Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31860 Publications
Laser Cooling of Ion Beams at Relativistic Energies
Bussmann, M.;
Laser cooling of ion beams can achieve unprecedented low momentum spreads and is strong enough to overcome intra-beam scattering and induce beam crystallization. When compared to stochastic cooling and electron cooling, laser cooling promises to show better performance than the latter two in cooling highly relativistic ion beams.

Thus, laser cooling at future facilities such as FAIR and HIAF has come into the focus of ion accelerator research.
This work is intended to give the reader a comprehensive overview of laser cooling at relativistic energies and related experiments at the storage rings ESR at GSI Darmstadt, S-LSR at ICR Kyoto and CSRe at IMP Lanzhou.
Keywords: laser, cooling, storage, ring
  • Open Access LogoContribution to external collection
    Y. Zhang, W. Zhou: ICFA Beam Dynamics Newsletter No. 65, Newport News, CA, USA: International Committee for Future Accelerators, 2014, 8-21

Publ.-Id: 23234 - Permalink

Steering laser plasma simulations towards reliable predictions: how to use accelerated computing for particle accelerators
Bussmann, M.;
Overview on HZDR simulation codes
Keywords: laser, plasma, simulation
  • Invited lecture (Conferences)
    SPIE Optics + Optoelectronics, 13.-16.04.2016, Praha, Ceska republika

Publ.-Id: 23233 - Permalink

Data- and hardware-independent methods for parallel analysis algorithms: Alpaka, GrayBat and other strange animals
Bussmann, M.;
We present abstract methods for parallel algorithms developed at HZDR
Keywords: hpc
  • Lecture (Conference)
    PNI-HDRI Spring meeting 2015, 13.-14.04.2015, Hamburg, Deutschland

Publ.-Id: 23232 - Permalink

High performant, staged data I/O and analysis: Say ADIOS to your data
Bussmann, M.;
Overview on data intensive computing at HZDR
Keywords: big data, hpc
  • Lecture (Conference)
    PNI-HDRI Spring meeting 2015, 13.-14.04.2015, Hamburg, Deutschland

Publ.-Id: 23231 - Permalink

Compact Cancer Killers ─ Simulating Next-Generation Laser-Driven Ion Accelerators
Bussmann, M.; Huebl, A.;
We present recent results on simulations of laserd riven ion acceleration for cancer therapy
Keywords: simulation, gpu, picongpu, titan, cancer, radiation, therapy
  • Lecture (Conference)
    GPU Technology Conference 2015, 17.-20.03.2015, San Jose, CA, United States of America

Publ.-Id: 23230 - Permalink

Breaking the Simulation/Analysis Chain
Bussmann, M.; Huebl, A.; Schmitt, R. W. F.; Podhorszki, S. G. N.; Pugmire, D.; Klasky, S.;
We discuss the future of simulation and data analysis
Keywords: hpc, data analysis, simulation
  • Invited lecture (Conferences)
    Supercomputing Frontiers 2015, 17.-20.03.2015, Singapore, Singapore

Publ.-Id: 23229 - Permalink

Femtosecond probing of fast transient plasma processes in high-power laser interaction with solids
Kluge, T.; Huang, L.; Gutt, C.; Bussmann, M.; Chung, H.; Zacharias, M.; Schramm, U.; Cowan, T.;
Ultra-intense laser-matter interactions are a major research area in in modern plasma physics. One of the essential elements is the relativistic electron generation and transport dynamics. At present, a predictive understanding of high-intensity laser-matter interactions is severely hampered by the lack of self-consistent models for the ionization dynamics, coupled with the complex electron transport.

We establish the feasibility of using XFEL femtosecond X-ray sources to probe the spatial correlations inside of the solid-density plasma using small angle X-ray scattering (SAXS) and resonant SAXS, to obtain for the first time information on the spatial and temporal evolution of the electron density and ionization dynamics with few fs and few nm resolution. The local and instantaneous ionization state can be measured when the X-ray beam is tuned to a bound-bound resonance of a particular charge state. The atomic scattering factor at the threshold of core electron excitation increases for example at Kα excitations in highly ionized Cu to a magnitude of more than 100 times the Thomson cross section per ion.
Keywords: xfel, saxs, laser, plasma
  • Lecture (Conference)
    DPG-Frühjahrstagung Bochum, 02.-05.03.2015, Bochum, Deutschland

Publ.-Id: 23228 - Permalink

Laser Cooling of High Energy Ion Beams - from ESR and CSRe to FAIR and HIAF
Bussmann, M.; Wen, W.; Winters, D.; Dimopoulou, C.; Nolden, F.; Steck, M.; Sanjari, S.; Giacomini, T.; Litvinov, Y.; Kozhuharov, C.; Kühl, T.; Lochmann, M.; Ullmann, J.; Sanchez, R.; Nörtershäuser, W.; Stöhlker, T.; Beck, T.; Rein, B.; Walther, T.; Tichelmann, S.; Birkl, G.; Wang, H.; Zhang, D.; Huang, Z.; Hai, B.; Yuan, Y.; Ma, X.; Löser, M.; Siebold, M.; Schramm, U.;
We present results from laser cooling experiments at ESR, GSI Darmstadt and CSRe, IMP Lanzhou. We show that with a cw laser system it is possible to cool ion beams with large initial momentum spread and that laser cooling can overcome intra-beam scattering, regardless of the initial ion beam current.

We furthermore discuss first laser cooling tests with a pulsed laser system and present an outlook on how to optimize laser cooling for heavy ion beams at highly-relativistic energies, focusing not only on laser technologies but also on optical beam diagnostics.
Keywords: laser cooling, relativistic, ion beam, storage rings
  • Lecture (Conference)
    DPG-Frühjahrstagung Wuppertal, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 23227 - Permalink

Don’t forget the wire
Bussmann, M.; Zacharias, M.; Schöne, S.; Jung, F.; Vogt, S.; Widera, R.; Lieber, S.; Konrad, U.; Kaever, P.; Bieberle, A.; Wagner, A.; Fiedler, F.;
Overview of HZDR DTS Activities in Parallel Data Analyis
Keywords: dts, data, analysis, parallel
  • Lecture (Conference)
    Matter and Technologies Kickoff Meeting, 23.-26.02.2015, Hamburg, Deutschland

Publ.-Id: 23226 - Permalink

Laser Cooling of Relativistic Ion Beams Recent Results and Future Perspectives
Bussmann, M.; Löser, M.; Seltmann, M.; Siebold, M.; Schramm, U.; Beck, T.; Rein, B.; Walther, T.; Tichelmann, S.; Birkl, G.; Sanchez-Alarcon, R.; Ullmann, J.; Lochmann, M.; Nörtershäuser, W.; Eidam, L.; Boine-Frankenheim, O.; Winters, D.; Kozhuharov, C.; Sanjari, S.; Litvinov, Y.; Giacomini, T.; Steck, M.; Dimopoulou, C.; Nolden, F.; Shevelko, S.; Stöhlker, T.; Spiller, P.; Wen, W.; Yang, J.; Zhang, D.; Ma, X.; Hannen, V.;
We discuss recent results and future perspectives of laser cooling of relativistic ion beams
Keywords: laser cooling, storage ring, relativistic, ion, beam
  • Invited lecture (Conferences)
    COOL Workshop 2015, 28.09.-02.10.2015, Newport News, VA, United States of America

Publ.-Id: 23225 - Permalink

Synthetic Diagnostics for kinetic Laser Plasma Interaction Resonant Coherent X-Ray Diffraction
Bussmann, M.; Kluge, T.; Huebl, A.; Chung, H. K.; Gutt, C.; Huang, L. G.; Schramm, U.; Zacharias, M.; Cowan, T. E.;
Overview on Resonant Coherent X-Ray Diffraction Simulations of Laser Plasma Interaction
Keywords: rcxdi, cfel, laser, plasma
  • Poster
    XFEL User Meeting, 28.-30.01.2015, Hamburg, Deutschland
  • Poster
    3rd International Conference on “Correlation Effects in Radiation Fields”, CERF'15, 13.-18.09.2015, Rostock, Deutschland

Publ.-Id: 23224 - Permalink

Alpaka, GrayBat and other spiritual animals that will help you survive in the dangerous world of HPC
Bussmann, M.; Eckert, C.; Huebl, A.; Jung, F.; Widera, R.; Worpitz, B.; Zacharias, M.; Zenker, E.; Juckeland, G.; Knüpfer, A.; Nagel, W.;
Implementing codes for simulations or large-scale, high rate data analysis on modern compute hardware can take much of the time that you initially wanted to spend on something entirely else. We present our tool box of simple yet powerful solutions for writing hardware-independent, scalable and performant codes that are maintanable and can survive the next compute hardware update. We show that with modern programming techniques it is possible to implement abstract interfaces that provide sustainable concepts for parallel programming while at the same time allowing for performance optimization. This talk is about real life applications that need to work. But it will also be cool.
Keywords: hpc, c++, simulation, plasma, imaging, abstraction
  • Invited lecture (Conferences)
    ZIH-Kolloquium, 28.01.2016, Dresden, Deutschland

Publ.-Id: 23223 - Permalink

Titan Targets Tumors
Gedenk, E.; Bussmann, M.;
German team makes large computational gains in laser-driven radiation therapy of cancer
Keywords: titan, supercomputer, radiation therapy, tumor, laser, ion, acceleration

Publ.-Id: 23222 - Permalink

Graphene-based fibers for supercapacitor applications
Chen, L. L.; Liu, Y.; Zhao, Y.; Chen, N.; Qu, L. T.;
Energy conversion and storage devices play an important role in industry and society with the rapid growth of energy consumption. Supercapacitors are very attractive due to their superior power density, fast charge/discharge rates and long cycle lifetime. Graphene fiber (GF), a fascinating material, has drawn considerable attention and shown great potential as an active material in the field of supercapacitors owing to its unique and tunable nanostructure, high electrical conductivity, excellent mechanical flexibility, light weight, and ease of functionalization. This review focuses on the recent significant advances in the fabrication and application of graphene-based fiber as electrode material in supercapacitors. The synthetic strategies and application in the supercapacitor are presented, accompanied with the summary and outlook for the future development of GFs.
Keywords: flexible electronics; graphene fiber; supercapacitor

Publ.-Id: 23221 - Permalink

Efficient laser-driven proton acceleration for radiobiological studies using ultra short laser pulses
Zeil, K.; Schlenvoigt, H.-P.; Brack, F.; Metzkes, J.; Kluge, T.; Bussmann, M.; Cowan, T. E.; Kraft, S. D.; Sauerbrey, R.; Schramm, U.; Becker, G.; Hornung, M.; Lötzsch, R.; Kaluza, M.; Kämpfer, T.; Reislöhner, J.; Uschmann, I.;
Presentation about laser-proton acceleration at HZDR with 100 TW Laser, cell irradiation experiments, study on filamented proton beam profiles and reduced mass targets.
  • Invited lecture (Conferences)
    Laser Plasma Acceleration Workshop, 15.5.2015, Guadeloupe, France

Publ.-Id: 23220 - Permalink

Laser proton acceleration of mass-limited-targets of different materials
Zeil, K.; Schlenvoigt, H.-P.; Brack, F.; Metzkes, J.; Kluge, T.; Bussmann, M.; Cowan, T. E.; Kraft, S. D.; Sauerbrey, R.; Schramm, U.; Becker, G.; Hornung, M.; Lötzsch, R.; Kaluza, M.; Kämpfer, T.; Reislöhner, J.; Uschmann, I.;
Reproducible series of mass-limited targets, manufactured with lithographic techniques, and varying in size, thickness, and mounting geometry were irradiated at the 150 TW Draco Laser facility of the Helmhotz-Zentrum Dresden-Rossendorf with ultrashort (30 fs) laser pulses of intensities of about 8 · 10^20 W/cm^2. A robust maximum energy enhancement of almost a factor of two was found when compared to reference irradiations of plain foils of the same thickness and material. The performance gain was, however, restricted to lateral target sizes of about 50 μm which was attributed to edge and mounting structure influences. In a recent experiments these mass-limited targets of similar size and thickness but different materials, such as Al, Ti and Au were irradiated at the diode-pumped high-power laser system POLARIS at the Helmholtz-Zentrum Jena, in order to study the influence of the material on to the laser proton acceleration performance. The effect of target size dependent bulk heating was studied with characteristic X-ray imaging and spectroscopy.
  • Lecture (Conference)
    Laser Plasma Targetry Workshop, 21.4.2015, Paris, France

Publ.-Id: 23219 - Permalink

Effect of superimposed DC magnetic field on an AC induction semi-levitated molten copper droplet
Bojarevics, A.; Beinerts, T.; Grants, I.; Kaldre, I.; Sivars, A.; Gelfgat, Y.; Gerbeth, G.;
While a piece of copper on a ceramic substrate was inductively melted by a 9 to 18 kHz AC magnetic field with an axial magnetic DC field superimposed, the liquid metal stably semi-levitated in the expected free surface shape. The diameter of the liquid metal at the base was 30 mm, the volume more than 20 cm3. Replacing the ceramic substrate with a non-wetted glassy carbon crucible causes instability of the semi-levitated copper droplet. In the absence of the DC field severe chaotic instabilities of the liquid metal shape occurred, causing splashes and uncontrolled contact with the crucible walls. When an axial DC magnetic field with induction 0.35T was superimposed, the liquid metal droplet exhibited a harmonic azimuthal wave deformation of the free surface. Higher frequencies lead to smaller characteristic wavelength. The transverse DC magnetic field direction suppressed the travelling wave deformations of the droplet shape. The stabilizing effect of the DC magnetic field during induction melting has been shown for axial and transverse directions of the DC magnetic field. These results experimentally demonstrate the possibilities to improve the stability of levitated metal volumes by a superimposed DC magnetic.
  • Magnetohydrodynamics 15(2015), 437-443

