power Plant (FDNPP), Japan. The prepared samples were comprehensively characterised by powder X-ray diffraction and X-ray absorption spectroscopy, indicating that the major phases formed are UO2, U3O8 and ZrO2 with an additional formation of mixed U-Ze oxide phases.
Keywords: Nuclear fuel debris, FDNPP, uranium, zirconium, oxide, solid solution, powder X-ray diffraction, X-ray absorption spectroscopy, speciation, characterisation
  • Lecture (Conference)
    Annual Meeting of the Atomic Energy Society of Japan, 26.-28.03.2018, Osaka University, Japan

Permalink: https://www.hzdr.de/publications/Publ-26553
Publ.-Id: 26553


A Study on the Influence of the Tube Layout on Sub-channel Hydrodynamics in a Bubble Column with Internals

Möller, F.; Lau, Y. M.; Seiler, T.; Hampel, U.; Schubert, M.
In this work, the hydrodynamics of a bubble column with vertical heat exchanger internals in a narrow bubble column of D_i = 0.1 m inner diameter with a clear liquid height of L_c = 1.1 m was comprehensively studied. We applied ultrafast X-ray tomography to obtain hydrodynamic parameters, such as, gas holdup, bubble size distribution, bubble number flux and flow patterns at hitherto inaccessible positions within the sub-channels of the tube bundles. To investigate the influence of the tube bundle patterns, square and triangular pitches were considered. Tubes of d_o = 8 and 13 mm outer diameter were installed to study the effect of tube size, while maintaining approx. A_c = 25 % coverage of the cross-sectional area, which is typical for e.g. Fischer-Tropsch process operated in bubble column reactors. The superficial gas velocity was varied from u_g = 2 to 20 cm s-1 to cover homogeneous and heterogeneous flow regimes. Internals’ type and tube diameter were found to crucially influence the gas holdup distribution across the column diameter, which is known to generate liquid circulation, to shape the gas velocity profile and to cause intensive bubble interactions. The higher flow resistance induced by triangular tube configurations and dense tube patterns, which is attributed to the smaller hydraulic diameter of the respective configurations, forces bubbles to preferably rise near the column wall. Within the tube bundle, the radial holdup profiles show a pronounced non-parabolic trend, indicating zones of reverse liquid flow directions between the internal tubes. Furthermore, the gas-liquid flow morphology within various sub-channels was analyzed revealing a slug-like flow formation at superficial gas velocities larger than 10 cm s-1.
Keywords: Bubble column, heat exchanger internals, sub-channel analysis, local hydrodynamics, ultrafast X ray tomography.

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Publ.-Id: 26552


Entwicklung Radium-bindender Verbindungen als Voraussetzung für deren Einsatz bei der Alpha-Therapie

Stipurin, S.
In der vorliegenden Arbeit sollen neue Radium-bindende Liganden entwickelt werden, die als potentielle bifunktionelle Chelatoren zur Entwicklung von Radiotherapeutika zur Krebsbehandlung beitragen sollen. Hierzu soll ein Calix[4]aren, bei dem bereits ein effektives und selektives Extraktionsverhalten von Barium nachgewiesen wurde, nachsynthetisiert und charakterisiert werden. Um den Einfluss und die Notwendigkeit der Überbrückung durch die Polyethereinheit auf die Chelatisierung von Metallionen genauer zu untersuchen, sollen verschiedene Trifluormethansulfonamidcalix[4]arene in der cone-Konformation synthetisiert werden. Es soll geprüft werden, wie sich der Austausch von Sauerstoff- gegen Stickstoffdonoren, aber auch eine sterisch anspruchsvollere Brücke auf die Komplexbildung auswirkt. Außerdem soll die Brückeneinheit komplett durch Trifluormethansulfonamidfunktionen ersetzt werden. Anschließend sollen die synthetisierten Verbindungen mittels NMR- und UV/Vis-Spektroskopie auf ihre Fähigkeit untersucht werden, Bariumionen zu binden. Aufgrund der ähnlichen chemischen Eigenschaften und Ionenradien lassen die Ergebnisse auch Schlüsse auf die Komplexierung von Radium zu.
Keywords: Calix[4]aren, Kronenether, Radium, Barium
  • Master thesis
    TU Dresden, 2017
    Mentor: Dr. habil. Constantin Mamat
    103 Seiten

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Publ.-Id: 26551


Clinical feasibility of single-source dual-spiral 4D dual-energy CT for proton treatment planning within the thoracic region

Wohlfahrt, P.ORC; Troost, E. G. C.; Hofmann, C.; Richter, C.; Jakobi, A.
Purpose: Single-source dual-spiral dual-energy computed tomography (DECT) provides additional patient information but is prone to motion between both consecutively acquired CT scans. Here, the clinical applicability of dual-spiral time-resolved DECT (4D-DECT) for proton treatment planning within the thoracic region was evaluated.

Methods and Materials: Dual-spiral 4D-DECT scans of three lung-cancer patients were acquired. For temporally averaged datasets and 4 breathing phases, the geometrical conformity of 80/140kVp 4D-DECT scans before image post-processing was assessed by normalized cross correlation (NCC). Additionally, the conformity of the corresponding DECT-derived 58/79keV pseudo-monoenergetic CT datasets (MonoCTs) after image post-processing including deformable image registration (DIR) was determined. To analyze the reliability of proton dose calculation, clinical (PlanClin) and artificial worst-case (PlanWorstCase, targeting diaphragm) treatment plans were calculated on 140kVp and 79keV datasets and compared with gamma analyses (0.1% dose-difference, 1mm distance-to-agreement criterion). The applicability of patient-specific DECT-based stopping-power-ratio (SPR) prediction was investigated and proton range shifts compared to the clinical heuristic CT-number-to-SPR conversion (HLUT) were assessed. Finally, the delineation variability of an experienced radiation oncologist was quantified on DECT-derived datasets.

Results: Dual-spiral 4D-DECT scans without DIR showed a high geometrical conformity with average NCC (±1SD) of 98.7(±1.0)% including all patient voxel or 88.2(±7.8)% considering only lung. DIR clearly improved the conformity leading to average NCC of 99.9(±0.1)% and 99.6(±0.5)%, respectively. PlanClin dose distributions on 140kVp and 79keV datasets were similar with average gamma passing rate of 99.9% (99.2%-100%). The worst-case evaluation still revealed high passing rates (average: 99.3%, minimum: 92.4%). Clinically relevant mean range shifts of 2.2(±1.2)% were determined between patient-specific DECT-based SPR prediction and HLUT. The intra-observer delineation variability could be slightly reduced by additional DECT-derived datasets.

Conclusions: 79keV MonoCT datasets can be consistently obtained from dual-spiral 4D-DECT and are applicable for proton dose calculation. Patient-specific DECT-based SPR prediction performed appropriately and potentially reduces range uncertainty in proton therapy of lung-cancer patients.
Keywords: dual-energy CT, proton range, range uncertainty, non-small cell lung cancer, 4DCT

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Permalink: https://www.hzdr.de/publications/Publ-26550
Publ.-Id: 26550


Energy scaling of laser accelerated protons at the Draco laser facility at HZDR

Obst, L.; Brack, F.-E.; Bock, S.; Bussmann, M.; Cochran, G.; Cowan, T. E.; Curry, C. B.; Gauthier, M.; Gebhardt, R.; Glenzer, S. H.; Göde, S.; Helbig, U.; Irman, A.; Jahn, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Metzkes, J.; Poole, P.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schumaker, D.; Zeil, K.; Ziegler, T.; Schramm, U.
We present various approaches to increase the generated proton energy in laser driven proton acceleration. Recent results gained at our in-house laser system deploying different laser and target parameters are shown.
  • Poster
    Doktorandenseminar des HZDR, 16.-18.10.2017, Seiffen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26549
Publ.-Id: 26549


(+)-[18F]Flubatine ein neuer α4β2 nikotinischer Acetylcholin-Rezeptor (nAChR) PET Radioligand - Ergebnisse der First-In-Human Studie bei Patienten mit Alzheimer Demenz (AD) und gesunden Probanden (HC).

