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34118 Publications

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

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

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

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.

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.; 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

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
    ISSN: 2191-8708, eISSN: 2191-8716

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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

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


Elektrostatische Kontrolle des Stofftransports in mikro- und nanoskaligen Elektrolytsystemen

Kubeil, C.

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.; 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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Permalink: https://www.hzdr.de/publications/Publ-26573
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

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.

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

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

Permalink: https://www.hzdr.de/publications/Publ-26569
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.

Permalink: https://www.hzdr.de/publications/Publ-26568
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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Permalink: https://www.hzdr.de/publications/Publ-26567
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.

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

Permalink: https://www.hzdr.de/publications/Publ-26563
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


Interaction of Discoidin Domain Receptor 1 with a 14-3-3-Beclin-1-Akt1 Complex Modulates Glioblastoma Therapy Sensitivity

Vehlow, A.; Klapproth, E.; Jin, S.; Hannen, R.; Hauswald, M.; Bartsch, J.-W.; Nimsky, C.; Temme, A.; Leitinger, B.; Cordes, N.

Glioblastoma (GBM) is highly refractory to therapy and associated with poor clinical outcome. Here, we reveal a critical function of the promitotic and adhesion-mediating discoidin domain receptor 1 (DDR1) in modulating GBM therapy resistance. In GBM cultures and clinical samples, we show a DDR1 and GBM stem cell marker co-expression that correlates with patient outcome. We demonstrate that inhibition of DDR1 in combination with radiochemotherapy with temozolomide in GBM models enhances sensitivity and prolongs survival superior to conventional therapy. We identify a 14-3-3-Beclin-1-Akt1 protein complex assembling with DDR1 to be required for prosurvival Akt and mTOR signaling and regulation of autophagy-associated therapy sensitivity. Our results uncover a mechanism driven by DDR1 that controls GBM therapy resistance and provide a rationale target for the development of therapy-sensitizing agents.

Keywords: DDR1; autophagy; radiochemoresistance; GBM stem-like cells; orthotopic GBM mouse model

Permalink: https://www.hzdr.de/publications/Publ-26557
Publ.-Id: 26557


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.; 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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Permalink: https://www.hzdr.de/publications/Publ-26552
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

Permalink: https://www.hzdr.de/publications/Publ-26551
Publ.-Id: 26551


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

Wohlfahrt, P.; 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

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.; Rehwald, M.; Brack, F.; Curry, C.; Gauthier, M.; Glenzer, S.; Göde, S.; Kraft, S. D.; Metzkes, J.; Obst, L.; Rödel, C.; Schlenvoigt, H.-P.; Zeil, K.; Schramm, U.

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.; 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

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.

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

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.

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

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

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

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

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.; Kupka, N.; Peuker, U. A.; Rudolph, M.

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.; Pausch, R.; Couperus, J. P.; Zarini, O.; Krämer, J. M.; Kurz, T.; Debus, A.; Bussmann, M.; Schramm, U.; 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.; 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.; 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.; 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.; 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

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

Downloads:

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

Downloads:

  • 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

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

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

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

Downloads:

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

Downloads:

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

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

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

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

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


Prediction of bubble size distributions in large-scale bubble columns using computational fluid dynamics

Besagni, G.; Inzoli, F.; Ziegenhein, T.; Lucas, D.

A precise estimation of bubble size distributions is of fundamental and practical importance to understand the fluid dynamics and to estimate the mass transfer in bubble columns. Multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions from the fluid flow conditions by using coalescence and breakage kernels. In particular, this study concerns the prediction of the bubble size distributions in the “pseudo-homogeneous” flow regime, which is characterized by a wide spectrum of bubble sizes and is generally observed in industrial applications. Reliable predictions of the “pseudo-homogeneous” flow regime are, however, 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 and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been further extended to the “pseudo-homogeneous” flow regime by comparing experimental and numerical bubble size distributions at different axial positions in a large-diameter and large-scale bubble column. The results have been critically analysed and may serve as basis to improve the coalescence and break-up closures.

