Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Flow Regime Transitions in a Bubble Column with Internals Based On a Novel Approach
Nedeltchev, S.; Möller, F.; Hampel, U.; Schubert, M.ORC
In this work the main flow regime boundaries in a bubble column with internals were investigated based on a novel statistical-chaotic method. The latter was applied to gas holdup fluctuations recorded by means of a wire-mesh sensor (8 x 8 wires). The bubble column (0.1 m in ID) was operated with an air-deionized water system at ambient conditions. 37 vertical tubes (arranged in a square pitch with a diameter of 8 x 10-3 m) were installed as internals. Based on an original combination of statistical and chaotic parameters was found that in the core of the bubble column with internals, the first transition velocity Utrans-1 (end of homogeneous regime) occurred at superficial gas velocity UG of 0.06 m/s, whereas the second transition velocity Utrans-2 (end of heterogeneous regime) appeared at UG = 0.13 m/s. At these critical velocities the new parameters exhibited well pronounced minima. In the core of the column the existence of transition flow regime was not identified. In the annulus of the bubble column with internals, three transition velocities (at UG = 0.03, 0.06 and 0.10 m/s) were identified. The first transition velocity identified the end of the gas maldistribution regime. The second and third critical velocities distinguished the ends of the homogeneous and heterogeneous regimes, respectively. The processing of the gas holdup data in the entire cross-section of the column revealed that the Utrans-1 and Utrans-2 values occurred at somewhat lower UG values (0.05 and 0.08 m/s). These critical gas velocities identified both the lower and upper boundaries of the transition regime.
Keywords: Bubble Column, Internals, New Statistical-Chaotic Method, Flow Regime Identification, Wire-Mesh Sensor

Publ.-Id: 26563 - Permalink


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

Publ.-Id: 26562 - Permalink


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

Publ.-Id: 26561 - Permalink


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

Publ.-Id: 26560 - Permalink


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

Publ.-Id: 26559 - Permalink


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

Publ.-Id: 26558 - Permalink


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

Publ.-Id: 26553 - Permalink


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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  • Secondary publication expected

Publ.-Id: 26552 - Permalink


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

Publ.-Id: 26551 - Permalink


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

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

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

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

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  • Secondary publication expected from 10.07.2019

Publ.-Id: 26550 - Permalink


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

Publ.-Id: 26549 - Permalink


(+)-[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

Publ.-Id: 26548 - Permalink


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

Publ.-Id: 26545 - Permalink


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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Publ.-Id: 26544 - Permalink


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

Publ.-Id: 26543 - Permalink


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

Publ.-Id: 26542 - Permalink


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

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Publ.-Id: 26541 - Permalink


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 LogoContribution 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

Publ.-Id: 26540 - Permalink


Ultrafast X-ray tomographic imaging of multiphase flow in bubble columns - Part 2: Characterisation of bubbles in the dense regime
Lau, Y. M.; Möller, F.; Hampel, U.; Schubert, M.ORC
Opaqueness and visual accessibility in turbulent bubbly flows are the main cause of difficulty for conventional experimental techniques to extract properties from the bulk flow. Ultrafast X-ray tomography presents an unique possibility to visualise the dense bubbly flows and to provide the ability to characterise the bubbles. With this technique, temporally resolved measurements can be obtained from a scanning plane. The post-processed images are stacked in time, resulting in a three-dimensional matrix with two spatial and one temporal resolutions. The gas flow structures are given straightforward by the image stack, which provides unique insights of the bubbly flow dynamics. However, sizing the bubbles requires the velocity to be known, which can be achieved by means of measurement or assumption. Typically, a second measurement plane is needed for the velocity estimation. However, the employment of dual plane measurement data is limited to dilute bubbly flows. To characterise bubbles in the dense regime, a method is presented using only single plane data for size extraction without the need of velocity data. The procedure comprises determinating the Sauter diameter (d32), which depicts the ratio between volume and surface area of the bubble. Contrary to the use of dual plane measurements, here, the bubble diameter is firstly determined and from the bubble size with the assumption of the bubble’s shape, the absolute bubble velocity can be roughly estimated. This method is verified with synthetic data of simple ideal-shaped bubbles. Subsequently, real bubbly flow measurements in bubble columns (with and without internals) are applied for the assessment of the resulting bubble sizes and velocity trend.
Keywords: Ultrafast X-ray tomography, Bubble column, Flow structure, Bubble size, Sauter diameter, Bubble velocity