Tiepolt, S.; Becker, G. A.; Wilke, S.; Cecchin, D.; Meyer, P. M.; Barthel, H.; Hesse, S.; Patt, M.; Rullmann, M.; Wagenknecht, G.; Deuther-Conrad, W.; Ludwig, F. A.; Wagner, A.; Gertz, H. J.; Smits, R.; Hoepping, A.; Brust, P.; Sabri, O.
Abstract wird nachgereicht
  • Abstract in refereed journal
    Nuklearmedizin 57(2018), V103
  • Lecture (Conference)
    56. Jahrestagung der DGN, 18.-21.04.2018, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26548
Publ.-Id: 26548


Cognitive correlates of α4β2 nicotinic acetylcholine receptor (α4β2-nAChR) availability in mild Alzheimer's dementia (AD) investigated with (-)-[F-18]Flubatine PET

Meyer, P. M.; Gräf, S.; Hesse, S.; Wilke, S.; Becker, G. A.; Rullmann, M.; Patt, M.; Luthardt, J.; Wagenknecht, G.; Hoepping, A.; Smits, R.; Franke, A.; Sattler, B.; Tiepolt, S.; Fischer, F.; Deuther-Conrad, W.; Hegerl, U.; Barthel, H.; Schönknecht, P.; Brust, P.; Sabri, O.
Abstract wird nachgereicht
  • Abstract in refereed journal
    Nuklearmedizin 56(2018)-V104

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Permalink: https://www.hzdr.de/publications/Publ-26545
Publ.-Id: 26545


Messung des prompten γ-Strahlungsspektrums aus der Spontanspaltung von ²⁴²Pu

Urlaß, S.
The prompt gamma-ray spectrum of fission fragments (in the following PFGS) is important role for the dynamics of the fission process, as well as for nuclear engineering through gamma-ray heating in nuclear reactors. In this thesis the prompt gamma-ray spectrum from the spontaneous fission of ²⁴²Pu was measured. The gamma-quanta were detected with high time- and energy-resolution using LaBr₃ scintillators and High Purity Germanuim detectors in coincidence with spontaneous fission events of ²⁴²Pu fission chamber. This chamber was recently developed at the Helmholtz-Zentrum Dresden - Rossendorf. The aquired results show a much reduced statistical uncertainty in comparison with previous measurements. The PFGS measured with the HPGe detectors shows structures that allow conclusions about the nature of the gamma-ray transitions in the fission fragments.
The measured data can be used to test and improve statistical model calculations of the PFGS, e.g in the GEF-model.
Keywords: prompt fission gamma-ray spectrum, spontaneous fission, GEF code
  • Master thesis
    TU Dresden, 2018
    Mentor: Dr. Arnd R. Junghans
    113 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-26544
Publ.-Id: 26544


Realisierung kompakter, hochintensiver Röntgenlaser mittels Traveling-Wave Thomson-Streuung

Steiniger, K.
Öffentlicher Verteidigungsvortrag der Dissertation "High-Yield Optical Undulators Scalable to Optical Free-Electron Laser Operation by Traveling-Wave Thomson-Scattering" von Herrn Klaus Steiniger
  • Lecture (others)
    Öffentliche Verteidigung, 15.12.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26543
Publ.-Id: 26543


Probing of ultra-high contrast laser-plasma interaction from condensed hydrogen jet

Ziegler, T.ORC; Rehwald, M.ORC; Brack, F.; Curry, C.ORC; Gauthier, M.ORC; Glenzer, S.; Göde, S.; Kraft, S. D.ORC; Metzkes, J.; Obst, L.ORC; Rödel, C.; Schlenvoigt, H.-P.ORC; Zeil, K.; Schramm, U.ORC
To advance the development of laser proton accelerators for highly demanding applications like cancer treatment a stable source of energetic particles at high repetition rates is required.
During our last experimental campaign at the Helmholtz-Zentrum Dresden-Rossendorf we therefore employed a pure condensed hydrogen jet as a renewable target for the 100TW Draco laser. Draco is a ultra-high power Ti:Sa laser system which delivers pulses of 30fs and 3J on target at 800nm with a repetition rate of 10Hz. A recollimating single plasma mirror results in an improved temporal contrast represented by an ASE level of 10-13.
The expanding jet was monitored on-shot with a separate phase locked diode-pumped ps-laser at a wavelength of 515 nm. By that over-exposure of the CCD resulting from strong plasma self-emission which had been observed in earlier experiments to be at the harmonics of the pump laser, could be avoided. The probe beam was split in two parts oriented perpendicular and parallel with respect to the pump laser axis in order to precisely determine the jet position and its density profile.
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26542
Publ.-Id: 26542


Combination of KLOE σ(e+e → π+π γ(γ) measurements and determination of aμπ+π- in the energy range 0.10 < s < 0.95 GeV2

Anastasi, A.; Babusci, D.; Berlowski, M.; Bloise, C.; Bossi, F.; Branchini, P.; Budano, A.; Caldeira Balkeståhl, L.; Cao, B.; Ceradini, F.; Ciambrone, P.; Curciarello, F.; Czerwiński, E.; D’Agostini, G.; Danè, E.; de Leo, V.; de Lucia, E.; de Santis, A.; de Simone, P.; Di Cicco, A.; Di Domenico, A.; Domenici, D.; D’Uffizi, A.; Fantini, A.; Fantini, G.; Fermani, P.; Fiore, S.; Gajos, A.; Gauzzi, P.; Giovannella, S.; Graziani, E.; Ivanov, V. L.; Johansson, T.; Kisielewska-Kamińska, D.; Kang, X.; Kozyrev, E. A.; Krzemien, W.; Kupsc, A.; Loffredo, S.; Lukin, P. A.; Mandaglio, G.; Martini, M.; Messi, R.; Miscetti, S.; Morello, G.; Moricciani, D.; Moskal, P.; Passeri, A.; Patera, V.; Perez Del Rio, E.; Raha, N.; Santangelo, P.; Schioppa, M.; Selce, A.; Silarski, M.; Sirghi, F.; Solodov, E. P.; Tortora, L.; Venanzoni, G.; Wiślicki, W.; Wolke, M.; Keshavarzi, A.; Müller, S. E.ORC; Teubner, T.
The three precision measurements of the cross section σ(e + e − → π + π − γ(γ)) using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for σ( e e → π π γ(γ) ). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range 0.10 < s < 0.95 GeV2 of aμπ+π- = (489.8 ± 1.7stat ± 4.8sys ) × 10−10 .

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Permalink: https://www.hzdr.de/publications/Publ-26541
Publ.-Id: 26541


Selective Recovery of Molybdenum from Rhenium Containing Sulphate Model Solutions by Solvent Extraction with Organophosphorus and Oxime Reagents

Helbig, T.; Scharf, C.
In various primary or secondary raw materials, for example in molybdenite or in so called “Theisenschlamm”, rhenium and molybdenum appear together. Consequently, processing of those materials can lead to aqueous solutions containing both elements. In order to obtain a separation of these elements the selective recovery of molybdenum by organophosphorus (D2EHPA, Cyanex 272) and oxime (LIX 63, LIX 84, LIX 860, LIX 984) reagents diluted in kerosene is investigated. The selectivity for the extraction of molybdenum over rhenium is compared and D2EHPA, Cyanex 272 as well as LIX 984 are chosen for extraction tests from sulphate model solutions containing zinc(II), iron(III), copper(II), molybdenum(VI), rhenium(VII), antimony(V), germanium(IV) and cobalt(II). Cyanex 272 achieves the highest selectivity for molybdenum. Due to that extraction isotherms of molybdenum with Cyanex 272 are constructed.
  • Open Access Logo Contribution to proceedings
    21st International Solvent Extraction Conference, 05.-09.11.2017, Miyazaki, Japan
  • Lecture (Conference)
    21st International Solvent Extraction Conference, 05.-09.11.2017, Miyazaki, Japan

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Permalink: https://www.hzdr.de/publications/Publ-26540
Publ.-Id: 26540


Ultrafast X-ray tomographic imaging of multiphase flow in bubble columns - Part 2: Characterisation of bubbles in the dense regime

Lau, Y. M.; Möller, F.; Hampel, U.; Schubert, M.ORC
Opaqueness and visual accessibility in turbulent bubbly flows are the main cause of difficulty for conventional experimental techniques to extract properties from the bulk flow. Ultrafast X-ray tomography presents an unique possibility to visualise the dense bubbly flows and to provide the ability to characterise the bubbles. With this technique, temporally resolved measurements can be obtained from a scanning plane. The post-processed images are stacked in time, resulting in a three-dimensional matrix with two spatial and one temporal resolutions. The gas flow structures are given straightforward by the image stack, which provides unique insights of the bubbly flow dynamics. However, sizing the bubbles requires the velocity to be known, which can be achieved by means of measurement or assumption. Typically, a second measurement plane is needed for the velocity estimation. However, the employment of dual plane measurement data is limited to dilute bubbly flows. To characterise bubbles in the dense regime, a method is presented using only single plane data for size extraction without the need of velocity data. The procedure comprises determinating the Sauter diameter (d32), which depicts the ratio between volume and surface area of the bubble. Contrary to the use of dual plane measurements, here, the bubble diameter is firstly determined and from the bubble size with the assumption of the bubble’s shape, the absolute bubble velocity can be roughly estimated. This method is verified with synthetic data of simple ideal-shaped bubbles. Subsequently, real bubbly flow measurements in bubble columns (with and without internals) are applied for the assessment of the resulting bubble sizes and velocity trend.
Keywords: Ultrafast X-ray tomography, Bubble column, Flow structure, Bubble size, Sauter diameter, Bubble velocity

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Permalink: https://www.hzdr.de/publications/Publ-26539
Publ.-Id: 26539


Ultrafast X-ray tomographic imaging of bubbly flow - Part 1: Image processing and reconstruction comparison