Publ.-Id: 23218 - Permalink

Time evolution of Kelvin-Helmholtz vortices associated with collisionless shocks in laser produced plasmas
Kuramitsu, Y.; Mizuta, A.; Sakawa, Y.; Tanji, H.; Ide, T.; Sano, T.; Koenig, M.; Ravasio, A.; Pelka, A.; Takabe, H.; Gregory, C. D.; Woolsey, N.; Moritaka, T.; Matsukiyo, S.; Matsumoto, Y.; Ohnishi, N.;
We report experimental results on Kelvin-Helmholtz (KH) instability and resultant vortices in laser-produced plasmas. By irradiating a double plane target with a laser beam, asymmetric counterstreaming plasmas are created. The interaction of the plasmas with different velocities and densities results in the formation of asymmetric shocks, where the shear flow exists along the contact surface and the KH instability is excited. We observe the spatial and temporal evolution of plasmas and shocks with time resolved diagnostics over several shots. Our results clearly show the evolution of transverse fluctuations, wavelike structures and circular features, which are interpreted as the KH instability and resultant vortices. The relevant numerical simulations demonstrate the time evolution of KH vortices and show qualitative agreements with experimental results. Shocks and thus the contact surfaces are ubiquitous in the universe; our experimental results show general consequences where two plasmas interact.
Keywords: Plasmas, Instabilities, Vortices, Turbulence, Waves, Laboratory astrophysics

Publ.-Id: 23216 - Permalink

Lithium/Sulfur Batteries Upon Cycling: Structural Modifications and Species Quantification by In Situ and Operando X-Ray Diffraction Spectroscopy
Walus, S.; Barchasz, C.; Bouchet, R.; Leprêtre, J.-C.; Colin, J.-F.; Martin, J.-F.; Elkaïm, E.; Baehtz, C.; Alloin, F.;
A quantitative analysis of in situ and operando X-ray diffraction studies allows for deeper insight into the mechanism of Li2S formation and consumption. A two-step reaction process is proposed for both discharge and charge. Changing selectivity for Li2S formation is estimated, with solely Li2S being formed during the earliest step, followed by possible concurrent formation of Li2S2 intermediate in the further step of discharge.
Keywords: Lithium/Sulfur Battery; x-Ray diffraction, XRD, EXAFS, in operando

Publ.-Id: 23215 - Permalink

Pulsed Power Technology in the Field of Laser Plasma Physics
Kroll, F.;
The presented work will summarize the development of pulsed high-field magnets and power converter technology at HZDR in 2014 for application in laser-plasma physics. The talk will focus on miniature magnetic solenoids, pulsed multipole magnets and the generation of high-current pulses.
  • Lecture (others)
    Annual Meeting of the LIGHT collaboration, 12.-13.01.2015, GSI Darmstadt, Deutschland

Publ.-Id: 23214 - Permalink

Influence of microstructure and mechanical stress on behavior of hydrogen in 500 nm Pd films
Vlcek, M.; Lukác, F.; Vlach, M.; Wagner, S.; Uchida, H.; Baehtz, C.; Shalimov, A.; Pundt, A.; Cízek, J.;
Pd films can be used as a model system to examine the influence of microstructure and stress on the hydrogen absorption. In this work we study 500 nm Pd films deposited on different substrates with different binding strengths. The films were electrochemically loaded with hydrogen up to hydride concentration. Development of lattice constant during hydrogen loading of Pd films was investigated by in situ X-ray diffraction using synchrotron radiation. The influence of microstructure and mechanical stress in the films on the phase transition from Pd to Pd hydride was examined.
Keywords: Hydrogen Palladium Thin films

Publ.-Id: 23213 - Permalink

Thermal expansion of polycrystalline gallium nitride: an X-ray diffraction study
Minikayev, R.; Paszkowicz, W.; Piszora, P.; Knapp, M.; Bähtz, C.; Podsiadlo, S.;
Gallium nitride is studied at ambient and nonambient temperatures by powder X-ray diffraction followed by Rietveld refinement of the structure. The structure is reported for the ambient temperature on the basis of laboratory data. The diffraction data collected using a synchrotron beam serve for derivation of the lattice parameter and thermal expansion dependencies on temperature. The variation of unit-cell size on temperature was studied in detail in a broad range 11 K < T < 1073 K. The obtained dependencies of a, c and V and thermal expansion coefficients are smooth, and the results are consistent with previously collected data. The c/a ratio shows an almost linear decreasing trend with rising temperature. The magnitude of thermal expansion obtained in the described experiments is similar to a recently reported theoretical one.
Keywords: Thermal expansion, x-ray diffraction, gallium nitride

Publ.-Id: 23212 - Permalink

Characterization of laser driven ions
Brack, F.-E.; Kraft, S. D.; Kroll, F.; Metzkes, J.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Zeil, K.; Schramm, U.;
Durch die Fokussierung eines ultrakurzen und hochintensiven Laserpulses auf ein Festkörpertarget können Pulse von Protonen und anderen positiv geladenen Ionen erzeugt werden. Auf Basis des etablierten TNSA (target-normal sheath acceleration) Prozesses konnten am Helmholtz-Zentrum Dresden-Rossendorf mit dem 150 TW Ultrakurzpulslaser Draco Protonenpulse mit Energien bis zu 20 MeV erzeugt und charakterisiert werden. Die Charakterisierung dieser Teilchenstrahlung erfordert die Identifizierung der Ionenspezies und die Bestimmung ihrer spektralen Verteilung möglichst nach jedem Puls, wofür standardmäßig Thomsonspektrometer verwendet werden. In den letzten Jahren wurde das DRACO-Lasersystem bis zu einer Pulsleistung über 500 TW erweitert. Aufbauend auf dem bisherigen Spektrometerdesign wurde in dieser Arbeit ein kompaktes Spektrometer für einen höheren Energiebereich bis über 80 MeV entworfen. Besonders wichtig dabei ist die Identifizierung möglicher das Messergebnis verfälschender Sekundärstrahlungsquellen, die mit Hilfe von Monte-Carlo Simulation analysiert werden müssen.
  • Lecture (Conference)
    DPG-Frühjahrstagung Wuppertal 2015, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 23211 - Permalink

Reflective probing of laser-driven plasma for ion acceleration
Rehwald, M.; Metzkes, J.; Zeil, K.; Kraft, S.; Schramm, U.;
Plasmas driven by intense, ultra-short laser pulses can support electrical field strengths of up to TV/m, making this concept promising for compact particle accelerators in which ions can gain MeV energies on a micrometer scale. For the acceleration, the laser pulse is focused onto a thin target which quickly ionized and transformed into a plasma in which electrons gain MeV energies in the laser field. These electrons leave the target volume and thereby create quasi-static charge-separation fields along the target surfaces in which the ion acceleration takes place. The acceleration is strongly influenced by the plasma conditions at the target during the main pulse interaction, which are determined by light preceding the intense main pulse or by the rising edge of the main pulse itself.

In this talk, we present a reflective pump probe method which allows to temporally resolve the lateral and longitudinal expansion of the critical plasma density. First experimental results with a pure imaging technique will be shown, in which the front and rear surface plasma were characterized. This technique is currently developed to include interferometry, in that way increasing the sensitivity in longitudinal direction. We will discuss the simulation results and a corresponding experimental setup.
  • Lecture (Conference)
    DPG-Frühjahrstagung Wuppertal 2015, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 23210 - Permalink

Phase transformations in Ni/Ti multilayers investigated by synchrotron radiation-based x-ray diffraction
Cavaleiro, A. J.; Ramos, A. S.; Martins, R. M. S.; Braz Fernandes, F. M.; Morgiel, J.; Baehtz, C.; Vieira, M. T.;
X-ray diffraction using synchrotron radiation was used for real-time investigation of the phase evolution of Ni/Ti multilayer thin films during annealing. These multilayers were deposited onto Tie6Ale4V substrates by dc magnetron sputtering from pure Ni and Ti targets. The deposition parameters were adjusted in order to obtain a near equiatomic chemical composition and modulation periods (L) below 25 nm. Along the entire thickness of the films, well-defined structures with alternate Ni- and Ti-rich layers are observed, even for L ¼ 4 nm. In this case, a halo characteristic of an amorphous structure is obtained, while for L of 12 and 25 nm the as-deposited thin films are nanocrystalline being possible to identify the (111) Ni and (002) Ti diffraction peaks. The nanolayered structure vanishes during annealing due to interdiffusion followed by reaction. The reaction between Ni and Ti to produce NiTi in the cubic B2 structure occurs in a short delay of time and within a narrow temperature range. For L of 25, 12 and 4 nm, the reaction temperature is close to 320, 350 and 385 C, respectively. For higher temperatures, in addition to the austenitic phase, the NiTi2 phase is identified. The diffusion of Ti from the substrate and Ni towards the substrate could favour the precipitation of NiTi2.
Keywords: Thin films Transition metal alloys and compounds Vapour deposition Phase transition Synchrotron radiation Transmission electron microscopy

Publ.-Id: 23209 - Permalink

High-repetition-rate laser-proton acceleration employing a cryogenic hydrogen jet as a target
Rehwald, M.; Göde, S.; Obst, L.; Sommer, P.; Brack, F.; Schramm, U.; Gauthier, M.; Macdonald, M.; Roedel, C.; Glenzer, S.; Zeil, K.; Metzkes, J.; Schumaker, W.; Schlenvoigt, H.-P.;
Applications of laser-accelerated protons demand a stable, high-energy and high-repetition rate particle source. We present the results of our experimental campaign in cooperation with the HED group at SLAC, performed at the 10 Hz Ti:Sa laser Draco of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), employing a cryogenic Hydrogen jet as a renewable target. Draco delivers pulses of 30 fs and 5 J at 800 nm, focussed to a 3 µm spot by a F/2.5 off-axis parabolic mirror. The cylindrical jet has a diameter of 2 µm or 5 µm and a nominal electron density of 30 times the critical density. Preliminary results show a mono-species proton acceleration in a solid angle of at least +/-45° with respect to the incoming laser beam and proton energies exceeding 10 MeV. Radiochromic film stacks in forward direction show signatures of two acceleration mechanisms, one being the conventional TNSA and a second one leading to filament-like structures, possibly stemming from an instability within the plasma. Among other results, an on-shot monitoring of the stability of the jet by means of a temporally synchronized probe beam will be shown in the presentation.
  • Lecture (Conference)
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola, Isola d'Elba, Italien

Publ.-Id: 23208 - Permalink

Nucleation Control for Large, Single Crystalline Domains of Monolayer Hexagonal Boron Nitride via Si-Doped Fe Catalysts
Caneva, S.; Weatherup, R. S.; Bayer, B. C.; Brennan, B.; Spencer, S. J.; Mingard, K.; Cabrero-Vilatela, A.; Baehtz, C.; Pollard, A. J.; Hofmann, S.;
The scalable chemical vapor deposition of monolayer hexagonal boron nitride (h-BN) single crystals, with lateral dimensions of ∼0.3 mm, and of continuous h-BN monolayer films with large domain sizes (>25 μm) is demonstrated via an admixture of Si to Fe catalyst films. A simple thin-film Fe/SiO 2/Si catalyst system is used to show that controlled Si diffusion into the Fe catalyst allows exclusive nucleation of monolayer h-BN with very low nucleation densities upon exposure to undiluted borazine. Our systematic in situ and ex situ characterization of this catalyst system establishes a basis for further rational catalyst design for compound 2D materials.
Keywords: Hexagonal boron nitride (h-BN), chemical vapor deposition (CVD), borazine (HBNH)3, in situ X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), Fe catalyst

Publ.-Id: 23207 - Permalink

Spin waves going 3D - chiral effects in curved magnetic nanowires
Otalora, J. A.; Yan, M.; Lindner, J.; Fassbender, J.ORC; Hertel, R.; Kakay, A.
Recent progress in material science has enabled the first experimental studies concerning the static magnetization characterization of samples with tubular geometry to be carried out [1]. Although investigating spin-wave and domain-wall dynamics remains a challenge from an experimental point of view, theory predicts that it is fundamentally different than in previously investigated flat geometries. Here, we discuss the effect of the curvature on the dynamics of domain walls and spin waves. Using extensive finite element micromagnetic simulations, we demonstrate that a typical vortex-type domain wall formed in a ferromagnetic tube exhibits advantageous properties regarding the domain wall speed and stability. For topological reasons, these robust domain walls do not encounter the Walker breakdown in certain nanotubes and can propagate with velocities faster than the spin wave phase velocity [2]. Above a critical velocity, the domain wall triggers a Cherenkov-type spin wave radiation. A characteristic of ferromagnetic nanotubes is that the chiral symmetry of the domain wall propagation is broken [3]. This is attributed to the lack of local inversion symmetry due to the curved surface of the nanotube [4]. Our micromagnetic as well as analytical studies show that this lack of inversion symmetry leads to a non-reciprocal dispersion relation for the spin waves with regards to the sign of the propagation vector k. The split in the frequencies for spin waves traveling in opposite directions is of the order of several GHz for tubes below 100 nm in diameter. This effect is the largest when the nanotube radius is comparable with the wavelength of the traveling spin waves and is already present for bended thin films that form a half or even less than a half nanotube only. The split and the minima of the dispersion, however, can be tuned with a circular field. The analytical formula obtained for the dispersion allows for a systematic study of the dispersion relation of nanotubes with different geometry, material parameters, applied circular and/or axial fields, without the need for the expensive 3 dimensional finite element micromagnetic simulations.
[1] R. Streubel, et al., Nano Lett. 14, 3981 (2014)
[2] M. Yan et al., Appl. Phys. Lett. 99, 122505 (2011)
[3] M. Yan et al., Appl. Phys. Lett. 100, 25402 (2012)
[4] R. Hertel, SPIN 3, 1340009 (2013)
Keywords: Nanotube, chiral, curved, spin waves, Cherenkov, non-reciprocal
  • Invited lecture (Conferences)
    603. WE-Heraeus-Seminar: Magnonics – Spin Waves Connecting Charges, Spins and Photons, 05.-08.01.2016, Bad Honnef, Deutschland