Keywords: Bubbly flow; bubble shape; bubble column; CFD

  • Contribution to proceedings
    14th International Conference of Multiphase Flow in Industrial Plant, 13.09.2017, Desenzano del Garda, Italy

Permalink: https://www.hzdr.de/publications/Publ-26496
Publ.-Id: 26496


Two-phase bubble column fluid dynamics: a review

Besagni, G.; Ziegenhein, T.; Inzoli, F.

We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer. We also discuss how the operating parameters (i.e., pressure, temperature, and gas and liquid flow rates), the operating modes (i.e., the co-current, the counter-current and the batch modes), the liquid and gas phase properties, and the design parameters (i.e., gas sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we present the experimental techniques for studying the global and local fluid dynamic properties. Finally, we present the modeling approaches to study the global and local bubble column fluid dynamics, and we outline the major issues to be solved in future studies.

Keywords: Bubble column; flow regimes; gas holdup; bubble size distribution; multi-scale; modeling

Permalink: https://www.hzdr.de/publications/Publ-26495
Publ.-Id: 26495


Dependency of bubble column flow regime on bubble size distribution

Ziegenhein, T.; Lucas, D.

The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. As shown by Lucas et al.
(2005) the lateral lift force may have an important influence on this transition. Interactions between local and global instabilities of a bubble column were discussed by Lucas et al. (2007).
As shown experimentally by Tomiyama et al. (2002) and by numerous direct numerical simulations (e.g. Dijkhuizen et al., 2010) the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions (Ziegen-hein et al., 2017 and Ziegenhein and Lucas, 2017a). The well-known correlation of Tomiyama et al. (2002) fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water, deionized water was used in the experiments. Replacing the Wellek- correlation by a correlation based on bubble shapes that are observed in bubble columns (Ziegenhein and Lucas, 2017b) the critical diameter for the change of the sign is about 5.14 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. (2005) derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The sparger consists of 6 holes that can be equipped with different needles. The holes are separated into two groups that hold different needle sizes to produce a certain poly-disperse flow. The total gas volume flow was fixed to 1.0 l/min for all experiments. The gas flow through the sparger group was varied to vary the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive.


The liquid velocity profile was determined by particle tracking using microbubbles and 100 µ m PMMA particles. The bubble sizes and the gas volume fraction were determined by high-speed camera observations. Measurements were done for different height positions in
the column. Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. (2005) these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.

Keywords: bubble size; lift force; stability

  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26494
Publ.-Id: 26494


Entwicklung simulations- und messtechnischer Methoden zur Effizienzsteigerung verfahrenstechnischer Prozesse in großtechnischen Anlagen

Reinecke, S. F.; Herrmann-Heber, R.; Mohseni, E.; Hampel, U.