Lau, Y. M.; Hampel, U.; Schubert, M.ORC
Ultrafast X-ray tomography is a recently developed imaging technique for multiphase flows. As conventional X-ray tomography it involves reconstruction of images from X-ray projection data. If used for multiphase flow measurements it moreover needs to be complemented with automated image processing algorithms for the extraction of flow features, such as gas holdup profiles, bubble/particle size distributions or disperse phase velocities. So far image reconstruction was carried out with the standard filtered backprojection technique, which is fast but may not be optimal in the presence of noisy or corrupted data. As the latter is a frequent issue, search for optimal image reconstruction and data processing algorithms is continuously ongoing. This paper serves as a foundation of the image reconstruction and processing framework for the application to multiphase flow. A description is given of the procedure from reconstruction to thresholding to properties extraction of ultrafast X-ray tomographic images. Two reconstruction techniques, FBP and SART are employed based on phantom measurements. Each technique is evaluated separately, for FBP regarding the choice of filter and for SART regarding the termination criteria. Image reconstruction resolution, computational costs and sensitivity to the threshold value are investigated. Based on the analysis, FBP with the Ram-Lak filter is selected for image processing purposes. Furthermore it is shown that from experiments with moving objects, there is fair agreement between measurements and the phantom dimensions. The described imaging process can be applied to different attenuation materials, simulating gas-solid and gas-liquid properties.
Keywords: Ultrafast X-ray tomography, Multiphase flows, Reconstruction, Thresholding, Image processing

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Permalink: https://www.hzdr.de/publications/Publ-26537
Publ.-Id: 26537


A Flow Pattern Adaptive Multi-field Two-fluid Concept for turbulent two-phase flows

Schlegel, F.; Meller, R.; Oertel, R.
Industrial applications feature a huge variety of different flow patterns, such as bubbly flow, slug flow or annular flow. Thereby the issue of a big range of different physical scales is involved. With the objective of reproduction of occurring phenomena with one single multifluid solver, we present an Euler-Euler-approach, which combines a number of different methods for treatment of the partial aspects. The implementation into OpenFOAM is always with focus on sustainable research, including a state-of-the-art IT concept. A segregated approach is used for treatment of the phase momentum equations, phase fraction equations and the pressure equation, featuring a consistent momentum interpolation scheme (Cubero et al., 2014). To fulfill the kinematic condition at resolved interfaces between different continuous phases, the latter may be coupled either by an isotropic (Strubelj and Tiselj, 2011) or by an anisotropic drag. In both cases, the immensely strong phase coupling requires an adapted numerical method. State and evolution of bubble size distribution in disperse phase context is solved with either class or moment methods. The overall objective is to take interactions between the all different aspects, such as disperse phases, resolved interfaces and turbulence with effects on momentum and mass transfer into account.
  • Poster
    15th Multiphase Flow Conference & Short Course, 14.-17.11.2017, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-26536
Publ.-Id: 26536


Severe accident management measures for a generic German PWR. Part I: Station blackout

Wilhelm, P.; Jobst, M.; Kozmenkov, Y.; Schäfer, F.; Kliem, S.
This paper focuses on analysis of severe accident management measures for a generic German PWR of type Konvoi. A nuclear power plant model based on the severe accident code ATHLET-CD was developed in order to assess the code applicability for simulation of accident scenarios with core degradation. It was applied for investigation of two main groups of accident scenarios: station blackout and small-break lossof-coolant accident.

Part I of series of two papers analyses the plant response in case of hypothetical station blackout severe accident. Assessment of accident management measures in the preventive and in the mitigative domain is performed, where a focus is given on the combination of primary pressure reduction and injection by portable equipment directly into the reactor circuit. Key timings for operator actions are deduced. Both positive and negative effects of the investigated accident management measures are discussed. The results from the station blackout simulations showed that the time until core degradation can be delayed by application of primary side depressurization and usage of mobile pump as accident management measures. Depending on the time of injection significant reduction of the hydrogen and fission products releases can be obtained. In case that early water injection is possible, severe core damage might be prevented.
Keywords: Severe accident, Station blackout, PWR, Konvoi, Accident management

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-26535
Publ.-Id: 26535


Tetravalent actinide complexes with N,O-donor ligands: Synthesis and characterisation

März, J.
A fundamental understanding of tetravalent actinides can be achieved by series of analogue coordination compounds with organic ligands bearing typical biologically relevant binding functions like N and O donors. Complex series with different actinides (Th, U, Np) or slightly modified ligands show differences in binding modes and complex geometry. Structural information can also be gained from NMR studies of the paramagnetic complexes.
  • Invited lecture (Conferences)
    Gruppenseminar, 08.12.2017, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26534
Publ.-Id: 26534


Struktur-Wirkungsbeziehungen zwischen f-Elementen und organischen Ligandsystemen

Brunner, E.; März, J.
Um die Wechselwirkungen von f-Elementen in natürlichen Systemen beschreiben zu können, sind kleine Modellverbindungen nötig, die die Bindungsverhältnisse der Bioliganden wiederspiegeln. Es werden die Komplexe drei- und vierwertiger Lanthanide und Actinide mit umweltrelevanten Liganden untersucht und die zu untersuchenden grundlegenden Eigenschaften abgeleitet.
  • Lecture (Conference)
    3. Projektstatusgespräch zur BMBF-geförderten Nuklearen Sicherheitsforschung, 27.-28.04.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26533
Publ.-Id: 26533


Centrality determination of Au+Au collisions at 1.23A GeV with HADES

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcy, G.; Kornakov, G.; Kotte, R.; Kühn, W.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.
The centrality determination for Au+Au collisions at 1.23A GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-of-mass energy of sqrt(s_NN) = 2.42 GeV special investigations were per-formed. As a result a well defined procedure to determine centrality classes for ongoing analyses of heavy-ion data is established.

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Permalink: https://www.hzdr.de/publications/Publ-26532
Publ.-Id: 26532


Stability of U(VI) and Cm(III) doped calcium silicate hydrate phases in high saline brines

Wolter, J.-M.; Schmeide, K.; Huittinen, N. M.; Stumpf, T.
U(VI) and Cm(III) doped calcium silicate hydrate (CSH) phases with different C/S ratios (1.0-2.0) were synthesized directly in presence of either U(VI) or Cm(III) and characterized by time-resolved laser-induced fluorescence spectroscopy (TRLFS), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The time-dependent release of Ca, Si, U and Cm from CSH phases into brines that contained either 2.5 M NaCl, 2.5 M NaCl/0.02 M Na2SO4, 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3 for U(VI) doped CSH phases or 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3 for Cm(III) doped CSH phases was monitored in batch leaching experiments for 30 or 60 days, respectively. Subsequently, leaching induced changes of the CSH structure and of the U(VI) or Cm(III) coordination environment were investigated with TRLFS, IR spectroscopy and XRD.
Site-selective TRLFS studies of the Cm(III)/CSH binding at 4 K revealed a fluent transition between two sorption sites causing a luminescence line-narrowing effect. The leached CSH phases showed pronounced differences in terms of decomposition behavior and actinide release depending on their C/S ratio and type of incorporated actinide. CSH phases with a lower C/S ratio were influenced strongly by NaHCO3 and showed a mobilization of U(VI) as Ca2UO2(CO3)3(aq). In contrast, Cm(III) was not leached out but as detected by site-selective TRLFS it is incorporated into calcite and vaterite (Fig. 1 (r.), 608 and 612.8 nm) formed during leaching in NaHCO3. The comparison between leaching experiments performed in 0.02 M NaHCO3 and 2.5 M NaCl/0.02 M NaHCO3 revealed that the presence of 2.5 M NaCl increases the U(VI) mobilization for CSH phases with high C/S ratios while no influence on the Cm(III) release was detectable.
Keywords: CSH phases, curium, site-selective, TRLFS, leaching, carbonate, sodium chloride, cement, saline, salt
  • Contribution to proceedings
    2nd Workshop on Calcium Silicate Hydrates containing Aluminium: C-A-S-H II, 23.-24.04.2018, Dübendorf, Schweiz
    Proceedings of the 2nd Workshop on Calcium Silicate Hydrates containing Aluminium
  • Poster
    2nd Workshop on Calcium Silicate Hydrates containing Aluminium: C-A-S-H II, 23.-24.04.2018, Dübendorf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-26531
Publ.-Id: 26531


Calix[4]aren-based Ligands as Extracting Agents for f-Elements

Jäschke, A.
Summary of yielding results which were achieved in the SE-FLECX project. This short talk should give the members of the FENABIUM project an overview of the main concept of this project.
  • Lecture (others)
    FENABIUM-Projekttreffen, 04.12.2017, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26530
Publ.-Id: 26530


A superradiant THz undulator source for XFELs

Tanikawa, T.; Karabekyan, S.; Kovalev, S.; Casabuoni, S.; Asgekar, V.; Serkez, S.; Geloni, G.; Gensch, M.
The generation of frequency-tunable, narrow-bandwidth and carrier-envelope-phase stable THz pulses with fields in the MV/cm regime that can be appropriately timed to the femtosecond X-ray pulses from free-electron-lasers is of highest scientific interest. It will enable to follow the electronic and structural dynamics stimulated by (non)linear selective excitations of matter on few femtosecond time and Ångstrom length scales. In this article, a scheme based on superradiant undulator emission generated just after the XFEL is proposed. The concept utilizes cutting edge superconducting undulator technology and provides THz pulses in a frequency range between 3 and 30 THz with exceptional THz pulse energies. Relevant aspects for realization and operation are discussed point by point on the example of the European XFEL.
Keywords: XFEL, superradiant, undulator, THz control

