Vorträge im SS 2010

Dr. Edward W. Cliver , Space Vehicles Directorate Air Force Research Laboratory

Solar Drivers of 11-yr and Long-term Cosmic Ray Modulation (16. Juli 2010)

The key solar influences on galactic cosmic ray (GCR) intensity at Earth are solar polarity reversal (particle drift) and the 11-yr and long-term variability of the solar wind magnetic field strength (particle diffusion). Drift effects are clearly revealed via differing cosmic ray intensity responses to changes in solar wind magnetic field strength (B) during the Sun’s two magnetic polarity cycles. This effect can be explained in terms of the effect of curvature and gradient drifts on the entry of GCRs into the inner heliosphere. The fact that GCR intensity is a multi-valued function of the tilt angle for both polarity cycles argues that particle drift is not the principal mechanism of cosmic ray modulation, either at solar maximum or solar minimum. Single-valued functions of GCR intensity with B for both polarity epochs indicate that modulation is dominated by diffusion. A decomposition of the solar wind into high-speed streams, slow solar wind, and coronal mass ejections (CMEs), reveals that the Sun transmits its message of changing magnetic field to the heliosphere primarily through CMEs at solar maximum and high speed streams at solar minimum. We suggest that the disconnect between solar wind B and the sunspot number (and cosmic ray intensity) during cycle 20 is related to high-latitude CMEs which are not detected in situ at Earth. Long-term reconstructions of solar wind B are in general agreement for the ~1900-present interval. For earlier epochs, however, a recent 10Be-based reconstruction covering the Holocene shows nine abrupt and relatively short-lived drops of B to ~0 nT, with the first of these corresponding to the Spörer minimum. Such dips are at variance with the recent suggestion, based on geomagnetic data, that B has a minimum or floor value of ~3 nT.
Prof. Dr. Frank B. McDonald, Institute of Physical Science and Technology, University of Maryland

A New Look at the Heliosphere and Solar Modulation (15. Juli 2010)

Galactic cosmic rays entering our heliosphere encounter an outward-flowing solar wind carrying a turbulent magnetic field. The interaction between these energetic particles and the interplanetary medium reduces the cosmic ray intensity throughout our solar system below its level in the local interstellar region. Studying this solar modulation process is important: to understand the transport of energetic particles in large-scale, complex astro- physical plasma; to determine the local interstellar properties of galactic cosmic rays; and, to explore the large scale structure and dynamics of the outer heliosphere. The Deep Solar Minimum of Cycle 23/24 (that apparently ended in December, 2009) produced unusual interplanetary conditions that resulted in time-histories and intensities of galactic and anomalous cosmic rays over this period that are very different from those of previous solar minima at the same phase of the heliomagnetic cycle – for example 200 MeV/n GCR He are 30% above their 1987 solar minimum value. Since ~ 2005.6 there has been an on-going increase (except for one brief transient decrease) that has now lasted for 4.4 years. The relative rigidity dependences of these increases compared to previous cycles are complex and should provide insight into the role of various solar and interplanetary phenomena in the modulation process. In the distant heliosheath cosmic ray data from Voyager 1 and 2 are showing significant increases in the galactic cosmic ray ion and electron intensity that reflects the changes that are occurring in the magnetic fields in the distant heliosphere and play an important role in the 1 AU enhancements.
Prof. Dr. Carsten Greiner, Universität Frankfurt

Die Suche nach der Materie aus Quarks (6. Juli 2010)

Hundert Jahre nach der Entdeckung der Kernmaterie als Massetragender Bestandteil des Atoms hat man ihren mikroskopischen Aufbau detailliert untersucht und die Struktur der Atomkerne in großen Teilen verstanden. Eines der Forschungsziele der modernen Kern- und Hadronenphysik ist die Suche nach einer neuen Form der Materie, dem sogenannten Quark-Gluon-Plasma (QGP). Ein derartiger Zustand sollte vor über zehn Milliarden Jahren im frühen Universum vorgelegen haben. Ein Bruchteil einer Sekunde nach dem kosmologischen Urknall ("big bang") und bei Temperaturen von mehreren Billionen Grad bestand die Materie im Universum nicht aus den heutigen Atomen mit ihren Atomkernen, sondern aus einer dichten Suppe der noch elementareren Materie-Bausteine, den Quarks und Gluonen. Diese fundamentalen Teilchen bauen in einem Atomkern deren Konstituenten, die Protonen und Neutronen, auf. Zum Studium dieser extremen Form von Materie werden schwere Ionen bei sehr hohen Energien zur Kollision gebracht. Man versucht also einen "little bang", d.h. einen kleinen Urknall, im Labor zu erzeugen. In den letzten Jahren wurde sowohl am Großforschungslaboratorium CERN in der Schweiz und am Brookhaven National Laboratory in den USA starke Evidenz für das Auffinden eines QGPs geäußert. Einige Beispiele, welche Signatu- ren für das QGP darstellen, und deren Interpretation werden besprochen.
Prof. Dr. Christof Kunz