Die Entsorgung und die Aufbereitung des im kommunalen und industriellen Umfeld anfallenden Abwassers zur Vermeidung der Verschmutzung und Eutrophierung von Fließgewässern ist von zentraler Bedeutung für einen nachhaltigen Umgang mit der Ressource Wasser. Die Abwasserkette umfasst im Wesentlichen den Wasserverbraucher, das Kanalnetz, die Kläranlagen und das Oberflächengewässer, in welches das gereinigte Wasser eingeleitet wird. Das allein im kommunalen Bereich anfallende Abwasser wird in 10,000 Abwasseraufbereitungsanlagen mit einem jährlichen Energieaufkommen von 4.400 GWh behandelt (Fricke, 2009). Damit tragen diese Anlagen 20% des in den Kommunen anfallenden Energieverbrauches. Davon entfallen bis zu 80% auf die biologischen Reinigungsstufen (Fricke, 2009).
Ziel dieser Forschung 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 und nach ihrer Umsetzung an der konkreten Anlage mit Hilfe innovativer Sensorik messtechnisch validiert werden. Damit soll eine grundlegende Verbesserung der Hydrodynamik von Belebungsbecken in Verbindung mit der Effizienzsteigerung der Anlage basierend auf numerischen Simulationen und innovativen Sensortechnologien möglich werden.
Weiterhin ist die Forschung in diesem Bereich auf die Entwicklung effizienter Gaseintragssysteme fokussiert. Die etablierte Technik für den Gaseintrag in kommunalen Kläranlagen sind am Boden montierte Druckbegaser mit flexiblen, perforierten Membranen. Mit dieser Begasertechnik wird jedoch nur eine begrenzte Sauerstoffeintragseffizienz von 40-60% erreicht (Wang et al. 2010). Die Sauerstoffeintragseffizienz wird maßgeblich durch die initiale Blasengröße am Begaser bestimmt. Davon hängen wiederum die Blasenverweilzeit und der Gasgehalt ab. Um eine wesentliche Steigerung der Sauerstoffeintragseffizienz zu erzielen, sind Gasblasen im Submillimeterbereich erforderlich. Nur so kann eine ausreichend große Fläche für einen effizienten Sauerstoffübergang von der Gas- in die Flüssigphase erreicht und der biologische Abbauprozess trotzdem stabil gehalten werden.

  • Lecture (others)
    TKoR Netzwerktreffen Technologie- und Kompetenzzentrum organisches Reststoffrecycling, 13.12.2017, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26493
Publ.-Id: 26493


GGR Biennial Critical Review: Analytical Developments Since 2014

Linge, K. L.; Bédard, L. P.; Bugoi, R.; Enzweiler, J.; Jochum, K. P.; Kilian, R.; Jingao, L.; Marin-Carbonne, J.; Merchel, S.; Munnik, F.; Morales, L. F. G.; Rollion-Bard, C.; Souders, A. K.; Sylvester, P. J.; Weis, U.

This GGR biennial critical review covers developments and innovations in key analytical methods published since January 2014, relevant to the chemical, isotopic and crystallographic characterisation of geological and environmental materials. In nine selected analytical fields, publications considered to be of wide significance are summarised, background information is provided and their importance evaluated. In addition to instrumental technologies, this review also presents a summary of new developments in the preparation and characterisation of rock, microanalytical and isotopic reference materials, including a précis of recent changes and revisions to ISO guidelines for reference material characterisation and reporting. Selected reports are provided of isotope ratio analyses by both solution-nebulisation MC-ICP-MS and laser ablation-ICP-MS, as well as of radioactive isotope geochronology by LA-ICP-MS. Most of the analytical techniques elaborated continue to provide new applications for geochemical analysis, however it is noted that instrumental neutron activation analysis has become less popular in recent years, mostly due to the reduced availability of nuclear reactors to act as a neutron source. Many of the newer applications reported here provide analysis at increasingly finer resolution. Examples include atom probe tomography, a very sensitive method providing atomic scale information, nanoscale SIMS, for isotopic imaging of geological and biological samples, and micro-XRF, which has a spatial resolution many orders of magnitude smaller than conventional XRF.

Keywords: TIMS; isotopic analysis; geochronology; ICP-MS; laser ablation; mass spectrometry; MC-ICP-MS; calibration; environmental sampling; FIB; SIMS; AMS; Ion Beam Analysis; radionuclides; INAA; reference materials; microanalysis; atom probe tomography

Permalink: https://www.hzdr.de/publications/Publ-26492
Publ.-Id: 26492


Validation of the DYN3D-Serpent code system for SFR cores using selected BFS experiments. Part II: DYN3D calculations.

Rachamin, R.; Kliem, S.