Publ.-Id: 23206 - Permalink

Non-reciprocal spin-wave dispersion in bent thin-film stripes
Zahn, F.; Lindner, J.; Fassbender, J.ORC; Kakay, A.
Spin waves are considered as promising candidates to carry information in future technology applications, therefore in the last decades they have been studied intensively in ferromagnetic thin films. Recent developments in material research enabled the manufacturing of more complex structures than planar thin films; especially nanotubes and bent structures of varying curvature can be produced. It has recently been shown by theory that in nanotubes the curvature has an impact on both the domain wall and spin-wave propagation [1][2]. Moreover, the dispersion relation in nanotubes is non-reciprocal regarding the sign of the propagation vector. These effects are attributed to the lack of local inversion symmetry due to the curved surface of the nanotube [3]. As predicted by theory the spin-wave dynamics is fundamentally different from that known from thin films. Here, we studied the spin-wave propagation and the spin-wave dispersion in bent Permalloy thin-film stripes in the form of quarter-tubes, half-tubes and threequarter tubes. Compared to nanotubes, these systems only posses the curvature but not the specific boundary condition of nanotubes. For the simulations we used our GPU accelerated Finite Element micromagnetic code TetraMag [4]. The partial tubes had a homogenous magnetization along the circumference or azimuthal direction in cylindrical coordinates. The spin waves are excited with an external field applied in the radial direction at the middle of the sample. Therefore the spin waves propagate toward the ends of the considered structures, in a Damon-Eshbach geometry. For a given frequency the simulation is run until the steady state is reached. The wave vector correponding to this excitation frequency is determined by a Fourier analysis of the radial component of the magnetization along the z-axis, using a given snapshot in time. The resulting dispersion relations show a non-reciprocity regarding the sign of the propagation vector, similarly to those reported for nanotubes. The spin wave assymetry, defined as the ratio between the difference of the frequencies and their sum for a given wave vector but with opposite signs, can be as high as 5%. This is equivalent to a difference of about 500MHz for spin waves travelling with a given wave vector but opposite signs. We believe this assymetry can be verified experimentally, providing further prospects for research.
[1] M. Yan et al., Appl. Phys. Lett. 99, 122505 (2011)
[2] M. Yan et al., Appl. Phys. Lett. 100, 25402 (2012)
[3] R. Hertel, SPIN 3, 1340009 (2013)
[4] A. Kakay et al., IEEE Trans. Magn. 46, 2303 (2010)
Keywords: Spin waves, non-reciprocal, dispersion, curvature induced
  • Poster
    603. WE-Heraeus-Seminar: Magnonics – Spin Waves Connecting Charges, Spins and Photons, 05.-08.01.2016, Bad Honnef, Deutschland

Publ.-Id: 23205 - Permalink

An affine equivariant multivariate normal score transform for compositional data
van den Boogaart, K. G.; Mueller, U.; Tolosana-Delgado, R.;
The geostatistical treatment of continuous variables often includes a step of transformation to normal scores. In the case of analysing a composition, it has been suggested that standard methods can be applied to (isometric) logratio transformed compositions. Several logratio transformations are available and invariance of the final results under the choice of logratio transform is desirable. Unfortunately, a geostatistical procedure which includes marginal normal scores transformations of the individual logratio scores via quantile matching will not have this invariance property, nor will the resulting vectors of scores show a joint multivariate normal distribution. In this paper an affine-equivariant normal score transform is proposed. The method is based on a continuous deformation of the underlying logratio space to a Gaussian space. The properties and performance of this method are illustrated and positively compared with existing alternatives using a simulated setting and a case study from a banded iron formation ore mining operation from Western Australia. The proposed method is also suitable for the study of other multivariate non-compositional cases.
Keywords: additive logratio transform; alr; flow; Gaussian anamorphosis; ordinary differential equation

Publ.-Id: 23204 - Permalink

PENELOPE laser system update – on the way to first light
Albach, D.; Siebold, M.; Loeser, M.; Roeser, F.; Eiselt, P.; Schramm, U.;
We present the current status of the PENELOPE laser system presently under construction at the Helmholtz-Zentrum Dresden-Rossendorf. We aim for the activation of the first major amplification stage boosting available energies to the Joule-level, as well as initial results for the stretcher-compressor module. An update on the development status of the last amplification stage and future front end improvements will be given.
Keywords: Penelope, laser, Ytterbium, diode pumping, CaF2
  • Lecture (Conference)
    The 5th Advanced Lasers and Photon Sources (ALPS’16), 17.-20.05.2016, Yokohama, Japan

Publ.-Id: 23203 - Permalink

An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays
Schubert, M.; Piechotta, M.; Beyer, M.; Schleicher, E.; Hampel, U.; Paschold, J.;
Non-uniform flow patterns on distillation trays can result in significant losses in separation efficiency compared to conditions with straight chordal flow paths. To improve flow pattern via tray design revamps as well as for more accurate prediction of achievable separation efficiency, better understanding of the flow formation is required. This is, however, not straight forward since the evolving patterns depend on column and tray design as well as on operating conditions and may cover configurations with continuous liquid being pushed through a curtain of rising bubbles (bubble regime) or a continuous gas phase carrying the liquid as droplets (spray regime).
In this study, the wire-mesh sensor technique was used to visualize flow patterns on larger trays. The technique tracks conductivity tracer pulses during their passage across the tray. A proper calibration routine was developed and a methodology is proposed to determine point liquid residence time distributions and weir-to-weir liquid velocities. Experiments were carried out in a tray column of 800 mm diameter. The feasibility study included experiments at different liquid capacities and various outlet weir obstructions. Tray benchmark data at high spatio-temporal resolution were obtained, which are suitable for validation of CFD models for flow simulation of industrial-scale sieve trays.
Keywords: distillation column, sieve tray, wire-mesh sensor, tray flow pattern, residence time distribution, liquid velocity

Publ.-Id: 23202 - Permalink

Liquid metal two-phase flows
Strumpf, E.; Roshchupkina, O.; Shevchenko, N.; Eckert, S.; Gerbeth, G.;
The ascents of single Argon bubbles and bubble chains are investigated by means of Ultrasound Doppler Vecolimetry and X-ray radiography. A cuboid benchmark experiment of dimensions 144 x 144 x 12 mm³ is used and filled with eutectic alloy GaInSn. Furthermore the effects on the bubble behaviour and flow structure is investigated by superimposing a strong magnetic transversal DC field up to 1.1 T.
Keywords: liquid metal, two phase flow, bubble, magnetic field, UDV, X-ray
  • Poster
    LIMTECH midterm evaluation, 28.-30.09.2015, Dresden, Deutschland

Publ.-Id: 23201 - Permalink

Liquid metal two-phase flows
Strumpf, E.; Roshchupkina, O.; Shevchenko, N.; Eckert, S.; Gerbeth, G.;
The ascents of single Argon bubbles and bubble chains are investigated by means of Ultrasound Doppler Vecolimetry and X-ray radiography. A cuboid benchmark experiment of dimensions 144 x 144 x 12 mm³ is used and filled with eutectic alloy GaInSn. Furthermore the effects on the bubble behaviour and flow structure is investigated by superimposing a strong magnetic transversal DC field up to 1.1 T.
Keywords: liquid metal, two phase flow, bubble, magnetic field, UDV, X-ray
  • Poster
    LIMTECH annual meeting 2015, 16.-17.11.2015, Hannover, Deutschland

Publ.-Id: 23200 - Permalink

Magnetische Momente und mächtige Magnete
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    „Physik am Samstag“ der Fachrichtung Physik der TU Dresden, 05.12.2015, Dresden, Deutschland
  • Invited lecture (Conferences)
    Vorlesung im Studium Generale "Naturwissenschaften Aktuell", 20.10.2016, Dresden, Deutschland

Publ.-Id: 23199 - Permalink

AIDA – Apparatus for In-situ Defect Analysis
Trinh, T. T.;
AIDA – Apparatus for In-situ Defect Analysis
  • Lecture (Conference)
    PhD-Seminar of HZDR, 06.10.2015, Altenberg, Germany

Publ.-Id: 23198 - Permalink

Spin-lattice interactions of frustrated magnets in high magnetic fields
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    SFB 1143 Retreat workshop, 21.-23.09.2015, Krippen, Deutschland

Publ.-Id: 23197 - Permalink

Apparatus for In-situ Defect Analysis (AIDA) Investigations by Positron Annihilation Spectroscopy
Trinh, T. T.; Liedke, M. O.; Anwand, W.; Wagner, A.; Potzger, K.; Krause-Rehberg, R.;
A unique high vacuum system for defect manipulation and analysis has been developed and installed at the Helmholtz-Zentrum Dresden-Rossendorf. The setup combines several experimental techniques for that purpose, e.g., material evaporation, ion beam modifications, and temperature treatment with the positron annihilation spectroscopy, and sheet resistance measurements.

AIDA utilizes a monoenergetic positron beam which is tungsten moderated, magnetically guided and pre-accelerated in the range of 30 eV to 35 keV. The positron beam is extracted from an intense 22Na source and enables sample depth profiling by Doppler broadening spectroscopy. The coincidence Measurements are performed by two HPGe detectors with energy resolution of (780 ± 20) eV at 511 keV, whereas the standard single HPGe detector Doppler broadening with energy resolution of (1.09 ± 0.001) keV is applicable for the varied energy scans. AIDA consist of a load lock chamber mechanism for halogen preliminary heating up to 150°C and loading a sample holder through a linear transfer to the MBE chamber by a basic pressure of 10-7 mbar. The sample holder is then mounted on a sophisticated 5 axis manipulator which is available for resistometry investigations by a 4-point probe module during isochronal annealing by a resistive heater at a base pressure of about 10-8 mbar. Thus, defects can be annealed up to 1300 K or stabilized down to 50 K and meanwhile residual resistivity measurements can be performed. In order to determine influence of vacancy complexes and their distribution onto magnetic, structural, and morphological sample properties, simultaneously ion irradiation by an energy range from (0.001 – 5) keV can be realized. The Ion Source is suitable for depth profiling and enables operation with reactive and noble gases by a current density of <200 µA/cm2. A Quartz oscillator provides a useful and progressive indication of coating thickness during the deposition process. Eventual, defect role during a dynamic formation of nanostructures on the semiconductor surface, e.g. Si or Ge, can be investigated during ion irradiation.
Keywords: Positron Annihilation Spectroscopy, In-situ
  • Poster
    28th International Conference on Defects in Semiconductors, 27.07.2015, Espoo, Finland

Publ.-Id: 23196 - Permalink

Magnetic and structural studies of Mg2Fe(x)Si(1-x) – hydrides
Trinh, T. T.; Yildirim, O.; Anwand, W.; Liedke, O. M.; Grenzer, J.; Potzger, K.; Lindner, J.; Asano, K.; Dam, B.; (Editors)
Mg2Fe(x)Si(1-x) – hydride is a promising multifunctional material in terms of magnetic applications due to a dramatic change in their magnetic, optical and electronic properties upon hydrogen loading. Therefore they are capable of potential applications, e.g. hydrogen sensors for use as safety monitors wherever hydrogen is used, stored, or produced and storage devices.
In order to understand the physical background of Mg2(FeSi) based systems as well as their hydrides, comprehensive investigations were performed on as-grown and hydrogen loaded 250 nm thick Mg2Fe(x)Si(1-x) (x= 0; 0.25; 0.50; 0.75; 0.90; 1.00) films using magnetometry, X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS).
Magnetometry results revealed that upon hydrogen loading volume magnetic properties of the system transforms from superparamagnetic- and spin glass-like behavior to ferromagnetic behavior with high Curie temperature. Likewise, it is found that the hydrogen loading and Fe concentration have direct consequences on the structural properties, these can be explained either by an amorphisation process or by the formation of very small nanocrystalline particles probed by XRD measurements. Furthermore, different sizes and chemical decoration of open-volume defects has been observed by PAS.
The knowledge gained from these studies can be use for monitoring those characteristics that change in the presence of hydrogen.
Keywords: Magnetic application, positron annihilation spectroscopy
  • Poster
    Gordon research conference on hydrogen-metal systems, 12.-17.07.2015, Easton, MA, USA

Publ.-Id: 23195 - Permalink

Mg2FexSi1-x thin films: The interplay between the defects and magnetic structure properties of hydrogenation
Trinh, T. T.; Munnik, F.;
Mg2Fe hydride belongs to the most promising candidates for application as light weight storage material in a future hydrogen economy. Recently, it has also been shown that due to chemochromism, Mg2Fe is a low-cost and rare-earth-free candidate for switchable mirrors upon hydrogen loading. Besides the Mg2Fe hydride, a new compound of Mg2FexSi1-x will be presented. The additional content of Si promises an optimization of hydrogen absorption and desorption processes. Comprehensive investigations at the facilities of HZDR on Mg2FexSi1-x system showed that hydrogen induced changes in structure, electronic, optical and magnetic properties. I.e., volume magnetic properties transform from superparamagnetism to ferromagnetism with a high Curie temperature.
As a member of the Helmholtz Association, HZDR provides a unique infrastructure for researchers. Large scale research facilities, i.e. the ion beam center and the linear electron accelerator ELBE of the HZDR are also briefly presented. A suite of materials analysis techniques based on ion beams and the generated radiation of the electron beam is available. A few methods are introduced such as Rutherford Backscattering Spectrometry (RBS), Resonant Nuclear Reaction Analysis (NRA) and Positron annihilation spectroscopy (PAS), which enable the cross-disciplinary collaboration between researchers.
Keywords: Metal hydride, switchable mirror, Superparamagnetism
  • Invited lecture (Conferences)
    ENERGYPOLIS Seminar, 12.11.2015, Sion, Switzerland