Publ.-Id: 26539 - Permalink


Ultrafast X-ray tomographic imaging of bubbly flow - Part 1: Image processing and reconstruction comparison
Lau, Y. M.; Hampel, U.; Schubert, M.ORC
Ultrafast X-ray tomography is a recently developed imaging technique for multiphase flows. As conventional X-ray tomography it involves reconstruction of images from X-ray projection data. If used for multiphase flow measurements it moreover needs to be complemented with automated image processing algorithms for the extraction of flow features, such as gas holdup profiles, bubble/particle size distributions or disperse phase velocities. So far image reconstruction was carried out with the standard filtered backprojection technique, which is fast but may not be optimal in the presence of noisy or corrupted data. As the latter is a frequent issue, search for optimal image reconstruction and data processing algorithms is continuously ongoing. This paper serves as a foundation of the image reconstruction and processing framework for the application to multiphase flow. A description is given of the procedure from reconstruction to thresholding to properties extraction of ultrafast X-ray tomographic images. Two reconstruction techniques, FBP and SART are employed based on phantom measurements. Each technique is evaluated separately, for FBP regarding the choice of filter and for SART regarding the termination criteria. Image reconstruction resolution, computational costs and sensitivity to the threshold value are investigated. Based on the analysis, FBP with the Ram-Lak filter is selected for image processing purposes. Furthermore it is shown that from experiments with moving objects, there is fair agreement between measurements and the phantom dimensions. The described imaging process can be applied to different attenuation materials, simulating gas-solid and gas-liquid properties.
Keywords: Ultrafast X-ray tomography, Multiphase flows, Reconstruction, Thresholding, Image processing

Publ.-Id: 26537 - Permalink


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

Publ.-Id: 26536 - Permalink


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 from 06.09.2019

Publ.-Id: 26535 - Permalink


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

Publ.-Id: 26534 - Permalink


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

Publ.-Id: 26533 - Permalink


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.

Downloads:

  • Secondary publication expected from 24.05.2019

Publ.-Id: 26532 - Permalink


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

Publ.-Id: 26531 - Permalink


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

Publ.-Id: 26530 - Permalink


Superradiant Undulator Radiation for Selective THz Control Experiments at XFELs
Tanikawa, T.; Karabekyan, S.; Kovalev, S.; Casabuoni, S.; Asgekar, V.; Gensch, M.; Geloni, G.;
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 Angstroem lengthscales. In this article a scheme based on superradiant undulator Radiation, generated just after the XFEL is proposed. The concept utilizes cutting edge superconducting undulator Technology and provides THz pulses in a frequencvy 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
  • Open Access LogoXFEL Technical Report (2018)

Publ.-Id: 26529 - Permalink


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

Publ.-Id: 26528 - Permalink


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

Downloads:

  • Secondary publication expected

Publ.-Id: 26527 - Permalink


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

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

Publ.-Id: 26526 - Permalink


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

Publ.-Id: 26525 - Permalink


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

Publ.-Id: 26524 - Permalink


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

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

Publ.-Id: 26523 - Permalink


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

Publ.-Id: 26522 - Permalink


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

Publ.-Id: 26521 - Permalink


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

Publ.-Id: 26520 - Permalink


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

Publ.-Id: 26519 - Permalink


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

Publ.-Id: 26518 - Permalink


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

Publ.-Id: 26517 - Permalink


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

Publ.-Id: 26516 - Permalink


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:

  • Secondary publication expected

Publ.-Id: 26515 - Permalink


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

Publ.-Id: 26514 - Permalink


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

Publ.-Id: 26512 - Permalink


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

Publ.-Id: 26511 - Permalink


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

Publ.-Id: 26510 - Permalink


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

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  • Secondary publication expected from 01.04.2020

Publ.-Id: 26509 - Permalink


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

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  • Secondary publication expected from 21.06.2019

Publ.-Id: 26508 - Permalink


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

Publ.-Id: 26507 - Permalink


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

Publ.-Id: 26506 - Permalink


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

Publ.-Id: 26505 - Permalink


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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  • Secondary publication expected

Publ.-Id: 26504 - Permalink


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

Publ.-Id: 26502 - Permalink


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

Publ.-Id: 26501 - Permalink


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

Publ.-Id: 26500 - Permalink


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.

Publ.-Id: 26499 - Permalink


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

Publ.-Id: 26498 - Permalink


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

Publ.-Id: 26497 - Permalink


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

Publ.-Id: 26496 - Permalink


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

Publ.-Id: 26495 - Permalink


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

Publ.-Id: 26494 - Permalink


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

Publ.-Id: 26493 - Permalink


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

Publ.-Id: 26492 - Permalink


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

Publ.-Id: 26490 - Permalink


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

Publ.-Id: 26489 - Permalink


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

Publ.-Id: 26488 - Permalink


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

Publ.-Id: 26487 - Permalink


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

Publ.-Id: 26486 - Permalink


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

Publ.-Id: 26485 - Permalink


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

Publ.-Id: 26484 - Permalink


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

Publ.-Id: 26483 - Permalink


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

Publ.-Id: 26482 - Permalink


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

Publ.-Id: 26481 - Permalink


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

Publ.-Id: 26480 - Permalink


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

Publ.-Id: 26479 - Permalink


Engineering of high-temperature ferromagnetic Si1–xMnx (x ≈ 0.5) alloyed films by pulsed laser deposition: Effect of laser fluence
Pandey, P.; Drovosekov, A. B.; Wang, M.; Xu, C.; Nikolaev, S. N.; Chernoglazov, K. Y.; Savitsky, A. O.; Kreines, N. M.; Maslakov, K. I.; Cherebilo, E. A.; Mikhalevsky, V. A.; Novodvorskii, O. A.; Tugushev, V. V.; Rylkov, V. V.; Helm, M.; Zhou, S.;
Thin films of Si1xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤ 40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤4.4 J/cm2.
Keywords: Si-Mn alloys High-temperature ferromagnetism Magnetic properties Ferromagnetic resonance

