Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32216 Publications
Does the coordination geometry of CuII bispidine complexes influence the radiopharmacological properties?
Fähnemann, S.; Stephan, H.; Walther, M.; Steinbach, J.; Haaf, C.; Comba, P.;
3,7-Diazabicyclo[3.3.1]nonane derivatives (bispidines) represent a versatile platform for the development of new copper radiopharmaceuticals.[1] An extensive research effort has shown that bispidines with additional donor substituents form very stable complexes with copper(II) (L1, logK = 16.3). The CuII complexes of these so-called 1st generation hexadentate bispidine ligands (L1-Cu) enforce a distorted octahedral geometry which is well preorganized for CuII.

Recently, the 2nd generation of bispidine derivatives has been reported (L2 – L3).[2, 3] These ligands yield very high complex stabilities with CuII (logK from 19.5 to 26.4) similar to [CuII(cyclam)]2+ (logK = 27.2). In contrast to the 1st generation bispidines they provide exclusively aliphatic nitrogen atoms in the backbone, combined with one (L2) or two (L3) rigid diazacycloheptane rings for tetra- or hexadentate coordination, leading to distorted trigonal bipyramidal or distorted trigonal prismatic coordination geometries.

Ligands L1 – L3 have been labeled with 64Cu, and their radiopharmacological data, e.g. labeling efficiency and kinetics, lipophilicity and in vitro stability will be discussed.

[1] S. Juran, M. Walther, H. Stephan, R. Bergmann, L. Steinbach, W. Kraus, F. Emmerling, P.Comba; Bioconjugate Chem. 2009, 20, 347-59.
[2] P. Comba, C. Haaf, H. Wadephol; Inorg. Chem. 2009, 48, 6604-6614.
[3] P. Comba, C. Haaf, A. Lienke, A. Muruganantham, H. Wadepohl: Chem.-Eur. J., 2009, 41, 10880-10887.
  • Poster
    3rd EuCheMS Chemistry Congress, 29.08.-02.09.2010, Nürnberg, D

Publ.-Id: 14690 - Permalink

Octahedral rhenium cluster/glycodendrimer associates: A new tailor-made drug delivery system?
Kubeil, M.;
In recent years polynuclear metal complexes have become increasingly important due to their antitumoral as well as antiviral properties. [1] Their wide variety of biochemical, chemical and physical properties gives the opportunity to create tailor-made drugs. In this perspective, the enhancement of the hydrolytic stability and in particular the improvement of the in vivo selectivity of inorganic cluster compounds represents the major burden to circumvent.

Appropriate nanocontainers may be utilized to enable the cluster compounds to be transported and released within target tissues. Of great interest is the encapsulation of potential drug molecules by non-covalent binding at the interior of dendritic structures which provide well-defined cavities. In this context, dendritic nanocontainer with maltose-modified shell [2] appears appealing to act as a host for nanometer sized anionic rhenium cluster compounds.

The inclusion and release phenomena of an octahedral rhenium cluster with six terminal hydroxo ligands [Re6S8(OH)6]4- [3] into poly(propylene amine) dendrimers (POPAM, generation 4 and 5) with dense maltose shell have been studied in detail applying different physico-chemical methods, e.g. UV/vis, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser induced liquid bead ion desorption (LILBID) mass spectrometry.

On average, 4 – 5 cluster anions can be captured in the interior of the investigated sugar-coated dendrimers, and a slow release of cluster complexes was observed under physiological conditions.

Altogether, the studied system shows the possibility for the development of dendritic nanocarriers with specific targeting and paves the way for therapeutic applications.

[1] J. T. Rhule, C. L. Hill, D. A. Judd, R. F. Schinazi, Chem. Rev.1998, 98, 327-357.
[2] B. Klajnert, D. Appelhans, H. Komber, N. Morgner, S. Schwarz, S. Richter, B. Brutschy, M. Ionov, A. K. Tonkikh, M. Bryszewska, B. Voit, Chem. Eur. J. 2008, 14, 7030.
[3] K. A. Brylev, Y. V. Mironov, S. S. Yarovoi, N. G. Naumov, V. E. Fedorov, S.-J. Kim, N. Kitamura, Y. Kuwahara, K. Yamada, S. Ishizaka, Y. Sasaki, Inorg. Chem. 2007, 46, 7414-7422.
  • Lecture (Conference)
    IWTMC-II International Workshop on Transition Metal Clusters-II, 30.09.-02.10.2010, Rostock, D

Publ.-Id: 14689 - Permalink

Improved environmental resistance of Ti-alloys at elevated temperatures by a combined Al- and F-treatment
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
Titanium is widely used as a structural material because of its low specific weight, good mechanical properties and excellent corrosion resistance at low temperatures due to the formation of a passive TiO2layer. The melting point (1677°C) is very high. Usually the maximum tolerable operating temperature is lower than 600°C. Because of increased oxidation and environmental embrittlement Ti-Alloys can not be used at higher temperatures in oxidizing environments. An enrichment of Al in the surface zone of Ti-alloys leads to an improvement of the oxidation resistance by the formation of intermetallic TixAly-phases but this is not sufficient. A fluorine treatment on TiAl-alloys results in the formation of a protective alumina scale by the so called fluorine effect. Therefore, the combination of Al-enrichment in the surface zone so that a TiAl-layer is formed and an additional F-treatment gives good results. The alumina scale is very protective against environmental attack and also prevents oxygen inward diffusion which causes embrittlement. In this paper the results of isothermal and thermocyclic oxidation tests at 600°C of several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment, with single Al-treatment, pure F-treatment and the combination of both. Aluminium was either enriched by a powder pack process or by magnetron sputtering. Fluorine was applied by several ways e.g. by a liquid phase process. Post experimental investigations like SEM revealed the formation of thin oxide layers on samples with the combined Al + F-treatment. Hardness measurements showed that no embrittlement was observed on the treated samples while untreated specimens showed increased hardness values in the oxygen enriched zone.
  • Lecture (Conference)
    Materials Science & Technology 2010 Conference and Exhibition - combined with the ACerS 112th Annual Meeting (MS&T 2010), 17.-21.10.2010, Houston, USA

Publ.-Id: 14688 - Permalink

Protection of TiAl-components against high temperature oxidation with fluorine
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
Titanium aluminides are very promising light weight materials for several high temperature applications e.g. in aero or automotive engines but due to their insufficient oxidation resistance at temperatures above roughly 800°C they can not be used for longer times. The oxidation behaviour of TiAl-alloys can be improved significantly by microalloying of small amounts of fluorine into the subsurface zone. The use of TiAl-components after fluorine treatment is possible up to temperatures above 1000°C in oxidizing atmospheres due to the formation of a thin protective alumina layer. One possibility to apply fluorine to the surface of complex TiAl-components is the PI³-technique (plasma immersion ion implantation). The use of an Ar/CH2F2-plasma for the F-PI³ into small coupons leads to a positive effect which is as good as the beamline implantation of elemental fluorine gas into samples of the same size. Other treatments are using liquid or gaseous fluorine containing compounds which react with the surface of the specimens. The oxidation kinetics of F-treated TiAl-alloys will be discussed in the paper. Several more complex TiAl-samples and turbine blades as examples for real TiAl-components have been treated. Their oxidation behaviour will be shown. Post exposure investigations like SEM reveal a thin protective alumina scale on the surface of the implanted samples in contrast to a thick mixed scale (TiN/TiO2/Al2O3) growing on untreated samples during high temperature exposure in air.
  • Lecture (Conference)
    Materials Science & Technology 2010 Conference and Exhibition - combined with the ACerS 112th Annual Meeting (MS&T 2010), 17.-21.10.2010, Houston, USA

Publ.-Id: 14687 - Permalink

Suppression of oxygen-induced embrittlement in Ti by plasma immersion ion implantation (PIII)-based processing
Yankov, R. A.; Kolitsch, A.; Munnik, F.; von Borany, J.;
Titanium has a large strength-to-weight ratio and good corrosion resistance at moderate temperatures, which make it an important structural material in a number of advanced technical applications. A major problem with the use of Ti is its high affinity to oxygen giving rise to massive oxygen in-diffusion at temperatures of about 550° to 600°C. The presence of large amounts of oxygen renders the material brittle and deteriorates its mechanical properties. In this work, we describe an effective way of overcoming the oxygen-induced embrittlement problem by forming a surface barrier to the diffusion of oxygen. Surface processing has involved two steps, namely enrichment of the Ti near-surface region with Al, and introduction of fluorine. For the Al enrichment, a novel hybrid system has been developed to implant Al into Ti. The apparatus consists basically of a PIII chamber configured with two magnetrons having an Al target each, and facing the RF antenna. The magnetrons are synchronized with the bias applied to the sample holder in such a way that the accelerating high-voltage pulse is triggered with a certain delay, i.e. during the time when the Al plasma generated by the magnetrons is most dense, thereby minimizing deposition. Alternative aluminization techniques have involved either magnetron sputtering of Al onto Ti followed by a thermal drive-in step or pack processes. Fluorine has been subsequently introduced by PIII employing a mixture of CH2F2 and Ar as the precursor gas. A variety of analytical techniques such as elastic recoil detection analysis (ERDA), Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and x-ray diffraction (XRD) have been used for characterization. Optimized PIII-based processing has been found to produce a continuous, adherent alumina scale on the Ti surface. Thus, the resulting material is inherently resistant to oxygen absorption and is not embritteled upon extended exposure to oxygen-containing environments at elevated temperatures up to about 600° C.
  • Poster
    12th International Conference on Plasma Surface Engineering - PSE 2010, 13.-17.09.2010, Garmisch-Partenkirchen, Germany

Publ.-Id: 14686 - Permalink

Improvement of the oxidation behaviour of complex shaped TiAl-alloys by plasma immersion ion implantation with fluorine
Kolitsch, A.; Yankov, R.; Donchev, A.;
Titanium aluminides are of great interest for several structural high temperature applications because of their low specific weight (about 4 g/cm3) and their excellent high temperature strength. They could replace the much heavier high temperature steels or Ni-based superalloys (up to 9 g/cm3) which are usually in service. The implementation of this new group of intermetallic alloys in e.g. the aerospace or automotive industry is therefore due to economic and ecologic reasons. The use of TiAl-based alloys is still limited to a temperature of about 750 °C because of their poor oxidation resistance despite of their good mechanical properties which would allow the use at higher temperatures. The oxidation resistance can be improved significantly by small amounts of halogens such as fluorine, chlorine, bromine and iodine (so called halogen effect).
A defined dose of these halogens has to be provided at the metal/oxide interface of the component. The halogens promote the selective formation of gaseous Al-halides at temperatures above 700 °C which are oxidised to Al2O3 during their outward diffusion through the naturally grown oxide scale. So finally a protective alumina scale is formed which is stable for long times even under thermocyclic exposure and wet atmospheres. In this presentation the results of isothermal and thermocyclic high temperature oxidation tests of technical TiAl-alloys with and without fluorine ion implantation are shown.
  • Poster
    18th International Conference on Ion Implantation Technology, 06.-11.06.2010, Kyoto, Japan

Publ.-Id: 14685 - Permalink

Formation of an alumina-containing scale for the surface protection of TiAl alloys and Ti against environmental degradation at elevated temperatures
Yankov, R. A.; Kolitsch, A.; Munnik, F.; von Borany, J.;
Ti and TiAl alloys are lightweight materials that hold great promise for advanced aerospace, automotive and power generation applications. They are, however, limited in applicability by their poor oxidation resistance above 600°C. We have developed a process for enhancing the high-temperature oxidation resistance of these materials. For TiAl, the process involves a single step, i.e. plasma immersion implantation (PIII) of fluorine relying on the so-called "halogen effect". Optimum conditions have been established under which the alloys acquire a stable, adherent and highly protective alumina scale upon subsequent high-temperature oxidation in air. The extent of oxidation protection has been evaluated by testing F-implanted TiAl samples at temperatures up to 1050°C. Results from characterization by elastic recoil detection, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis have proven the possibility of forming a protective alumina scale on both laboratory coupons and components such as turbine blades and turbochargers. In the case of Ti, surface processing involves two steps, i.e. Al enrichment of the Ti near-surface, and introduction of F by PIII. The Ti samples so modified have shown marked environmental stability at temperatures up to 700°C.
  • Poster
    CIMTEC 2010 - 12th International Conference on Modern Materials and Technologies, 12th International Ceramic Congress, 06.-11.06.2010, Montecatini Terme, Italy

Publ.-Id: 14684 - Permalink

Enhanced resistance of Ti-alloys against environmental attack by a combined Al- and F-treatment
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
Titanium alloys cannot be used at elevated temperatures above approximately 500°C because of their limited environmental stability. Several ways have been investigated so far to improve the environmental stability of Ti-alloys e.g. coatings but these attempts in a majority of cases have not been really successful. A new way to improve the performance of these alloys is the combination of Al-enrichment in the surface zone plus additional fluorine treatment. The Al-enrichment leads to the formation of intermetallic phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment on top of the Al-enriched surface leads to the formation of a stable alumina scale due to the fluorine effect. In this paper results from oxidation and other tests performed on Ti-samples without any treatment, with single Al- or F-treatment and with a combination of both are presented and the results are discussed.
  • Lecture (Conference)
    TMS 2010 (The Minerals, Metals and Materials Society), 139th Annual Meeting & Exhibition, 14.-18.02.2010, Seattle, USA

Publ.-Id: 14683 - Permalink

Comparison of fluorination treatments to improve the high temperature oxidation resistance of TiAl alloys in SO2 containing environments
Masset, P. J.; Yankov, R.; Kolitsch, A.; Schütze, M.;
Surfaces of titanium aluminides were treated with fluorine either physically by plasma immersion ion implantation (PIII) or chemically using a F-based polymer. Under optimum conditions of fluorination, both treatments were shown to improve the oxidation resistance of the alloys even in aggressive environments containing sulfur dioxide (0.1 vol. %). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen was found to be reduced in the presence of SiO2.