The capability of the DYN3D-Serpent codes system to simulate highly heterogeneous sodium-cooled fast reactor cores has been studied. The BFS-73-1 and the BFS-62-3A critical assemblies were chosen for the investigation. The study was performed in two parts. In the first part of the study, a 3D full model of each of the assemblies was simulated using the Serpent Monte-Carlo (MC) code, and the basic neutronic characteristics were evaluated and compared against experimental values. In the second part of the study, which is the subject of this paper, the assemblies were modeled using the DYN3D nodal diffusion code. The few-group cross-sections for the DYN3D analysis were generated using the Serpent MC code. The generation of effective few-group cross-sections of such assemblies is quite a challenge due to the substantial heterogeneity of the assemblies configuration. Therefore, the use of homogenization techniques was considered and evaluated. Initially, the GET and SPH techniques were applied for the analysis of the BFS-73-1 assembly core fuel rods, and of selected fuel rods from the BFS-62-3A assembly. Then, the SPH method was implemented and demonstrated for a pin-by-pin calculation of the BFS-73-1 assembly. It was shown that the GET and the SPH method noticeably improve the prediction accuracy of the DYN3D code. The results of the DYN3D pin-by-pin calculation with the SPH correction agree very well with that of the full assembly Serpent results, which in turn agree very well with the experimental data.

Keywords: SFR; BFS experiments; Group constant generation; ADF; SPH; Serpent and DYN3D

Permalink: https://www.hzdr.de/publications/Publ-26490
Publ.-Id: 26490


Eulerian multiphase flow modelling – Advanced concepts

Lucas, D.

Advanced concepts for Euler-Euler-modelling of gas-liquid flow were presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. A baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them.

Keywords: Poly-disperse flows; Large interfaces; Multi-scale modelling; Flow pattern transition

  • Invited lecture (Conferences)
    Computational Fluid Dynamics in Metallurgy - Advanced Seminar, 04.-06.12.2017, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26489
Publ.-Id: 26489


Euler-Euler-modelling of poly-disperse bubbly flows

Lucas, D.

Bubbly flows occur in various industrial processes. For medium and large industrial scales the Euler-Euler approach is frequently applied in CFD-simulations. To derive the corresponding balance equations for mass, momentum and energy averaging procedures are applied and in the result information on the gas-liquid interface gets lost. Models reflecting the physics at the non-resolved scale are required to close the problem. This concerns the momentum transfer between bubbles and liquid (bubble force models), modulation of turbulence by the bubbles (BIT – bubble induced turbulence), bubble-bubble interactions (coalescence and breakup) and mass and heat transfer between the phases (boiling, condensation, heterogeneous chemical reactions). Most of these closure models sensitively depend on the bubble size and even may change their sign in dependency on the bubble size (lateral lift force). Correspondingly an appropriate modelling requires the consideration of the bubble size distribution and in general also the sub-division of the gas phase in phases representing bubbles of a specific range of sizes.
Still there is no consensus on the closure models in literature. Often closures and open parameters are tuned to obtain agreement with experimental data. To achieve a consolidation of the modelling and more reliable predictions the so-called baseline model concept was proposed by HZDR. In the baseline model all closure models including constants are well defined and the fixed model is used for the simulation of different flow situations involving bubbles in the mm-range and larger without any modification.
The lecture presents the baseline model concept, introduces the baseline model for poly-disperse bubbly flows (including the definition of closures for bubble forces, BIT, coalescence and breakup), the inhomogeneous MUSIG model for the consideration of the bubble size distribution and the modelling of phase transfer and chemical reaction. The baseline model for poly-disperse bubbly flows was validated for more than 150 single experiments. Examples for the validation are given and perspectives of the future modelling are discussed.

Keywords: CFD; Euler-Euler; bubbly flow; baseline model

  • Invited lecture (Conferences)
    ERCOFTAC Best Practice Guidance Seminar, CFD for Dispersed Multi-Phase Flows,, 20.-21.11.2017, Magdeburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26488
Publ.-Id: 26488


CFD-model for industrial bubbly flows

Lucas, D.; Rzehak, R.; Ziegenhein, T.; Krepper, E.; Liao, Y.