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Publ.-Id: 26478 - Permalink


Modeling of Reactive Mass-Transfer in Bubbly Flows
Rzehak, R.; Krauß, M.;
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. Concerning the fluid dynamics of bubbly flows a certain degree of predictive capability has been reached recently. However, concerning mass transfer both with and without an accompanying chemical reaction only few studies have been performed to date.
The present contribution focusses on the so-called enhancement factor which describes the effect of a chemical reaction on the mass transfer. Different models available from the literature are compared. The reactive absorption of CO2 in aqueous NaOH is considered as an example. Simulations are compared with a set of experimental data reported by Darmana et al. [Chemical Engineering Science 62 (2007), 2556 - 2575]. Using an adequate model for the enhancement factor and taking into account the complete reaction network, an improved match with the data is obtained. Experimental conditions are suggested, for which further aspects of the system behavior become manifest.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics, Mischvorgänge, 16.-17.03.2017, Dresden, Deutschland

Publ.-Id: 26477 - Permalink


Euler-Euler Modeling of Reactive Bubbly Flows
Rzehak, R.; Krauß, M.;
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. To achieve predictive capability, all details of the closure models have to be fixed in advance without reference to any measured data.
Concerning the fluid dynamics of bubbly flows a baseline model has recently been proposed to this end and shown to work for a range of different applications in a unified manner [1,2]. This provides a reliable background which is well suited to add more complex physics.
Concerning mass transfer in bubbly flows both with and without an accompanying chemical reaction only few studies have been performed to date [e.g. 3 and Refs. therein]. For the mass transfer coefficient, a variety of entirely different closures have been applied in rather similar situations. To facilitate predictive applications, a standard model which is validated for a broad range of conditions yet has to be developed. The effect of a chemical reaction on the mass transfer is described by an enhancement factor which depends on the type of the reaction. As an example for which some measured data are available for comparison [4], the absorption of CO2 in NaOH is considered.

[1] Rzehak, R., Ziegenhein, T., Kriebitzsch, S., Krepper, E., and Lucas, D. (2017), Unified modeling of bubbly flows in pipes, bubble columns, and airlift columns, Chem. Eng. Sci. 157, 147-158.
[2] Rzehak, R., Krauß, M., Kovats, P., and Zähringer, K. (2017), Fluid dynamics in a bubble column: New experiments and simulations, Int. J. Multiphase Flow 89, 299-312.
[3] Rzehak, R., and Krepper, E. (2016), Euler-Euler simulation of mass-transfer in bubbly flows, Chem. Eng. Sci. 155, 459-468.
[4] Darmana, D., Henket, R., Deen, N. and Kuipers, J. (2007), Detailed modelling of hydrodynamics, mass transfer and chemical reactions in a bubble column using a discrete bubble model, Chem. Eng. Sci. 62, 2556–2575.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brüssel, Belgien

Publ.-Id: 26476 - Permalink


Durchführung Von Euler-Euler Simulationen
Fleck, S.;
Es werden Strömungssimulationen für verschieden Testfälle an Blasensäulen mit Hilfe des am HZDR entwickelten Baseline- Modells der Hydrodynamik von Blasenströmungen erstellt. Diese Simulationen werden im Anschluss ausgewertet und anhand von experimentellen Daten validiert. im Anschluss daran sind ggf etwaige Modellerweiterungen zu beachten und zu implementieren. Diese werden ausgewertet und mit den vorangegangenen Ergebnissen verglichen. Das verwendete Smulationsprogramm ist Ansys CFX.
Keywords: Strömungsmechnaik, disperse gas-flüssig Mehrphasenströmungen, Euler-Euler zwei-Fluid-Modell, CFD Simulation, Modellvalidierung, Blasensäulen
  • Study thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. habil. Rüdiger Lange

Publ.-Id: 26475 - Permalink


Guest Editorial Special Issue on Sensors for Process Imaging
Bieberle, A.; Tan, C.; Soleimani, M.; Silva, M. J. D.; (Editors)
Sustainable industrial production requires the use of advanced sensors and controls. In many industrial activities, the sensing and monitoring of processes provides valuable information for controlling and decision-making strategies as well as supporting the understanding and modeling of the phenomena involved. Since safety and efficiency requirements are continuously growing, the quality of information is becoming more and more important. A current trend to accomplish such requirements is the use of imaging sensors and systems generating and processing multidimensional data to extract key information from the processes. Further work is required to ensure that these imaging technologies are actually providing information that can be easily adapted and used in process control. This requires a holistic look at these sensing methods and data analysis.
Keywords: Special issues and sections Tomography Sensor phenomena and characterization Mechanical sensors Magnetic sensors Optoelectronic and photonic sensors Sensor systems and applications