Publ.-Id: 14682 - Permalink

Surface Morphology of Heterogeneous Nanocrystalline Rutile/Amorphous Anatase TiO2 Films Grown by Reactive Pulsed Magnetron Sputtering
Gago, R.; Vinnichenko, M.; Redondo-Cubero, A.; Czigany, Z.; Vazquez, L.;
Titaniumdioxide filmswere grown on unheated substrates bymid-frequency (100 kHz) reactive pulsed magnetron sputtering at different O2 partial pressures in an Ar/O2 atmosphere. X-ray diffraction and absorption measurements reveal a transition from amorphous anatase to nanocrystalline rutile with [O2], with a mixture of both phases at intermediate values. Atomic forcemicroscopy shows that the promotion of rutile is accompanied by surface roughening due to the apparition of hollow structures (holes) on the surface, in contrast with the extremely smooth morphology of amorphous anatase films. The number and size of holes increase with [O2] and growth time in such a way that they eventually coalesce and percolate to lead to a rough surface for those growth conditions for which a rutile rich filmis obtained. Transmission electron microscopy analysis shows the growth evolution of a heterogeneous phase mixture and provides unambiguous correlation between the hole (smooth) morphology and the underlying rutile (anatase) phase. Therefore, the surface morphology results fromthe slower local growth rate of nanocrystalline rutile compared to that of the surrounding amorphous anatase flat regions as well as from the fast (slow) lateral (vertical) growth rate of the rutile domains.
Keywords: Amorphous oxides, TiO2, magnetron, pulsed discharges, thin films

Publ.-Id: 14681 - Permalink

Tumour bed irradiation of human tumour xenografts in a nude rat model using a common X-ray tube
Tokalov, S.; Enghardt, W.; Abolmaali, N.;
Studies that investigate the radiation of human tumour xenografts require an appropriate radiation source and highly standardized conditions during radiation. This work reports on the design of a standardized irradiation device using a commercially available X-ray tube with a custom constructed lead collimator with two circular apertures and an animal bed plate, permitting synchronous irradiation of two animals. Dosimetry and the corresponding methodology for radiotherapy of human non-small cell lung cancer xenograft tumours transplanted to and growing subcutaneously on the right lower limb in a nude rat model were investigated. Procedures and results described herein prove the feasibility of use of the device, which is applicable for any investigation involving irradiation of non-tumorous and tumorous lesions in small animals.

Publ.-Id: 14680 - Permalink

Improvement of radiation-mediated immunosuppression of human NSCLC tumour xenografts in a nude rat model
Tokalov, S.; Enghardt, W.; Abolmaali, N.;
Human tumour xenografts in a nude rat model have consistently been used as an essential part of preclinical studies for anticancer drugs activity in human. Commonly, these animals receive whole body irradiation to assure immunosuppression. But whole body dose delivery might be inhomogeneous and the resulting incomplete bone marrow depletion may modify tumour behaviour. To improve irradiation-mediated immunosuppression of human non-small cell lung cancer (NSCLC) xenografts in a nude rat model irradiation (2 + 2 Gy) from opposite sides of animals has been performed using a conventional X-ray tube. The described modification of whole body irradiation improves growth properties of human NSCLC xenografts in a nude rat model. The design of the whole body irradiation mediated immunosuppression described here for NSCLC xenografts may be useful for research applications involving other types of human tumours.

Publ.-Id: 14679 - Permalink

Advanced bio-composite materials for water treatment
Raff, J.; Pollmann, K.;
Bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example is the binding of metalloids, heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins avoid the uptake and any sustainable damage of the cell by toxic and/or radioactive elements. The proteins possess additionally self-assembling properties and form symmetric lattices. These properties altogether qualifies the protein for nano-technological purposes and allow the production of advanced bio-composite materials such as metal filters, (photo)catalysts, functionalized membranes or biosensors for the treatment of water.
Keywords: S-layer, photocatalysts, water treatment
  • Poster
    POLEKO 2010, Internationale Fachausstellung für Umwelt, Energie, Ökologie, 23.-26.11.2010, Posen, Polen

Publ.-Id: 14678 - Permalink

Untersuchungen zur U(VI)-Komplexierung durch Milchsäure sowie zur U(VI)-Sorption an Opalinuston in Abwesenheit und Gegenwart von organischen Modellliganden in Abhängigkeit von der Temperatur
Joseph, C.; Steudtner, R.; Schmeide, K.;
Die U(VI)-Komplexierung durch Milchsäure in Abhängigkeit von der Temperatur (7-65°C) wurde mittels UV/VIS-Spektroskopie und TRLFS untersucht. Dabei konnten zwei U(VI)-Lactat-Komplexe, UO2Lac+ und UO2Lac2, identifiziert werden. Die entsprechende Enthalpie und Entropie der U(VI)-Komplexierung wurde bestimmt.
Die U(VI)-Sorption an Opalinuston (OPA) in Abhängigkeit von Modellliganden und der Temperatur (25-60°C) wurde untersucht. Dabei beeinflussten die Modellliganden die U(VI)-Sorption an OPA in folgender Reihenfolge: Citronensäure > Weinsäure > Milchsäure ≈ Essigsäure > Ameisensäure. Die U(VI)-Sorption nahm mit steigender Ligandenkonzentration ab, nahm aber mit steigender Temperatur zu. Bei 60°C wurde ein Sprung im Kd-Wert des Urans verzeichnet. Milchsäure hatte dabei keinen signifikanten Einfluss auf die Enthalpie und Entropie der U(VI)-Sorption an OPA in Abhängigkeit von der Temperatur.
HTO-Diffusionsversuche mit OPA bei 25°C und 60°C wurden durchgeführt um die Diffusionsparameter (effektiver Diffusionskoeffizient, Porosität) der Tonproben zu bestimmen. Die experimentellen Werte bestätigten die Literaturdaten.
Keywords: uranium(VI), complexation, TRLFS, UV/VIS, lactate, citric acid, sorption, Opalinus Clay, temperature-dependent, diffusion, HTO
  • Lecture (others)
    9. Workshop des Verbundprojekts "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 05.-06.10.2010, Mainz, Deutschland

Publ.-Id: 14677 - Permalink

Design, Synthesis and Preliminary in vitro and in vivo Pharmacological Evaluation of 2-{4-[4-(2,5-disubstituted thiazolyl)phenylethyl] piperazin-1-yl}-1,8-naphthyridine-3- carbonitriles as Atypical Antipsychotic Agents
Chandra Sekhar, K. V. G.; Rao, V. S.; Deuther-Conrad, W.; Reddy, A. S.; Brust, P.; Kumara, M. M. K.;
A series of 2-{4-[4-(2,5-disubstituted thiazolyl)phenylethyl] piperazin-1-yl}-1,8-naphthyridine-3-carbonitriles were synthesized in an effort to prepare novel atypical antipsychotic agents. The compounds were synthesized by either microwave irradiation technique or by conventional synthesis and were characterized by spectral data (IR, 1H NMR, and MS) and the purity was ascertained by microanalysis. The D2 and 5-HT2A affinity of the synthesized compounds was screened in vitro by radioligand displacement assays on membrane homogenates isolated from rat striatum and rat cortex, respectively. Furthermore, all the synthesized compounds were screened for their in vivo pharmacological activity in Swiss albino mice. The D2 antagonism studies were performed using climbing mouse assay model and 5-HT2A antagonism studies were performed using quipazine induced head twitches in mice. It was observed that none of the new chemical entities exhibited catalepsy and 10f is the most active among the synthesized compounds with 5-HT2A/D2 ratio of 1.1286 while the standard drug risperidone exhibited 5-HT2A/ D2 ratio of 1.0989
Keywords: schizophrenia, atypical antipsychotics, D2 antagonists, 5-HT2A antagonists

Publ.-Id: 14675 - Permalink

A prototype coordinate detector based on granulated thin-walled drift tubes
Bazylev, S. N.; Davkov, K. I.; Gregor, I.; Haas, D.; Mouraviev, S. V.; Myalkovskiy, V. V.; Naumann, L.; Peshekhonov, V. D.; Rembser, C.; Rufanov, I. A.; Russakovich, N. A.; Senger, P.; Shutov, A. V.; Slepnev, I. V.; Smirnov, S. Y.; Tikhomirov, V. O.; Zhukov, I. A.;
A prototype detector based on thin-walled segmented tubes has been developed and its parameters have been studied. The detector contains 360 registration channels with a straw diameter of 4mm. The prototype granularity is 4 cm2 and the length of insensitive region due to straw internal elements is less than 5% of its full sensitive area. Deterioration of the spatial resolution near these elements is observed for 1.0% of the detector sensitive area. The time and spatial parameters of the detector do not differ from those of conventional tracking detectors based on drift tubes.
Keywords: Coordinate detector Granulated thin-walled drift tube Straw Spatial resolution

Publ.-Id: 14674 - Permalink

Exploring uranium chemistry with computational chemistry
Tsushima, S.;
there is no abstract for this talk
  • Lecture (Conference)
    User's meeting of Zentrum für Informationsdienste und Hochleistungsrechnen (ZIH), TU Dresden, 06.-07.12.2010, TU Dresden, Germany

Publ.-Id: 14673 - Permalink

Ni-Ti Surface Modification by Plasma Immersion Ion Implantation
Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Carmezim, M. J.; Fernandes, T. M. S. J. C. S.;
The plasma immersion ion implantation (PIII) technique was used to modify and improve the surface of a Ni-Ti alloy (» 50.2 at.% Ni) for biomedical applications. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material. Ion implantation of oxygen was carried out. The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer. The working plan also comprised ion implantation of nitrogen. In this case, the formation of titanium oxynitride (TiNxOy) was observed. The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with 40 keV.
Keywords: plasma immersion ion implantation, PIII, ion implantation, Ni-Ti
  • Poster
    MM & FGM 2010 - 11th International Symposium on Multiscale, Multifunctional and Functionally Graded Materials, 26.-29.09.2010, Guimarães, Portugal

Publ.-Id: 14672 - Permalink

Medical Imaging Experience from the Past 10 Years and State-of-the-Art
Enghardt, W.;
no abstract available
  • Lecture (Conference)
    ENVISION General Meeting Stockholm, 05.09.2010, Stockholm, Schweden

Publ.-Id: 14671 - Permalink

Neue Entwicklungen in der medizinischen Strahlenphysik
Enghardt, W.;
no abstract available
  • Invited lecture (Conferences)
    43. Sitzung des Arbeitskreises Strahlenbiologie/Strahlenwirkung Dresden, 21.-22.06.2010, Dresden, Deutschland

Publ.-Id: 14670 - Permalink

Laser-Radioonkologie: Auf dem Weg vom Konzept zur Klinik
Enghardt, W.;
no abstract available
  • Invited lecture (Conferences)
    Symposium anlässlich der Emeritierung von Prof. Dr. Thomas Herrmann, 19.02.2010, Dresden, Deutschland

Publ.-Id: 14669 - Permalink

Prospects in Medical Imaging - Summary Workshop
Enghardt, W.;
no abstract available
  • Invited lecture (Conferences)
    „Physics for Health in Europe“, 02.-04.02.2010, Geneva, Schweiz

Publ.-Id: 14668 - Permalink

Wissensvermittlung im Studiengang „Medical Radiation Sciences“ an der Medizinischen Fakultät der TU Dresden Sitzung des Fachausschusses Strahlenschutz des Länderausschusses für Atomkernenergie
Enghardt, W.;
no abstract available
  • Invited lecture (Conferences)
    Sitzung des Fachausschusses Strahlenschutz des Länderausschusses für Atomkernenergie, 18.02.2010, Bonn, Deutschland