Computational Fluid Dynamics (CFD) is an accepted tool for design and optimisation in many single-phase flow applications, e.g. in automotive or aviation industries. In principle, CFD has the same potential also for multiphase flows, but it is not yet mature for routine applications because of the complexity of such flows. For medium and large scale industrial applications the Euler-Euler approach is most suited and the interactions between the phases have to be reflected by closure models. In bubbly flows such interactions between the liquid flow field and the deformable bubble interfaces have an important influence on the flow characteristics. CFD-models should depend on local flow characteristics as e.g. shear rate, turbulence, and bubble sizes. Locally such properties may be very similar even in quite different flow situations like bubbly pipe flows, bubble columns or air-lift reactors. Instead of case by case tuning the development of a unified model for bubbly flows seems to be a promising way to increase the reliability of predictions obtained from CFD-simulations. Such a model was established at HZDR and has been applied to many different bubbly flow situations without any modification. This contribution presents this model and some examples for application to different industrial relevant bubbly flows.

Keywords: CFD; Euler-Euler; bubbly flow; polydispers; baseline

  • Contribution to proceedings
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy
  • Lecture (Conference)
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy

Permalink: https://www.hzdr.de/publications/Publ-26487
Publ.-Id: 26487


Influence of the bubble size distribution on bubble column stability

Lucas, D.; Ziegenhein, T.; Schipp, J. F.

Bubble columns are widely used in industrial processes. The performance in case of chemical reactions between liquid and gaseous substances depends on characteristic parameters as interfacial area density, turbulence level, or kLa-values. Transitions between the homogeneous and the heterogeneous operating regime dramatically change such characteristic parameters and are for this reason subject of many investigations. Many of them tried to correlate the transition with the gas superficial velocity Jg or equivalent integral parameters, but there is no general valid critical value for the transition. Lucas et al. (2005) discussed the influence of the bubble size distribution on the stability of a homogeneous bubbly flow. Depending on the sign of the lateral lift force, which changes with the bubble size (Tomiyama et al., 2002), it can stabilize (positive lift force coefficient – small bubbles) or destabilize (negative lift force coefficient – large bubbles) the flow. Basing on a linear stability analysis finally a criterion was obtained for the stability of a homogeneous bubbly flow in dependence on the bubble size distribution. Indirectly it also depends on Jg since usually bubble sizes increase with increasing Jg caused by larger size of the injected bubbles and by increased coalescence. Lucas et al. (2007) discussed the complex relations between local and global instabilities that may be quite complex basing on CFD-simulations. Akbar et al. (2013) showed the influence of injection and bubble size on the flow structure in a rectangular bubble column.
The bubble size distribution clearly has an influence on the transition between the homogeneous and heterogeneous regime in bubble columns which can be explained by effects of the lateral lift force. It interacts with other phenomena like inlet induced instabilities and coalescence processes. A detailed investigation on these effects is presented in this contribution.

Keywords: bubble column; flow regime; regime transition; lift force; bubbly flow

  • Contribution to proceedings
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-26486
Publ.-Id: 26486


Simulation of flow pattern transitions in the Euler-Euler framework

Lucas, D.; Krepper, E.; Höhne, H.; Oertel, R.; Schlegel, F.