Publ.-Id: 23194 - Permalink

Luminescence mechanism for Er3+ ions in a silicon-rich nitride host under electrical pumping
Berencén, Y.; Illera, S.; Rebohle, L.; Ramírez, J. M.; Wutzler, R.; Cirera, A.; Hiller, D.; Rodríguez, J. A.; Skorupa, W.; Garrido, B.;
A combined experimental and theoretical study on the electroluminescent excitation mechanism for trivalent erbium (Er3+) ions in a silicon-rich nitride (SiNx) host is presented. Direct impact by hot electrons is demonstrated to be the fundamental excitation mechanism. The Er3+ excitation by energy transfer from silicon nanostructures and/or defects is shown to be marginal under electrical pumping. A bilayer structure made of a SiO2 electron-accelerating layer and an Er-implanted SiNx layer has been sandwiched between a metal–insulator–semiconductor structure with a highly doped N-type silicon substrate and an indium–tin–oxide window functioning as a transparent electrode. Monte Carlo (MC) simulations are used to model hot electron transport in the proposed device structure. Acoustic, polar and non-polar optical electron–phonon scattering mechanisms are considered as well as a new scattering process related to the trapping/detrapping on energetically shallow traps in the band gap of silicon nitride. For SiO2 layers around 20 nm-thick and beyond, the number and kinetic energy of hot electrons before entering the SiNx layer are maximal. A significant enhancement of the 1.54 μm electroluminescence power efficiency of two orders of magnitude is observed in devices composed of a 20 nm-thick SiO2 layer compared to those composed of 10 nm-thick SiO2. We demonstrate by MC simulations that such a difference, in terms of power efficiency, is ascribed to the high-energy tail of the hot electron energy distribution, which becomes more pronounced as the SiO2 electron-accelerating layer thickness increases. It is also unveiled that direct excitation of the 1.54 μm Er3+ main radiative transition requiring an excitation energy of only 0.8 eV is inefficient, and that the major part of the Er3+ ions are excited via higher level energy states. The obtained results are sufficiently consistent to be extended to other trivalent rare-earth ions inside similar insulating material environments.
Keywords: erbium, silicon-rich nitride, hot electrons, electroluminescence, direct impact excitation, Monte Carlo, light emitting devices

Publ.-Id: 23193 - Permalink

Die Jagd nach dem Feldrekord - Europas höchste Magnetfelder
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Lecture (others)
    Dresden-Open-Minded, Culture Container Festival, 12.-23.02.2015, Dresden, Deutschland

Publ.-Id: 23192 - Permalink

Investigation of single bubbles and bubble chains in liquid metal under the influence of magnetic fields
Strumpf, E.; Roshchupkina, O.; Shevchenko, N.; Eckert, S.;
In the present study the ascents of single bubbles and of bubble chains in a liquid metal are investigated. For this purpose a benchmark experiment is set up, a cuboid vessel of the dimensions 144 x 144 x 12 mm³, which is filled with eutectic alloy GaInSn. A transversal magnetic field up to 1.1 T is imposed to this vessel. Ultrasound Doppler Velocimetry (UDV) is used to map the flow in the continuous phase of bubble chain regimes as well as the ascent velocity of single bubbles. X-ray radioscopy is applied to obtain detailed information within the disperse phase of bubble chains, such as bubble diameter, shape, trajectory etc.
Keywords: liquid metal, bubble, magnetic field, UDV, X-ray, two-phase flows
  • Lecture (Conference)
    MHD Days 2015, 07.-09.12.2015, Ilmenau, Deutschland

Publ.-Id: 23191 - Permalink

Mono-energetic Positron Source (MePS) – a large-scale facility for Porosimetry at ELBE
Trinh, T. T.; Liedke, M. O.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.;
Positron annihilation lifetime spectroscopy serves as an excellent tool for studies of open-volume defects in solid materials such as vacancies, vacancy agglomerates, dislocations, pores and voids. The intense mono-energetic positros beamline (MePS) at the ELBE accelerator developed for positron life-time and conventional Doppler Broadening experiments offers a non-destructive investigation method to study of porous media as well as thin film as a function of thickness.
Keywords: Positron annihilation lifetime spectroscopy, Doppler Broadening, Porous
  • Poster
    Porosimetry Workshop, 21.10.2015, HZDR, Germany

Publ.-Id: 23190 - Permalink

From anti‐dots to sponge: Positron Annihilation Spectroscopy of Ge+ irradiated Ge
Liedke, M. O.; Böttger, R.; Liedke, B.; Facsko, S.; Anwand, W.; Wagner, A.;
Ion irradiation of Ge drives the surface morphology throughout a rich variety of nanostructure formations, i.e., from ordered nanohole and nanodot patterns to nanoporous and sponge-like structures [1]. Moreover, due to ion energy depth resolution functional modifications of Ge are not only limited to the surface but extend easily to several tens of nm depth. That is especially relevant for fuel [2], and solar cells [3], as well as for filters [4], and gas sensors [5] applications. Possible fundamental implications are under a debate as well, e.g., does the mechanism for porous Ge formation originate mainly from the vacancy clustering [1] or microexplosions [6]? In addition, surprisingly porous structures have not been found in ion irradiated Si that is in appearance virtually a very similar material to Ge.
The driving force for the irradiation induced morphology evolution is mainly related to the kinetics of ion beam induced defects. For Ge+ self-irradiation with low ion energies the sample surface remains first (i) smooth (EGe<4keV), followed by (ii) the self-organized formation of nanoholes (EGe=5-7keV), and finally (iii) at EGe>8keV porous/sponge structures develop. Increasing ion energy allows to tailor depth and porosity. For Bi+ irradiation surface morphology evolves in a similar fashion besides for EBi=7-12keV, where initial hexagonally ordered nanohole patterns reorganize into homogeneously distributed nanodots [1]. Again for larger ion energies porous and sponge-like structures evolve. The kinetics beneath ion irradiation of Ge can be drawn as follows: (i) defect distribution and number at a certain sample depth scales with ion energy, whereas (ii) increasing ion fluence forms amorphous Ge layer due to continuous creation of interstitials and vacancies. The former (iii) because of their mobility, formation volume and energy compare to interstitials can cluster and grow into pores. Once, such a small void is created and is far enough from the surface it grows by attracting additional vacancies [7]. The overall surface morphology evolution has been simulated by means of kinetic Monte Carlo (kMC) modeling [1]. Both hole and sponge structures have been visualized without, however, hexagonal ordering of patterns nor the nanodot formation found from Bi+ irradiation could be realized.
Positron annihilation lifetime spectroscopy (PALS) and Doppler Broadening (DB) measurements will allow to probe the open-volume distribution and its complexes as well as the pores size as a function of depth. Thus, it should give an insight into the evolution of surface morphology during ion irradiation of semiconductors. These results can be of importance for further kMC modeling. Preliminary investigations by DB will be performed at the SPONSOR/AIDA setup in order to estimate positron annihilation line parameters as a function of positron energy.
  • Lecture (Conference)
    Treffen deutscher Positronengruppen (TdP‐2015), 12.-13.11.2015, München, Deutschland

Publ.-Id: 23189 - Permalink

Open volume defects and magnetic phase transition in Fe60Al40 transition metal aluminide
Liedke, M. O.; Anwand, W.; Bali, R.; Cornelius, S.; Butterling, M.; Trinh, T. T.; Wagner, A.; Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H.; Potzger, K.;
Magnetic phase transition in the Fe60Al40 transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000°C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation and Mössbauer spectroscopy. The positron annihilation spectroscopy (PAS) has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis (AIDA) that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate importance of the open volume defects onto the magnetic phase transition.
Magneto-optical measurements of the ordered Fe60Al40 as well as disordered sample after each annealing step have been done ex-situ at room temperature. A set of magnetization reversal loops is presented in Figure 1(a). The ordered sample shows no magnetic signal at room temperature at all, whereas the disordered one is represented by a magnetic reversal curve with coercivity of about 65 Oe. Due to annealing both the remanence and coercivity drop significantly and already at 500°C the magnetic signal vanishes. The SEM images [see inset of Fig. 1(a)] reveal continuous film surface at 500°C, whereas at 1000°C darker and bright island-like regions were found that possibly correspond to the former FeAl film and Al-AlO segregations, respectively. The light gray color surrounding the island-like regions in the 1000°C case represents most probably the SiO2 substrate.

Two different positron annihilation spectroscopy (PAS) measurement types have been utilized for defect analysis after each temperature step: (i) room temperature standard Doppler broadening as a function of positron energy E for depth profiling, (ii) RT coincident Doppler broadening measurements at fixed energy after each temperature step that can in detail reveal information of the chemical environment of defects with higher energy resolution [Fig. 1(b)]. In both cases two specific annihilation line parameters have been extracted: (i) the shape parameter S that corresponds to the fraction of positrons annihilating with the low-momentum electrons localized close to the middle of the annihilation line, and (ii) the wing parameter W that takes into appoint positron annihilation with high-momentum electrons at the outer region of the annihilation line. In general, the S parameter is sensitive to the open volume defects amount and their size, whereas the W parameter is a fingerprint of the annihilation site chemical environment, thus defects decoration by neighboring matrix elements [1].

cDB results are summarized in Figure 1(b), where the annihilation line parameters are plotted as a function of the annealing temperature. We can clearly see that up to 600°C both S and W parameters are more or less constant, whereas a jump followed by another plateau in the S parameter value for higher temperatures is visible. The jump of the S parameter can correspond to a slight increase of the open volume number and/or its size, whereas the decrease of W shifts the defect decoration in direction of Al. The S parameter difference at the jump is of about 1.5% that can be considered as low, nevertheless a step-like dependence is visible. A drop of about 5.5% in W cannot be neglected. Moreover W recovers to its original value at 1000°C that suggests larger occupation of the neighboring defect sites with Fe as well as a slight change of film stoichiometry due to annealing.

Summarizing, no evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400-600°C) has been found, whereas higher temperatures showed an increase in the vacancy concentration. Still, in the surface region of the sample reasonably large annihilation line parameters variations have been found showing sufficient sensitivity of our experimental tools, and ruling out possible signal saturation due to too high vacancies concentration. At higher temperatures a slightly larger defect concentration as well as different defect decorations were found that is likely a result of temperature driven material decomposition leading to a complete film melt at 1000°C. Magnetic and structural changes have been tracked using PAS, XRD, and CEMS measurements. The magnetic phase transition from para- to ferro-magnetic behavior appears to be driven by chemical disordering alone, and is independent of the vacancy concentration. These results help understand the role of defects in materials that show disorder-induced ferromagnetism.

This work has been partially financed by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442).

[1] - R. Krause-Rehberg and H. Leipner, Positron Annihilation in Semiconductors, Solid-State Sciences. Berlin: Springer, vol. 127 (1999)
  • Poster
    22nd International Colloquium on Magnetic Films and Surfaces, 12.-17.07.2015, Kraków, Polska

Publ.-Id: 23188 - Permalink

Nature of low-lying electric dipole resonance exditations in 74Ge
Negi, D.; Wiedeking, M.; Lanza, E. G.; Litvinova, E.; Vitturi, A.; Bark, R. A.; Bernstein, L. A.; Bleuel, D. L.; Bvumbi, S.; Bucher, T. D.; Daub, B. H.; Dinoko, T. S.; Erasmus, N.; Easton, J. L.; Görgen, A.; Guttormsen, M.; Jones, P.; Kheswa, B. V.; Khumalo, N. A.; Larsen, A. C.; Lawrie, E. A.; Lawrie, J. J.; Majola, S. N. T.; Masiteng, L. P.; Nchodu, M. R.; Ndayishimye, J.; Newman, R. T.; Noncolela, S. P.; Orce, J. N.; Papka, P.; Pellegri, L.; Renstrom, T.; Roux, D. G.; Schwengner, R.; Shirinda, O.; Siem, S.; Sithole, P. S.; Uwitonze, P. C.;
Isospin properties of dipole states in 74Ge are investigated using the (alpha,alpha') reaction and compared to (gamma,gamma') data. The results indicate that the dipole states in the excitation energy region of 6 to 8 MeV adhere to the scenario of the recently found splitting of the region of dipole states into two separated parts: one at low energy being populated by both isoscalar and isovector probes and the other at high energy excited only by the electromagnetic probe. RQTBA calculations show a reduction in the isoscalar E1 strength with an increase in excitation energy which is consistent with the measurement.
Keywords: Alpha-particle scattering, cross sections, E1 strength, RQTBA calculations.

Publ.-Id: 23187 - Permalink

High energy Yb:YAG active mirror laser system for transform limited pulses bridging the picosecond gap
Siebold, M.; Loeser, M.; Röser, F.; Albach, D.; Bussmann, M.; Eckhardt, S.; Lasagni, A.-F.; Sauerbrey, R.; Schramm, U.;
We present a diode-pumped Yb:YAG MOPA-System for the unprecedented generation of variable pulse duration transform limited pulses in the range between 10ps and 100ps. First applications relying on unique pulse parameters as modulation free spectrum, tunability and coherence length, namely the direct laser interference patterning (DLIP) and laser cooling of stored relativistic ion beams are highlighted. Pulses are generated by a mode-locked fs-oscillator while the spectral bandwidth is narrowed in the subsequent regenerative amplifier by an intra-cavity grating monochromator. Two alternative booster amplifiers were added to increase the pulse energy to 100µJ and 10mJ, respectively.
Keywords: Lasers, ytterbium Laser amplifiers Pulse shaping Diffraction gratings

Publ.-Id: 23186 - Permalink

Local probe of disorder-induced magnetism in Fe60Al40 thin films by CEMS
Smekhova, A.; Walecki, D.; Salamon, S.; Bali, R.; Potzger, K.; Cornelius, S.; Liedke, M. O.; Lindner, J.; Wende, H.;
The phenomenon of chemical disorder-induced magnetism in the bulk FeAl system is known for decades [e.g. Ref.1] and has been intensively studied by Mössbauer spectroscopy. The majority of literature reports are dedicated to studies of ball-milled FeAl alloys of different stoichiometry that exhibit a hyperfine field splitting depending on the milling time and temperature. Nowadays it is possible to create such a disorder in a much more controlled and delicate manner also in thin films: the ion beam irradiation technique allows to effectively vary the number of Fe nearest-neighbors and interatomic distances by increasing either the ion energy or the irradiation dose.
Fe60Al40 (40nm and 250nm)/SiO2/Si thin films have been prepared by magnetron sputtering with further annealing and 20 keV Ne+ irradiation as reported in [2]. XRD scans demonstrate that the irradiation destroys the chemical ordering but preserves the structural integrity. MOKE and VSM magnetometry measurements confirm that chemically disordered films (A2 phase) are clearly ferromagnetic contrary to the annealed ones (B2 phase).
CEMS studies of as-prepared, annealed and irradiated thin films of 40nm were performed at room and low (80K) temperatures in normal or “magic angle” incidence geometry. The evident paramagnetic-ferromagnetic phase transition is shown in Fig.1: the experimental single line from an annealed sample (B2 phase) is replaced by a sextet with a hyperfine field distribution from the irradiated one (A2 phase). Measurements performed at 80K revealed further transformation of the subspectra: the subspectrum related to the paramagnetic phase almost vanishes while the subspectrum related to the ferromagnetic phase exhibits an enlarged hyperfine field splitting. Such a behavior may be attributed to the enhanced contribution of ferromagnetic Fe-rich areas in the sample [as in Ref. 3] that could have different Curie temperatures below RT. For 250nm thick samples annealed at 500°C or 1000°C, the parameters of the CEMS subspectra (isomer shifts, quadrupole splitting and doublet intensity ratio) obtained within a model suggested in [4] could be interpreted as an indication of different amounts of thermal vacancies in the samples studied. A comparison of results from CEMS and X-ray element-specific spectroscopy is in progress and will be reported.
[1] G. P. Huffman et al., J.Appl. Phys. 38, 735 (1967).
[2] R. Bali et al, Nano Lett. 14, 435 (2014).
[3] L. Zamora et al., Phys. Rev. B 79, 094418 (2009).
[4] J. Bogner et al., Phys. Rev. B 58, 14922 (1998).
  • Poster
    The International Conference on the Applications of the Mössbauer Effect (ICAME), 13.-18.09.2015, Hamburg, Deutschland