Publ.-Id: 14667 - Permalink

Runtime Experience and Impurity Investigations at the ELBE Cryogenic Plant
Schneider, C.; Michel, P.; Haberstroh, C.;
The superconducting linear accelerator ELBE at the Forschungszentrum Dresden/Rossendorf has two superconducting accelerator modules and a superconducting photo injector (SRF-Gun). They are operated by a cryogenic Helium plant with a cooling power of 200 W at 1.8 K. Since the commissioning of the plant in 1999 minor and major impurity problems have influenced the operation stability of the plant. The presentation will give an overview of the ELBE cryogenic system and will focus on the different sources of plant contamination and their effects on the plant operation, which have been found during the nearly 10 years of plant lifetime. Especially the contamination with oil brake up components as well as air and water from different sources have limited the run periods of the plant and effected special service and maintenance procedures.
Keywords: superconducting linear accelerator, cryogenetic
  • Contribution to proceedings
    The first International Particle Accelerator Conference, IPAC’10, 23.-28.05.2010, Kyoto, Japan
    Proceedings of IPAC'10, 3828-3830
  • Poster
    The first International Particle Accelerator Conference, IPAC’10, 23.-28.05.2010, Kyoto, Japan

Publ.-Id: 14666 - Permalink

Untersuchungen zur Anwendung der Elektronenstrahl-Röntgen-Tomographie für die Kleintierbildgebung
Loitsch, S.;
Die ultraschnelle Röntgentomographie wird am FZD vorrangig für die Untersuchung von Zweiphasenströmungen eingesetzt. Potentielle Anwendungsgebiete sind aber auch auf dem medizinischen Sektor zu erwarten. Daher soll die Möglichkeit des Einsatzes der ultraschnellen Röntgentomographie für die Kleintierbildgebung untersucht werden. In dieser Diplomarbeit wurden statische und dynamische Labormodelle entwickelt, mit deren Hilfe die Abbildungseigenschaften für die Kleintierdiagnostik evaluiert werden können.
Keywords: ultrafast imaging, X-ray computed tomography, small animals
  • Diploma thesis
    Fachhochschule Lübeck, 2010
    63 Seiten

Publ.-Id: 14665 - Permalink

Filtration material inspired by microorganisms
Kutschke, S.; Pollmann, K.; Raff, J.; Matys, S.;
Detoxification strategy of bacteria, living in uranium mining waste piles, is one part of radio-ecological investigation at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf. On that account several isolates were subsequently analyzed regarding their growth in presence of different heavy metals and their heavy metal binding properties, particularly using uranium. Some isolates show a high and selective binding for uranium, cadmium, lead, and a few other heavy metals. Interestingly, the heavy metals were immobilized on the cell surface, preventing any sustainable damage of the cell. Responsible for the binding of heavy metals outside the cell is a proteinaceous cell envelope, a so-called surface layer (S-layer).
Using these heavy metal binding properties of bacterial cells and S-layer different filter materials were developed. These include the production of biofilm based materials and the protein immobilization on conventional carriers. Thereby, a different binding behaviour between whole cells and their corresponding S-Layers could be observed. Moreover the S-layer based filter materials bind also some precious metals. So a metal selective filter material for the removal of heavy metals and precious metals from aqueous solutions is developing.
Keywords: Proteinous bacterial surface layer (S-layer) Metal binding capacities of S-layer Application potential
  • Invited lecture (Conferences)
    Synthetic Fibre Talks- Membranes and Filters, 29.-30.04.2010, Aachen, Deutschland

Publ.-Id: 14663 - Permalink

Sorption of thallium(I) onto geological materials: Influence of pH and humic matter
Liu, J.; Lippold, H.; Wang, J.; Lippmann-Pipke, J.; Chen, Y.;
The sorption behaviour of the severely toxic heavy metal thallium (Tl) as a monovalent cation onto three representative materials (goethite, pyrolusite and a natural sediment sampled from a field site) was examined as a function of pH in the absence and presence of two natural humic acids (HAs), using 204Tl(I) as a radiotracer. In order to obtain a basic understanding of trends in the pH dependence of Tl(I) sorption with and without HA, sorption of HAs and humate complexation of Tl(I) as a function of pH were investigated as well. In spite of the low complexation between Tl(I) and HAs, the presence of HAs results in obvious alterations of Tl(I) sorption onto pyrolusite and sediment. An influence on Tl(I) sorption onto goethite was not observed. Predictions of Kd (distribution coefficient) for Tl(I) on goethite in the presence of HAs, based on a linear additive model, agree well with the experimental data, while a notable disagreement occurs for the pyrolusite and sediment systems. Accordingly, it is suggested that HAs and goethite may act as a non-interacting sorbent mixture under the given conditions, but more complex interactions may take place between the HAs and the mineral phases of pyrolusite or sediment.
Keywords: goethite; pyrolusite; humic acid; modelling

Publ.-Id: 14661 - Permalink

Cold quark stars from hot lattice QCD: a comparison
Schulze, R.; Kämpfer, B.;
Based on a quasiparticle model for \beta stable and electrically neutral deconfined matter we address the possibility of pure quark stars. The model is adjusted to recent hot lattice QCD results for 2+1 flavors with almost physical quark masses. Using stability and binding arguments general statements can be made concerning the existence of such compact stellar objects.
  • Lecture (Conference)
    TORIC 2010, 26.-30.09.2010, Villasimius/Sardinia, Italy

Publ.-Id: 14660 - Permalink

Superconductivity in Group IV Semiconductors
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Posselt, M.; Skorupa, W.; Helm, M.; Gobsch, G.;
es hat kein Abstract vorgelegen
  • Lecture (Conference)
    Punktdefekttreffen, 07.-08.10.2010, Dresden, Deutschland

Publ.-Id: 14659 - Permalink

Spin manipulation in Co-doped ZnO
Schmidt, H.;
The magnetoresistance of n-type conducting, paramagnetic Co-doped ZnO films prepared by pulsed laser deposition on sapphire substrates has been studied experimentally and theoretically. Positive magnetoresistance (MR) of 124% has been observed in the film with the lowest electron concentration, while only a negative MR of −1.9% was observed in the film with a large electron concentration at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin splitting of the conduction band. The negative MR is attributed to the magnetic field suppressed weak localization. Voltage control of the electron concentration in Schottky diodes revealed a drastic change of the magnetoresistance and demonstrated the electrically controllable magnetotransport behavior in Co-doped ZnO. The magnetically controllable spin polarization in Co-doped ZnO has been demonstrated at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom electrode and Co as a top electrode. There spin-polarized electrons were injected from Co-doped ZnO to a crystallized Al2O3 layer and tunnelled through an amorphous Al2O3 barrier. Our studies demonstrate the spin polarization and manipulation in Co-doped ZnO.
Keywords: ZnO, spin polarization, spin-polarized transport
  • Invited lecture (Conferences)
    12th International Ceramics Congress, 06.-11.06.2010, Montecatini Terme, Italy

Publ.-Id: 14658 - Permalink

Lung tumour motion during treatment: Should we match on bone or on tumour?
Hoinkis, C.; Richter, C.; Enghardt, W.; Zips, D.; Baumann, M.;
During the session titled "The use of PET-CT for lung cancer" several topics will be addressed, such as the technical background of PET-CT and an overview of the possibilities offered by PET imaging in lung cancer. The aim of all PET imaging in treatment planning for tumours is an improved delineation of the Gross Tumour Volume (GTV). Knowing exactly the position and extent of the vital tumour should increase local control and lead to longer survival of patients. As long as the target is immobile as is the case in the brain fusion of the PET information into the planning CT seems to be effortless. But problems arise when PET imaging is to be used for moving targets such as in lung. Therefore, the issue to be discussed in this presentation is "Should we match on bone or on tumour?". Necessity of motion comprehension during PET-CT imaging: In PET-CT imaging two different motion-related effects have to be considered:
(1) the direct effect of motion on the CT and PET modalities separately, and
(2) the effect of improper attenuation correction caused by a mismatch in the temporal resolutions of the two data sets.Examples of direct effects are artefacts in the region between the lung and liver in 3D-CT data and motion-induced smearing of the activity concentration in 3D-PET data. These artefacts are unavoidable in 3D imaging but can be overcome with the introduction of 4D imaging (4D-CT and 4D-PET). The second effect (i.e. smearing) has to be considered in both 3D- and 4D-imaging. In 3D-imaging the 3D-CT artefacts described above can propagate into the PET data set due to attenuation correction. One example given by Beyer et al. shows 3D PET-CT data that appears to show soft tissue in the lung, but which in fact is part of the moving liver (Eur J Nucl Med Mol Imaging 2003). Additionally, the different temporal resolution of 3D-PET and 3D-CT can generate artefacts in attenuation corrected data sets although both 3D-CT and uncorrected 3D-PET are free of artefacts. One impressive example of this phenomenon was shown by Osman et al. (J Nucl Med 2003), where liver metastases appeared in the lung region. In 4D-imaging, artefacts due to improper attenuation correction can be avoided if the different datasets of the 4D-PET are corrected with corresponding datasets of the 4D-CT, as has been demonstrated by Pnisch et al. (Med Phys 2008).
Possibilities for motion compensation during treatment: Several technical approaches have been introduced into clinical practice to compensate for motion during radiotherapy.
Two questions have to be addressed: a) How can the motion be turned into a signal and b) how can this signal be used to compensate the motion? Answering question a), helpful techniques which can be mentioned include spirometry, pressure based systems or optical systems detecting the motion of points on the thorax or of the whole body surface. In all these techniques, the motion leads to a signal that represents more or less precisely the motion of the patient. However, it is not proven that any signal also exactly follows the motion of the tumour. Answering question b), two approaches can be mentioned: "Gating" and "Tracking". Gating uses the motion signal to trigger the linear accelerator according to a defined "gate", i.e. to turn the beam on and off in synchronization with the breathing motion. Tracking is a method in which the motion of the target is followed (tracked) either by motion of the leaves in the MLC or by motion of the table. Verification of motion in the chain from planning to treatment: 4D treatment planning including 4D-PET/4D-CT and breathing-synchronized radiotherapy for lung cancer patients need a carefully considered concept of verification.
In contrast to conventional verification procedures at the linear accelerator, where the position of the patient is verified only by bony anatomy (brain), target motion adapted methods require appropriate additional imaging in the treatment room. Either radioopaque markers or kV-CT images are necessary. For organs with mainly interfractional motion such as the prostate, correct positioning of the target before the start of the fraction is essential. The treatment of intrafractional moving targets imposes more complexity. Besides verification of the baseline, the amplitude of the motion is a second point to be considered. The most important in the verification of a breathing synchronized radiotherapy is the comparison with the 4D treatment planning dataset. The basic principle is the use of the identical motion signal both for 4D imaging and for the 4D treatment. Only then a possible shift between real tumour motion and visualized tumour motion can be neglected.
Conclusions: Should we match on bone or on tumour? The short answer should be ON TUMOUR. But the longer answer is, BUT NOT FOR EVERY PATIENT. The challenge is the finding of clinical values used as guidance as to which patients will benefit from the high workload of 4D treatment planning and delivery.
  • Invited lecture (Conferences)
    ESTR0 29, 12.-16.09.2010, Barcelona, Espana
  • Abstract in refereed journal
    Radiotherapy and Oncology 96(2010)Suppl. 1, 64-65

Publ.-Id: 14657 - Permalink

Suppression of temperature fluctuations by rotating magnetic field in a large scale Rayleigh-Benard cell
Grants, I.; Gerbeth, G.;
Temperature fluctuations are observed experimentally in a cylinder of liquid mercury heated from below and cooled from above under action of a rotating magnetic field (RMF). The Grashof number (Gr) exceeds that of earlier studies by a factor of 10 at least. The setup models a proposed modification of the Czochralski crystal growth process where crucible rotation is replaced by RMF. It is known that the RMF characterized by the magnetic Taylor number Ta=15Gr0.8 suppresses buoyant temperature fluctuations in a cylinder cooled from above [1]. To achieve a comparable effect by a mechanical rotation of the crucible, a considerably higher rotation rate is required and the difference grows with Gr. The effect has been demonstrated up to Gr~5x107 that corresponds to a medium size gallium arsenide liquid encapsulated Czochralski process. Does the “0.8” scaling keep as Gr is increased? This is the central question of the study. One of the possible explanations of the phenomenon is a hypothetical stabilizing action of the core meridional flow. It is known that the angular velocity scaling Omega~Ta2/3 experiences a change at Ta~2x107 (that is able to stabilize the Gr~5x107 configuration). Besides, it is known that the product of mean radial velocity Vr and mean angular velocity Omega equals the magnetic force (Ta~V, Omega). Thus, if the meridional flow indeed plays a major role, then there should be a change of the Tacr(Gr) scaling above Gr~5x107. The experiment will allow Gr in the range [5x107 : 5x108]. It is prepared and scheduled for April 2010
  • Lecture (Conference)
    Modelling for Material Processing, 16.-17.09.2010, Riga, Lettland
  • Contribution to proceedings
    Modelling for Material Processing, 16.-17.09.2010, Riga, Lettland
    Suppression of temperature fluctuations by rotating magnetic field in a large scale Rayleigh-Benard cell, pp. 293-298