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Permalink: https://www.hzdr.de/publications/Publ-26529
Publ.-Id: 26529


Ressourceneffizienz durch Digitalisierung

Reuter, M. A.
Ressourceneffizienz gewinnt in kleinen und mittleren Unternehmen seit den letzten Jahren immer mehr an Bedeutung. Der wirtschaftliche Unternehmenserfolg kann durch optimierte Prozesse in der Produktion und einen effizienten Einsatz von Ressourcen deutlich gesteigert werden.
Welche Chancen die Digitalisierung für die Wirtschaft bietet und wie sich dadurch die sächsische Industrie verändert - all dies diskutieren Experten am 23. November 2017 im Deutschen Hygiene-Museum Dresden. Die Teilnehmer erwarten Praxisbeispiele speziell aus dem Bereich wirtschaftsstrategischer Rohstoffe. Vorgestellt werden auch regionale und bundesweite Unterstützungsmöglichkeiten und Förderprogramme für KMU in Sachsen.
Keywords: Ressourceneffizienz, Digitalisierung
  • Lecture (Conference)
    Ressourceneffizienz durch Digitalisierung - Trends und Chancen für KMU, 23.11.2017, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-26528
Publ.-Id: 26528


Flotation study of fine grained carbonaceous sedimentary apatite ore – Challenges in process mineralogy and impact of hydrodynamics

Hoang, D. H.ORC; Kupka, N.; Peuker, U. A.ORC; Rudolph, M.ORC
The flotation beneficiation of apatite for phosphate production is challenging for finely disseminated sedimentary ores rich in carbonates. Similarities in surface properties of the semi-soluble salt-type carbonate and phosphate calcium minerals combined with fine intergrowth are the main reasons for poor grade and low recoveries. Imperfect depression of the calcium/magnesium carbonate minerals, e.g. calcite and dolomite, will lead to weak hydrophobic surface properties and thus true flotation of this gangue. Furthermore, fine particles, even though sufficiently liberated, strongly affect the bubble-particle collection due to negative rheological effects within the pulp leading to a drop in flotation kinetics of the fine valuables and an increase in entrainment
of fine gangue particles.
This study presents the results and discussions based on automated mineralogy (conducted with a Mineral Liberation Analyzer – MLA) of size-by-size-by liberation analyses for various mineral groups. In addition, results on different turbulent hydrodynamic parameters are presented based on various tests in a lab cell.
Keywords: Carbonaceous sedimentary apatite; Automated mineralogy; MLA; Surface Liberation; Turbulent hydrodynamics; Flotation kinetics

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Permalink: https://www.hzdr.de/publications/Publ-26527
Publ.-Id: 26527


Betatron diagnostic for transverse electron beam dynamics in a nanocoulomb-class laser wakefield accelerator

Koehler, A.ORC; Pausch, R.; Couperus, J. P.ORC; Zarini, O.; Krämer, J. M.; Kurz, T.; Debus, A.; Bussmann, M.; Schramm, U.ORC; Irman, A.
Laser-plasma wakefield accelerators have shown generation of quasi-monoenergetic (QME) electron bunches with reaching to multiple GeVs range.
Scaling the accelerated charge within the QME bunch from pC to nC is one of the important issues for many applications.
This high charge naturally brings laser wakefield in the so-called beam loading regime, which can deteriorate the beam quality if not properly controlled.

In our recent experiments carried out with the Draco Ti:Sapphire laser we explore the influence of beam loading on the transverse electron beam dynamics.
Utilizing 2D x-ray spectroscopy technique we deduced the electron beam size close the plasma exit by analyzing the x-ray spectrum emitted as relativistic electrons perform betatron oscillation during acceleration.
Simultaneously electron spectra and divergence were recorded at a charge calibrated point-to-point imaging electron spectrometer.
We show that as the electron beam size increases with charge, the beam divergence reaches a minimum value at the optimum loading condition where, at the same time, the energy spread reaches a minimum.
We anticipate that this result will open a new path for beam optimization in high charge laser wakefield accelerators.
  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 24.09.2017, La Biodola, Isola d'Elba, Italia

Permalink: https://www.hzdr.de/publications/Publ-26526
Publ.-Id: 26526


Simulate what is measured: next steps towards predictive simulations

Debus, A.; Pausch, R.; Steiniger, K.; Hübl, A.; Garten, M.; Zacharias, M.; Burau, H.; Vorberger, J.; Widera, R.; Irman, A.; Kluge, T.; Zeil, K.; Kraus, D.; Schramm, U.; Cowan, T.; Bussmann, M.
Simulations of laser matter interaction at extreme intensities that have predictive power are nowadays in reach when considering codes that make optimum use of high performance compute architectures. Nevertheless, this is mostly true for very specific settings where model parameters are very well known from experiment and the underlying plasma dynamics is governed by Maxwell’s equations solely. When including atomic effects, prepulse influences, radiation reaction and other physical phenomena things look different. Not only is it harder to evaluate the sensitivity of the simulation result on the variation of the various model parameters but numerical models are less well tested and their combination can lead to subtle side effects that influence the simulation outcome.
We propose to make optimum use of future compute hardware to compute statistical and systematic errors rather than just find the mots optimum set of parameters fitting an experiment. This requires to include experimental uncertainties which is a challenge to current state of the art techniques. Moreover, it demands better comparison to experiments as inclusion of simulating the diagnostic’s response becomes important.
We strongly advocate the use of open standards for finding interoperability between codes for comparison studies, building complete tool chains for simulating laser matter experiments from start to end.
Keywords: synthectic diagnostics, big data, particle-in-cell code, PIC, Laser-produced plasmas, Plasma-based accelerators, Laser-wakefield acceleration, Traveling-wave electron acceleration, TWEAC, HPC
  • Invited lecture (Conferences)
    SPIE Optics + Optoelectronics 2017, Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers, 24.-26.04.2017, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-26525
Publ.-Id: 26525


Traveling-Wave Electron Acceleration: Breaking the dephasing and depletion limits of laser-wakefield acceleration

Debus, A.; Pausch, R.; Huebl, A.; Steiniger, K.; Widera, R.; Cowan, T.; Schramm, U.; Bussmann, M.
We show how to simultaneously solve several longstanding limitations of laser-wakefield acceleration that have thus far prevented laser-plasma electron accelerators (LWFA) to extend into the energy realm beyond 10 GeV. Most prominently, our novel Traveling-Wave Electron Acceleration (TWEAC) approach [1] eliminates both the dephasing and depletion constraints, which fundamentally limit the maximum energy gain of a single LWFA stage. This is complemented with a focusing geometry, which does not require any guiding structures, such as plasma-capillaries, and does not rely on laser self-guiding in plasma. This opens up acceleration regimes that were previously inaccessible.

The wakefield driver is a region of overlap of two obliquely incident, ultrashort laser pulses with tilted pulse-fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of subsequently accelerated electrons. First, such a laser geometry drives a wakefield moving at the vacuum speed of light instead of the sub-luminal group-velocity vg < c, thus preventing electrons from outrunning the plasma wave (dephasing limit). Secondly, this leads to a stable and experimentally controllable plasma cavity by having at every instant a new, unspoilt section of the laser pulse, which has not yet undergone self-phase modulation, transversely entering the plasma and, after only a short propagation distance, form the acceleration cavity in plasma regions previously unperturbed by lasers. That latter mechanism eliminates the pump depletion limit of LWFA.

TWEAC presents a prospect of vastly reducing or even completely disposing the problem of staging between several LWFAs to achieve higher energies and hence averts the loss of electron beam quality, such as charge decrease due to inter-stage beam transport or laser-stage-coupling inefficiencies. Given enough laser pulse energy and in contrast to LWFA and PWFA, TWEAC can arbitrarily be extended in length to higher electron energies without changing the underlying acceleration mechanism.

We show that TWEAC leads to quasi-static acceleration conditions, which do not suffer from laser self-phase modulation, parasitic self-injection or other plasma instabilities. Similarly, the TWEAC geometry greatly facilitates reducing beam transport distances between the laser-plasma accelerator and subsequent insertion devices, such as undulators, plasma lenses or colliding laser pulses, to below millimeters. This is especially critical for reducing emittance growth during beam transport.

We introduce the new acceleration scheme, show results from 3D particle-in-cell simulations using PIConGPU, discuss energy scalability for both laser and electrons and elaborate on experimental realization requirements.

References
[1] Debus et al., “Breaking the dephasing and depletion limits of laser-wakefield acceleration”, paper submitted.
Keywords: Laser-produced plasmas, Plasma-based accelerators, Laser-wakefield acceleration, LWFA, Traveling-wave electron acceleration, TWEAC
  • Lecture (Conference)
    IBS Conference on Laser Plasma Accelerators 2017, 27.08.-01.09.2017, Jeju island, Korea

Permalink: https://www.hzdr.de/publications/Publ-26524
Publ.-Id: 26524


Traveling-Wave Electron Acceleration (TWEAC) -- Electron acceleration

Debus, A.ORC; Pausch, R.; Huebl, A.; Steiniger, K.; Cowan, T. E.; Schramm, U.; Widera, R.; Bussmann, M.
Informal abstract via e-mail to organizer:
For the ANAR workshop community, the contribution shows a novel way of eliminating/curbing the use of multiple-stages, when aiming for high electron energies (i.e. in a laser-driven setting instead of a PWFA variant). Also, the new mechanism leads to quasi-static acceleration conditions and does not suffer from laser self-phase modulation, parasitic self-injection or other plasma instabilities. All of this could be of interest when discussing a roadmap to laser-plasma linear colliders.