Two-phase flows occurring in nature or industrial applications frequently involve gas-liquid interfaces which vary over a wide range of scales. Simultaneously, within one flow domain there might be very small bubbles or droplets, but also large interfaces as e.g. caused by stratification due to gravity. In addition transitions between these different morphologies may occur such as bubble entrainment by jets or breaking waves, droplet generation from wave crests or the generation of large gas structures out of smaller ones by coalescence. Such flow situations are very challenging from the modelling point of view. At least for medium and large size flow domains it is not possible to resolve all interfacial scales down to the smallest ones because this would lead to a number of cells of the numerical grid which would exceed todays computing capacity by far. Consequently there will be interfaces smaller and larger than the computational grid. Clearly the smaller ones should be considered by appropriate sub-grid models while the larger ones should be simulated.
Up to now there is no CFD approach established for such flow situations. One promising approach is the so-called GENeralized TwO-Phase Flow concept (GENTOP) which was recently developed at Helmholtz-Zentrum Dresden – Rossendorf. It bases on the two-fluid multi-field approach. Beside one or several fields representing the dispersed morphologies of gas and/or liquid potentially continuous phases for gas and liquid are introduced. Interfaces between these potentially continuous fields are statistically resolved if the local volume fraction is large enough. If this is not the case, closure models for the disperse phase are applied. For this reason it is called potentially continuous phase. The coupling of the dispersed and potentially continuous fields is done basing on a population balance. The knowledge on the typical length scale of a gas or liquid structure allows its presentation in the corresponding field. Transitions can be modelled as coalescence and breakup processes which are in agreement with the involved physical phenomena.
The concept was previously implemented in the CFX-code of ANSYS and tested considering only one continuous field for liquid, but disperse fields and a potentially continuous field for gas. Demonstration cases involve the bubble entrainment by a plunging liquid jet, generation of large bubbles out of small ones due to coalescence in a bubble column, collapse of a water column with transitions from continuous to disperse morphologies of the gas in the beginning and the vice versa process in the later phase and the simulation churn-turbulent pipe flows. Recently first simulations were done for boiling in a side wall heated vertical pipe. Single phase liquid enters the pipe from below with slight sub-cooling. Steam bubbles are generated at the wall and continue to increase and coalesce producing large bubbles which migrate to the pipe center caused by the inversion of the lateral lift force. Finally large gas structures are observed in the pipe center leasing to a transition to annular flow. The simulation involves the transition between bubbly flow and churn-turbulent flow regime and a starting transition to annular flow. In the talk the GENTOP concept and selected demonstration cases with focus on the new simulations on boiling in the heated pipe are presented. Also some recent developments to implement a similar approach in OpenFOAM are presented.

Keywords: multiscale; modelling; GENTOP; CFD; two-phase; boiling

  • Invited lecture (Conferences)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, ICNMMF-III, 26.-29.06.2017, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-26485
Publ.-Id: 26485


Dependency of bubble column flow regime on bubble size distribution

Ziegenhein, T.; Lucas, D.

The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. The lateral lift force may have an important influence on this transition. As shown experimentally and by numerous direct numerical simulations the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions. The well-known correlation of Tomiyama et al. fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water deionized water was used in the new HZDR experiments. Replacing the Wellek- correlation by a correlation based on the observed bubble shape the critical diameter for the change of the sign is about 4.5 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The gas flow through the sparger groups was varied to modify the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive. Measurements were done for different height positions in the column.
Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.

Keywords: bubble column; flow regime; lift force; bubbly flow; stability

  • Lecture (Conference)
    53rd European Two-Phase Flow Group Meeting, 22.-24.05.2017, Gdansk, Poland

Permalink: https://www.hzdr.de/publications/Publ-26484
Publ.-Id: 26484


Simulation based environmental assessment of processes

Reuter, M. A.

• Background to LCA for mineral and metallurgical process evaluation
• Introduction into HSC Sim 9 - LCA tool / Link to GaBi
• Step-by-step hands-on case of a simple reactor
• Application to own case of own choice with support from lecturer

  • Invited lecture (Conferences)
    A short course in Geometallurgy, 02.-06.10.2017, Liège, Belgium

Permalink: https://www.hzdr.de/publications/Publ-26483
Publ.-Id: 26483


SOS Metallurgy - Save our Smelters

Reuter, M. A.

Maintaining European metallurgy know-how and how to integrate metallurgy into sustainable primary and secondary raw material industry.