Publ.-Id: 23184 - Permalink

Electron beam final focus system for Thomson scattering
Krämer, J.; Jochmann, A.; Lehnert, U.; Budde, M.; Irman, A.; Schramm, U.;
Electron beam final focus system for Thomson scattering experiments is presented.
  • Poster
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola, Isola d'Elba, Italia

Publ.-Id: 23183 - Permalink

Developing the current experimental research into laser acceleration to a pre-commercial level
Krämer, J.; Lehnert, U.; Irman, A.; Budde, M.; Schramm, U.;
One of the main challenges in the field of laser acceleration is the beam transport of laser accelerated beams with a large energy spread. The same applies to a final focus system (FFS) for the high-flux laser-Thomson x-ray source at the conventional electron accelerator ELBE, where beams are chirped for longitudinal bunch compression. We found a telescope system consisting of four permanent quadrupole magnets to address the energy spread significantly better than a quadrupole triplet. We present the design of the system, magnet test results and emittance measurements at the interaction point.
  • Lecture (Conference)
    Laser Applications at Accelerators, 24.-27.03.2015, Palmanova, Spain

Publ.-Id: 23182 - Permalink

Linear and nonlinear Thomson scattering from the PHOENIX xray source
Krämer, J.; Jochmann, A.; Couperus, J. P.; Köhler, A.; Zarini, O.; Pausch, R.; Debus, A.; Wagner, A.; Lehnert, U.; Budde, M.; Bødker, F.; Kristensen, J.; Michel, P.; Irman, A.; Schramm, U.;
Development of advanced x-ray sources based on the laser-Thomson scattering mechanism is becoming important pushed by a strong demand for ultrashort hard x-ray pulses. These can serve as a tool for structural analysis of complex systems with unprecedented temporal and spatial resolution. We explored the spectral shape and bandwidth of the x-ray beam as a result from the interaction of electron and laser beam. The intensity dependence of the backscattered photon spectrum is investigated and compared to full-physics 3D ab-initio simulations. The realization of a non-linear Thomson scattering source qualifies as an initial step towards strong field physics research.
  • Lecture (Conference)
    International Conference on Extreme Light (ICEL), 23.-27.11.2015, Bucharest, Romania
  • Lecture (Conference)
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola,Isola d'Elba, Italia

Publ.-Id: 23181 - Permalink

Radiobiological characterization of laser driven particles
Beyreuther, E.; Baumann, M.; Brüchner, K.; Cowan, T.; Gotz, M.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schmidt, M.; Schramm, U.; Schürer, M.; Pawelke, J.;
The long-term aim of developing laser based particle acceleration towards clinical application requires not only substantial technological progress, but also new technical solutions for dose delivery and quality assurance as well as comprehensive research on the radiobiological consequences of ultra-short radiation pulses with high pulse dose.
During the last years the laser driven technology was developed at such a rate that cell samples and small animals can be irradiated. Within the joint research project “onCOOPtics” extensive in vitro studies with several human tumor and normal tissue cells were already performed revealing comparable radiobiological effects of laser driven and conventional electron and proton beams1,2. Using the same cell lines, these results were substantiated comparing the radiobiological response to ultra-short pulsed electron bunches (pulse dose rates of ≤1012 Gy/min) and continuous electron delivery at the radiation source ELBE3.
In a second translational step, in vivo experiments were established. Although the experiments were motivated by future proton trials, first attempts were performed with electrons at the laser system JETI4, since the delivery of prescribed homogeneous doses to a 3D target volume is easier for electrons than for protons. A full scale animal experiment was realized for the HNSCC FaDu grown on nude mice ear. The radiation induced tumor growth delay was determined and compared to those obtained after similar treatment at a conventional clinical LINAC. Again, no significant difference in the radiation response to both radiation qualities was revealed, whereas the successful performance of such a comprehensive experiment campaign underlines the stability and reproducibility of all implemented methods and setup components5.
During this experiment campaign the changing tumour take rate and a high rate of secondary tumours were identified as limitations of the model that have to be improved before proton experiments and tumour control studies can be performed. In order to optimize the model Matrigel as medium for tumor cell injection and the glioblastoma cell line LN229 as interesting entity for proton treatment were introduced. Results of this optimization process and the status of the experiments with laser driven protons at the laser system DRACO will be presented.
The work was supported by the German Government, Federal Ministry of Education and Research, grant nos. 03ZIK445 and 03Z1N511.

1Laschinsky L, Baumann M, Beyreuther E, Enghardt W, Kaluza M et al. (2012) Radiobiological effectiveness of laser accelerated electrons in comparison to electron beams from a conventional linear accelerator. J. Radiat. Res. 53(3): 395-403.
2Zeil K, Baumann M, Beyreuther E, Burris-Mog T, Cowan TE et al. (2012) Dose-controlled irradiation of cancer cells with laser-accelerated proton pulses. Appl. Phys. B 110(4): 437-444.
3Beyreuther E, Karsch L, Laschinsky L, Leßmann E, Naumburger D et al. (2015) Radiobiological response to ultra-short pulsed megavoltage electron beams of ultra-high pulse dose rate. Int. J. Radiat. Biol. 91(8): 643-652.
4Brüchner K, Beyreuther E, Baumann M, Krause M, Oppelt M et al. (2014) Establishment of a small animal tumour model for in vivo studies with low energy laser accelerated particles. Radiat. Oncol. 9(1): 57.
5Oppelt M, Baumann M, Bergmann R, Beyreuther E, Brüchner K et al. (2015) Comparison study of in vivo dose response to laser-driven versus conventional electron beam. Radiat. Environ. Biophys. 54(2): 155-166.
  • Lecture (Conference)
    ELIMEDICS Workshop, 03.-04.03.2016, Prag, Tschechische Republik
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine & Radiation Therapy 7(2016)4, 56
    DOI: 10.4172/2155-9619.C1.005

Publ.-Id: 23179 - Permalink

Geochemical transfer and preliminary health risk assessment of thallium in a riverine system in the Pearl River Basin, South China
Liu, J.; Wang, J.; Chen, Y.; Lippold, H.; Xiao, T.; Li, H.; Shen, C.-C.; Xie, L.; Xie, X.; Yang, H.;
Thallium is a highly toxic element, whose geochemical dispersion, transfer and potential health risks in aquatic systems are far from understood. This study aims to investigate the distribution of Tl in the surface water from an ultra-large Tl-bearing pyrite open-mining site and its associated riverine system of Yunfu city, western of the Pearl River Basin (PRB). Concentrations of 2.75–194.4 μg/L of Tl were found in the surface water from the mining site. Compared with other trace metals measured (Al, As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn), Tl experienced little precipitation by conventional lime-dosing treatment of mine water and readily moved through the river trace. The distribution of Tl in the river watershed during both the dry season (Tl: 0.01–9.15 μg/L) and wet season (Tl: 0.03–1.92 μg/L) generally followed a decreasing concentration pattern downstream of the pyrite mining site for the upper and middle reaches. However, some unexpected Tl elevations were observed in the lower reaches. Concentrations of Tl correlated well with concentrations of Ca, Mn, Sr, sulfate, total dissolved solids and water conductivity values for both the dry season and the wet season. Finally, health risk assessment suggests that Tl may pose non-carginogenic health risks to local residents over a long time. This study highlights not only anthropogenically-induced but also hidden naturally-occurring Tl enrichment in the hydrosphere of the PRB, and enhances the understanding of aqueous geochemistry of Tl.
Keywords: thallium; water safety; pyrite; health risk assessment; trace metal

Publ.-Id: 23178 - Permalink

Glutamic acid leaching of synthetic covellite – A model system combining experimental data and geochemical modeling
Barthen, R.; Karimzadeh, L.; Gründig, M.; Grenzer, J.; Lippold, H.; Franke, K.; Lippmann-Pipke, J.;
For Kupferschiefer mining established pyrometallurgical and acidic bioleaching methods face numerous problems. This is due to the finely grained and dispersed distribution of the copper minerals, the complex mineralogy, comparably low copper content, and the possibly high carbonate and organic content in this ore. Leaching at neutral pH seemed worth a try: At neutral pH the abundant carbonates do not need to be dissolved and therewith would not consume excessive amounts of provided acids. Certainly, copper solubility at neutral pH is reduced compared to an acidic environment; however, if copper complexing ligands would be supplied abundantly, copper contents in the mobile phase could easily reach the required economic level. We set up a model system to study the effect of parameters such as pH, microorganisms, microbial metabolites, and organic ligands on covellite leaching to get a better understanding of the processes in copper leaching at pH ≥ 6. With this model system we could show that glutamic acid and the microbial siderophore desferrioxamine B promote covellite dissolution. Both experimental and modeling data showed that pH is an important parameter in covellite dissolution. An increase of pH from 6 to 9 could elevate copper extraction in the presence of glutamic acid by a factor of five. These results have implications for both development of a biotechnological process regarding metal extraction from Kupferschiefer, and for the interaction of bacterial metabolites with the lithosphere and potential mobilization of heavy metals in alkaline environments.
Keywords: Covellite; Glutamic acid; Desferrioxamine B; Modeling; Neutrophilic bioleaching; Copper

Publ.-Id: 23177 - Permalink

Thallium transformation and partitioning during Pb-Zn smelting and environmental implications
Liu, J.; Wang, J.; Chen, Y.; Xie, X.; Qi, J.; Lippold, H.; Luo, D.; Wang, C.; Su, L.; He, L.; Wu, Q.;
Thallium (Tl) is a toxic and non-essential heavy metal. Raw Pb-Zn ores and solid smelting wastes from a large Pb-Zn smelting plant - a typical thallium pollution source in South China, were investigated in terms of Tl distribution and fractionation. A modified IRMM (Institute for Reference Materials and Measurement, Europe) sequential extraction scheme was applied on the samples in order to uncover the geochemical behavior and transformation of Tl during Pb-Zn smelting and to assess the potential environmental risk of Tl arising from this plant. Results showed that the Pb-Zn ore materials were relatively enriched with Tl (15.1-87.7 mg kg−1), while even higher accumulation existed in the electrostatic dust (3280-4050 mg kg−1) and acidic waste (13300 mg kg−1). A comparison of Tl concentration and fraction distribution in different samples clearly demonstrated the significant role of the ore roasting in Tl transformation and mobilization, probably as a result of alteration/decomposition of related minerals followed by Tl release and subsequent deposition/co-precipitation on fine surface particles of the electrostatic dust and acidic waste. While only 10-30% of total Tl amounts was associated with the exchangeable/acid-extractable fraction of the Pb-Zn ore materials, up to 90% of total Tl was found in this fraction of the electrostatic dust and acidic waste. Taking into account the mobility and bioavailability of this fraction, these waste forms may pose significant environmental risk.
Keywords: thallium fraction; Pb-Zn smelting; electrostatic dust; acidic waste; IRMM sequential extraction

Publ.-Id: 23176 - Permalink

Al in ZnO - From doping to alloying: An investigation of Al electrical activation in relation to structure and charge transport limits
Cornelius, S.; Vinnichenko, M.;
The electrical activation of Al in ZnO thin films grown by pulsed reactive magnetron sputtering is quantified experimentally for a wide range of Al concentrations. We find that the activation does not exceed 35% remaining constant for growth temperatures below a certain optimum value at which the highest free electron density and mobility are achieved. Above this temperature, the Al activation decreases rapidly, while Al is accumulating in the films and their micro-structure as well as electrical properties deteriorate significantly. The analysis of possible mechanisms of Al deactivation suggests that the observed effects may be explained only by considering Al doped ZnO as metastable solid solution showing a tendency to segregation of Al into secondary phases
Keywords: Sputtering; Transparent conductive oxide

Publ.-Id: 23175 - Permalink

Neue Lasermaterialien für Petawatt – Laser: Anforderungen und Erkenntnisstand
Röser, F.; Löser, M.; Albach, D.; Siebold, M.; Schramm, U.;
  • Lecture (others)
    2. Projekttreffen des VP5 „Hochreine Gläser“ im Rahmen des Wachstumskerns Pades, 04.03.2015, Dresden, Deutschland

Publ.-Id: 23174 - Permalink

Laserlab Europe – ILAT kick-off
Siebold, M.; Röser, F.; Löser, M.; Albach, D.; Harzendorf, G.; Nehring, H.; Eiselt, P.; Schramm, U.;
Laserlab Europe – ILAT kick-off presentation HZDR
  • Lecture (others)
    Laserlab Europe, 24.11.2015, Mailand, Italien

Publ.-Id: 23173 - Permalink

Stereotactic radiotherapy augments the immune response / Die stereotaktische Strahlentherapie unterstützt die Immunantwort
Troost, E. G. C.;
there ist no abstract

Publ.-Id: 23172 - Permalink

Plug Transfer System for GaAs Photocathodes
Murcek, P.; Arnold, A.; Teichert, J.; Xiang, R.; Burrill, A.;
The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.
Keywords: SRf gun, photo injector, GaAs photo cathode
  • Poster
    17th International Conference on RF Superconductivity SRF 2015, 13.-18.09.2015, Whistler, Canada

Publ.-Id: 23171 - Permalink

Preclinical Assessment of Efficacy of Radiation Dose Painting Based on Intratumoral FDG-PET Uptake.
Trani, D.; Yaromina, A.; Dubois, L.; Granzier, M.; Peeters, S. G.; Biemans, R.; Nalbantov, G.; Lieuwes, N.; Reniers, B.; Troost, E. G. C.; Verhaegen, F.; Lambin, P.;

We tested therapeutic efficacy of two dose painting strategies of applying higher radiation dose to tumor subvolumes with high FDG uptake (biologic target volume, BTV): dose escalation and dose redistribution. We also investigated whether tumor response was determined by the highest dose in BTV or the lowest dose in gross tumor volume (GTV).