Corresponding paper abstract:
Compact electron accelerators are paramount to next generation synchrotron light sources and free-electron lasers, as well as for advanced accelerators at the TeV energy frontier. Recent progress in laser-plasma driven accelerators (LPA) has extended their electron energies to the multi-GeV range and improved beam stability for insertion devices.
However, the sub-luminal group-velocity of plasma waves limits the final electron energy which can be achieved in a single LPA accelerator stage, also known as the dephasing limit.
Here we present the first laser-plasma driven electron accelerator concept without electrons outrunning the wakefield. Our scheme is robust against parasitic self-injection and self-phase modulation as well as drive-laser depletion and defocusing along the accelerated electron beam. It works for a broad range of plasma densities in gas targets.
This opens the way for scaling up electron energies towards TeV scale electron beams without the need for multiple laser-accelerator stages.
Keywords: Laser-produced plasmas, Plasma-based accelerators, Laser-wakefield acceleration, LWFA, Traveling-wave electron acceleration, TWEAC
  • Lecture (Conference)
    ANAR2017: Advanced and Novel Accelerators for High Energy Physics Roadmap Workshop 2017, 25.-28.04.2017, Cern, Geneva, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-26523
Publ.-Id: 26523


Laser pulses for Traveling-Wave Electron Acceleration and Thomson Scattering

Debus, A.ORC; Steiniger, K.; Pausch, R.; Albach, D.; Loeser, M.; Roeser, F.; Huebl, A.; Widera, R.; Cowan, T.; Schramm, U.; Siebold, M.; Bussmann, M.
Generating and controlling ultrashort, pulse-front tilted laser pulses is essential for Traveling-Wave Electron Acceleration (TWEAC), Traveling-Wave Thomson Scattering (TWTS) and Traveling-Wave Optical FELs (TWTS-OFELs). All these applications require controlling angular and group-delay dispersion, while keeping experimental setups as compact as possible. However, the varying requirements with respect to laser power, extent of focal region, incident angles and laser mode quality lead to differing strategies in designing experimental setups.
This overview poster provides answers to the question: What experimental efforts in terms of laser system and optics are necessary in current labs for first proof-of-principle realizations of the different applications of "Traveling-Wave" laser pulses -- ranging from low-bandwidth and yield-enhanced Thomson sources (TWTS), laser-based electron accelerators beyond the LWFA depletion and dephasing limits (TWEAC) and ultimately an optical free-electron laser (TWTS-OFEL)?
Keywords: Traveling-Wave Thomson Scattering, TWTS, Traveling-Wave Electron Acceleration, TWEAC, Traveling-Wave Thomson Scattering Optical FEL, TWTS-OFEL, Thomson Scattering
  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 24.-30.09.2017, La Biodola, Isola d'Elba, Italien

Permalink: https://www.hzdr.de/publications/Publ-26522
Publ.-Id: 26522


Traveling-Wave Electron Acceleration -- Beyond the dephasing and depletion limits of laser-wakefield acceleration

Debus, A.ORC; Pausch, R.; Huebl, A.; Steiniger, K.; Widera, R.; Cowan, T.; Schramm, U.; Bussmann, M.
We show how to simultaneously solve several long standing limitations of laser-wakefield acceleration that have thus far prevented laser-plasma electron accelerators (LWFA) to extend into the energy realm beyond 10 GeV. Most prominently, our novel Traveling-Wave Electron Acceleration (TWEAC) approach eliminates both the dephasing and depletion constraints. The wakefield driver is a region of overlap of two obliquely incident, ultrashort laser pulses with tilted pulse-fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of subsequently accelerated electrons.
TWEAC leads to quasi-static acceleration conditions, which do not suffer from laser self-phase modulation, parasitic self-injection or other plasma instabilities. Particularly, and in contrast to LWFA and PWFA, a single TWEAC-stage can arbitrarily be extended in length to higher electron energies without changing the underlying acceleration mechanism. Additionally, the TWEAC geometry greatly facilitates reducing beam transport distances between the laser-plasma accelerator and subsequent insertion devices, such as undulators, plasma lenses or colliding laser pulses, to below millimeters.
We introduce the new acceleration scheme, show results from 3D particle-in-cell simulations using PIConGPU, discuss energy scalability for both laser and electrons and elaborate on experimental realization requirements.
Keywords: Laser-produced plasmas, Plasma-based accelerators, Laser-wakefield acceleration, LWFA, Traveling-wave electron acceleration, TWEAC
  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 24.-30.09.2017, La Biodola, Isola d'Elba, Italien

Permalink: https://www.hzdr.de/publications/Publ-26521
Publ.-Id: 26521


Self-consistently modeling Traveling-Wave Thomson-Scattering Optical Free-Electron Lasers

Debus, A.ORC; Pausch, R.; Steiniger, K.; Albach, D.; Loeser, M.; Schramm, U.; Siebold, M.; Bussmann, M.
Traveling-Wave Thomson-Scattering (TWTS) provides optical undulators with hundreds to thousands of undulator periods from high-power, pulse-front tilted lasers pulses. These allow to realize optical free-electron lasers (OFELs) with state-of-the-art technology in electron accelerators and laser systems.
TWTS employs a side-scattering geometry where laser and electron propagation direction of motion enclose the interaction angle. Tilting the laser pulse front with respect to the wave front by half the interaction angle ensures continuous overlap over the whole laser pulse width while the electrons cross the laser beam path.
Scaling laws and analytical models allow identifying experimentally promising FEL regimes for feasible setup geometries. However, selfconsistently
including all non-ideal effects in a 3D FEL simulations is desirable for predicting TWTS-OFEL designs with quantitive performance and tolerance characteristics suitable for engineering an optimal proof-of-principle experiment. In this talk we outline the challenges that existing FEL codes cannot cope with the non-collinear geometry of TWTS-OFELs, show how we solve these using the particle-in-cell code PIConGPU as 3D-FEL code and present first results.
Keywords: Free-electron lasers, Freie-Elektronen Laser, optical free-electron laser, OFEL, TWTS, Traveling-wave Thomson Scattering, TWTS-OFEL, FEL, Particle-in-cell simulation, PIC simulation
  • Lecture (Conference)
    DPG-Frühjahrstagung Dresden 2017, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26520
Publ.-Id: 26520


Untersuchungen zum Komplexierungs- und Extraktionsverhalten des Calix[4]arens FG74 gegenüber Uran(VI) und Thorium(IV)

Bauer, A.; Jäschke, A.; Schmeide, K.
Die Untersuchungen zum Komplexierungs- und Extraktionsverhalten des Calix[4]arens FG74 gegenüber Uran(VI) und Thorium(IV) wurden vorgestellt. Dabei wurde vordergründig durch spektroskopische Methoden das Verhalten bzw. die Wechselwirkungen in Lösung untersucht. Ferner wurde das Extraktionsverhalten des Calix[4]aren-basierten Liganden gegenüber ausgewählter Actiniden untersucht und grundlegende Selektivitäten bestimmt.
  • Lecture (others)
    Projekttreffen SE-FLECX, 21.11.2017, Montabaur, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26519
Publ.-Id: 26519


Encoding micro-reactors with droplet chains in microfluidics

Song, W.; Lin, G.; Ge, J.; Fassbender, J.; Makarov, D.
Droplet-based high throughput biomolecular screening and combinatorial synthesis entail a viable indexing strategy to be developed for the identification of each micro-reactor. Here, we propose a novel indexing scheme based on the generation of droplet sequences on demand to form unique encoding droplet chains in fluidic networks. These codes are represented by multiunit and multilevel droplets packages, with each code unit possessing several distinct signal levels, potentially allowing large encoding capacity. For proof of concept, we use magnetic nanoparticles as the encoding material and a giant magnetoresistance (GMR) sensor-based active sorting system supplemented with an optical detector to generate and decode the sequence of one exemplar sample droplet reactor and a 4-unit quaternary magnetic code. The indexing capacity offered by 4-unit multilevel codes with this indexing strategy is estimated to exceed 104, which holds great promise for large-scale droplet-based screening and synthesis.
Keywords: droplet , millifluidics, magnetic field sensors, GMR sensors, encoding, indexing

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Permalink: https://www.hzdr.de/publications/Publ-26518
Publ.-Id: 26518