Publ.-Id: 26474 - Permalink


Development of innovative techniques for flow measurement in liquid sodium and lead-bismuth eutectic (LBE)
Eckert, S.; Wondrak, T.; Franke, S.; Krauter, N.; Ratajczak, M.; Stefani, F.; Timmel, K.;
In this talk a short overview about recent developments of measurement techniques for liquid metal with special focus on liquid metal cooled nuclear reactors is given.
  • Lecture (Conference)
    2nd Sino-German Symposium on Fundamentals of Advanced Nuclear Savety Technology (SG-FANS), 12.-15.09.2017, Karlsruhe, Deutschland

Publ.-Id: 26473 - Permalink


Measuring techniques for experimental investigations and monitoring of liquid metal flows
Wondrak, T.;
In this talk a short overview about different measurement techniques for liquid metals is given with a special focus on the application of liquid metal cooled nuclear reactors. This includes inductive methods, like the phase shift sensor and the and the contactless inductive flow tomography, as well as ultrasound techniques, like ultrasound Doppler velocimetry and the ultrasound transit time technique.
Keywords: liquid metal, flow measurement, inductive methods, ultrasound techniques
  • Invited lecture (Conferences)
    Heavy metal summer school, 12.-16.06.2017, Mol, Belgien

Publ.-Id: 26472 - Permalink


Numerische Untersuchungen zur Hydrodynamik und zum Stofftransport in Blasensäulen zur Validierung des Baseline-Modells
Kappelt, C.;
Die Anwendung von Computational Fluid Dynamics (CFD)-Methoden hat inzwischen einen hohen Entwicklungsstand erreicht, so dass sie für viele verschiedene Strömungsprobleme eingesetzt werden.
In der Industrie findet die numerische Berechnung zum Beispiel Anwendung bei der Prozessoptimierung oder beim Scale-up. Im groÿtechnischen Maÿstab sind Zwei-Phasen-Simulationen mit Hilfe der Euler-Euler Beschreibung möglich.
Für die Simulation von Blasensäulen wird am Helmholtz-Zentrum Dresden-Rossendorf ein geeignetes Modell basierend auf dem Euler-Euler-Ansatz zur Schlieÿung von Hydrodynamik und Stofftransport entwickelt. Das Ziel dabei ist, dass das Modell ein breites Anwendungsgebiet abdeckt und für die verschiedenen Fälle validiert ist. Für die Validierung werden Simulationsrechnungen durchgeführt und mit experimentellen Daten verglichen. Die vorliegende Masterarbeit soll einen Teil zur Validierung des entwickelten Modells beitragen. Die Arbeit befasst sich mit der Absorption von Sauerstoff in Wasser in einer Blasensäule.
Keywords: Stofftransport, disperse gas-flüssig Mehrphasenströmungen, Euler-Euler zwei-Fluid-Modell, CFD Simulation, Modellvalidierung
  • Master thesis
    Hochschule Anhalt, Köthen, 2017
    Mentor: Prof. Dr. Stefan Wollny

Publ.-Id: 26471 - Permalink


Recent developments on inductive measurement techniques for liquid metals
Wondrak, T.;
There is a growing interest in determining the flow properties of metal or semiconductor melts, such as flow rate, flow structure and gas distribution. Typical applications are melt refining, continuous steel casting, silicon crystal growth or cooling of the receiver of a concentrated solar thermal power plant. However, the opaqueness prevents the use of well established optical methods. Additionally, the high temperatures (e. g. 1500°C for liquid steel or liquid silicon) and the corrosiveness of those fluids demand for contactless measurement techniques. By exploiting the high electrical conductivity of those melts inductive methods can be used. In this talk several inductive measurement techniques will be presented including transient eddy current flow meter, contactless inductive flow tomography and mutual inductance tomography. Additionally, a short overview about ultrasound techniques will be given which can be used to verify the inductive methods.
Keywords: liquid metal, inductive sensors, flow measurement
  • Invited lecture (Conferences)
    Guest colloquium of the research training group Lorentz force velocimetry and Lorentz force eddy current testing, 19.12.2017, Ilmenau, Deutschland

Publ.-Id: 26470 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Ye, J.; Oktem, G.; Teschome, B.; Kiriy, A.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, two nanostructures i.e. DNA origami nanotube and DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, the DNA origami nanotubes are modified to assemble 14 gold nanoparticles (AuNPs) along with them. Then electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires. Similarly, AuNPs are also grown within the DNA origami molds. In order to investigate the transport properties of the so-fabricated two nanostructures, a method is developed using electron beam lithography. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami nanotube is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
  • Lecture (Conference)
    IHRS Nanonet Annual Workshop, 16.-18.08.2017, Klingenberg, Germany