  • Invited lecture (Conferences)
    Europe—From Mine to Market, 28.09.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26482
Publ.-Id: 26482


Modulation of magnetic properties at the nanometer scale in continuously graded ferromagnets

Fallarino, L.; Riego, P.; Kirby, B. J.; Miller, C. W.; Berger, A.

Ferromagnetic alloy materials with designed dopant composition depth profiles provide an efficient route for the control of magnetism at the nanometer length-scale. In this regard, cobalt-chromium and cobalt-ruthenium alloys constitute powerful model systems given that they exhibit easy to tune magnetic properties such as saturation magnetization MS and Curie temperature TC while preserving their crystalline structure in a wide composition range. In order to demonstrate this materials design potential, we have grown a series of graded Co(1-x)Cr(x) and Co(1-w)Ru(w) (10-10) epitaxial thin films, with x and w following predefined doping profiles. Structural analysis measurements verify the epitaxial nature and crystallographic quality of our entire sample sets, which were designed to exhibit in-plane c-axis orientation and thus an in-plane easy magnetic axis to suppress magnetostatic domain generation. Temperature and field-dependent magnetic depth profiles have been measured by means of polarized neutron reflectometry. In both investigated structures, TC and MS are found to vary as a function of depth in accordance with the predefined compositional depth profiles. Our Co(1-w)Ru(w) sample structures, which exhibit very steep material gradients, allow the determination of the localization limit for compositionally graded material, which we find to be of the order of 1 nm. The Co(1-x)Cr(x) systems show the expected U-shaped TC and MS depth profiles, for which these specific samples were designed. The corresponding temperature dependent magnetization profile is then utilized to control the coupling along the film depth, which even allows for a sharp onset of decoupling of top and bottom sample parts at elevated temperatures.

Keywords: ferromagnetic graded materials

Permalink: https://www.hzdr.de/publications/Publ-26481
Publ.-Id: 26481


Opportunities & Limits of the Circular Economy

Reuter, M. A.

Metallurgy is a key enabler of a circular economy, its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a circular economy, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a circular economy, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency of the circular economy system, connecting all stakeholders via digitalization.

Keywords: circular economy

  • Invited lecture (Conferences)
    Strategic Materials for a Low-Carbon Future: From Scarcity to Availability / Resource Availability Conference, 02.-03.11.2017, Oxford, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-26480
Publ.-Id: 26480


Construction and validation of a long-channel membrane test cell for representative monitoring of performance and characterization of fouling over the length of spiral-wound membrane modules

Siebdrath, N.; Ding, W.; Pietsch, E.; Kruithof, J.; Uhl, W.; Vrouwenvelder, J.

A long-channel membrane test cell (LCMTC) with the same length as full-scale elements was developed to simulate performance and fouling in nanofiltration and reverse osmosis spiral-wound membrane modules (SWMs). The transparent LCMTC enabled simultaneous monitoring of SWM performance indicators: feed channel pressure drop, permeate flux and salt passage. Both permeate flux and salt passage were monitored over five sections of the test cell and were related to the amount and composition of the accumulated foulant in these five sections, illustrating the unique features of the test cell. Validation experiments at various feed pressures showed the same flow profile and the same hydraulic behaviour as SWMs used in practice, confirming the representativeness and suitability of the test cell to study SWM operation and fouling. The importance to apply feed spacers matching the flow channel height in test cell systems was demonstrated. Biofouling studies showed that the dosage of a biodegradable substrate to the feed of the LCMTC accelerated the gradual decrease of membrane performance and the accumulation of biomass on the spacer and membrane sheets. The strongest permeate flux decline and the largest amount of accumulated biomass was found in the first 18 cm of the test cell. The LCMTC showed to be suitable to study the impact of biofilm development and biofouling control strategies under representative conditions for full-scale membrane elements.

Keywords: Feed spacer; RO spiral-wound module; NF; Permeate production; Membrane performance; Biofouling

Permalink: https://www.hzdr.de/publications/Publ-26479
Publ.-Id: 26479


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