Synchrotronstrahlung: Eine Erfolgsgeschichte (29. Juni 2010)

(Vortrag im Rahmen der Akademischen Gedächtnisfeier für Professor Dr. Ruprecht Haensel († 19.10.2009) Prof. Dr. Andreas Burkert, Universitätssternwarte München

Dynamics of redshift 2 galaxies (22. Juni 2010)

The redshift 2 Universe is one of the most interesting epochs of galaxy evolution. It is the era with the peak of the cosmic star formation rate. Between redshift 3 and 1 the total stellar mass density in galaxies increased from 15% to 70%. It is also the time of rapid galaxy assembly and the epoch where galaxy morphology was determined. I will discuss recent results of the SINS survey, a Spectroscopic Imaging survey of z=2 galaxies in the Near infrared with SINFONI. The SINS data show a diversity of galactic systems at redshift 2 with physical properties that are unparalleled in the z=0 Universe. These observations have opened a fascinating window into early galaxy evolution, revealing a rich variety of interacting dynamical processes that at the moment are far from being understood.
Prof. Dr. Ernst Meyer, Department of Physics, University of Basel

Atomic friction (15. Juni 2010)

Friction is an old phenomenon, which is still poorly understood from a fundamental point of view. Experiments, based on advanced force microscopy, give the opportunity to study friction on the nanometer scale. Novel phenomena, such as atomic stick-slip, are ob- served. The origins of energy dissipation, either electronic or phononic, are to be discussed. The transition from atomic-scale stick slip to continuous sliding, also called the transition to superlubricity, is presented and applied to control friction. Therefore, atomic friction can be switched on and off. In a second part, some high resolution force microscopy experiments in contact and non-contact will be shown, where submolecular resolu- tion is achieved.
Prof. Dr. Ursel Fantz, Max-Planck-Institut für Plasmaphysik, Garching und Lehrstuhl für Experimentelle Plasmaphysik, Universität Augsburg

Powerful plasma sources for negative hydrogen ions: A challenge to sustain the fire in ITER (8. Juni 2010)

Negative ion sources are an excellent example for the manifold of applications of low temperature plasmas which ranges from basic research to industrial applications. One of the outstanding features is their usage in fusion research as negative hydrogen ion sources as a central component of the neutral beam injection systems for heating and current drive of the international fusion project ITER. The fusion requirements initiated an ambitious development program for large and powerful negative hydrogen ion sources in Europe. The challenge to extract an ion current of 40 A from a low temperature hydrogen plasma at low pressure (0,3 Pa) is accompanied by the challenge to accelerate the beam to 1 MeV. Large RF sources with the size of a door operating at a power of up to 800 kW must deliver a uniform and stable negative hydrogen ion current density higher than 200 A/m2 over the total area for one hour. Simultaneously, the amount of co-extracted electrons should be kept lower than one in order to avoid severe damages of the extraction system. These requirements incorporate several challenges which can be met only by combining the disciplines of low temperature plasma physics, plasma surface interaction, ion beam optics, beam physics, and mechanical and electrical engineering. The state of the art and prospects of the negative hydrogen ion source development will be discussed with emphasis on the physical aspects.
Prof. Dr. Juerg Beer, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Schweiz

Polar Ice: A History book for Cosmic Rays, Climate Forcing and Climate Response (1. Juni 2010)

Nicht nur der Mensch führt Buch über seine Geschichte. Auch die Natur speichert auf vielfältige Art Informationen in Umweltarchiven wie Eisschildern, Sedimenten und Baumringen. Eis ist ein besonders interessantes Beispiel für ein Umweltarchiv, da es nicht nur Informationen über Klimaänderungen im Weltraum und auf der Erde enthält, sondern zusätzlich auch über die Ursachen (Forcings). Allerdings ist das Lesen und Entziffern dieser Informationen alles andere als einfach und bedarf spezieller analytischer Methoden wie der Beschleunigermassenspektrometrie.
Prof. Dr. Joachim Saur, Universität zu Köln

Die Suche nach flüssigem Wasser in unserem Sonnensystem (25. Mai 2010)

Flüssiges Wasser gilt als eine der wenigen essentiellen Voraussetzung zur Entstehung von Leben so wie wir es kennen. Aus diesem Grund kommt der Suche nach flüssigem Wasser eine Schlüsselrolle bei der Erkundung unseres Sonnensystems zu. Der einzige bisher bekannte Körper in unserem Sonnensystem, der flüssiges Wasser und Leben beheimatet, ist die Erde. Allerdings gibt es weitere Körper in unserem Sonnensystem, bei denen sich die Hinweise, dass dort ebenfalls flüssiges Wasser existieren könnte, immer mehr verdichten. Die drei Hauptkandidaten sind der Jupitermond Europa sowie die Saturnmonde Enceladus und Titan.
Prof. Dr. Ian Robinson, London Centre of Nanotechnology, University College, London, UK