Development of an active bremsstrahlung detector for laser-plasma experiments

Molodtsova, M.; Ferrari, A.; Laso Garcia, A.; Sobiella, M.; Stach, D.; Weinberger, D.; Cowan, T.
The use of high intensity, high power lasers recently increased in research facilities all over the world. By laser-matter interactions it is possible to study new mechanisms of ion/electron acceleration, and matter under extreme conditions via pump-probe experiments. At the X-ray Free Electron Laser in Hamburg (EuXFEL) such extreme conditions will be generated and studied at the High Energy Density (HED) instrument at the Helmholtz International Beamline for Extreme Fields (HIBEF). For such experiments a wide variety of novel detectors will be needed. One of the challenges will be the detection of the bremsstrahlung radiation emitted with ultrashort pulse widths (gamma flash) down to the fs range, at every laser shot.
To characterize the gamma flash usual spectrometry techniques using pulse height analysis can not be used, because of its short pulse width as well as its high intensity (~10^10 photons). A possible approach is to measure the energy deposited by photons in a detector with a layered structure, to obtain information about the longitudinal development of the electromagnetic shower. With this data the photon spectrum can be then reconstructed by using an unfolding technique. To perform a successful unfolding, detector materials and thicknesses have to be optimized to be able to resolve the photon spectrum in the dynamic range between 50 keV and 20 MeV.
An extensive simulation study has been performed with the FLUKA Monte Carlo code for different detector models. The model that showed the most promising set of response functions to perform a deconvolution, was chosen to realize the first prototype, which is being build currently.
In this poster the first results of this work are presented.
  • Poster
    European XFEL Users' Meeting 2017, 25.-27.01.2017, Hamburg, Deutschland
  • Poster
    MECMATPLA 2017 (Matter in extreme conditions : from material science to planetary physics), 29.01.-04.02.2017, Montgenèvre, France
  • Lecture (Conference)
    DPG-Frühjahrstagung 2017 der Sektion Materie und Kosmos (SMuK), 13.-17.03.2017, Bremen, Deutschland
  • Poster
    Workshop: High Intensity Laser Matter Science at the HED Instrument at the European XFEL, 05.-06.04.2017, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26517
Publ.-Id: 26517


An experimental method for determining turbulent kinetic energy dissipation rate in bubbly flows

Heßenkemper, H.; Ma, T.; Ziegenhein, T.; Lucas, D.
Many flow regimes in chemical engineering are gas-liquid flows with a continuous liquid phase and a dispersed gaseous phase. The turbulence of the liquid phase influences the local distribution of the dispersed phase, bubble coalescence and breakup and other important flow characteristics. Because of the importance of turbulence, it is necessary to consider its modification by bubbles.
A bubble column provides good experimental systems for the study of turbulent phenomena in bubbly flows and the development of computational models. In the present work, the combination of Particle Tracking Velocimetry system with Kolmogorov-order spatial and temporal resolutions and Particle Image Velocimetry was used for determining the liquid velocity fields in a bubble column. With this high-resolved measurement technique turbulent kinetic energy (TKE) dissipation rate is able to be accurately estimated based on an existing correction method.
Additionally, the data available cover one-point statistics for the liquid and the bubble distribution for different bubble Reynolds numbers. These completed measurement data are ideally suited for assessment of the existing bubble-induced turbulence models, not only in the traditional way by comparison of TKE but rather the values of the particular terms to be closed in the TKE equation of the liquid phase.
  • Poster
    ProzessNet Jahrestreffen, 14.-17.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26516
Publ.-Id: 26516


Particle Shadow Velocimetry (PSV) in bubbly flows

Heßenkemper, H.; Ziegenhein, T.
The interaction of gas bubbles and the surrounding liquid in bubbly flows is a complex hydrodynamic phenomenon. Precise measurements of the liquid velocity are mandatory to generate accurate models and CFD-validation data sets. For this purpose, methods for Particle Shadow Velocimetry (PSV) that are using a volume illumination and a small depth of field (DOF) are developed in the presented work. Experiments with an oscillating plume were conducted in a rectangular bubble column to test the PSV methods. The results obtained with a Particle Image Velocimetry (PIV) and a Particle Tracking Velocimetry (PTV) processing procedure agree very well with respect to velocity profiles and turbulence parameters. As discussed in previous work, PSV methods have a much simpler experimental setup and can handle much higher gas fractions. With the present findings, robust PSV algorithms for PIV and PTV in bubbly flows are now available.
Keywords: Particle Shadow Velocimetry, Multiphase Flow, Bubbly flow, Particle Image Velocimetry, Particle Tracking Velocimetry

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Permalink: https://www.hzdr.de/publications/Publ-26515
Publ.-Id: 26515


Aufbau einer CFD-Validierungsdatenbasis an einer mit Wasser und Ethanol betriebenen Blasensäule im Pilotanlagen-Maßstab

Ziegenhein, T.
Measuring the liquid velocity in large-scale bubble columns with optical methods is complex and usually limited to relatively low void fractions. In the present study, we complete a database for CFD validation that includes locally resolved information about the bubble size and gas void fraction with the information about the liquid velocity at different operating conditions. A particle identification and particle-tracking algorithm is developed, which are designed for the problems of particle tracking in bubbly flows. With a background illumination, the void fraction to which reasonable measurements can be executed is expanded compared to a laser illumination from the side. The time-averaged and transient liquid velocity field is intensively discussed for five superficial gas velocities and four superficial liquid velocities at two measuring heights. A filtering process is proposed with which the results for the turbulent kinetic energy are comparable to previous measurements in tabletop bubble columns. The detailed locally resolved information about the liquid velocity and the previously measured bubble size and gas void fraction is unique for such a large-scale bubble column. These data might help to validate and improve CFD codes for conditions closer to industrial relevant conditions. Moreover, it can help to improve the understanding of the hydrodynamics in bubble columns in general.
Keywords: bubbly flow, DFG, liquid velocity, turbulence, bubble column, PTV, PSTV
  • Other report
    Bonn: Deutsche Forschungsgemeinschaft, 2017

Permalink: https://www.hzdr.de/publications/Publ-26514
Publ.-Id: 26514


Experimental study of the liquid velocity and turbulence in a large-scale air-water counter-current bubble column

Ziegenhein, T.; Besagni, G.; Inzoli, F.; Lucas, D.
Measuring the liquid velocity in large-scale bubble columns with optical methods is complex and usually limited to relatively low volume fractions. In the present study, we complete a database for CFD validation that includes locally resolved information about the bubble size and gas volume fraction with the information about the liquid velocity at different operating conditions. A particle identification and particle-tracking algorithm is developed, which is designed for the problems of particle tracking in bubbly flows. With a background illumination, the volume fraction to which reasonable measurements can be executed is expanded compared to a laser illumination from the side. The time-averaged and transient liquid velocity field is intensively discussed for five superficial gas velocities and four superficial liquid velocities at two measuring heights. A filtering process is proposed with which the results for the turbulent kinetic energy are comparable to previous measurements in tabletop bubble columns. The detailed locally resolved information about the liquid velocity and the previously measured bubble size and gas volume fraction is unique for such a large-scale bubble column. These data might help to validate and improve CFD codes for conditions closer to industrial relevant conditions. Moreover, it can help to improve the understanding of the hydrodynamics in bubble columns in general.
Keywords: bubbly flows, Liquid velocity, PTV, PSIV, PSTV, Shadowgraphy, bubble column, validation

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  • Secondary publication expected from 17.10.2020

Permalink: https://www.hzdr.de/publications/Publ-26513
Publ.-Id: 26513


Bubble aspect ratio in dense bubbly flows: experimental studies in low Morton-numbers systems

Besagni, G.; Inzoli, F.; Ziegenhein, T.; Hessenkemper, H.; Lucas, D.
Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flow, which is far away from the flow field observed in multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape, at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. The results reveal that in the bubble column experiments almost the same shape is found whereas the shape in the pipe flows distinctly depends on the flow conditions. The conclusion may be drawn that in bubble columns the assumption of a constant shape regarding the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform the bubble distinctly.
Keywords: bubbly flows, bubble shape, bubble column
  • Contribution to proceedings
    35th UIT Heat Transfer Conference, 26.-28.06.2017, Ancona, Italy
  • Lecture (Conference)
    35th UIT Heat Transfer Conference, 26.-28.06.2017, Acona, Italy

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Permalink: https://www.hzdr.de/publications/Publ-26512
Publ.-Id: 26512


Bubble aspect ratio in dense bubbly flows: experimental studies in low Morton-number systems

Besagni, G.; Inzoli, F.; Ziegenhein, T.; Lucas, D.
Almost every modelling approach of bubbly flows includes assumptions concerning the bubble shape. Such assumptions are usually made based on single bubble experiments in quiescent flows, which is far away from the flow field observed in large-scale multiphase facilities. Considering low Morton-numbers and the highly deformable interface at medium and large Eötvös-numbers, the evaluation of the bubble shape in such systems under real flow conditions is highly desirable. In this study, we experimentally evaluate the bubble shape (in terms of aspect ratio), at low Morton-numbers, in different bubble column setups and a pipe flow setup under different operating conditions. The bubble shape in the bubble column experiments were obtained with cameras at Politecnico di Milano and Helmholtz-Zentrum Dresden Rossendorf (HZDR) whereas the shapes in the pipe flows were measured by the ultrafast electron beam X-ray tomography system (ROFEX) at HZDR. In the bubble column experiments almost the same shape is observed; conversely, the shape in the pipe flows distinctly depends on the flow conditions. In conclusion, in bubble columns the assumption of a constant shape regardless of the flow conditions is valid whereas in pipe flows the turbulence and shear rates can be strong enough to deform distinctly the bubbles.
Keywords: bubbly flow, bubble column, turbulent bubbly flow, bubble shape