Publ.-Id: 14656 - Permalink

Development and assessment of structural materials and heavy liquid metal technologies for transmutation systems (DEMETRA): highlights on major results
Fazio, C.; van den Bosch, J.; Martin Muñoz, F. J.; Henry, J.; Roelofs, F.; Turroni, P.; Mansani, L.; Weisenburger, A.; Gorse, D.; Abella, J.; Brissonneau, L.; Dai, Y.; Magielsen, L.; Neuhausen, J.; Vladimirov, P.; Class, A.; Jeanmart, H.; Ciampichetti, A.; Gerbeth, G.; Wetzel, T.; Karbojian, A.; Litfin, K.; Tarantino, M.; Zanini, L.;
The DEMETRA domain of the EUROTRANS project provides a wealth of experimental and theoretical results within key technological areas related to the Heavy Liquid Metal (HLM) Technology. HLMs as Pb and Lead-Bismuth Eutectic (LBE) are the reference coolant and spallation materials choices for the ADS facilities studied within the EUROTRANS project.
For these coolants the key items that have been addressed within DEMETRA are:
Coolant quality control in terms of oxygen and impurities control;
Materials compatibility in terms of corrosion, mechanical and irradiation resistance;
Thermal-hydraulics studies related to heat transfer in turbulent conditions through dedicated experiments on a single pin, a fuel bundle and integrated component tests;
Safety related studies through experimental and simulation studies on HLM/water interaction;
Support to component design and testing, where in particular substantial support has been given to the development of the windowless-neutron spallation target and the assessment of the window spallation target behaviour through the post test analysis of MEGAPIE;
Measurement and operational techniques development;

The technical work programme of DEMETRA is herein summarised and some major experimental results are discussed.
  • Lecture (Conference)
    Technology and components of accelerator-driven systems, 15.-17.03.2010, Karlsruhe, Germany

Publ.-Id: 14655 - Permalink

Einfluss der Pulslänge bei hohen Pulsdosen auf die Sättigungskorrektur von Ionisationskammern
Karsch, L.; Richter, C.; Pawelke, J.;
no abstract available
Keywords: hohe Pulsdosen, Ionisationskammern
  • Lecture (Conference)
    41. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 29.09.-02.10.2010, Freiburg, Deutschland
  • Contribution to proceedings
    41. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 29.09.-02.10.2010, Freiburg, Deutschland

Publ.-Id: 14654 - Permalink

Strömungsinstabilitäten bei der Kristallzüchtung im TMF
Gerbeth, G.;
Es wird eine übersicht gegeben zu Strömungen und deren Stabilität in magnetischen Wanderfeldern. Die Sensitivität der TMF-Strömung gegenüber geringen Achsenverschiebungen zwischen TMF und Schmelztiegel ist sehr hoch und sollte in der Praxis großen Einfluss auf die tatsächlichen Strömungen in Kristallzüchtungsprozessen haben.
  • Lecture (Conference)
    Magnetfelder in der Kristallzüchtung, 09.-10.09.2010, Potsdam, Deutschland

Publ.-Id: 14653 - Permalink

Elektromagnetische Strömungskontrolle lokaler Temperaturgradienten in einem Modell des Czochralski-Prozesses
Cramer, A.; Röder, M.; Pal, J.; Gerbeth, G.;
Die Gestalt der Kristallisationsfront und das damit verbundene monokristalline Wachstum im Czochralski-Kristallzuchtprozess hängt stark vom Verhältnis zwischen horizontalem und vertikalem Temperaturgradienten r*=deltaT_h/deltaT_v an der Schnittstelle zwischen Schmelze, Kristall und Atmosphäre ab. Der Wert von r* liegt dabei idealerweise in der Nähe von 1. Deshalb wurde ein Flüssigmetall-Modellexperiment aufgebaut, das die Untersuchung von r* unter dem Einfluss von Magnetfel-dern ermöglicht. Das zylindrische Flüssigmetallvolumen wird dabei homogen von unten geheizt, und um den wachsenden Kristall zu simulieren wird die Wärme oben konzentrisch mit einem Kühler entzogen, der die Oberfläche nur bis zu einem Drittel des Radius bedeckt. Ohne Strömungskontrolle findet sich ein von der Zielfunktion weit entfernter Wert von r*=3. Das Ziel r*=1 kann durch elektromagnetische Strömungsbeeinflussung erreicht werden.
  • Contribution to proceedings
    Workshop Elektroprozesstechnik, 23.-24.09.2010, Ilmenau - OT Heyda, Deutschland

Publ.-Id: 14652 - Permalink

A physical model for electromagnetic control of local temperature gradients in a Czochralski system
Cramer, A.; Röder, M.; Pal, J.; Gerbeth, G.;
The shape of the solidification front and the related mono-crystalline growth in the Czochralski crystal growth process is thought of being strongly influenced by the ratio of the horizontal and the vertical temperature gradient r* = deltaT_h / deltaT_v at the triple point liquid-solid-atmosphere, which ratio desirably should be in the order of unity. A liquid metal model experiment was therefore built that allows studying r* under the influence of magnetic fields. The cylindrical liquid metal column was homogeneously heated from below, whereas on top the heat was extracted in a centrical region covering only one third of the surface in order to simulate the growing crystal. Without flow control, r* ≈ 3 is far removed from unity. It was then possible to reach the target value r* = 1 for any temperature difference between the bottom and the top at a moderate field strength while applying a rotating magnetic field.
Keywords: crystal growth, Czochralski process, flow control, electromagnetic processing of materials, magnetic fields
  • Lecture (Conference)
    International Scientific Colloquium on Modelling for Material Processing, 16.-17.09.2010, Riga, Lettland
  • Contribution to proceedings
    International Scientific Colloquium Modelling for Material Processing, 16.-17.09.2010, Rīga, Latvija
    Proceedings of the 6th International Scientific Colloquium Modelling for Material Processing, 978-9984-45-223-4, 41-46
  • Magnetohydrodynamics 46(2010), 353-362

Publ.-Id: 14651 - Permalink

Magnetic field controlled single crystal growth and surface modification of titanium alloys exposed for biocompatibility
Hermann, R.; Calin, M.; Uhlemann, M.; Wendrock, H.; Gerbeth, G.; Büchner, B.; Eckert, J.;
The aim of the work is the growth and characterisation of Ti55Nb45 (wt %) single crystals with the floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced via additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. As a result, a tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards to outwards flows. Due to their attractive properties such as light, strong and totally biocompatible, titanium is one of few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations (-1,0,0) and (1,0,1) normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly define crystal orientation and orientation changes in the crystallographic textures. The elastic modulus, the shear modulus and the bulk modulus were determined in dependence on the crystal orientation using ultrasonic measurements. Moreover, the oxide formation behavior on Ti surfaces in dependence on the grain orientation was investigated, performed anodically from fluoride containing electrolyte.
  • Lecture (Conference)
    The 16th International Conference on Crystal Growth (ICCG-16), 08.-13.08.2010, Beijing, China
  • Journal of Crystal Growth 318(2011)1, 1048-1052
    DOI: 10.1016/j.jcrysgro.2010.10.196

Publ.-Id: 14650 - Permalink

Thermophysical properties of intermetallic Ti-Al alloys in the liquid state
Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.;
TiAl intermetallic alloys were developed as potential materials for high temperature applications because of their excellent chemical and physical properties such as low density, high modulus and corrosion resistance. These characteristics are attractive for applications in aerospace and automotive industries but also for chemical and biomedical application. However, their low ductility at room temperature limits their application. Also microscopic factors like volume fraction of the apparent phases, the distribution of orientation variants, fineness of the microscopic structure strongly affect the mechanical properties.
  • Lecture (Conference)
    Liquid and Amorphous Metals Conference (LAM 14), 11.-16.07.2010, Rom, Italy

Publ.-Id: 14649 - Permalink

Thermophysical and structure-sensitive properties of low-temperature ternary liquid metal eutectics
Plevachuk, Y.; Sklyarchuka, V.; Gerbeth, G.; Eckert, S.;
Investigation of thermophysical and structure-sensitive properties of liquid low-temperature ternary metal eutectic alloys are stimulated both by pure academic as well as by applied science. In particular, there exist few reliable experimental data on the electrophysical, transport and surface properties of multicomponent alloys and, therefore, they are often estimated with analytical approaches. In order to prove any theory, experimental results are needed.
The favorable combination of the technical characteristics of Ga-based melts brought about their extensive application as sliding contacts, the working medium of magnetohydrodynamic devices, heat-sensitive elements of liquid-metal thermometers and thermocouples, and the base for conducting magnetic fluids. The GaInSn eutectic alloy is a suitable alternative to mercury since it exhibits an equilibrium melting point of 284 K. Bi-Pb-Sn liquid eutectics are chosen as model substances for experimental
  • Poster
    XIV Liquid and Amorphous Metals Conference (LAM 14), 11.-16.07.2010, Rom, Italy

Publ.-Id: 14648 - Permalink

Saturation correction of an ionization chamber for short and intense beam pulses
Karsch, L.; Richter, C.; Pawelke, J.;
no abstract available
Keywords: saturation correction, ionization chamber, short and intense beam pulse
  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14647 - Permalink

An integrated dosimetry and cell irradiation device for in vitro cell experiments with laser accelerated protons
Richter, C.; Akhmadaliev, S.; Dammene, Y.; Karsch, L.; Reinhardt, S.; Sobiella, M.; Schürer, M.; Weber, A.; Pawelke, J.;
no abstract available
Keywords: dosimetry, cell irradiation, in vitro cell experiments, laser accelerated protons
  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14646 - Permalink

Liquid metal modelling of continuous steel casting
Gerbeth, G.; Eckert, S.; Timmel, K.; Miao, X.;
Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present the new experimental facility CONCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, experimental results will be presented on the impact of a steady magnetic field on the outlet flow from the nozzle, obtained at a smaller-scale set-up working with the room-temperature alloy GaInSn. Local velocities in both facilities are measured by Ultrasound Doppler Velocimetry and contactless inductive flow tomography. The latter is attractive also for real-scale steel casting.
  • Lecture (Conference)
    TMS Annual meeting "Jim Evans Honorary Symposium", 14.-18.02.2010, Seattle, USA
  • Contribution to proceedings
    TMS Annual meeting, 14.-18.02.2010, Seattle, USA
    "Jim Evans Honorary Symposium", 55-62

Publ.-Id: 14645 - Permalink

Radiobiological preparation of in vitro cell experimentes with laser accelerated protons
Beyreuther, E.; Dammene Debbih, Y.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Richter, C.; Schürer, M.; Pawelke, J.;
no abstract available
Keywords: in vitro cell experimentes, laser accelerated protons
  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14644 - Permalink

Influence of ultra-high pulse dose rate on biological effectiveness of laser accelerated electrons
Laschinsky, L.; Beyreuther, E.; Karsch, L.; Leßmann, E.; Naumburger, D.; Richter, C.; Schürer, M.; Pawelke, J.;
no abstract available
Keywords: ultra-high pulse dose rate, biological effectiveness, laser accelerated electrons
  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14643 - Permalink

Biological effectiveness of laser-accelerated electrons in comparison to conventional accelerated electrons
Naumburger, D.; Beyreuther, E.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H. P.; Baumann, M.;
no abstract available
Keywords: biological effectiveness, laser-accelerated electrons, electrons
  • Poster
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14642 - Permalink

Research of the laser-radiooncology (onCOOPtics) group
Pawelke, J.;
no abstract available
Keywords: laser radiooncology
  • Invited lecture (Conferences)
    OncoRay Retreat, 27.-28.01.2010, Bautzen, Deutschland