FDG uptake was evaluated in rat rhabdomyosarcomas prior to irradiation. BTV was defined as 30% of GTV with the highest (BTVhot) or lowest (BTVcold) uptake. To test efficacy of dose escalation, tumor response (time to reach two times starting tumor volume, TGTV2) to Hot Boost irradiation (40% higher dose to BTVhot) was compared with Cold Boost (40% higher dose to BTVcold), while mean dose to GTV remained 12 Gy. To test efficacy of dose redistribution, TGTV2 after Hot Boost was compared with uniform irradiation with the same mean dose (8 or 12 Gy).

TGTV2 after 12 Gy delivered heterogeneously (Hot and Cold Boost) or uniformly were not significantly different: 20.2, 19.5, and 20.6 days, respectively. Dose redistribution (Hot Boost) with 8 Gy resulted in faster tumor regrowth as compared with uniform irradiation (13.3 vs. 17.1 days; P = 0.026). Further increase in dose gradient to 60% led to a more pronounced decrease in TGTV2 (10.9 days; P < 0.0001).

Dose escalation effect was independent of FDG uptake in target tumor volume, while dose redistribution was detrimental in this tumor model for dose levels applied here. Our data are consistent with the hypothesis that tumor response depends on the minimum intratumoral dose. Clin Cancer Res; 21(24); 5511-8. ©2015 AACR.

Publ.-Id: 23170 - Permalink

HPV and beyond-looking out for biomarkers for distinguishing the good prognosis from the bad prognosis group in locally advanced and clinically high risk HNSCC.
Lohaus, F.; Linge, A.; Baumann, M.;
There is no abstract

Publ.-Id: 23169 - Permalink

Annual Report 2015 Institute of Resource Ecology
Stumpf, T.; Foerstendorf, H.; Bok, F.; Richter, A.; (Editors)
The Institute of REsource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”...
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-067 2016
    ISSN: 2121-8708


Publ.-Id: 23168 - Permalink

Cancer stem cell related markers of radioresistance in head and neck squamous cell carcinoma.
Kurth, I.; Hein, L.; Mäbert, K.; Peitzsch, C.; Koi, L.; Cojoc, M.; Kunz-Schughart, L.; Baumann, M.; Dubrovska, A.;
Despite recent advances in understanding of the molecular pathogenesis and improvement of treatment techniques, locally advanced head and neck squamous cell carcinoma (HNSCC) remains associated with an unfavorable prognosis. Compelling evidence suggests that cancer stem cells (CSC) may cause tumor recurrence if they are not eradicated by current therapies as radiotherapy or radio-chemotherapy. Recent in vitro studies have demonstrated that CSCs may be protected from treatment-induced death by multiple intrinsic and extrinsic mechanisms. Therefore, early determination of CSC abundance in tumor biopsies prior-treatment and development of therapeutics, which specifically target CSCs, are promising strategies to optimize treatment. Here we provide evidence that aldehyde dehydrogenase (ALDH) activity is indicative for radioresistant HNSCC CSCs. Our study suggests that ALDH+ cells comprise a population that maintains its tumorigenic properties in vivo after irradiation and may provide tumor regrowth after therapy. We found that ALDH activity in HNSCC cells can be attributed, at least in part, to the ALDH1A3 isoform and inhibition of the ALDH1A3 expression by small interfering RNA (siRNA) decreases tumor cell radioresistance. The expression dynamic of ALDH1A3 upon irradiation by either induction or selection of the ALDH1A3 positive population correlates to in vivo curability, suggesting that changes in protein expression during radiotherapy are indicative for tumor radioresistance. Our data indicate that ALDH1A3+ HNSCC cells may contribute to tumor relapse after irradiation, and inhibition of this cell population might improve therapeutic response to radiotherapy.
Keywords: aldehyde dehydrogenase; cancer stem cells; head and neck squamous cell carcinoma (HNSCC); radioresistance

Publ.-Id: 23167 - Permalink

Acceleration of volume decomposition of supersaturated Al+4 wt.% Cu solid solution under irradiation with Ar+ ions
Gushchina, N. V.; Ovchinnikov, V. V.; Mücklich, A.;
Effect of irradiation with Ar+ ions on the decomposition processes of model precipitation-hardening alloy Al+4wt.% Cu has been studied. Using X-ray diffraction, high-resolution electron microscopy methods and micro hardness measurements, it was established, that, already at low temperatures (T<60°C), ion irradiation causes accelerated decomposition of solid solution, with precipitation of θ′- and θ-phase particles at a depth greatly exceeding the Ar+ ions projected range.
Keywords: Aluminum alloy; Ion irradiation; Long-range effect; Supersaturated solid solution decomposition

Publ.-Id: 23166 - Permalink

Global Task Force on Radiotherapy for Cancer Control.
Jaffray, D. A.; Knaul, F. M.; Atun, R.; Adams, C.; Barton, M. B.; Baumann, M.; Lievens, Y.; Lui, T. Y.; Rodin, D. L.; Rosenblatt, E.; Torode, J.; van Dyk, J.; Vikram, B.; Gospodarowicz, M.;
there is no abstract

Publ.-Id: 23165 - Permalink

SRF Gun Characterization – Phase Space and Dark Current Measurement at ELBE
Panofski, E.; Jankowiak, A.; Kamps, T.; Lu, P.; Teichert, J.;
RF photoelectron sources with superconducting cavities provide the potential to generate high quality, high brightness electron beams for future accelerator applications. At Helmholtz-Zentrum Dresden Rossendorf, such an electron source was operated for many years. The commissioning of an improved SRF Gun with a new high-performance gun cavity with low field emission and a superconducting solenoid inside the gun cryomodule (SRF Gun II) has started in June 2014. Simulations of the experimental set-up with ASTRA and ELEGANT were performed. First low current measurements as well as studies of unwanted beam transport using SRF Gun II with Cu photocathode and an acceleration gradient up to 9 MV/m will be presented. First beam characterization of the SRF Gun in combination with ELBE, a two-stage superconducting linear accelerator will be discussed.
Keywords: electron source, SRF gun, photo injector, superconducting RF
  • Poster
    International Beam Instrumentation Conference IBIC2015, 13.-17.09.2015, Melbourne, Australia
  • Open Access LogoContribution to proceedings
    International Beam Instrumentation Conference IBIC2015, 13.-17.09.2015, Melbourne, Australia
    Proceedings of the IBIC 2015: Jacow

Publ.-Id: 23164 - Permalink

Increased evidence for the prognostic value of primary tumor asphericity in pretherapeutic FDG PET for risk stratification in patients with head and neck cancer.
Hofheinz, F.; Lougovski, A.; Zöphel, K.; Hentschel, M.; Steffen, I. G.; Apostolova, I.; Wedel, F.; Buchert, R.; Baumann, M.; Brenner, W.; Kotzerke, J.; van den Hoff, J.;

In a previous study, we demonstrated the first evidence that the asphericity (ASP) of pretherapeutic FDG uptake in the primary tumor provides independent prognostic information in patients with head and neck cancer. The aim of this work was to confirm these results in an independent patient group examined at a different site.

FDG-PET/CT was performed in 37 patients. The primary tumor was delineated by an automatic algorithm based on adaptive thresholding. For the resulting ROIs, the metabolically active part of the tumor (MTV), SUVmax, SUVmean, total lesion glycolysis (TLG) and ASP were computed. Univariate Cox regression with respect to progression free survival (PFS) and overall survival (OS) was performed. For survival analysis, patients were divided in groups of high and low risk according to the parameter cut-offs defined in our previous work. In a second step, the cut-offs were adjusted to the present data. Univariate and multivariate Cox regression was performed for the pooled data consisting of the current and the previously described patient group (N = 68). In multivariate Cox regression, clinically relevant parameters were included.

Univariate Cox regression using the previously published cut-off values revealed TLG (hazard ratio (HR) = 3) and ASP (HR = 3) as significant predictors for PFS. For OS MTV (HR = 2.7) and ASP (HR = 5.9) were significant predictors. Using the adjusted cutoffs MTV (HR = 2.9/3.3), TLG (HR = 3.1/3.3) and ASP (HR = 3.1/5.9) were prognostic for PFS/OS. In the pooled data, multivariate Cox regression revealed a significant prognostic value with respect to PFS/OS for MTV (HR = 2.3/2.1), SUVmax (HR = 2.1/2.5), TLG (HR = 3.5/3.6), and ASP (HR = 3.4/4.4).

Our results confirm the independent prognostic value of ASP of the pretherapeutic FDG uptake in the primary tumor in patients with head and neck cancer. Moreover, these results demonstrate that ASP can be determined unambiguously across different sites.

Publ.-Id: 23163 - Permalink

Proton therapy of pediatric rhabdomyosarcoma: Same tumor control as photon therapy, with less adverse effects / Protonentherapie von Rhabdomyosarkompatienten im Kindesalter: Gleiche lokale Tumorkontrolle wie bei Photonentherapie mit weniger Nebenwirkungen
Gurtner, K.; Baumann, M.;
there is no abstract

Publ.-Id: 23162 - Permalink

Comprehensive analysis of signal transduction in three-dimensional ECM-based tumor cell cultures.
Eke, I.; Hehlgans, S.; Zong, Y.; Cordes, N.;
Analysis of signal transduction and protein phosphorylation is fundamental to understanding physiological and pathological cell behavior and identifying novel therapeutic targets. Despite the fact that the use of physiological three-dimensional cell culture assays is increasing, 3D proteomics and phosphoproteomics remain challenging due to difficulties with easy, robust and reproducible sample preparation. Here, we present an easy-to-perform, reliable and time-efficient method for the production of 3D cell lysates that does not compromise cell adhesion before cell lysis. The samples can be used for western blotting as well as phosphoproteome array technology. This technique will be of interest for researchers working in all fields of biology and drug development.
Keywords: 3D cell culture; extracellular matrix; phosphoproteomics; protein analysis; signaling

Publ.-Id: 23161 - Permalink

Cell-ECM interactions control DDR
Dickreuter, E.; Cordes, N.;
there ist no abstract
Keywords: KEYWORDS: DNA repair; cell-ecm interactions; integrins
  • Open Access LogoOncoscience 2(2015)8, 679-680

Publ.-Id: 23160 - Permalink

Hyperfractionated accelerated radiation therapy (HART) of 70.6 Gy with concurrent 5-FU/Mitomycin C is superior to HART of 77.6 Gy alone in locally advanced head and neck cancer: long-term results of the ARO 95-06 randomized phase III trial.
Budach, V.; Stromberger, C.; Poettgen, C.; Baumann, M.; Budach, W.; Grabenbauer, G.; Marnitz, S.; Olze, H.; Wernecke, K. D.; Ghadjar, P.;

To report the long-term results of the ARO 95-06 randomized trial comparing hyperfractionated accelerated chemoradiation with mitomycin C/5-fluorouracil (C-HART) with hyperfractionated accelerated radiation therapy (HART) alone in locally advanced head and neck cancer.

The primary endpoint was locoregional control (LRC). Three hundred eighty-four patients with stage III (6%) and IV (94%) oropharyngeal (59.4%), hypopharyngeal (32.3%), and oral cavity (8.3%) cancer were randomly assigned to 30 Gy/2 Gy daily followed by twice-daily 1.4 Gy to a total of 70.6 Gy concurrently with mitomycin C/5-FU (C-HART) or 16 Gy/2 Gy daily followed by twice-daily 1.4 Gy to a total dose of 77.6 Gy alone (HART). Statistical analyses were done with the log-rank test and univariate and multivariate Cox regression analyses.

The median follow-up time was 8.7 years (95% confidence interval [CI]: 7.8-9.7 years). At 10 years, the LRC rates were 38.0% (C-HART) versus 26.0% (HART, P=.002). The cancer-specific survival and overall survival rates were 39% and 10% (C-HART) versus 30.0% and 9% (HART, P=.042 and P=.049), respectively. According to multivariate Cox regression analysis, the combined treatment was associated with improved LRC (hazard ratio [HR]: 0.6 [95% CI: 0.5-0.8; P=.002]). The association between combined treatment arm and increased LRC appeared to be limited to oropharyngeal cancer (P=.003) as compared with hypopharyngeal or oral cavity cancer (P=.264).

C-HART remains superior to HART in terms of LRC. However, this effect may be limited to oropharyngeal cancer patients.

Publ.-Id: 23159 - Permalink

Quantifying the Kelvin-Helmholtz instability in interstellar jets with radiation observable on Earth
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present a new diagnostic method to both identify the presence of the Kelvin-Helmholtz instability (KHI) in interstellar plasma jets and determine its growth rate by measuring the emitted radiation.

Based on the electron dynamics inside the KHI vortices, we derive the emitted radiation power and polarization and show their correlation to the magnetic field evolution, driving the instability. These correlations are verified against simulations of the relativistic KHI using the 3D3V particle-in-cell code PIConGPU. It determines the angularly resolved radiation spectra for billions of electrons using generally valid Liénard-Wiechert potentials. The simulation shows that the growth rate correlation between radiation power and magnetic field agrees over orders of magnitude for the entire linear phase of the KHI while the polarization signature allows a clear identification of this phase.