Publ.-Id: 26469 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Teschome, B.; Schonherr, T.; Erbe, A.;
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, two nanostructures i.e. DNA origami nanotube and DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, the DNA origami nanotubes are modified to assemble 14 gold nanoparticles (AuNPs) along with them. Then electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires. Similarly, AuNPs are also grown within the DNA origami molds.6 In order to investigate the transport properties of the so-fabricated two nanostructures, a method is developed using electron beam lithography. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami nanotube is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
  • Poster
    Future Trends in DNA based Nanotechnology, 29.05.-02.06.2017, Dresden, Germany

Publ.-Id: 26468 - Permalink


Functionalized DNA Origami Mold Nanostructures for Molecular Electronics
Bayrak, T.; Ye, J.; Helmi, S.; Teschome, B.; Schonherr, T.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami molds are used for the fabrication of nanoelectronic devices. To this end, electroless gold deposition is used to selectively grow the AuNPs and create eventually continues nanowires within the DNA origami molds. In order to investigate the transport properties of the so-fabricated nanostructures, a method is developed using electron beam lithography and 1D DNA origami-based metallic wires were electrically characterized from room temperature to 4.2K. Additionally, the assembly of heterogeneous nanostructures, i.e. AuNPs and semiconductor quantum dots (QDs), on a single DNA origami structure is demonstrated and further metalized, thus representing a first step toward the future fabrication of DNA origami-templated quantum dot transistors.
Keywords: DNA Origami, Charge Transport, Low Temperature Electrical Characterization
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, United States of America

Publ.-Id: 26467 - Permalink


Single-shot high dynamic range pulse contrast measurements at the Draco laser system in combination with plasma mirrors
Bock, S.; Oksenhendler, T.; Pueschel, T.; Helbig, U.; Gebhardt, R.; Moeller, D.; Metzkes, J.; Obst, L.; Schlenvoigt, H. P.; Pausch, R.; Lötfering, J. J.; Zeil, K.; Irman, A.; Bizouard, P.; Albert, O.; Schramm, U.;
We report on high pulse contrast operation modes of the Draco laser with focus on the on-shot characterization of the few-ps-contrast by novel techniques based on tilted beam self-referenced spectral interferometry with 108 dynamic range.
  • Lecture (Conference)
    Ultrafast Optics Conference XI, 08.-13.10.2017, Jackson Hole, WY, United States of America

Publ.-Id: 26465 - Permalink


First demonstration of multi-MeV proton acceleration from a cryogenic hydrogen ribbon target
Kraft, S.; Obst, L.; Metzkes-Ng, J.; Schlenvoigt, H.-P.; Zeil, K.; Michaux, S.; Chatain, D.; Perin, J.-P.; Chen, S. N.; Fuchs, J.; Gauthier, M.; Cowan, T. E.; Schramm, U.;
We show efficient laser driven proton acceleration up to 14\,MeV from a 50\,$\mu$m thick cryogenic hydrogen ribbon. Pulses of the short pulse laser ELFIE at LULI with a pulse length of $\approx 350$\,fs at an energy of 8\,J per pulse are directed onto the target. The results are compared to proton spectra from metal and plastic foils with different thicknesses and show a similar good performance both in maximum energy as well as in proton number. Thus, this target type is a promising candidate for experiments with high repetition rate laser systems.

Publ.-Id: 26464 - Permalink


On-shot characterization of single plasma mirror temporal contrast improvement
Obst, L.ORC; Metzkes-Ng, J.; Bock, S.; Cochran, G. E.ORC; Cowan, T. E.ORC; Oksenhendler, T.; Poole, P. L.ORC; Prencipe, I.; Rehwald, M.ORC; Rödel, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Schumacher, D. W.ORC; Ziegler, T.; Zeil, K.ORC
We report on the setup and commissioning of a compact recollimating single plasma mirror (PM) for temporal contrast enhancement at the Draco 150 TW laser during laser-proton acceleration experiments. The temporal contrast with and without PM is characterized single-shot by means of self-referenced spectral interferometry with extended time excursion at unprecedented dynamic and temporal range. This allows for the first single-shot measurement of the PM trigger point, which is interesting for the quantitative investigation of the complex pre-plasma formation process at the surface of the target used for proton acceleration. As a demonstration of high contrast laser plasma interaction we present proton acceleration results with ultra-thin liquid crystal targets of similar to 1 mu m down to 10 nm thickness. Focus scans of different target thicknesses show that highest proton energies are reached for the thinnest targets at best focus. This indicates that the contrast enhancement is effective such that the acceleration process is not limited by target pre-expansion induced by laser light preceding the main laser pulse.
Keywords: laser plasma interaction, plasma mirrors, laser proton acceleration

Publ.-Id: 26463 - Permalink


MHz repetition rate Yb:YAG disk laser-amplifier for transform limited pulses, tunable between 10 ps and 100 ps
Siebold, M.; Loeser, M.; Bernert, C.; Albach, D.; Schramm, U.;
We present an Yb:YAG laser system for transform limited pulses with variable tuning range between 10ps and 100ps. The spectral bandwidth of fs pulses is narrowed by an intra-cavity grating monochromator in a regenerative amplifier.