Publ.-Id: 14641 - Permalink

Modelling, Simulation and Experiments to Boiling in Pressurized Water Reactors in the framework of the R&D program “Energie 2020+”
Krepper, E.;
Der Vortrag gibt einen Überblick zu diesem Verbundprojekt. Die im Rahmen des Förderprogramms Energie 2020+ durch das Bundesministerium für Bildung und Forschung geförderten und gemeinsam von den Partnern Forschungszentrum Dresden-Rossendorf (FZD), Technische Universität Dresden (TUD), Hochschule Zittau/Görlitz (HSZG), Karlsruher Institut für Technologie (KIT), Ruhr-Universität Bochum (RUB), Technische Universität München (TUM) und ANSYS Germany durchgeführten Arbeiten sind der Weiterentwicklung und Validierung von CFD-Modellen für Siedevorgänge in Druckwasserreaktoren, vom Blasensieden bis hin zu Phänomenen des Filmsiedens, gewidmet. Das auf die Grundlagen orientierte Vorhaben schließt die Modellentwicklung, die Simulation und Experimente in verschiedenen Maßstäben ein. Kleinskalige Experimente an den Hochschulen dienen der Aufklärung mikroskopischer Phänomene. An der Großversuchsanlage TOPFLOW wird ein Bündelexperiment zur integralen Validierung der Modelle aufgebaut. Die Ausrüstung dieses Experiments mit schneller Röntgentomographie wird störungsfrei zeitlich und räumlich hoch aufgelöste Daten liefern, die für die Entwicklung und Validierung von CFD-Modellen geeignet sind. Die TU Dresden wird den Einfluss chemischer Zusätze auf die Ausprägung kritischer Siedezustände an der Versuchsanlage BORAN untersuchen. Durch den Einsatz neuester und zum Teil eigens zu entwickelnder Messtechnik wird ein signifikanter Erkenntniszuwachs gegenüber dem Stand von Wissenschaft und Technik erreicht werden.
Keywords: CFD, boiling, model development, small scale experiments, large scale tests
  • Lecture (Conference)
    Sitzung des CFD-Verbundes, 21.-22.07.2010, Jülich, Deutschland

Publ.-Id: 14640 - Permalink

CFD modelling of boiling in rod bundles
Krepper, E.; Rzehak, R.;
The presentation shows the application of the CFD wall boiling model on the computation of a rod bundle. The data of the OECD/NEA Benchmark Based on NUPEC PWR Subchannel and Bundle Test (PSBT) were used. Besides the parameters of the wall boiling model the simulation of turbulence in the narrow channels is essential.
Keywords: CFD, two phase flow, wall boiling, rod bundle, OECD benchmark PSBT
  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Publ.-Id: 14639 - Permalink

Development and validation of the wall boiling model in ANSYS CFD
Frank, T.; Lifante, C.; Burns, A.; Krepper, E.; Rzehak, R.;
The presentation shows the actual state of model implementation of a wall boiling model in the code ANSYS/CFX. Publisherd experimental data are used to validate the model
Keywords: CFD, two phase flow, wall boiling, model development, validation
  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Publ.-Id: 14638 - Permalink

Contactless inductive flow tomography: principles and applications
Wondrak, T.; Stefani, F.; Gerbeth, G.; Gundrum, T.;
There is a growing interest in the determination of the velocity field of metal or semiconductor melts in many industrial applications, such as steel casting and silicon growth. Due to the opaqueness of those fluids optical methods are not applicable. Furthermore these fluids are often very hot or chemically aggressive, so a contactless measuring technique would be highly desirable. Interestingly, those metal and semiconductor melts are characterized by a relatively high electrical conductivity. Exposing the flow of such melts to an externally applied magnetic field, electrical currents are induced which give rise to a perturbation of the applied field. This flow induced field perturbation, which is detectable outside the fluid volume, contains information about the flow structure and can be exploited to reconstruct the velocity field. By applying consecutively the external magnetic field in different directions, different induced currents and magnetic fields can be produced from the same velocity. This enables a tomographic reconstruction of the flow field. Such a contactless inductive flow tomography (CIFT) was proposed, and later verified experimentally. The determination of the velocity from the measured induced magnetic field is an ill-posed linear inverse problem. One of the key problems is the inherent non-uniqueness of the reconstruction. For the velocity reconstruction we circumvent this non-uniqueness problem by using Tikhonov regularization and the method of the L-curve to identify automatically the best regularization parameter. At the point of strongest curvature (the knee) of the L-curve one expects the most reasonable compromise between the fit of the modeled magnetic fields to the measured ones on one hand, and the minimum kinetic energy on the other hand. One possible application of CIFT is the continuous casting process which is widely used in the steel producing industry. The flow structure in the mould, where the steel starts to solidify, is of particular interest since it is mainly responsible for the quality of the produced steel slabs. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external field. We show that the CIFT method is able to reconstruct a numerically determined flow field with an empirical correlation coefficient of about 75 per cent. Then we apply the method to different flow configurations in a real model and show that typical flow features can be reliably detected.
Keywords: velocity measurement, liquid metals, continuous casting, inverse problems
  • Lecture (Conference)
    5th International Conference: Inverse Problems: Modeling and Simulation, 24.-29.05.2010, Antalya, Türkei

Publ.-Id: 14637 - Permalink

Use of electromagnetic induction tomography for monitoring liquid metal/gas flow regimes on a model of an industrial steel caster
Terzija, N.; Yin, W.; Peyton, A.; Gerbeth, G.; Stefani, F.; Timmel, K.; Wondrak, T.;
Monitoring of the steel flow through the submerged entry nozzle (SEN) during continuous casting presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould. Electromagnetic inductance tomography (EMT) presents an attractive tool to visualize the steel flow profile within the SEN.
In this paper, we investigate various flow regimes over a range of stopper positions and gas volume flow rates on a model of a submerged entry nozzle. A scaled (approx. 10:1) experimental rig consisting of a tundish, stopper rod, nozzle and mould was used. Argon gas was injected through the centre of the stopper rod and the behaviour of the two phase GaInSn / Argon flow was studied. The experiments were performed with GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at the room temperature. The electromagnetic system used in our experiments to monitor the behavior of the two phase GaInSn / Argon flow consisted of an array of 8 equally spaced inductive coils arranged around the object, a data acquisition system and a host computer. The present system operates with a sinusoidal excitation waveform with a frequency of 20 kHz and the system has a capture rate of 40 frames per second.
The results show the ability of the system to distinguish the different flow regimes and to detect the individual bubbles. Sample tomographic images given in the paper clearly illustrate the different flow regimes.
Keywords: two­phase flow study, electromagnetic inductance tomography, industrial steel caster model
  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography, 06.-9.9.2010, Peking, China, 1033-1041
  • Measurement Science and Technology 22(2011)1, 015501
    DOI: 10.1088/0957-0233/22/1/015501

Publ.-Id: 14636 - Permalink

Contactless inductive flow tomography: principles and application to a model of continuous casting
Wondrak, T.; Stefani, F.; Timmel, K.; Galindo, V.; Gundrum, T.; Gerbeth, G.;
In many metal casting processes the flow structure in the mould is very important for the produced material. For instance the flow field in the mould in the continuous casting process plays an important role for slug entrainment and surface defects. The measurement of that velocity field is very difficult due to the opaqueness and the high temperature of the liquid steel. One possible measurement technique is the contactless inductive flow tomography (CIFT), which is able to reconstruct the three dimensional velocity field in electrically conducting melts from externally measured induced magnetic fields.
Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external magnetic field and to measure the induced fields at the narrow faces of the mould. We utilize CIFT for visualizing the flow of GaInSn in a model of continuous steel casting. In a first step we show that a numerically determined flow field can be reconstructed by CIFT with an empirical correlation coefficient of nearly 80 per cent. Then we apply the method to the real model and show that typical flow features can be reliably detected.
Keywords: velocity measurement, liquid metals, continuous casting
  • Lecture (Conference)
    6th World Congress on Industrial Process Tomography, 06.-9.9.2010, Peking, China
  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography, 06.-9.9.2010, Peking, China
    6th World Congress on Industrial Process Tomography, 1051-1066

Publ.-Id: 14635 - Permalink

Contribution of Lattice Vibrations to the Thermodynamics of Vacancy Clusters in bcc-Fe
Talati, M.; Posselt, M.; Bonny, G.; Al-Motasem, A. T.; Bergner, F.;
During the long operation time of nuclear reactors, vacancies and vacancy clusters (VC) may play an intermediary role in the formation of copper-rich precipitates (CRP), which are considered to be the main cause of hardening and embrittlement of Cu-bearing RPV steels since these defects act as obstacles to dislocation motion within the grains of polycrystalline bcc-Fe. The effect of irradiation on the microstructure of RPV steels and consequently on their mechanical properties is a multiscale phenomenon. The evolution of VCs over realistic time and length scales can be effectively studied by rate theory. However, many parameters used, such as the free binding energies of precipitates, are not very well known from experimental investigations. Atomic-level computer simulations can provide these data. The few previous attempts to include the effect of lattice vibrations into thermodynamics of Cu-precipitates in bcc-Fe did not lead to consistent results [1, 2].The present investigations are focused on the phonon contributions to the thermodynamics of VCs. In all calculations the Mendelev potential for bcc Fe is used [3]. Molecular dynamics simulations at different temperatures are performed in order to determine the velocity autocorrelation function which can be transformed into the vibrational density of states (VDOS). VDOS is also obtained using dynamical matrix method under harmonic approximation. This quantity is then used to calculate the contributions of lattice vibrations to the total free energy of bcc-Fe as well as to the free energy of formation and free binding energy of VCs. The vibrational contribution to the total free energy of bcc-Fe is compared with available CALPHAD data and with the values obtained using other interatomic potentials. At a temperature of 600 K the vibrational contribution to the free binding energy leads to a reduction of the absolute value of the corresponding zero-Kelvin free binding energy of the VC by about 10%.

[1] K. Yuge, A. Seko, I. Tanaka, S. R. Nishitani, Phys. Rev. B 72 (2005) 174201.
[2] K. Yuge, A. Seko, K. Kobayashi, T. Tatsuoka, S. R. Nishitani, H. Adachi, Mater. Trans. 45 (2004) 1473.
[3] M. I. Mendelev, S. Han, D. J. Srolovitz, G. Ackland, D. Y. Sun, M. Asta, Philo. Mag. 83 (2003) 3977.
Keywords: Vibrational Density of States, Total free energy, Free binding energy, bcc-Fe , Thermodynamics, Molecular Dynamics Simulation
  • Poster
    The fifth International Conference on Multiscale Materials Modeling (MMM-2010), 04.-08.10.2010, Freiburg, Germany

Publ.-Id: 14634 - Permalink

Boiling models for CFD
Rzehak, R.; Krepper, E.;
CFD for Boiling Flows requires models to represent bubble dynamics during ebullition cycle. At present, mostly empirical correlations are used to this end, which have only a limited range of applicabiblity. Hence, there is a strong desire to replace these correlations by physical models. A survey of available approaches to this issue is given and need for further research identified.
Keywords: CFD, boiling
  • Lecture (Conference)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland

Publ.-Id: 14633 - Permalink

Measurement technique developments for LBE flows
Buchenau, D.; Eckert, S.; Gerbeth, G.; Stieglitz, R.; Dierckx, M.;
We report on the development of measurements techniques for flows in lead-bismuth eutectic alloys (LBE). This paper covers the test results of newly developed contact-less flow rate sensors as well as the development and test of the LIDAR technique for operational free surface level detection. The flow rate sensors are based on the flow-induced disturbance of an externally applied AC magnetic field which manifests itself by a modified amplitude or a modified phase of the AC field. Another concept of a forcefree contactless flow meter uses a single cylindrical permanent magnet. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The operation of those sensors has been demonstrated at liquid metal test loops for which comparative flow rate measurements are available, as well as at the LBE loops THESYS at KIT and WEBEXPIR at SCK-CEN. For the level detection a commercial LIDAR system was successfully tested at the WEBEXPIR facility in Mol and the THEADES loop in Karlsruhe.
Keywords: Liquid metal, LBE, Phase-shift sensor, EMFM, Rotating magnet, LIDAR
  • Lecture (Conference)
    Int. DEMETRA Workshop, 02.-04.03.2010, Berlin, Deutschland

Publ.-Id: 14632 - Permalink

Interfacial heat and mass tansfer models
Krepper, E.; Scheuerer, G.;
The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.
Keywords: CFD, Two fluid model, heat transfer, mass transfer, boiling, cavitation
  • Invited lecture (Conferences)
    7th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 26.-28.05.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    8th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 22.-24.06.2010, Dresden, Deutschland
  • Invited lecture (Conferences)
    9th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 08.-10.06.2011, Dresden, Deutschland

Publ.-Id: 14629 - Permalink

CFD models for the description of particle transport, deposition and (re)mobilization of deposited particles at walls
Barth, T.; Krepper, E.;
Radioactive aerosol deposition and the assessment of its resuspension during a design basis accident (DBA) in the primary circuit have been revealed in the past as a key issue in the development and certification of advanced pebble bed High Temperature Reactors (HTRs). The report describes the particle parametres to be expected. Actual CFD methods to model particle deposition and particle resuspension are reported.
Keywords: CFD, Euler/Lagrange, Particles, Deposition, Resuspension
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    22 Seiten

Publ.-Id: 14625 - Permalink

Extension of the MUSIG approach by considering gas/liquid-mass transfer
Krepper, E.; Lucas, D.; Schmidtke, M.;
The report describes the derivation of the corresponding equation and validations on the TOPFLOW condensation experiments (test series K16). The evolution of the cross-sectional averaged void fraction along the pipe were compared with experimental results. In the test K16_118 the condensation of steam was prevailing. The influence of the heat transfer model bubble – liquid (Ranz-Marshall, Hughmark, Tomiyama) was investigated and the influence of the initial bubble size distribution was shown. In the tests K16_140 reevaporation caused by decreasing hydrostatic pressure was found in the experiments and simulated.
Keywords: CFD, two phase flow, bubble population balance, mass transfer
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    22 Seiten

