166 research outputs found
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 fĂŒr das Cluster-Jet-Target des zukĂŒnftigen PANDA-Experiments des Beschleunigerkomplexes FAIR in Darmstadt dient. Mit diesem Target konnte eine Targetdichte von nahezu 1e15 Atome/cmÂł in einer Entfernung von 2 m hinter der Cluster-Quelle erreicht werden. Zudem wurden die Eigenschaften der erzeugten Cluster nĂ€her 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 DĂŒsenströmung 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 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
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 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
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