The method presented can resolve the question whether the KHI occurs in astro-physical particle jets and furthermore provides quantitative insides to the jet dynamics by analyzing the radiation observable on Earth.
Keywords: KHI, radiation, PIConGPU, spectra, polarization, interstellar jets
  • Lecture (Conference)
    DPG-Frühjahrstagung, 29.02.-04.03.2016, Hamburg, Deutschland

Publ.-Id: 23158 - Permalink

Expanding global access to radiotherapy
Atun, R.; Jaffray, D. A.; Barton, M. B.; Bray, F.; Baumann, M.; Vikram, B.; Hanna, T. P.; Knaul, F. M.; Lievens, Y.; Lui, T. Y.; Milosevic, M.; O'Sullivan, B.; Rodin, D. L.; Rosenblatt, E.; van Dyk, J.; Yap, M. L.; Zubizarreta, E.; Gospodarowicz, M.;
Radiotherapy is a critical and inseparable component of comprehensive cancer treatment and care. For many of the most common cancers in low-income and middle-income countries, radiotherapy is essential for effective treatment. In high-income countries, radiotherapy is used in more than half of all cases of cancer to cure localised disease, palliate symptoms, and control disease in incurable cancers. Yet, in planning and building treatment capacity for cancer, radiotherapy is frequently the last resource to be considered. Consequently, worldwide access to radiotherapy is unacceptably low. We present a new body of evidence that quantifies the worldwide coverage of radiotherapy services by country. We show the shortfall in access to radiotherapy by country and globally for 2015-35 based on current and projected need, and show substantial health and economic benefits to investing in radiotherapy. The cost of scaling up radiotherapy in the nominal model in 2015-35 is US$26·6 billion in low-income countries, $62·6 billion in lower-middle-income countries, and $94·8 billion in upper-middle-income countries, which amounts to $184·0 billion across all low-income and middle-income countries. In the efficiency model the costs were lower: $14·1 billion in low-income, $33·3 billion in lower-middle-income, and $49·4 billion in upper-middle-income countries-a total of $96·8 billion. Scale-up of radiotherapy capacity in 2015-35 from current levels could lead to saving of 26·9 million life-years in low-income and middle-income countries over the lifetime of the patients who received treatment. The economic benefits of investment in radiotherapy are very substantial. Using the nominal cost model could produce a net benefit of $278·1 billion in 2015-35 ($265·2 million in low-income countries, $38·5 billion in lower-middle-income countries, and $239·3 billion in upper-middle-income countries). Investment in the efficiency model would produce in the same period an even greater total benefit of $365·4 billion ($12·8 billion in low-income countries, $67·7 billion in lower-middle-income countries, and $284·7 billion in upper-middle-income countries). The returns, by the human-capital approach, are projected to be less with the nominal cost model, amounting to $16·9 billion in 2015-35 (-$14·9 billion in low-income countries; -$18·7 billion in lower-middle-income countries, and $50·5 billion in upper-middle-income countries). The returns with the efficiency model were projected to be greater, however, amounting to $104·2 billion (-$2·4 billion in low-income countries, $10·7 billion in lower-middle-income countries, and $95·9 billion in upper-middle-income countries). Our results provide compelling evidence that investment in radiotherapy not only enables treatment of large numbers of cancer cases to save lives, but also brings positive economic benefits.

Publ.-Id: 23157 - Permalink

First beam characterization of SRF gun II at ELBE with a Cu photocathode
Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.;
An improved SRF gun has been installed and commissioned at HZDR since 2014. This new gun replaces the first SRF gun at the superconducting linear accelerator ELBE which had been in operation since 2007. The new SRF gun II has an improved 3.5-cell niobium cavity and a superconducting solenoid inside the gun cryostat. The gun has been tested first with a Cu photocathode. Using the standard high repetition rate laser system, this allows low bunch charge beams of a few pC only. The beam parameters for these low charges have been measured, and the first beam has been guided into the ELBE accelerator. Since 2015 the photocathode transfer system is installed for future use of Cs2Te photocathodes with high quantum efficiency photocathodes.
Keywords: electron source, photo injector, photo cathode, superconducting RF
  • Invited lecture (Conferences)
    Workshop on Energy Recovery Linacs (ERL2015), 07.-12.06.2015, Stony Brook, USA
  • Open Access LogoContribution to proceedings
    Workshop on Energy Recovery Linacs (ERL2015), 07.-12.06.2015, Stony Brook, USA
    Proceedings of the ERL 2015: Jacow

Publ.-Id: 23156 - Permalink

Synthetic radiation diagnostics in PIConGPU - integrating spectral detectors into particle-in-cell codes
Pausch, R.; Debus, A.; Burau, H.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present the in-situ far field radiation diagnostics in the particle-in-cell code PIConGPU. It was developed to close the gap between simulated plasma dynamics and radiation observed in laser plasma experiments. Its predictive capabilities, both qualitative and quantitative, have been tested against analytical models. Now, we apply this synthetic spectral diagnostics to investigate plasma dynamics in laser wakefield acceleration, laser foil irradiation and plasma instabilities.

Our method is based on the far field approximation of the Liénard-Wiechert potential and allows predicting both coherent and incoherent radiation spectrally from infrared to x-rays. Its capability to resolve the radiation polarization and to determine the temporal and spatial origin of the radiation enables us to correlate specific spectral signatures with characteristic dynamics in the plasma. Furthermore, its direct integration into the highly-scalable GPU framework of PIConGPU allows computing radiation spectra for thousands of frequencies, hundreds of detector positions and billions of particles efficiently.

In this talk we will demonstrate these capabilities on resent simulations of laser wakefield acceleration (LWFA) and high harmonics generation during target normal sheath acceleration (TNSA).
Keywords: PIConGPU, radiation, LWFA, TNSA, HHG, synthetic diagnostics, spectra
  • Lecture (Conference)
    DPG-Frühjahrstagung, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23155 - Permalink

Laser Cooling of Relativistic Ion Beams at FAIR. From ESR to SIS100 and HESR
Bussmann, M.; Löser, M.; Seltmann, M.; Siebold, M.; Schramm, U.; Beck, T.; Rein, B.; Walther, T.; Tichelmann, S.; Birkl, G.; Sanchez-Alarcon, R.; Ullmann, J.; Lochmann, M.; Nörtershäuser, W.; Eidam, L.; Boine-Frankenheim, O.; Winters, D.; Kozhuharov, C.; Sanjari, S.; Litvinov, Y.; Giacomini, T.; Steck, M.; Dimopoulou, C.; Nolden, F.; Shevelko, S.; Stöhlker, T.; Spiller, P.; Wen, W.; Yang, J.; Zhang, D.; Ma, X.; Hannen, V.;
We present recent results and future perspectives on laser cooling of relativistic storage beams
Keywords: laser cooling, storage ring, relativistic, ion beam
  • Invited lecture (Conferences)
    Kick-off Meeting für APPA-Verbundforschung, 14.-15.01.2016, Darmstadt, Deutschland

Publ.-Id: 23154 - Permalink

The Power of Performant Code Abstraction in Real World HPC Applications
Bussmann, M.; Eckert, C.; Huebl, A.; Jung, F.; Widera, R.; Zacharias, M.; Zenker, E.;
Many-core architectures are going to stay for a while. Thus, scaling real world applications on HPC systems with thousands of nodes and hybrid architectures will be important to application developers. We present two real world applications, plasma simulations and high repetition rate data analysis, that strongly benefit from speed ups seen with accelerator hardware. From our viewpoint as users with real-world problems we discuss our path towards scalable, hardware-independent, performant application codes. Our focus is not to reinvent the wheel, but to make full use of the power of existing C++ codes by fully abstracting all parts of a code that require optimization, separating concepts used in the code from their optimized implementation. We do this by providing light-weight, single-purpose, zero-overhead interfaces to central code components. In the talk I will discuss our experiences with this approach, the reusable interfaces that have come out of this and the vision behind putting everything together.
Keywords: many core, picongpu, simulation, hpc
  • Invited lecture (Conferences)
    SPPEXA Annual Plenary Meeting, 25.-27.01.2016, Garching b. München, Deutschland

Publ.-Id: 23153 - Permalink

The fastest code in the field of laser-plasma physics
Döring, C;
Ultra fast, scalable and free of charge – what began as a “youth conducts research” project, is today one of the most powerful programme codes for calculations in the field of astrophysics and plasma physics.
Keywords: picongpu, laser plasma, cancer therapy, acceleration

Publ.-Id: 23152 - Permalink

Laser focus Simulations explore how a tumor-killing laser’s high-energy fields can rip matter apart.
Bussmann, M.;
Laser physicists are tantalizingly close to building a device that delivers highly focused beams of tumor-killing ionized particles and packing it in a compact unit that would fit in a doctor’s office. OncoRay, a research center in Dresden, Germany, is designing what would be the first prototype compact particle therapy units.
Keywords: cancer therapy, laser, simulation, picongpu

Publ.-Id: 23151 - Permalink

Hot electron currents in ultra-intense laser-solid interactions
Kluge, T.;
The generation and propagation of strong currents of laser-accelerated hot electrons in solid density foils is of importance in many applications such as resistive heating, generation of resistive magnetic fields and ion acceleration. We present results from particle-in-cell simulations for the scaling of hot electron currents in solids and demonstrate the importance of a full description of the currents with respect to its spectral distribution and spatio-temporal structure. Taking them into account, we derive analytic scalings from first principle conservation laws that as an input to models for heating, magnetic field generation or ion acceleration prove to be consistent with the simulations in contrast to simple expressions such as j=\gamma n_c.
  • Lecture (Conference)
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola, Italien

Publ.-Id: 23150 - Permalink

High Current LMIS for Ion Implanters and Single-ended Accelerators
Laufer, P.; Bock, D.; Pilz, W.; Bischoff, L.; Tajmar, M.;
An ion source module based on high current Liquid Metal Ion Sources (LMIS) will be presented for optional use of mon - or polyatomic ion currents of metallic or semiconducting elements [1, 2, 3]. Total emitted ion currents in the order of 100 µA can be reached which are formed to a nearly parallel ion beam of 2 mm diameter using an asymmetric ion-optical Einzel lens. fractions are in the range of per mil up to a few percent dependent on the emitted elements. A mass separation system (Wien filter) selects the desired ions while a quadrupole is used for beam adjustment. Few-atomic cluster ions are of interest to be implanted for an effective surface modification [4]. High cluster ion currents enable the formation of different nanostructures or even smooth surfaces over an area in cm2-range. The LMIS preparation and the performance of the ion beam module at certain experiments will be presented and discussed.
[1] M. Tajmar, et al., Ultramicroscopy 111 (2010) 1
[2] D. Bock, et. al., DPG Conference Dresden (2014) DS 17.6
[3] P. Laufer, et al., DPG Conference Berlin (2015) DS 19.9
[4] L. Bischoff, et al., Nucl. Instr. and Meth. B 272 (2012) 198
Keywords: Liquid Metal Ion Source, cluster ions, mass separation
  • Lecture (Conference)
    DPG Frühjahrstagung, 07.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23149 - Permalink

Nanometer-scale characterization of laser-driven plasmas, compression, shocks and phase transitions, by coherent small angle x-ray scattering
Kluge, T.;
Combining ultra-intense short-pulse and high-energy long-pulse lasers, with brilliant coherent hard X-ray FELs, such as the Helmholtz International Beamline for Extreme Fields (HIBEF) [1] under construction at the HED Instrument of European XFEL [2], or MEC at LCLS [3], holds the promise to revolutionize our understanding of many High Energy Density Physics phenomena. Examples include the relativistic electron generation, transport, and bulk plasma response [4], and ionization dynamics and heating [5] in relativistic laser-matter interactions, or the dynamics of laser-driven shocks, quasi-isentropic compression, and the kinetics of phase transitions at high pressure [3,6]. A particularly promising new technique is the use of coherent X-ray diffraction to characterize electron density correlations [4], and by resonant scattering to characterize the distribution of specific charge-state ions [5], either on the ultrafast time scale of the laser interaction, or associated with hydrodynamic motion. As well one can image slight density changes arising from phase transitions inside of shock-compressed high pressure matter. The feasibility of coherent diffraction techniques in laser-driven matter will be discussed. including recent results from demonstration experiments at MEC. Among other things, very sharp density changes from laser-driven compression are observed, having an effective step width of 10 nm or smaller. This compares to a resolution of several hundred
nm achieved previously [6] with phase contrast imaging.
[3] B. Nagler et al., J. Synchrotron Rad. 22, 520 (2015).
[4] T. Kluge et al, Phys. Plasmas 21, 033110 (2014).
[5] T. Kluge et al.,
[6] A. Schropp et al., Sci. Rep. 3, 1633 (2013).