Publ.-Id: 14624 - Permalink

Improvement of the turbulence modelling in Euler/Eulerian CFD simulation of gas/liquidflow
Krepper, E.; Schmidtke, M.; Lucas, D.;
In the Euler/Eulerian approach simulating bubbly flow, the influence of the bubbles on the turbulence of the liquid has to be modelled. Vice versa, the structures of the turbulent liquid flow influence the gas void fraction distribution, which is expressed as a turbulent dispersion force. Reliable models for turbulence are an urgent precondition for the improvement of models describing bubble coalescence and bubble breakup in any population balance model. In the present work the different approaches simulating the influence of bubbles on the turbulence are revised and compared to measurements using ANSYS-CFX. Models for the turbulent dispersion force are validated.
Keywords: CFD, two phase flow, turbulence
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    18 Seiten

Publ.-Id: 14623 - Permalink

Die supraleitende HF-Fotoelektronenquelle am ELBE-Beschleuniger im FZD
Teichert, J.;
kein Abstract vorhanden.
Keywords: SRF Gun, Cs2Te, electron injector
  • Lecture (others)
    MAMI Seminar, 28.01.2010, Mainz, Germany

Publ.-Id: 14622 - Permalink

Study of gas-liquid two-phase flow in pipes with ultrafast electron beam X-ray CT
Fischer, F.; Hampel, U.;
Electron beam X-ray CT is capable of fast measurement of multi-phase flows with frame rates of 1000 images per second and higher. The principle is based on the creation of a moving X-ray spot by electromagnetic deflection of a high-intensity electron beam across a circular target within an evacuated scanner enclosure. Together with a fixed fast X-ray detector this setup allows scanning of objects at frame rates well beyond that of classical CT machines. Our group has developed a scanner that is capable of scanning at up to 7 kHz frame rate and approximately 1 mm spatial resolution. The technique allows visualizing and measuring multiphase flows in vessels of moderate size. We have applied this fast electron X-ray tomography to the study of gas-liquid flow in a vertical pipe of 50 mm inner diameter. Different two-phase flow regimes from bubbly flow to churn-turbulent flow were produced and scanned. The data were processed using self-made image reconstruction software which implements the filtered backprojection technique and further post-processing algorithms for determination of gas-phase parameters, such as temporal and radial gas fraction profiles.
Keywords: Electron beam tomography, X-ray tomography, flow measurement, two-phase flow
  • Lecture (Conference)
    6th World Congress of Industrial Process Tomography, 06.-09.09.2010, Peking, China

Publ.-Id: 14619 - Permalink

Alfven wave experiments with liquid rubidium
Gundrum, T.; Hüller, J.; Stefani, F.; Gerbeth, G.; Galindo, V.; Herrmannsdörfer, T.; Arnold, F.; Putzke, C.;
Since their discovery by Hannes Alfvén in 1942, Alfvén waves have played an ever increasing role in explaining many phenomena in astrophysical and fusion related plasmas. The experimental investigation of Alfvén waves had started shortly after Alfvéns prediction, with first experiments using mercury and liquid sodium. Since those times, many Alfvén wave experiments have been carried out, both in liquid metals and, even more extensively, in plasmas.
Interestingly, the recent developments in reaching pulsed magnetic fields above 50 Tesla open up quite new prospects for Alfvén wave experiments with liquid metals. At those field strengths it happens that the Alfvén speed in higher alkalis metals reaches the sound speed (the threshold is 51 T for Caesium and 55 T for Rubidium). This threshold is of upmost importance for the character of Alfvén waves and its relation to slow and fast magnetoacoustic waves, and its crossing has been made responsible for the corona heating.In order to check the feasibility of experiments with higher alkali metals, we have carried out at Dresden High Magnetic Field Laboratory a preliminary experiment. This first test experiment has yielded a proof of concept, and first promising results have been achieved.
Keywords: Alfven, MHD, Rubidium, magnetoacoustic wave, liquid metal, high magnetic field
  • Lecture (Conference)
    Science in High Magnetic Fields, 05.-11.09.2010, Ameland, Niederlande

Publ.-Id: 14618 - Permalink

Use of Superconducting LINACS for Positron Generation: The EPOS System at Research Center Dresden-Rossendorf
Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.;
Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting Linac-based accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system at the Research Center Dresden-Rossendorf, will be described.
  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques, 01.-06.08.2010, North Queensland, Australia
  • Contribution to proceedings
    12th International Workshop on Slow Positron Beam Techniques, 01.-06.08.2010, North Queensland, North Queensland
    Use of Superconducting LINACS for Positron Generation: The EPOS System at Research

Publ.-Id: 14617 - Permalink

SRF Gun Experiments
Teichert, J.; Arnold, A.; Büttig, H.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staats, G.; Xiang, R.; Kneisel, P.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
kein Abstract vorhanden
  • Lecture (others)
    EuCARD-SRF Annual Review 2010, 07.-09.04.2010, Daresbury, UK

Publ.-Id: 14616 - Permalink

High Rep Rate Guns: FZD Superconducting RF Photogun
Teichert, J.; Arnold, A.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staats, G.; Staufenbiel, F.; Tietze, H.; Xiang, R.; Kneisel, P.; von der Horst, B.; Matheisen, A.; Stephan, J.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.; Volkov, V.;
A RF photo injector with a superconducting cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. This new and promising injector type allows CW operation and has the potential for the production of high-brightness electron beams. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed. In November 2007 the first beam was produced. In 2008 beam parameter measurements with Cs2Te photo cathodes were carried out. Due to problems during the cleaning of the cavity, the design gradient could not be reached. Thus the SRF gun is operating now with a peak field of 17.5 MV/m which corresponds to electron energy of 3 MeV. In 2009 the cathode transfer system was upgraded, the bunch lengths measurement based on Cherenkov radiation was put into operation, and the connection beamline to ELBE was installed in the winter shutdown. In February, the first beam of the SRF gun was injected to ELBE and accelerated. Parallel to the commissioning and operation of the SRF gun, an improved design for the gun cavity was created and two now cavities, one made of RRR300 Nb and one made of high-grain Nb was fabricated in collaboration with JLab.
  • Invited lecture (Conferences)
    FLS 2010 – ICFA Beam Dynamic Workshop, 01.-05.03.2010, Menlo Park, USA

Publ.-Id: 14615 - Permalink

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

Publ.-Id: 14613 - Permalink

Validierung des Inhomogenen MUSIG-Modells mit Phasenübergang
Schmidtke, M.; Krepper, E.; Lucas, D.;
Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in a 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a wire mesh sensor. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapour void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.
Keywords: steam bubble, condensation, Inhomogeneous MUSIG, TOPFLOW, phase transfer, Nusselt number
  • Lecture (Conference)
    3. Meilenstein Workshop / CFD-Forschungsverbund Entwicklung und Anwendung von Computational Fluid Dynamics (CFD) Programmen für Phänomene im Kühlkreislauf und Sicherheitseinschluss von Leichtwasserreaktoren, 23.09.2010, München-Holzkirschen, Deutschland

Publ.-Id: 14612 - Permalink

CFD Simulation zum Eintrag von Mineralwolle in den Reaktorkern
Höhne, T.; Grahn, A.; Kliem, S.; Weiss, F. P.;
Es wurden CFD-Analysen zum Eintrag von Mineralwolle in den Kern bei Sumpfbetrieb der Kernnotkühlung durchgeführt. Ziel der CFD-Rechnungen war der qualitative Nachweis der so genannten Durchbruchkanäle, die experimentell an der Versuchsanlage UPTF beobachtet wurden und durch die das heißseitig eingespeiste Notkühlwasser in den Kern gelangt, auch unter den Massenstrom- und Druckverhältnissen bei Ansaugung aus dem Sumpf. Zunächst wurde ohne Belastung des Kühlmittels mit Isoliermaterial gerechnet, während weiterführende Rechnungen die teilweise Belegung der oberen Abstandshalterebene durch eingetragene Mineralwollfasern berücksichtigten. Dafür musste die Verteilung der Ablagerung der Mineralwollfasern auf der oberen Abstandshalterebene ermittelt werden. Die Rechnungen zeigen eine zunächst bevorzugte Ablagerung der Fasern im Bereich der Durchbruchkanäle.
Keywords: CFD, Kernnotkühlung, Durchbruchkanäle, UPTF
  • Contribution to proceedings
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland-Fachtagung der KTG-Fachgruppen, 07.-08.10.2010, Forschungszentrum Dresden-Rossendorf, Deutschland
  • Invited lecture (Conferences)
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland-Fachtagung der KTG-Fachgruppen, 07.-08.10.2010, Forschungszentrum Dresden-Rossendorf, Deutschland

Publ.-Id: 14611 - Permalink

Thermal fluid dynamics research at Forschungszentrum Dresden-Rossendorf - sensors, systems and applications
Hampel, U.;
Understanding and modeling multiphase flows requires sophisticated imaging tools which can disclose physical information of such flows with high temporal and spatial resolution. At FZD a number of sensors and imaging systems are being developed and applied, which are able to obtain phase distribution information from multiphase flows with superior resolution and speed. Within the presentation we will introduce and discuss the methods of wire mesh imaging, gamma ray tomography and ultra fast X-ray tomography with respect to their functional principles and application in energy and process engineering.
Keywords: multiphase flow measurement, wire mesh sensor, computed tomography
  • Lecture (others)
    Meeting on the application of multiphase flow measurement techniques in reactor engineering, 28.09.2010, Eindhoven, The Netherlands

Publ.-Id: 14610 - Permalink

Thermal fluid dynamics research and multiphase flow measurement and imaging techniques at FZD
Hampel, U.;
The presentation gives an overview over the research activities in thermal fluid dynamics research at FZD. A focus is given on experiments on steam-water two-phase flows and innovative tomographic instrumentation. Research is carried out at the TOPFLOW thermal hydraulic test facility where steam-water flows under authentic nuclear reactor conditions can be investigated. In the recent past, new imaging sensors and technologies, such as wire mesh sensors and fast X-ray tomography have been developed and are being applied for such studies.
Keywords: two-phase flow, flow measurement, thermal fluid dynamics
  • Invited lecture (Conferences)
    Multiphase flow and microbubbles in oil and gas production: Son of DIPSS “Ideas Factory”, 27.09.2010, Sheffield, UK

Publ.-Id: 14609 - Permalink

The THz-FEL FELBE at the Radiation Source ELBE
Seidel, W.;
Two free-electron lasers (FELBE; 4-21 μm and 18-250 μm, respectively) have been in routine user operation for a wide range of IR experiments at the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf for several years. The lasers are driven by a superconducting RF linac that permits the generation of a cw-beam with a repetition rate of 13 MHz and a high average beam power. In addition, operation in a macropulse modus (pulse duration >100 µs, repetition rate ≤ 25 Hz) is possible. A few important experiments using the cw-operation are discussed. Furthermore, an outlook is given on the experiments which use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD provides pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010
  • Invited lecture (Conferences)
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden

Publ.-Id: 14608 - Permalink

A Laser-Activated Plasma Switch for the Extraction of Single FELBE Radiation Pulses
Seidel, W.; Winnerl, S.;
In order to decrease the average radiation power of the Rossendorf free-electron laser FELBE, as required for certain experiments (high pulse energies but moderate or low average power), the FEL repetition rate can be reduced from 13 MHz to 1 kHz. To this end, plasma switching of FEL radiation pulses was demonstrated for cw operation. The plasma switch is based on the principle of photo-induced reflectivity by an optically excited electron-hole plasma. Germanium or silicon serves as semiconductor material for the switch. The semiconductor was illuminated by a Nd:YAG laser amplifier system (1 kHz, wavelength 1064 nm, pulse duration16 ps, 1Watt), generating an electron-hole plasma on the front surface of the semiconductor. To integrate this plasma-switch into the existing experimental set-up we build an additional by-pass to the Germanium or Silicon slab which is under Brewster’s angle. To get a high contrast in the switched beam we adjust the polarization plane of the incoming beam to the right direction by using an additional polarization rotator. We will report on first results at different wavelength. Submitted as a poster to the FEL 2010 conference.
  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Publ.-Id: 14606 - Permalink

Conceptual Design of a THz Facility at the ELBE Radiation Source
Lehnert, U.; Helm, M.; Michel, P.; Schneider, H.; Seidel, W.; Winnerl, S.; Aksoy, A.;
To extend the wavelength range of possible experiments from the FIR into the THz region a dedicated beamline is planned at the ELBE Radiation Source. The beamline will deliver coherent transition radiation and coherent synchrotron radiation as broad-band (essentially single-cycle) radiation. Superradiant undulator radiation will be produced for a tunable narrow-band radiation source in the 100GHz to 3THz range. This requires a compression of the ELBE electron beam down to 150fs bunchlength. The beam transport and bunch compression scheme as well as the properties of the produced radiation are presented in detail.
  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Publ.-Id: 14605 - Permalink