Publ.-Id: 26461 - Permalink


Optical probing of high intensity laser interaction with micron-sized cryogenic hydrogen jets
Ziegler, T.ORC; Rehwald, M.ORC; Obst, L.ORC; Bernert, C.; Brack, F.; Curry, C. B.ORC; Gauthier, M.ORC; Glenzer, S. H.; Göde, S.; Kazak, L.; Kraft, S. D.ORC; Kuntzsch, M.; Loeser, M.; Metzkes-Ng, J.ORC; Rödel, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Siebold, M.ORC; Tiggesbäumker, J.; Wolter, S.; Zeil, K.
Probing the rapid dynamics of plasma evolution in laser-driven plasma interactions provides deeper understanding of experiments in the context of laser-driven ion acceleration and facilitates the interplay with complementing numerical investigations. Besides the microscopic scales involved, strong plasma (self-)emission, predominantly around the harmonics of the driver laser, often complicates the data analysis. We present the concept and the implementation of a stand-alone probe laser system that is temporally synchronized to the driver laser, providing probing wavelengths beyond the harmonics of the driver laser. The capability of this system is shown during a full-scale laser proton acceleration experiment using renewable cryogenic hydrogen jet targets. For further improvements, we studied the influence of probe color, observation angle of the probe and temporal contrast of the driver laser on the probe image quality.
Keywords: plasma diagnostic probes, laser-produced plasmas, plasma diagnostic, particle accelerator ion sources

Publ.-Id: 26460 - Permalink


Laser-driven ion acceleration via TNSA in the relativistic transparency regime
Poole, P.ORC; Obst, L.ORC; Cochran, G.ORC; Metzkes, J.; Schlenvoigt, H.ORC; Prencipe, I.; Kluge, T.ORC; Cowan, T. E.ORC; Schramm, U.ORC; Schumacher, D.ORC; Zeil, K.
We present an experimental study investigating laser-driven proton acceleration via Target Normal Sheath Acceleration (TNSA) over a target thickness range spanning the typical TNSA-dominant region (~1 μm) down to below the relativistic laser-transparency regime (< 40 nm), enabled by freely adjustable target film thickness using liquid crystals along with high contrast (via plasma mirror) laser interaction (~ 2.65 J, 30 fs, I > 1 × 10^21 W/cm^2). Thickness dependent maximum proton energies scale well with TNSA models down to the thinnest targets, while those under ~ 40 nm indicate transparency-enhanced TNSA via differences in light transmission, maximum proton energy, and proton beam spatial profile. Oblique laser incidence (45°) allowed additional diagnostics to be fielded to diagnose the interaction quality: a suite of ion energy and spatial distribution diagnostics in the laser axis and both front and rear target normal directions as well as reflected and transmitted light measurements on-shot collectively verify the dominant acceleration mechanism as TNSA from high contrast interaction, even for ultra-thin targets. Additionally, 3D particle-in-cell simulations support the experimental observations of target-normal-directed proton acceleration from ultra-thin films.
Keywords: laser proton acceleration, laser plasma interaction
  • Open Access LogoNew Journal of Physics 20(2018), 13019
    DOI: 10.1088/1367-2630/aa9d47
  • Poster
    European Physical Society Division of Plasma Physics Conference 2018, 02.07.2018, Prag, Tschechische Republik

Publ.-Id: 26459 - Permalink


Laser proton acceleration from liquid crystal films of different thicknesses with ultra-high laser contrast
Obst, L.ORC; Poole, P.ORC; Metzkes, M.; Kluge, T.ORC; Cochran, G.ORC; Schlenvoigt, H.ORC; Kraft, S. D.; Prencipe, I.; Rehwald, M.ORC; Schumacher, D.ORC; Schramm, U.ORC; Zeil, K.
We present an experimental study which shows a possible pathway towards the robust and reliable generation of applicable, energetic, high-quality laser-driven proton beams at high repetition rates. This is enabled through the combination of ultra-high contrast laser pulses and liquid crystal film targets, which can be generated and characterized in situ within a thickness range from 10 μm to 10 nm at low cost.
Pulses from our in-house Ti:Sa laser (~3 J, 30 fs, I~10^20 W/cm^2) incident obliquely on target in order to distinguish between ion acceleration mechanisms. Increasing target normal proton energy cut-offs are observed for decreasing thicknesses, with > 25 MeV protons recorded for ultra-thin (< 50 nm) targets. The results are in agreement with the dominance of target normal sheath acceleration (TNSA) down to ultra-thin target thicknesses, in line with the observed robustness of the acceleration performance.
Keywords: laser plasma interaction, laser proton acceleration
  • Poster
    3. Annual MT Meeting, 31.01.-01.02.2017, Darmstadt, Deutschland
  • Lecture (Conference)
    SPIE Optics & Optoelectronics 2017, 24.-28.4.2017, Prag, Tschechische Republik