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Permalink: https://www.hzdr.de/publications/Publ-26511
Publ.-Id: 26511


The Bubble Shape in Contaminated Bubbly Flows: Results for Different NaCl Concentrations in Purified Water

Ziegenhein, T.; Lucas, D.; Besagni, G.; Inzoli, F.
The bubble shape influences the transfer of momentum and heat/mass between the bubble and the surrounding fluid as well as the flow field around the bubble. The shape is determined by the interaction of the fluid field in the bubble, the physics on the surface, and the surrounding flow field. It is well known that contaminations can disturb the surface physics so that the bubble shape can be influenced. Indeed, an influence of sodium chloride (NaCl) on the hydrodynamics of bubbly flows was shown for air/water systems in previous studies. The aim of the present work is to investigate if, and to what extent, the NaCl concentration affects the bubble shape in bubble columns. For this purpose, several experiments at the Helmholtz-Zentrum Dresden-Rossendorf and at the pilot-scale bubble column at the Politecnico di Milano are evaluated. The experiments were executed independently from each other and were evaluated with different methods. All experiments show that the bubble shape is not distinctly affected in the examined concentration range from 0 to 1 M NaCl, which is in contrast to a previous study on single bubbles. Therefore, the effect of NaCl on the hydrodynamics of bubbly flows is not induced by the bubble shape.
Keywords: bubble column; contaminations; surfactants; optical measurement; pilot-plant scale; nuclear safety engineering; sodium chloride

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Permalink: https://www.hzdr.de/publications/Publ-26510
Publ.-Id: 26510


The critical bubble diameter of the lift force in technical and environmental, buoyancy-driven bubbly flows

Ziegenhein, T.; Lucas, D.
The lift force as part of the so-called non-drag forces influences distinctly the span-wise gas void fraction in bubbly flows. Towards larger bubble sizes, experiments at single bubbles show that the lift force changes its sign at a critical diameter. This effect would cause a separation of small and large bubbles in bubbly flows when a liquid velocity profile with gradients is present. In the present work, this separation is studied for different bubble columns setups in order to identify such a critical diameter. For all setups, almost the same critical diameter is found. Since the lift force is the only known force that could cause a separation of different bubble sizes, it can be concluded that the found critical diameter is indeed the diameter at which the lift force changes its sign. Therefore, a simple method is obtained with which the sign change of the lift force can be determined under realistic flow conditions.
Keywords: Lift force, bubbly flows, critical diameter, bubble column

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  • Secondary publication expected from 01.04.2020

Permalink: https://www.hzdr.de/publications/Publ-26509
Publ.-Id: 26509


A new measuring concept to determine the lift force for distorted bubbles in low Morton number system: Results for air/water

Ziegenhein, T.; Tomiyama, A.; Lucas, D.
The lift force, which strongly influences the spatial bubble distribution, is one of the most important non-drag forces. However, measurements in systems with a low Morton number are limited. In the present work, a time-averaging measurement method with which this gap can be closed is discussed. The experimental setup is kept as simple as possible, avoiding any moving parts.
The single bubble movement through a linear shear field was observed three-dimensional over 75 minutes. In total, 85 measurement points cover 13 bubble sizes at 7 different shear rates. The results reveal that former empirical correlations obtained from experiments and simulations in predominantly high Morton number systems are applicable. In this context, the characteristic length scale that is used to describe the lift force needs to be carefully defined.
From the present results, the major axis seems to be the most reasonable choice for wobbling bubbles. However, the major axis might be dependent on the flow properties, which leads to a flow dependent lift force formulation.
Keywords: Bubbly flows, Lift coefficient, Wobbling bubbles, Bubble shape

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Permalink: https://www.hzdr.de/publications/Publ-26508
Publ.-Id: 26508


Influence of the bubble size distribution on the stability of bubble columns

Ziegenhein, T.; Schipp, J.; Lucas, D.
Bubble columns are a fundamental operation unit in chemical engineering; nevertheless, their dimensioning is still based on empirical models. Here, one of the most important parameter is the point of change from the homogenous to the heterogeneous regime. Despite intensive research in the past decades, no deeper understanding of the underlying, local processes was gained. From theoretical deliberations, the lift force was identified as the possibly crucial parameter for the stability in bubble columns in the past (Lucas et al. 2005). The pre-factor of the lift force, the lift force depends on the shear rate, changes its sign when the bubbles reach a certain size (Tomiyama et al. 2002). Consequently, large bubbles tend to velocity peaks in a bubble column, which amplify the heterogeneous character; small bubbles, on the other hand, are driven away from velocity peaks, which homogenizes the flow.
Based on experiments, the turnover from the homogeneous regime to the heterogeneous by solely changing the bubble size distribution (BSD) is shown. For this purpose, the volume flow in a bubble column with evenly distributed needle spargers is kept constant; the BSD is varied by using different needles. By means of the BSD and the liquid velocity at different heights, the theoretically obtained stability criterion (Lucas et al. 2005) is compared to the experiments. The findings presented help to better understand the local process in a bubble column that lead to the turnover to the heterogeneous regime. In the end, with general, local models for these processes, bubble columns of arbitrary shape and other facilities can be specially designed to reach the desired homogenous regime at higher gas hold ups.
Keywords: bubbly flow, bubble column, stability, lift force
  • Poster
    Jahrestreffen Dresden - Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-26507
Publ.-Id: 26507


The pseudo-homogeneous flow regime in large-scale bubble columns: experimental benchmark and Computational Fluid Dynamics modeling

Besagni, G.; Inzoli, F.; Ziegenhein, T.; Lucas, D.
A precise prediction of the fluid dynamics in bubble columns is of fundamental importance to correctly design “industrial-scale” reactors. It is known that the fluid dynamics in bubble columns is related to the prevailing bubble size distribution existing in the systems. In this respect, multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions and, thus, the global fluid dynamics from the fluid flow conditions and by applying modeling closured. In particular, in in “industrial-scale” reactors, owing to the large gas sparger openings, the “pseudo-homogeneous” flow regime—characterized by a wide spectrum of bubble sizes—is typically observed. Unfortunately, reliable predictions of the “pseudo-homogeneous” flow regime are limited up to now: one important drawback concerns the selection of appropriate models for the coalescence and break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge. Recently, the authors have extended the validation of this set of closure relations to the “pseudo-homogeneous” flow regime, by comparing the numerical predictions to a comprehensive experimental dataset (gas holdup, bubble size distributions and local flow measurements). Unfortunately, the previous study suffers from some limitations; in particular, in the previous experimental dataset, the bubble size distributions concerned only one axial position and a detailed characterization of the gas sparger was missing. This study contributes to the existing discussion and proposed a step ahead in the study of the “pseudo-homogenous” flow regime. To this end, we propose an experimental study, to improve the comprehensive dataset previously obtained. The novel dataset—obtained for two gas velocities—concerns bubble size distributions at different axial and radial positions and a precise characterization of the gas sparger. The comprehensive bubble size distribution dataset may serve as basis to improve the coalescence and break-up closures; conversely, the precise characterization of the gas sparger served as an improved input to the numerical simulations. The numerical results, with two different lift force implementations, have been compared with the whole dataset and have been critically analyzed. Reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as basis for future studies.
Keywords: bubbly flow, modelling, bubble column

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Permalink: https://www.hzdr.de/publications/Publ-26506
Publ.-Id: 26506


Development of an active bremsstrahlung detector for laser-plasma experiments

Molodtsova, M.; Ferrari, A.; Cowan, T.
The use of high intensity, high power lasers recently increased in research facilities all over the world. By laser-matter interactions it is possible to study new mechanisms of ion/electron acceleration, and matter under extreme conditions via pump-probe experiments. At the X-ray Free Electron Laser in Hamburg (EuXFEL) such extreme conditions will be generated and studied at the High Energy Density (HED) instrument at the Helmholtz International Beamline for Extreme Fields (HIBEF). For such experiments a wide variety of novel detectors will be needed. One of the challenges will be the detection of the bremsstrahlung radiation emitted with ultrashort pulse widths (gamma flash) down to the fs range, at every laser shot.
To characterize the gamma flash usual spectrometry techniques using pulse height analysis can not be used, because of its short pulse width as well as its high intensity (~10^10 photons). A possible approach is to measure the energy deposited by photons in a detector with a layered structure, to obtain information about the longitudinal development of the electromagnetic shower. With this data the photon spectrum can be then reconstructed by using an unfolding technique. To perform a successful unfolding, detector materials and thicknesses have to be optimized to be able to resolve the photon spectrum in the dynamic range between 50 keV and 20 MeV.
An extensive simulation study has been performed with the FLUKA Monte Carlo code for different detector models. The model that showed the most promising set of response functions to perform a deconvolution, was chosen to realize the first prototype.
In this poster the first results of this work are presented.
  • Poster
    20th German Conference of Women in Physics, 03.-06.11.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26505
Publ.-Id: 26505