A Tapered-Undulator Experiment at the ELBE FIR Oscillator FEL
Lehnert, U.; Asgekar, V. B.; Michel, P.;
A tapered undulator experiment was carried out at the Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The main motivation was to see whether the presence of a dispersive medium due to the partially waveguided resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering (i.e. a decrease of undulator field amplitude over the beam path) proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.
  • Poster
    Free Elektron Laser Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    FEL Conference 2010, 23.-27.08.2010, Malmö, Schweden
    Proceedings of the FEL 2010

Publ.-Id: 14604 - Permalink

Im Kern die Sicherheit
Weiss, F.-P.;
Wirtschafts- und Klimafaktor Kernenergie; Ausbau der Kernenergie-globaler Trend; Sicherheit von Kernkraftwerken; Anforderungen an die (Sicherheits-)Forschung im aktuellen Kontext; Zukunftsvision der nuklearen Sicherheitsforschung
  • Invited lecture (Conferences)
    FDP Technologieforum, 27.05.2010, Dresden, Deutschland

Publ.-Id: 14603 - Permalink

The Fritz Haber Institute THz FEL Status
Bluem, H.; Dowell, D.; Park, J.; Todd, A. M. M.; Christina, V.; Rathke, J.; Young, L. M.; Douglas, D.; Dalesio, L. B.; Gewinner, S.; Junkes, H.; Meijer, G.; Schöllkopf, W.; von Helden, G.; Zhang, W. O.; Lehnert, U.; Michel, P.; Seidel, W.; Wuensch, R.; Jordan, K.; Gottschalk, S. C.; Kelly, R. N.;
The Fritz Haber Institute of the Max Planck Society in Berlin, Germany will celebrate its Centennial in 2011. Coincident with this event, they will christen a THz Free Electron Laser (FEL) that will operate from 3 to 300 microns. A linac with a gridded thermionic gun is required to operate from 15 to 50 MeV at 200 pC while delivering a transverse rms emittance of 20 mm-mrad in a 1 psec rms, 50 keV rms energy spread bunch at the wigglers. Mid-IR and far-IR wigglers enable this electron beam to deliver the required radiation spectrum. In addition to the longitudinal emittance, a key design requirement is the minimization of the micropulse and macropulse jitter to ensure radiation wavelength stability and timing consistency for pump probe experiments. We present the completed physics and engineering design that delivers the required performance for this device. Shipment is scheduled for the end of the calendar year and the status of fabrication will be summarized.
  • Contribution to proceedings
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of FEL 2010
  • Poster
    Free Electron Laser Conference, 23.-27.08.2010, Malmö, Sweden

Publ.-Id: 14602 - Permalink

ELBE and the upgrade project towards a National Centre for High Power Radiation Sources 4th National Congress on Particle Accelerators and Applications
Michel, P.;
A superconducting *E*lectron *L*inac with high *B*rilliance and low *E*mittance (ELBE) which provides an average beam current of 1 mA with maximum beam energy of 36 MeV was constructed in the Forschungszentrum Dresden-Rossendorf, Germany. The electron beam is used to generate infrared light (Free Electron Lasers), MeV-Bremsstrahlung, X-rays (electron channelling), fast neutrons and positrons. The ELBE secondary beams are used for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations.
Furthermore a 150 TW Ti:Sa Laser delivers high intense and very short laser pulses used for laser plasma acceleration of electrons and protons.

Until 2014 ELBE will be upgraded to a Centre for High Power Radiation Sources. The concept contains additional broad and narrow band coherent THz sources and the development of a 500 TW Ti:Sa Laser and even a 2 PW diode pumped Laser system. Laser plasma electron acceleration and proton acceleration experiments for medical applications are planed.
Additionally coupled electron laser beam experiments like Thomson scattering or injection of ELBE electron into the laser plasma will be done.
Keywords: Superconducting Electron; infrared light, MeV Bremsstrahlung, X-rays, 500 TW Ti:Sa Laser
  • Lecture (Conference)
    Congress on Particle Accelerators and Applications (UPHUK-4), 30.08.-01.09.2010, Bodrum, Turkey

Publ.-Id: 14601 - Permalink

Modeling of Ruddlesden-Popper surfaces and oxygen vacancies in strontium titanate
Zschornak, M.; Gutmann, E.; Stöcker, H.; Shakverdova, I.; Meyer, D. C.; Gemming, S.;
Strontium titanate (STO) is an oxide crystallizing with cubic perovskite-type of structure that exhibits a high tunability of dielectric, electric, mechanical and optical properties by means of defects. Apart from dopants, also intrinsic oxygen vacancies or ordered stacking faults, e.g. Ruddlesden-Popper (RP) phases SrO(SrTiO3)n, influence these properties.
We have investigated structural stability, electronic properties and surface energies of such RP phases up to n = 5 by means of density-functional theory. We find a significant gain of formation energy up to n = 3 and can approximate the interaction range of neigh-boring stacking faults to 11.7 Angs.. Surfaces in [001] and [100] direction with all possible unreconstructed crystal terminations have been modeled and stability is compared. In contrast to pure STO, the near-surface SrO-OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO2 surface rumpling, to stabilize SrO termination in SrO-rich surrounding or to increase the band gap for TiO2 termination.
Further, we have theoretically verified a rever-sible elastic softening along an O-deficient 001 direction recently found in nano-inden-tation of SrTiO3 under influence of an electric field. Results from an isotropic and anisotropic model of a SrTiO3-d super cell are discussed.
Keywords: ferroelectrics, surface, Ruddlesden-Popper, STO, strontium titanate, DFT, density-functional, stacking faults, planar defect, complex oxide
  • Poster
    ICAMM 2010 - International Conference on Advanced Materials Modelling, 07.-10.07.2010, Nantes, France

Publ.-Id: 14600 - Permalink

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

Keywords: GaP, gallium phosphide, surface, interface, silicon, semi-conductor, DFT, density-functional
  • Poster
    STC 2010, 27.-30.09.2010, Münster, Deutschland
  • Lecture (others)
    Arbeitstreffen GaP-based Devices, 12.11.2010, Berlin, Deutschland

Publ.-Id: 14598 - Permalink

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

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

[1] Kunze, T.; et al.; Phys. Rev. B 81, 115401 (2010).
[2] Popov, I.; et al.; Nano Lett. 8, 4093-4097 (2008).
[3] Seidel, J.; et al.; Nature Materials 8, 229-234 (2009).
Keywords: nanostructures, ion-beam, surface modification, ripples, transport, break junction, DFT, classical rate theory
  • Lecture (others)
    Physikalisches Kolloquium, 07.07.2010, Freiberg (S), Deutschland

Publ.-Id: 14597 - Permalink

Oxygen vacancy contribution on the polarization dependent DAFS of Rutile TiO2
Zschornak, M.; Richter, C.; Novikov, D.; Stöcker, H.; Leisegang, T.; Gemming, S.; Meyer, D. C.;
In order to develop a method to reconstruct the density of unoccupied electronic states in between Fermi energy and vacuum level, we performed combined anisotropic anomalous scattering and diffraction anomalous fine structure (AAS-DAFS) scans. Examining the energy dependence of the dipole-dipole transition near the Ti-K absorption edge in rutile TiO2 [2], special interest was given to the stability of the symmetry restrictions imposed by the Ti site symmetry on the dipole-dipole transition. Here we present new results, extending former findings from studying the sample orientation dependent, diffracted intensity on different allowed and forbidden reflections at the specific resonance photon energy of E = 4985 eV exclusively [3], in respect to the energy dependence.
Keywords: DAFS, rutile, O vacancy, point defect, X-Ray, simulation
  • Poster
    European Crystallographic Meeting, ECM-26, 30.08.-02.09.2010, Darmstadt, Deutschland

Publ.-Id: 14596 - Permalink

Correlation of structure and conductance in nanowires
Gemming, S.;
In nanostructured materials spatial confinement effects lead to structure-dependent deviations from the bulk transport properties. Such modifications may in part be accounted for by classical transport simulations, but a microscopically more detailed and mostly parameter-free picture is obtained from quantum-mechanical density-functional theory (DFT). DFT calculations yield the atom arrangement and electronic structure of nanotubes and nanowires in the electronic ground state. Additionally, an extension by a Green’s function formalism leads to the determination and analysis of electronic transport through contacted nanostructures. A combination of both approaches allows to correlate structural and transport properties of nanostructures. The applicability of this approach will be demonstrated for a mechanically triggered metal-insulator transition in nanowires.
Kibsgaard et al. Nano Lett 8 (2008) 3928; [2] Popov et al. Nano Lett 8 (2008) 4093.
Keywords: transport, nanotubes, nanowires, crystallography, DFT, transition metal chalcogenides, MoS, molybdenum sulfide
  • Poster
    European Crystallographic Meeting, ECM-26, 30.08.-02.09.2010, Darmstadt, Deutschland

Publ.-Id: 14595 - Permalink

Transport in Nanostructured Materials
Gemming, S.;
In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.
Keywords: transport, calculation DFT, simulation, multi-scale, nano-electronics, molecular electronics, multiferroics
  • Invited lecture (Conferences)
    FAHL Academia 2010: Transparent and flexible Electronics, 28.09.2010, Leipzig, Deutschland

Publ.-Id: 14594 - Permalink

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

Publ.-Id: 14593 - Permalink

Superconductivity in Gallium-doped Germanium
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Poster
    2nd EuroMagNET Summer School 2010 at Ameland, 05.-11.09.2010, Ameland, Niederlande

Publ.-Id: 14592 - Permalink

The Dresden High Magnetic Field Laboratory - Recent Research Results
Wosnitza, J.;
The Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), situated at the outskirts of Dresden, has opened its doors for external users in 2007. Since then, an increasing number of scientists from all over the world applied for magnet time and had, after approval, the possibility to conduct their high-field research in the pulsed fields at the HLD. A variety of magnets with pulsed fields up to 70 T are available and a European record field of 87.2 T has been reached. Numerous experimental methods are available allowing to measure electrical transport, magnetization, magnetostriction, ultrasound, ESR, and even NMR, often with very high resolution. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented. This includes e.g. the detection of Shubnikov-de Haas oscillations in electron-doped high-temperature superconductors that allowed to unravel a drastic change of the Fermi-surface topology upon doping. Furthermore, pulsed-field experiments at the HLD allowed to observe the field-induced conductance switching in single-walled carbon nanotubes.
  • Invited lecture (Conferences)
    Seminar at the National Institute for Materials Science, 21.09.2010, Tsukuba, Japan

Publ.-Id: 14591 - Permalink

Electron Injectors, The Determining Part For Beam Quality At Accelerators
Arnold, A.;
The electron source essentially determines the properties of the entire accelerator system. As part of the 1st doctoral seminar in Oybin (Zittauer Gebirge), the talk explains the working principles of two different electron sources. The first part is dealing with the established thermionic source of ELBE (Electron Linac for beams with high Brilliance and low Emittance). While in the second part the benefits of the new superconducting electron source (SRF gun) are presented.
Keywords: electron, source, SRF, Gun
  • Lecture (others)
    1st FZD Graduate Students PhD Seminar, 11.-13.10.2006, Oybin, Germany


Publ.-Id: 14590 - Permalink

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

Publ.-Id: 14589 - Permalink

Bunch Length Measurements at the Radiation Source ELBE
Kaya, C.;
At the ELBE Free Electron Laser (FEL) at Forschungszentrum Dresden Rossendorf (FZD) electron bunches having lengths between 1 to 4 ps are generated. It is required to compress these electron bunches to lenghts below 1 ps which necessitates diagnosis of the electron bunch parameters. We use a Martin-Puplett interferometer (MPI) which is a modification of the Michelson interferometer, where the beams are linearly polarized at specific orientations. It measures the autocorrelation function of the coherent transition radiation (CTR) from a view screen which is an optical replication of the electron bunch.
The interferometer setup consists of various optical components like polarizers, beam splitter, mirrors and Golay cell detectors. In our measurement a wire grid was used as a polarizer and also as a beam splitter. A thorough understanding of the response of the optical components, as a function of the CTR wavelength range of our interest, is required for correct analysis of the measured signal. We have therefore simulated the response of the entire interferometer setup including the diffraction losses and the window transmission and compared the results to experimental measurements.
Keywords: electron bunch length, Martin-Puplett interferometer
  • Poster
    DIPAC 2009, 25.-27.05.2009, Basel,, Switzerland