Author T. Kluge on behalf of HIBEF User Consortium, for the Helmholtz International Beamline for Extreme Fields at the European XFEL.
  • Invited lecture (Conferences)
    57th Annual Meeting of the APS Division of Plasma Physics, 16.-20.11.2015, Savannah, GA, USA

Publ.-Id: 23148 - Permalink

Nanometer-scale characterization of laser-driven compression, shocks and phase transitions, by coherent x-ray diffraction
Kluge, T.; Rödel, C.; Rödel, M.; Pelka, A.; Mcbride, E.; Galtier, E.; Fletcher, L. B.; Lee, H. J.; Nagler, B.; Gutt, C.; Garcia, L.; Zeil, K.; Metzkes, J.; Obst, L.; Chung, H.-K.; Schropp, A.; Schroer, C.; Glenzer, S. H.; Schramm, U.; Cowan, T. E.;
Concept of solid plasma diagnostics with Small Angle X-ray Scattering, experimental feasibility of SAXS at femtosecond and nanosecond laser driven solid material, and beyond electron-electron correlations: Resonant SAXS for ion distribution measurements
  • Poster
    European XFEL User Meeting, 27.-29.01.2016, Hamburg, Deutschland

Publ.-Id: 23147 - Permalink

Proton and electron Irradiation in oxynitrided gate 4H-SiC MOSFET: A recent open issue
Michel, P.; Florentin, M.; Alexandru, M.; Constant, A.; Monserrat, J.; Millan, J.; Godignon, P.;
Long-term degradation of MOS devices has to be avoided in different harsh irradiated environments, especially for aerospace or military applications. In this paper, an overview of the irradiation experiments recently performed on 4H-SiC MOSFETs having an oxynitrided gate oxide is given, with a special focus on the threshold voltage and the effective channel mobility drifts. The general mechanisms taking place during irradiation and post-annealing treatments are described. Finally, new open issues recently observed by performing the temperature measurement on irradiated MOSFETs are introduced and discussed.
Keywords: Charge trapping; Electron; Irradiation; Mobility; Proton; SiC MOSFET; SiO2/SiC interface; Threshold voltage; Time bias stress instability
  • Contribution to proceedings
    European Conference on Silicon Carbide and Related Materials, ECSCRM 2014, Grenoble, France 21-25 September 2014, 21.-25.09.2014, Grenoble, France
    Materials Science Forum, Volume 821-823, 667-672
    DOI: 10.4028/

Publ.-Id: 23146 - Permalink

PET imaging for the monitoring of particle therapy: from GSI experience to new developments
Rohling, H.;
History and current challenges of PET for particle therapy with the focus on GSI experiences.
  • Invited lecture (Conferences)
    Arbeitstreffen Kernphysik, 19.-26.02.2015, Schleching / Oberbayern, Deutschland

Publ.-Id: 23145 - Permalink

Aqueous chemistry of tetravalent cerium (Ce(IV)): Characterisation of polymer and cluster complexes formed via hydrolysis
Ikeda-Ohno, A.;
Because of their high charge density, the aqueous chemistry of f-elements with lower valences (i.e. tri- and tetravalent) is predominantly controlled by strong hydrolysis producing a variety of hydroxide species. Interestingly enough, this strong hydrolysis often induces the intrinsic formation of polymer and nano-sized cluster complexes which are stable even in aqueous solutions. This talk will provide a recent overview of the hydrolysis-induced polymer/cluster formation of tetravalent f-elements, with a special focus on tetravalent cerium (Ce(IV)), primarily from the viewpoint of structural chemistry, as well as the associated characterisation techniques (e.g. X-ray absorption spectroscopy or X-ray scattering).
Keywords: Actinides, lanthanides, f-elements, tetravalent, aqueous chemistry, hydrolysis, characterisation, X-ray, synchrotron
  • Invited lecture (Conferences)
    Internal Scientific Seminar at Joint Research Centre - Institute for Transuranium Elements, 02.02.2016, JRC-ITU, Karlsruhe, Germany

Publ.-Id: 23144 - Permalink

Broadband(UV-VIS), Single-shot spectometer for fs electron bunches
Zarini, O.; Debus, A.; Köhler, A.; Couperus, J. P.; Seidel, W.; Irman, A.; Schramm, U.;
Broadband(UV-VIS), Single-shot spectometer for fs electron bunches is presented.
Keywords: Broadband(UV-VIS), Single-shot spectometer, electron bunch
  • Lecture (Conference)
    The 4.annual meeting of the LAOLA collaboration, 23.-24.06.2015, Wismer, Deutschland

Publ.-Id: 23143 - Permalink

Broadband (UV - mid-IR) spectrometer for single-shot femtosecond electron bunch duration measurement
Zarini, O.; Debus, A.; Couperus, J. P.; Köhler, A.; Jochmann, A.; Seidel, W.; Irman, A.; Schramm, U.;
Measurement of coherent transition radiation (CTR) spectra of ultrashort electron bunches from LWFA by using a high-resolution, broadband spectrometer for single-shot bunch duration measurements.
Keywords: broadband spectrometer, Single-shot bunch length measurement, coherent transition radiation, absolute calibration
  • Poster
    3rd ARD ST3 workshop, 15.-17.07.2015, Karlsruhe, Deutschland

Publ.-Id: 23142 - Permalink

Studies of a Proton Phase Beam Monitor for Range Verification in Proton Therapy
Werner, T.; Dreyer, A.; Golnik, C.; Hueso-Gonzalez, F.; Enghardt, W.; Straessner, A.; Petzoldt, J.; Roemer, K.; Pausch, G.; Kormoll, T.;
A primary subject of the present research in particle therapy is to ensure the precise irradiation of the target volume. The prompt gamma timing (PGT) method provides one possibility for in vivo range verification during the irradiation of patients. Prompt gamma rays with high energies are emitted promptly due to nuclear reactions of protons with tissue. The arrival time of these gammas to the detector reflects the stopping process of the primary protons in tissue and are directly correlated to the range. Due to the time resolution of the detector and the proton bunch time spread, as well as drifts of the bunch phase with respect to the accelerator frequency, timing spectra are smeared out and compromise the accuracy of range information intended for future clinical applications. Nevertheless, counteracting this limitation and recovering range information from the PGT measured spectra, corrections using a phase beam monitor can be performed. A first prototype of phase beam monitor was tested at GSI Darmstadt, where measurements of the energy profile of the ion bunches were performed. At the ELBE accelerator Helmholtz-Zentrum Dresden-Rossendorf (HZDR), set up to provide bremsstrahlung photons in very short pulses, a constant fraction algorithm for the incoming digital signals was evaluated, which is for optimizing the time resolution. Studies of scattering experiments with different thin targets and detector positions are accomplished at Oncoray Dresden, where a clinical proton beam is available. These experiments allow a basic characterization of the proton bunch structure and the detected yield.
Keywords: Range Verification, Proton Therapy
  • Lecture (Conference)
    ANIMMA 2015, 20.-24.04.2015, Lisboa, Portugal

Publ.-Id: 23141 - Permalink

Measurements of the Time Spread of Proton Pencil Beams at a Clinical Therapy Facility
Petzoldt, J.; Roemer, K. E.; Kormoll, T.; Enghardt, W.; Fiedler, F.; Helmbrecht, S.; Hueso-González, F.; Golnik, C.; Rohling, H.; Werner, T.; Pausch, G.;
In proton therapy, high dose conformality and the finite range of the projectiles are exploited to reduce the dosage to healthy tissue while increasing the dose inside the tumor volume compared to conventional radiotherapy. However, those benefits can be diminished by range uncertainties. An online range verification and in-vivo dosimetry is therefore highly desired.
The prompt gamma ray timing (PGT) method utilizes the detection time of high energetic photons emitted during treatment. The time distribution of the gamma rays contains essential information about the range of the protons. However, PGT spectra are smeared by the time spread of the proton bunches. Knowledge about this time spread would help to disentangle the PGT data and to give better input parameters to simulation procedures.
At the UniversitaetsProtonenTherapieDresden (Dresden, Germany), a dedicated experiment was realized to measure the time spread of a clinical proton pencil beam created by a Cyclone 230 fixed energy cyclotron from Ion Beam Applications. Two phoswich detectors each made out of plastic scintillator and BGO were placed under 90 degrees to detect coincident protons originating from elastic pp-scattering at a thin slice of PMMA. The time spread was measured for incident proton energies between 70 MeV and 225 MeV as well as for several positions of the momentum limiting slits of the energy selection system. Additionally, the absolute transmission of protons from point of extraction to beam exit was determined.
Summarizing, the measured data will help to create reasonable range verification procedures using the PGT method in clinical routine.
Keywords: proton therapy, prompt gamma ray timing
  • Lecture (Conference)
    2015 IEEE Nuclear Science Symposium & Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA

Publ.-Id: 23140 - Permalink

Pair production by Schwinger and Breit-Wheeler processes in bi-frequent fields
Otto, A.; Nousch, T.; Seipt, D.; Kämpfer, B.; Blaschke, D.; Panferov, A. D.; Smolyansky, S. A.; Titov, A. I.;
Counter-propagating and suitably polarized light (laser) beams can provide conditions for pair production. Here, we consider in more detail the following two situations: (i) In the homogeneity regions of anti-nodes of linearly polarized ultra-high intensity laser beams, the Schwinger process is dynamically assisted by a second high-frequency field, e.g. by a XFEL beam. (ii) A high-energy probe photon beam colliding with a superposition of co-propagating intense laser and XFEL beams gives rise to the laser assisted Breit-Wheeler process. Prospects of such bi-frequent field constellations with respect to the feasibility of conversion of light into matter are discussed.

Publ.-Id: 23139 - Permalink

Determination of the carrier envelope phase for short, circularly polarized laser pulses
Titov, A. I.; Kämpfer, B.; Hosaka, A.; Nousch, T.; Seipt, D.;
We analyze the impact of the carrier envelope phase on the differential cross sections of the Breit-Wheeler and the generalized Compton scattering in the interaction of a charged electron (positron) with an intensive ultra-short electromagnetic (laser) pulse. The differential cross sections as a function of the azimuthal angle of the outgoing electron have a clear bump structure, where the bump position coincides with the value of the carrier phase. This effect can be used for the carrier envelope phase determination.


Publ.-Id: 23138 - Permalink

Quantum processes in short and intensive electromagnetic fields
Titov, A. I.; Kämpfer, B.; Hosaka, A.; Takabe, H.;
This work provides an overview of our recent results in studying two most important and widely discussed quantum processes: electron-positron pairs production off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field or generalized Breit-Wheeler process, and a single a photon emission off an electron interacting with the laser pules, so-called non-linear Compton scattering. We show that the probabilities of particle production in both processes are determined by interplay of two dynamical effects, where the first one is related to the shape and duration of the pulse and the second one is non-linear dynamics of the interaction of charged fermions with a strong electromagnetic field. We elaborate suitable expressions for the production probabilities and cross sections, convenient for studying evolution of the plasma in presence of strong electromagnetic fields.

Publ.-Id: 23137 - Permalink

Strange hadron production at SIS energies: an update from HADES
Lorenz, M.; Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gill, K.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcy, G.; Kornakov, G.; Kotte, R.; Krasa, A.; Krebs, E.; Kuc, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim8, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.;
We present and discuss recent experimental activities of the HADES collaboration on open and hidden strangeness production close or below the elementary NN threshold. Special emphasis is put on the feed-down from φ mesons to antikaons, the presence of the Ξ- excess in cold nuclear matter and the comparison of statistical model rates to elementary p+p data. The implications for the interpretation of heavy-ion data are discussed as well.

Publ.-Id: 23136 - Permalink

RF-bunching of relativistic 12 C 3+ ion beam for laser cooling experiment at the CSRe
Wang, H. B.; Wen, W. Q.; Ma, X.; Huang, Z. K.; Zhang, D. C.; Bussmann, M.; Winters, D. F. A.; Yuan, Y. J.; Zhu, X. L.; Zhao, D. M.; Mao, R. S.; Li, J.; Mao, L. J.; Yang, J. C.; Zhao, H. W.; Xu, H. S.; Xiao, G. Q.; Xia, J. W.;
To prepare the upcoming experiment of laser cooling of relativistic 12 C 3+ ion beams at the experimental cooler storage ring (CSRe), a test experiment was performed with 12 C 3+ ion beams at an energy of 122 MeV/u on the CSRe, at the Institute of Modern Physics, Lanzhou, China. In this experiment, the main storage ring of CSRm was employed to accumulate and accelerate the ion beam which was injected into the CSRe for the experiments. The number of 12 C 3+ ions at the CSRe reached 5×10 8 for every injection, which satisfied the experimental requirement. To fulfil the laser cooling experiment, the 12 C 3+ ion beams were bunched by sinusoidal waveforms with fixed and sweeping frequencies, respectively. A resonant Schottky pick-up was employed to record the Schottky spectra of these ion beams. The test experimental results demonstrated that the RF-buncher and diagnostic systems at the CSRe worked well and the CSRe was very stable with 12 C 3+ ion beams, hereby the CSRe is suitable for laser cooling experiment.
Keywords: rf bunching, relativistic, ion beam, storage ring, dynamics

Publ.-Id: 23135 - Permalink

Broadband(UV- mid-IR) spectrometer for single-shot femtosecond electron bunch measurement first experiment @ HZDR
Zarini, O.; Debus, A.; Couperus, J. P.; Köhler, A.; Jochmann, A.; Irman, A.; Schramm, U.;
Laser-wakefield accelerators (LWFA) feature electron bunch durations ranging from several fs to tens of fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top Xray light-sources and remains a big challenge due to the resolution limit of existing diagnostic techniques.
Measurement of broadband coherent and incoherent transition radiation produced when LWFA electron bunches pass a metal foil is a promising way to analyze longitudinal characteristics of these bunches.
Because of the limited reproducibility due to the nonlinear nature of the electron source this characterization requires single-shot capability.
Our ultra-broadband spectrometer combines the TR spectrum in UV/VIS (200-1000nm), NIR (0.9-1.7µm) and mid-IR (1.6-12µm). A high spectral sensitivity, dynamic bandwidth and spectral resolution are realized by three optimized dispersion and detection systems to a single-shot spectrometer.
A complete characterization and calibration of the spectrometer has been done with regard to wavelengths, relative spectral sensitivities and absolute photometric sensitivity, also taking into account for the light polarization.
Our spectrometer is able to characterize electron bunches with charges as low as 1 pC and resolve time-scales from 0.7 to 40 fs.
Keywords: Broadband spectrometer, coherent transition radiation, electron bunch duration, longitudinal profile, absolute calibration
  • Lecture (Conference)
    2nd European Advanced Accelerator Concepts Workshop (EAAC), 13.-19.09.2015, La Biodola, Isola d'Elba, Italien
  • Lecture (Conference)
    DoKDoK 2015, 10.-15.10.2015, Eisenach, Deutschland

Publ.-Id: 23134 - Permalink

Bechmann, N.; Kniess, T.; Pietzsch, J.; König, J.; Köckerling, M.;
kein Abstract verfügbar
Keywords: crystal structure; d-chlorobutyl; phenyl ketone; hyrogen bonding

Publ.-Id: 23133 - Permalink

Dynamics of bulk electron heating and ionization in solid plasmas driven by ultra-short relativistic laser pulses
Huang, L. G.; Kluge, T.; Bussmann, M.; Chung, H. K.; Cowan, T. E.;
We investigate the dynamics of bulk electron heating and ionization in solid density plasmas driven by ultra-short relativistic laser pulses. During laser-plasma interactions, the solid plasma absorbs a fraction of laser energy and converts it into kinetic energy of electrons. A part of the electrons with high kinetic energy travels through the solid plasma and transfers energy into bulk electrons, which results in bulk electron heating by return current. The bulk electron temperatures in the interest of bulk region agrees very well with the theory based on Ohmic heating mechanism by treating the return current correctly. The bulk electron heating is finally translated into bulk ionization dynamics, which is modeled by Thomas-Fermi ionization mechanism in our studies.
Keywords: bulk heating, ionization, high power laser, solid plasmas
  • Poster
    Novel Light Sources from Laser-Plasma Interactions, 20.-24.04.2015, Dresden, Germany

Publ.-Id: 23131 - Permalink

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