The HEXNEM3 nodal flux expansion method for the hexagonal geometry in the code DYN3D

Bilodid, Y.; Grundmann, U.; Kliem, S.
This paper describes the derivation of the nodal flux expansion method HEXNEM3, its implementation into the nodal diffusion code DYN3D and the corresponding testing versus benchmarks. As in the earlier versions of expansion method HEXNEM1 and HEXNEM2, the neutron flux in a hexagonal node is expanded into superposition of orthogonal polynomials and exponential functions. The main difference of the HEXNEM3 method is the additional use of tangentially weighted exponential functions and the coupling of neighboring nodes by tangentially weighted fluxes and currents on node surfaces.
The HEXNEM3 method was tested in several benchmark problems, including numerical benchmarks with given cross sections set and reference solutions by fine-mesh finite difference diffusion and a real plant benchmark with Monte Carlo reference solution. The test results demonstrate good agreement with reference solutions and improvement of method accuracy in comparison with HEXNEM1 and HEXNEM2.
Keywords: HEXNEM, nodal diffusion, hexagonal-z geometry, DYN3D

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Permalink: https://www.hzdr.de/publications/Publ-26504
Publ.-Id: 26504


Impact of surface characteristics to microlayer, bubble dimensions and departure in nucleate boiling

Ding, W.; Sarker, D.; Hampel, U.
In this work, an experimental and theoretical investigation about the impact of surface characteristics (wettability and roughness) on the microlayer is reported. Stainless steel heaters with five different surface characteristics were employed in the experiment. Laser polishing, wet-etching, and self-assembled monolayer (SAM) coating were applied to control the roughness and wettability of the heater surface. The experiments were carried out in a vertical boiling process with deionized water at atmospheric pressure. Based on these experimental results, the impact of surface characteristics to the effective microlayer thickness was quantitatively analyzed and formulated. Moreover, after the bubble is complete evaporated, the dry spot underneath bubble determines the surface tension of the bubble, which is also investigated in this work. The surface tension impacts the bubble motions and departure. Consequently, in the paper, the impact of surface characteristics on the microlayer, bubble dynamics and the impact mechanisms is quantitatively analyzed. The understanding and findings from this work will be helpful to improve the modelling of bubble dynamics.
Keywords: Bubble departure, surface characteristics, microlayer thickness
  • Contribution to proceedings
    16th International Heat Transfer Conference (IHTC-16), 10.-15.08.2018, Beijing, China
    Proceedings of the 16th International Heat Transfer Conference

Permalink: https://www.hzdr.de/publications/Publ-26502
Publ.-Id: 26502


Absolute charge calibration and degeneration studies of various scintillation screens used in laser Wakefield acceleration

Kurz, T.; Couperus, J. P.; Krämer, J. M.; Ding, H.; Kuschel, S.; Hollatz, D.; Köhler, A.; Zarini, O.; D’Arcy, R.; Schinkel, D.; Schwinkendorf, J. P.; Zepf, M.; Osterhoff, J.; Irman, A.; Schramm, U.; Karsch, S.
Scintillation screens are generally used as the electron beam diagnostics in Laser Wakefield Accelerators. We present an absolute charge calibration of the electron detector i.e. a scintillating screen with a layer of powdered rare earth phosphor (Gd2O2S:Tb). The calibration was designed to investigate the absolute light/charge–ratio and saturation effects of various screens used in current laser–electron accelerators.
The scintillation screens show a linear photon response to the applied charge up to an upper boundary caused by saturation effects. We also report about degeneration studies of some of these screens which were excited with a similar condition compared to Wakefield experiments.
  • Lecture (Conference)
    DPG Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26501
Publ.-Id: 26501


Visualization of bubble coalescence in bubble chains rising in a liquid metal

Keplinger, O.; Shevchenko, N.; Eckert, S.
Bubble coalescence in liquid metals was studied by considering the case of a bubble chain rising in the eutectic alloy GaInSn. The experiments were performed in a flat vessel with a rectangular cross section. High frame-rate X-ray radiography was used for visualizing the interaction between the bubbles. Essential process parameters such as bubble sizes, bubble shapes, velocities and distance of their closest approach are obtained from image processing. Different coalescence schemes occurring inside the bubble chain are discusses and demonstrated. The results are compared to collision cases where the bubbles bounce off each other. The material properties of the liquid metal differ significantly from those of water or other transparent fluids. In particular, the low viscosity, the high density and the high surface tension result in low values of the Mo number, Mo ≈ 2x10-13 and high Reynolds numbers of Re ~ 104. Nevertheless, the process of bubble approach, collision and coalescence was found to proceed in a qualitatively similar way as reported by previous studies for the case of water or highly viscous fluids. From the analyzed data, it was difficult to define a quantitative criterion that would allow predicting whether a pair of colliding bubbles would coalesce or bounce off. The observations indicate that the turbulent flow in the immediate vicinity of the bubbles has an important influence on whether coalescence occurs or not.
Keywords: Liquid metal; GaInSn; Bubble chain; Bubble coalescence; X-ray radiography; Two-phase flow

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-26500
Publ.-Id: 26500


Euler-Euler modeling and X-ray measurement of oscillating bubble chain in liquid metals

Liu, L.; Keplinger, O.; Ziegenhein, T.; Shevchenko, N.; Eckert, S.; Yan, H.; Lucas, D.
An Euler-Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection in the range of moderate gas flow rates results in the formation of bubble chains undergoing distinct oscillations of the bubble trajectories. A set of interfacial closures and a shear stress transport k-ω (SST) turbulence model, namely the baseline model for bubbly flow (Rzehak, R., & Krepper, E. (2013), Nuclear Engineering and Design 265, 701-711.) was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the two-phase flow in a flat container and allow for determining essential bubble quantities such as the size, shape, trajectory and velocity. The comparison between numerical simulations and experimental data showed a very good qualitative and quantitative agreement with respect to the distribution of the void fraction and the dynamics of the bubble chain. Wrong results were obtained by simulations where the effect of the bubble induced turbulence (BIT) was neglected. Two BIT models were applied within this study, the baseline BIT model and the Sato BIT model. Both models showed a good agreement with the experimental observations, while the results of the baseline model were even closer to the measurements. Thus, the baseline model originally developed for the air-water system has proved to be capable of reproducing the complex transient behavior of oscillating bubble chains in liquid metals.
Keywords: Liquid metal; Bubble chain; X-ray radiography; CFD; Euler-Euler two-fluid model; Two-phase flow.

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Permalink: https://www.hzdr.de/publications/Publ-26499
Publ.-Id: 26499


Electronic proprioception

Makarov, D.
Augmented reality devices such as Smart Glasses are destined to be an integral part of our information intensive society, assisting us to acquire data and process information in an ever faster paced society. Although impressive in their realization and demonstrations, an often-neglected drawback of conventional optics-based motion detection systems is their bulkiness, energy inefficiency and the stringent requirement to be at line of sight with any object. We envision that future augmented reality systems will rely on compliant wearable and on-skin interactive electronics. When equipped with motion tracking sensory systems, electronic skins would offer complimentary information on the surrounding and enable novel means of manipulating physical or even virtual objects.
We demonstrate electronic skins capable of perceiving direction in space. Our highly compliant magnetosensory system enables real time tracking of the position of a body in space as well as the touchless manipulation of (virtual) objects based on the interaction with magnetic fields exclusively. We foresee exciting possibilities not only for business or gaming industries but also for safety and security applications, where the somatic manipulation of objects, e.g. turning regulation knobs located in a restricted environment, is undesirable or even prohibited.
  • Invited lecture (Conferences)
    Invited talk at the Microsoft, Applied Sciences Group, 04.12.2017, Redmond, USA

Permalink: https://www.hzdr.de/publications/Publ-26498
Publ.-Id: 26498


Magnetosensitive e-skins with directional perception for augmented reality

Cañón Bermúdez, G. S.; Karnaushenko, D. D.; Karnaushenko, D.; Lebanov, A.; Bischoff, L.; Kaltenbrunner, M.; Fassbender, J.; Schmidt, O. G.; Makarov, D.
Electronic skins equipped with artificial receptors are able to extend our perception beyond the modalities that have naturally evolved. These synthetic receptors offer complimentary information on our surrounding and endow us with novel means of manipulating physical or even virtual objects. Here, we realize highly compliant magnetosensitive skins with directional perception that enable magnetic cognition, body position tracking and touchless object manipulation. Transfer printing of eight high performance spin valve sensors arranged into two Wheatstone bridges onto 1.7 µm thick polyimide foils ensures mechanical imperceptibility. This resembles a new class of interactive devices extracting information from the surrounding through magnetic tags. We demonstrate this concept in augmented reality systems with virtual knob turning functions and the operation of virtual dialing pads, based on the interaction with magnetic fields. This technology will enable a cornucopia of applications from navigation, motion tracking in robotics, regenerative medicine, sports and gaming to interaction in supplemented reality.
Keywords: flexible electronics, magnetic field sensors

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Permalink: https://www.hzdr.de/publications/Publ-26497
Publ.-Id: 26497


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