Publ.-Id: 14588 - Permalink

Longitudinal Electron Bunch Profile Measurement with Electro Optic Sampling at the Radiation Source ELBE
Kaya, C.;
At the ELBE Accelerator at the Forschungszentrum Dresden (FZD) we want to perform longitudinal electron bunch profile measurement with Electro Optic Sampling (EOS) technique. We present the preliminary measurement results. The EOS technique is based on the change in the optical characteristics of a birefringent crystal due to the electric field induced by the passage of electrons in the vicinity of the crystal. Therefore we use femtosecond laser (Ti:Sa) pulses to probe the change of birefringence in the electro-optic ZnTe crystal. The resolution in the experiment is limited to about 250 fs by the bandwidth of the detection equipment.
One of the important steps in the measurement is to synchronize the Ti:Sa laser pulses emitted with a repetition frequency of 78 MHz with the 13 MHz radio frequency from the superconducting accelerator with low time jitter. The set-up required for determination of the temporal overlap of the femtosecond laser pulse with the real electron bunch was assembled with a OTR sensitive photodiode. The last synchronization step was tuning the time delay of the femtosecond laser relative to the electron bunch by an optical delay unit. By splitting the signal from the ZnTe crystal in a balance detector we achieve information about the longitudinal electron bunch profile.
Keywords: Electro Optic Sampling, bunch length, ZnTe
  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Germany

Publ.-Id: 14587 - Permalink

Bunch Length Measurements at the Radiation Source ELBE
Kaya, C.;
At the ELBE Free Electron Laser (FEL) at Forschungszentrum Dresden Rossendorf (FZD) electron bunches having lengths between 1 to 4 ps are generated. It is required to compress these electron bunches to lenghts below 1 ps which necessitates diagnosis of the electron bunch parameters. We use a Martin-Puplett interferometer (MPI) which is a modification of the Michelson interferometer, where the beams are linearly polarized at specific orientations. It measures the autocorrelation function of the coherent transition radiation (CTR) from a view screen which is an optical replication of the electron bunch.
The interferometer setup consists of various optical components like polarizers, beam splitter, mirrors and Golay cell detectors. In our measurement a wire grid was used as a polarizer and also as a beam splitter. A thorough understanding of the response of the optical components, as a function of the CTR wavelength range of our interest, is required for correct analysis of the measured signal. We have therefore simulated the response of the entire interferometer setup including the diffraction losses and the window transmission and compared the results to experimental measurements.
Keywords: electron bunch, Martin-Puplett interferometer
  • Lecture (Conference)
    DIPAC 2009, 25.-27.05.2009, Basel, Switzerland

Publ.-Id: 14586 - Permalink

Morphology Induced Magnetic Anisotropy of Thin Films on Nanoscale MgO- and Si-Ripples
Lenz, K.; Körner, M.; Liedke, M. O.; Fritzsche, M.; Cizmar, E.; Ranjan, M.; Facsko, S.; Fassbender, J.ORC
Ion beam erosion techniques allow for the creation of well ordered ripple patterns with nanometer periodicity. Moreover, the periodicity can be tuned over a wide range by changing the ion beam energy [1]. The ripple pattern is directly transferred to the surface of films grown on these substrates. This offers the possibility of tailoring the magnetic properties by inducing additional magnetic anisotropy as well as modifying the intrinsic magnetic damping by adding relaxation mechanisms due to the structural modifications.
We study the influence of rippled vs. flat Si substrates for 10 nm thin Fe and Co films, as well as technologically relevant Heusler alloys (Fe3Si and Co2FexMn1-xSi). The magnetic anisotropy as well as damping is measured by frequency and angle-dependent vector network analyzer ferromagnetic resonance. The ripple morphology of the magnetic layers induces a strong uniaxial magnetic anisotropy. The intrinsic magnetic damping is influenced by mosaicity related inhomogeneous broadening and additional two-magnon scattering.
This work was supported by DFG grant no. FA 314/6-1.
Keywords: Magnetism Magnetic Anisotropy Nanoscale Ripples
  • Poster
    IEEE 7th International Symposium on Metallic Multilayers (MML 2010), 19.-24.09.2010, Berkeley, CA, USA

Publ.-Id: 14585 - Permalink

electron bunch length measurement at the radiation source ELBE
Kaya, C.;
In this study, measurement of electron bunch length at the ELBE Free Electron Laser (FEL) in the Forschungszentrum Dresden (FZD) is represented. Transition radiation is emitted when an electron passes the interface of two mediums of different dielectric constants. In case that the wavelength of the radiation is longer than the bunch length, coherent transition radiation (CTR) is emitted. The time profile of the CTR is a copy of the electron bunch longitudinal profile. The Martin- Puplett interferometer (MPI) is used to measure the autocorrelation function of the CTR pulse. The power spectrum and the bunch length information is obtained by Fourier transforming the measured autocorrelation function. There are different approaches for obtaining the bunch length from the MPI measurements. The data can be evaluated in the time domain as well as in the frequency domain. We can derive the longitudinal shapes of the electron bunch by analyzing the frequency information. The Measurement of the longitudinal electron bunch length is compared with the frequency domain method.
Keywords: electron bunch length
  • Lecture (Conference)
    DPG Frühjahrstagung 2009, 09.-13.03.2009, Munich, Germany

Publ.-Id: 14584 - Permalink

A Diplexer to Operate Two Cavity Eigen modes in Parallel
Arnold, A.;
To fulfil the demand of future high power and high luminosity FEL and storage ring sources, an intensive electron beam with short bunch length, small emittance and large bunch charge is required. Normal conducting (NC) laser driven radio frequency (RF) photocathode guns can deliver 1 nC bunches with an emittance of 1 π µrad. But to realize the demand on high average currents, a superconducting (SC) RF gun appears to be the best solution. First long term operation has been demonstrated at FZD [1]. In difference to the NCRF guns, the application of static magnetic fields near the cathode is not possible. Instead, the use of the magnetic field of a transverse electric (TE) mode in parallel to the accelerating mode was proposed. Numerical simulations have shown that this RF focusing can be applied to compensate the emittance growth [2].
This contribution will introduce a possibility to use the existing coaxial RF coupler of TESLA like cavities, as a RF power input for TE modes in parallel to its normal operation. The additional coupler component outside the module accomplishes the task of combining two different frequencies from different sources to one load. Thus, it corresponds to the working principle of a high power RF diplexer. Based on the 31/2 cell Rossendorf SRF-Gun [3], a concrete technical implementation and results of its operation at the cold SRF-Gun cavity will be presented.
Keywords: RF, Diplexer, TE-Mode, Magnetic Mode, Focussing, Emittance, Compensation, SRF, Gun, Accelerator, Injector
  • Poster
    25th Linear Accelerator Conference (LINAC10), 12.-17.09.2010, Tsukuba, Japan
  • Contribution to proceedings
    25th Linear Accelerator Conference (LINAC10), 12.-17.09.2010, Tsukuba, Japan
    A Diplexer to Operate Two Cavity Eigen modes in Parallel
  • Lecture (others)
    Work in Progress (WIP) Seminar Serie, 29.05.2009, Dresden, Germany


Publ.-Id: 14583 - Permalink

Short Overview of Superconducting Photo Injectors
Arnold, A.; Teichert, J.;
The success of most of the proposed ERL based electron accelerator projects for future storage ring replacements (SRR) and high power IR-FELs is contingent upon the development of an appropriate source. Electron beams with an unprecedented combination of high brightness, low emittance and high average current (hundreds of mA) are required to meet future FEL specifications.
An elegant way to create such an unique beam is to combine the high beam quality of a normal conducting RF photo guns with the superconducting technology. Such superconducting RF photo injectors (SRF gun) based on different approaches are under investigation at a growing number of institutes and companies (AES, Beijing University, BESSY, BNL, DESY, FZD, TJNAF, Niowave, NPS, Wisconsin University). Lot of progress could be achieved during the last years and first long term operation was demonstrated at the FZD.
Keywords: ERL, FEL, SRF, Gun, Injector, Electron, Superconducting
  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland


Publ.-Id: 14582 - Permalink

Druckabfall an verstopften Ansaugsieben, Stand der Modellierung
Grahn, A.;
Der Kühlmittelverluststörfall im Primärkühlkreislauf eines Kernreaktors lässt sich in eine Früh- und eine Spätphase unterteilen. In der Frühphase wird Isoliermaterial in der Umgebung des Lecks durch das unter hohem Druck ausströmende Kühlmedium ausgetragen und gelangt weiter in den Containmentsumpf. Dort befinden sich die Ansaugkammern der Umwälzpumpen des Notkühlkreislaufs. Gitterroste oder Lochbleche am Ende der Ansaugkammern dienen als Rückhaltevorrichtungen, an denen Feststoffe vom Kühlmedium abgetrennt und am Weitertransport über die Pumpen zurück in den Reaktorkern gehindert werden sollen. An diesen Rückhaltevorrichtungen bilden sich Packungen des Feststoffs, die unter dem Einfluss des Strömungswiderstandes kompaktiert werden und den Druckverlust erhöhen. In der Spätphase, wenn die Bildung der Feststoffpackungen bereits abgeschlossen ist, bilden sich durch den Kontakt des Kühlmediums mit metallischen und nichtmetallischen Oberflächen des Containments sowie seiner Einbauten Partikelsuspensionen, die in die Feststoffpackungen an den Rückhaltevorrichtungen eindringen und über längere Zeiträume zu einem weiteren Anstieg des Druckverlusts führen. Die Feststoffpackungen wirken in der Spätphase demnach als Tiefenfiltrationsmedium. Im Vortrag werden die Fortschritte bei der Modellierung des Druckabfalls an der Rückhaltevorrichtung in beiden Phasen des Störfalls berichtet. Es wird die Implementierung eines Siebmodells und dessen Einbettung in den Strömungssimulationscode ANSYS-CFX dargestellt. Transiente Testrechnungen zeigen die Anwendbarkeit des Siebmodells zur der Simulation des Druckaufbaus an ungleichmäßig beladenen Rückhaltevorrichtungen. Die Implementierung eines Tiefenfiltrationsmodells wird vorgestellt, mit dessen Hilfe der Differenzdruckanstieg in der Spätphase durch Eintrag von Partikelsuspensionen berechnet werden kann. Des Weiteren wird die Vorgehensweise bei der experimentellen Parameterbestimmung der verwendeten empirischen Modellgleichungen erläutert.
  • Lecture (Conference)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 "Isolationsmaterialbelastete Kühlmittelströmung", 03.03.2010, Dresden, Deutschland

Publ.-Id: 14581 - Permalink

Coupling of the CFD code ANSYS CFX with the 3D neutron kinetic core model DYN3D
Kliem, S.; Grahn, A.; Rohde, U.; Schütze, J.; Frank, T.;
The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled within the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for two small-size test problems confirm the correctness of the implementation of the prototype coupling. The first test problem was a mini-core consisting of nine real-size fuel assemblies with quadratic cross section. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the DYN3D/ANSYS CFX codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power in the same mini-core. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.
The same calculations were carried for a mini-core with seven real-size fuel assemblies with hexagonal cross section in order to prove the applicability of the coupled code to cores with hexagonal fuel assemblies. The differences between the results of coupled calculations and those of the stand-alone DYN3D code are in the same range as for the quadratic mini-core.
  • Lecture (Conference)
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
  • Contribution to proceedings
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
    Proceedings of the 20th Symposium of AER on VVER Reactor Physics and Reactor Safety, CDROM paper 5.5, Budapest: KFKI AEKI

Publ.-Id: 14580 - Permalink

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

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

The given presentations and the discussions can be attributed to the following topics:
- Code validation and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP
- Safety analyses and code developments
- Future activities

A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files can be obtained from the chairman.
  • Lecture (Conference)
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
  • Contribution to proceedings
    20th Symposium of AER on VVER Reactor Physics and Reactor Safety, 20.-24.09.2010, Espoo, Finnland
    Proceedings of the 20th Symposium of AER on VVER Reactor Physics and Reactor Safety, CDROM paper 5.1, Budapest: KFKI AEKI

Publ.-Id: 14579 - Permalink

Operation of the superconducting RF photo gun at ELBE
Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
As the first superconducting rf photo-injector (SRF gun) in practical operation, the FZD SRF gun has been successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for the users of ELBE radiation source. The SRF gun consists of a 3½ 1.3GHz SC cavity and a normal conducting photocathode. A modified 3½ niobium cavity has been fabricated and tested, which will increase the RF gradient in the gun and thus improve the beam parameters further. The electron beam of 3 MeV with the max bunch charge of about 400pC has been routinely produced for conditioning. In this paper the status of the SRF gun injection to the linac will be presented, and the latest results of the beam experiments will be discussed.
  • Lecture (Conference)
    PESP2010 - Workshop on Sources of Polarized Leptons and High Brightness Electron Beams, 21.-24.09.2010, Bonn, Germany
  • Open Access LogoJournal of Physics: Conference Series 298(2011), 012008
    DOI: 10.1088/1742-6596/298/1/012008

Publ.-Id: 14578 - Permalink

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