Strained Nanocrystals (8. Mai 2010)

I will describe my group’s latest Coherent X-ray Diffraction techniques, which are capable of imaging nanometre-sized crystals in three dimensions. The method is different from many other imaging methods in that it uses data measured around individual Bragg peaks of the crystal studied. For this reason, it is highly sensitive to strain fields present in the crystal under investigation, which are therefore mapped in three dimensions. The latest development is to measure several Bragg peaks from the same nanocrystal to reveal multiple components of the displacement field and the resulting strain tensor. The method is interesting for the study of nanowire materials where strains are expected along the surfaces and at the heterojunction interfaces. It also shows fascinating patterns of strain associated with defects in metal nanocrystals and induced by chemical modification.
Prof. Dr. Nathan Schwadron, Boston University

Understanding the first maps of the global heliosphere from the Interstellar Boundary Explorer Mission (11. Mai 2010)

The Interstellar Boundary Explorer (IBEX) mission has recently completed the first global energetic neutral atom (ENA) maps of the heliosheath. Global models provide critical insight for the interpretation of these unprecedented observations. Models have explored the influence of the conditions of local interstellar medium (LISM) on ENA maps, but the models make fundamental assumptions about the energy and pitch-angle distributions of the heliosheath protons, and the LISM conditions. The directly observed energy distributions of ENAs by IBEX test the assumed energy distributions used in models (e.g., kappa and Maxwellian distributions), and suggest areas where the models may be missing significant physical ingredients. This talk explorers the implications of IBEX observations for the global heliosphere and describes recent attempts to explain the unexpected features observed by IBEX.
Prof. Dr. May-Britt Kallenrode, Universität Osnabrück Vortrag im Rahmen der Reihe: Frauen, die forschen

Energiereiche Teilchen in der Atmosphäre (4. Mai 2010)

Polarlichter sind die offensichtliche Manifestation energiereicher Teilchen in der Atmosphäre. Polarlichtbeobachtungen und ihre Interpretation sind in diesem Vortrag der Ausgangspunkt für ein abstrakt klingendes Phänomen, dass sich an der Schnittstelle von Weltraumwetter, Atmosphärenphysik und –chemie sowie Klimavariabilität abspielt. Die energiereichen Teilchen erzeugen neben Polarlichtern auch Stick- und Wasserstoffoxide, die ihrerseits zu einem Ozonabbau beitragen. Da Ozon ein treibhauswirksames Spurengas ist, beeinflussen Änderungen im Ozon auch den Energiehaushalt der Atmosphäre und damit das Klima. Neben der Einführung in die Phänomene und ihre Erklärung soll der Vortrag auch einen Einblick in die Herausforderung der Forschung in einem komplexen natürlichen Umfeld geben – und damit die Faszination erklären, die wissenschaftliche Forschung ausübt.
Prof. Dr. Stefan Heinze, Institut für Theoretische Physik und Astrophysik, CAU Kiel

New challenges in nanomagnetism: From single atoms to skyrmion lattices (27. April 2010)

Recent advances in experimental techniques to create articial magnetic nanostructures at surfaces atom-by-atom, to synthesize new materials such as molecular magnets, and to locally probe their magnetic and transport properties at the atomic level challenge our theoretical understanding of nanoscale magnets. Because of its predictive power density functional theory and its wide applications e.g. to quantum transport or in combination with model Hamiltonians have become driving forces in nanoscience. Based on these theoreti- cal tools we can explain and even predict the structural, electronic, chemical, magnetic, and transport properties of a diverse spectrum of systems. To illustrate this I will show how we can explore the complex magnetic phase space at surfaces, discovering novel spin textures such as skyrmion lattices, explain and suggest experiments using scanning tun- neling and exchange force microscopy, tailor and manipulate molecular magnets, and understand ballistic transport in nanomagnets.
Prof. Dr. Paul Evenson, University of Delaware, Newark

The IceCube Neutrino Observatory - Construction and Initial Results (20. April 2010)

When fully installed in 2011 the IceCube Neutrino Observatory will consist of approximately 5000 photomultipliers embedded in a cubic kilometer of ice at the South Pole, together with an air shower array on the surface. Deployment began in 2004, and the partially completed observatory has been taking data as the world‘s largest neutrino detector for some time now. Completion of the most fundamental objectives of IceCube will require operation for the full 15 year projected lifetime, but several important results have already emerged. Design, construction, and scientific objectives of IceCube will be discussed, as will some of the findings to date.