Entwicklung und Untersuchung von Cluster-Jet-Targets höchster Dichte

Ziel dieser Arbeit war der Aufbau und die Untersuchung eines Cluster-Jet-Targets das in Geometrie und Dichte den Anforderungen moderner Speicherring-Experimente entspricht. Im Rahmen dieser Arbeit wurde hierzu eine Cluster-Quelle, das MCT2, konstruiert, aufgebaut und betrieben, die als Prototyp für das Cluster-Jet-Target des zukünftigen PANDA-Experiments des Beschleunigerkomplexes FAIR in Darmstadt dient. Mit diesem Target konnte eine Targetdichte von nahezu 1e15 Atome/cm³ in einer Entfernung von 2 m hinter der Cluster-Quelle erreicht werden. Zudem wurden die Eigenschaften der erzeugten Cluster näher untersucht. Von besonderem Interesse ist hier die Verteilung der Clustergeschwindigkeiten die im Rahmen dieser Arbeit gemessen wurden. Des Weiteren konnte durch ein quasi-eindimensionales Modell der Düsenströmung unter Verwendung der Zustandsgleichung nach Van-der-Waals die mittlere Clustergeschwindigkeit reproduziert werden

High density cluster jet target for storage ring experiments

The design and performance of a newly developed cluster jet target installation for hadron physics experiments are presented which, for the first time, is able to generate a hydrogen cluster jet beam with a target thickness of above $10^{15}\,\mathrm{atoms/cm}^2$ at a distance of two metres behind the cluster jet nozzle. The properties of the cluster beam and of individual clusters themselves are studied at this installation. Special emphasis is placed on measurements of the target beam density as a function of the relevant parameters as well as on the cluster beam profiles. By means of a time-of-flight setup, measurements of the velocity of single clusters and velocity distributions were possible. The complete installation, which meets the requirements of future internal fixed target experiments at storage rings, and the results of the systematic studies on hydrogen cluster jets are presented and discussed.Comment: 10 pages, 18 figure

A recoil detector for the measurement of antiproton-proton elastic scattering at angles close to 90∘^{\circ}

The design and construction of a recoil detector for the measurement of recoil protons of antiproton-proton elastic scattering at scattering angles close to 90$^{\circ}$ are described. The performance of the recoil detector has been tested in the laboratory with radioactive sources and at COSY with proton beams by measuring proton-proton elastic scattering. The results of laboratory tests and commissioning with beam are presented. Excellent energy resolution and proper working performance of the recoil detector validate the conceptual design of the KOALA experiment at HESR to provide the cross section data needed to achieve a precise luminosity determination at the PANDA experiment.Comment: 10 pages, 15 figure

High temperature ferromagnetism of Li-doped vanadium oxide nanotubes

The nature of a puzzling high temperature ferromagnetism of doped mixed-valent vanadium oxide nanotubes reported earlier by Krusin-Elbaum et al., Nature 431 (2004) 672, has been addressed by static magnetization, muon spin relaxation, nuclear magnetic and electron spin resonance spectroscopy techniques. A precise control of the charge doping was achieved by electrochemical Li intercalation. We find that it provides excess electrons, thereby increasing the number of interacting magnetic vanadium sites, and, at a certain doping level, yields a ferromagnetic-like response persisting up to room temperature. Thus we confirm the surprising previous results on the samples prepared by a completely different intercalation method. Moreover our spectroscopic data provide first ample evidence for the bulk nature of the effect. In particular, they enable a conclusion that the Li nucleates superparamagnetic nanosize spin clusters around the intercalation site which are responsible for the unusual high temperature ferromagnetism of vanadium oxide nanotubes.Comment: with some amendments published in Europhysics Letters (EPL) 88 (2009) 57002; http://epljournal.edpsciences.or