Publ.-Id: 26458 - Permalink


Metabolism-dependent bioaccumulation of uranium by Rhodosporidium toruloides isolated from the flooding water of a former uranium mine
Gerber, U.; Hübner, R.; Rossberg, A.; Krawczyk-Bärsch, E.; Merroun, M. L.;
Remediation of former uranium mining sites represents one of the biggest challenges worldwide that have to be solved in this century. The former uranium mine Königstein (Germany) displays one of these sites and is currently remediated by controlled flooding of the underground. The flooding water is cleaned up by a conventional chemical waste water treatment plant. During the last years, the search of alternative strategies involving environmentally sustainable treatments has started. Bioremediation, the use of microorganisms to clean up polluted sites in the environment, is considered one of the best alternative. By means of culture-dependent methods, we isolated an indigenous yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water and investigated its interactions with uranium(VI). Our results highlight distinct adaptive mechanisms towards high uranium concentrations on the one hand, and complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high uranium tolerance being able to grow up to 5 mM, and also high ability to accumulate this radionuclide (350 mg uranium/g dry biomass in 48 hours). The removal of uranium by KS5 displays a temperature- and cell viability-dependent process. By STEM investigations we observed that uranium was removed by two mechanisms, inactive biosorption and active bioaccumulation. EXAFS analysis revealed that the molecular speciation of uranium associated with the cells is similar to that of meta-autunite-like minerals. The present study highlights the potential of KS5 as a representative of indigenous species which might play a key role in bioremediation of uranium-contaminated sites.
Keywords: Bioremediation, Uranium, Rhodosporidium toruloides, Bioaccumulation, Biosorption

Publ.-Id: 26457 - Permalink


Making spectral shape measurements in inverse Compton scattering a tool for advanced diagnostic applications
Krämer, J. M.ORC; Jochmann, A.; Budde, M.; Bussmann, M.; Couperus, J. P.; Cowan, T. E.; Debus, A.; Köhler, A.; Kuntzsch, M.; Laso García, A.; Lehnert, U.; Michel, P.; Pausch, R.; Zarini, O.; Schramm, U.; Irman, A.
Interaction of relativistic electron beams with high power lasers can both serve as a secondary light source and as a novel diagnostic tool for various beam parameters. For both applications, it is important to understand the dynamics of the inverse Compton scattering mechanism and the dependence of the scattered light’s spectral properties on the interacting laser and electron beam parameters. Measurements are easily misinterpreted due to the complex interplay of the interaction parameters. Here we report the potential of inverse Compton scattering as an advanced diagnostic tool by investigating two of the most influential interaction parameters, namely the laser intensity and the electron beam emittance. Established scaling laws for the spectral bandwidth and redshift of the mean scattered photon energy are refined. This allows for a quantitatively well matching prediction of the spectral shape. Driving the interaction to a nonlinear regime, we spectrally resolve the rise of higher harmonic radiation with increasing laser intensity. Unprecedented agreement with 3D radiation simulations is found, showing the good control and characterization of the interaction. The findings advance the interpretation of inverse Compton scattering measurements into a diagnostic tool for electron beams from laser plasma acceleration.

Publ.-Id: 26453 - Permalink


Infrared nanoscopy down to liquid helium temperatures
Lang, D.; Döring, J.; Nörenberg, T.; Butykai, Á.; Kézsmárki, I.; Schneider, H.; Winnerl, S.; Kehr, S. C.; Eng, L. M.; Helm, M.;
We introduce a scattering-type scanning near-field infrared microscope (s-SNIM) for the local scale near-field sample analysis and spectroscopy from room (RT) down to liquid helium (LHe) temperatures. The extension of s-SNIM down to T=5K is in particular crucial for low-temperature phase transitions, e.g. for the examination of superconductors, as well as low energy excitations. The LT s-SNIM performance is tested with CO2-IR excitation at T=7K using a bare Au reference and a structured Si/SiO2-sample. Furthermore, we quantify the impact of local laser heating under the s-SNIM tip apex by monitoring the light-induced ferroelectric-to-paraelectric phase transition of the skyrmion-hosting multiferroic material GaV4S8 at T=42K. We apply LT s-SNIM to study the spectral response of GaV4S8 and its lateral domain structure in the ferroelectric phase by the mid-IR to THz free-electron laser-light source FELBE at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Notably, our s-SNIM is based on a non-contact atomic force microscope (AFM), and thus can be complemented in-situ by various other AFM techniques, such as topography profiling, piezo-response force microscopy (PFM) and/or Kelvin-probe force microscopy (KPFM). The combination of these methods support the comprehensive study of the mutual interplay in the topographic, electronic and optical properties of surfaces from room temperature down to 5K.
Keywords: near-field microscopy, free-electron laser, mid-infrared, low temperature, phase transition, scanning force micropscopy

Publ.-Id: 26447 - Permalink


Development of an efficient high-current ion source for Accelerator Mass Spectrometry
Bregolin, F. L.; Hofsäss, H.; Rugel, G.; Akhmadaliev, S.; Merchel, S.; Feige, J.;
A new high-current negative ion source for Accelerator Mass Spectrometry (AMS) is being built to quantify the ratios of long-lived cosmogenic radionuclides in micrometeorites, which are of great astrophysical interest. Measuring these extremely small ratios is at the technological limits of present AMS systems. The new source is designed specifically to provide a higher AMS detection sensitivity by having an optimal ion-optics design, incorporating new concepts for the construction and operation of the Cs ionizer, optimized Cs ion beam currents and Cs vapor transport. The operation with higher cathode, extraction and pre-acceleration voltages than usual is possible. Moreover, its design is modular providing ease of access and simplifying maintenance while having better mechanical stability at the same time. Several operational parameters can be controlled and measured during operation to achieve a higher ion source performance. Detailed ion-optics simulations of the ion source are compared with test measurements, and the design optimized based on its results. The authors would like to thank the Federal Ministry of Education and Research of Germany for its financial support (project 05K2016), and the HZDR’s Ion Beam Center for its essential contribution to the realization of this project.
Keywords: AMS, ion source, micrometeorites
  • Poster
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 26446 - Permalink


Nachweis von Beryllium-10 aus exotischen Zerfällen mit Hilfe von Beschleunigermassenspektrometrie (AMS)
Forstner, O.; Merchel, S.; Lachner, J.; IS541 Kollaboration;
Der Ein-Neutronen Halokern 11Be geht über einen Beta-Minus-Zerfall in 11B über (t1/2 = 13,76 s). In seltenen Fällen jedoch erfolgt über eine anschließende Emission eines Protons die Umwandlung zu 10Be. Ziel dieser Studie ist es, das nach theoretischen Vorhersagen bei unter 10−7 liegende Verzweigungsverhältnis dieses raren Zerfallskanals zu messen. Mit Hilfe der Möglichkeiten der AMS zur Messung extrem niedriger Isotopenverhältnisse ist dies erstmalig experimentell gelungen und wurde zu 8,3(0,9) × 10−6 bestimmt [1].
Zur Bestimmung dieser Rate wurde an ISOLDE / CERN ein Strahl radioaktiver 11Be Ionen produziert und in Kupfer-Targets implantiert. Daraus wurde chemisch Beryllium extrahiert und mittels AMS das Verhältnis 10Be/9Be bestimmt sowie die Menge des implantierten 10Be berechnet. Aufgrund des niedrigen Verzweigungsverhältnisses und der daraus resultierenden niedrigen Zahl von entstehenden 10Be-Atomen ist eine möglichst hohe Effizienz und niedriger Untergrund im 9Be-Trägermaterial [2] essentiell. Für die Datenanalyse wurde besonderes Augenmerk auf die Methodik der Produktion gelegt, um mögliche systematische Fehler ausschließen zu können.
[1] K. Riisager, et al., Phys. Lett. B 732 (2014) 305
[2] S. Merchel, et al., Nucl. Instr. and Meth. B 266 (2008) 4291
Keywords: AMS, Protonenemission, Implantation
  • Invited lecture (Conferences)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 26445 - Permalink


Ion irradiation effects on a magnetic Si/Ni/Si trilayer and lateral magnetic-nonmagnetic multistrip patterning by focused ion beam
Dev, B. N.; Banu, N.; Fassbender, J.; Grenzer, J.; Schell, N.; Bischoff, L.; Grötzschel, R.; McCord, J.;
Fabrication of a multistrip magnetic/nonmagnetic structure in a thin sandwiched Ni layer [Si(5 nm)/Ni(15 nm)/Si] by a focused ion beam (FIB) irradiation has been attempted. A control experiment was initially performed by irradiation with a standard 30 keV Ga ion beam at various fluences. Analyses were carried out by Rutherford backscattering spectrometry, X-ray reflectivity, magnetooptical Kerr effect (MOKE) measurements and MOKE microscopy. With increasing ion fluence, the coercivity as well as Kerr rotation decreases. A threshold ion fluence has been identified, where ferromagnetism of the Ni layer is lost at room temperature and due to Si incorporation into the Ni layer, a Ni0.68Si0.32 alloy layer is formed. This fluence was used in FIB irradiation of parallel 50 nm wide stripes, leaving 1 mu m wide unirradiated stripes in between. MOKE microscopy on this FIB-patterned sample has revealed interacting magnetic domains across several stripes. Considering shape anisotropy effects, which would favour an alignment of magnetization parallel to the stripe axis, the opposite behaviour is observed. Magneto-elastic effects introducing a stress-induced anisotropy component oriented perpendicular to the stripe axis are the most plausible explanation for the observed behaviour.
Keywords: ion irradiation, ion beam analysis, magnetism

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Publ.-Id: 26444 - Permalink


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