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Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Mircea D. Driga. Vita. Includes bibliographical references. Available also from UMI company.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 124-132). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 124-132). Also available on the Internet.

No description available.

The acceleration of electrons in a laser produced plasma wave was studied experimentally. A plasma with a modulated density was produced by illuminating a grating with a ruby laser at an intensity of 10¹⁰ W/cm². The plasma expanding above the surface of the grating was diagnosed using interferometry, shadowgraphy and Raman-Nath scattering. The plasma density was found to be modulated with an amplitude of [formula omitted]/n=8% for grating spacings ranging from 6 to 35 µm. A CO₂ laser of intensity 7xlO¹¹ W/cm2 then irradiated this modulated plasma and generated plasma waves. The phase speeds of the plasma waves are v[formula omitted] = ±[formula omitted]k[formula omitted], where k[formula omitted] is the wavenumber of the grating and [formula omitted] is the frequency of the CO₂ laser. Electrons were injected at an energy of 25 keV in one of the plasma waves. In order for the phase speed of the wave to synchronize with the accelerating electrons, a grating with constantly increasing line spacing was used. No conclusive evidence of electron acceleration was obtained, even after the injection energy was increased to 92 keV. This lack of evidence was the result of a large electric field perpendicular to the surface of the grating, which deflected the electrons onto the grating. This detrimental electric field is produced when fast electrons are emitted by the plasma and leave it positively charged. At the low laser intensity used in this experiment, the origin of these electrons could not be identified. Some techniques to remedy this difficulty are proposed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Für viele Anwendungen in der Grundlagenforschung, Medizin und industriellen Entwicklung sind Beschleuniger der entscheidende Antrieb. Vor allem Elektronenbeschleuniger sind als Synchrotronquellen unter den brillantesten Quellen für Strahlung im Infrarot- bis Röntgenbereich und damit unerlässlich für eine Vielzahl von Anwendungen und analytischen Methoden. Photoinjektoren stellen als Elektronenquellen für Beschleuniger eine wichtige Komponente für die Entwicklung von Lichtquellen wie Freie-Elektronen-Laser, sowie für neue Beschleunigerkonzepte wie Linearbeschleuniger mit Energierückgewinnung dar. Die Photokathode und der Anregungslaser definieren dabei mit der Quantenausbeute (QE) und der intrinsischen Emittanz zentrale Kenngrößen des Photoinjektors. Diese Arbeit beschreibt die Entwicklung von Alkali-Antimonid Photokathoden für die Anwendung in einem Photoinjektor mit supraleitendem Hochfrequenz-Resonator. Alkali Antimonide zeigen generell eine hohe QE und Cäsium Kalium Antimonid (Cs-K-Sb) im speziellen verspricht eine geringe intrinsische Emittanz aufgrund der Ionisierungsenergie, die nur knapp unter der Photonenenergie der grünen Anregungslaser liegt. Mit der Inbetriebnahme eines Präparations- und Analysesystems konnte die Abscheidung dünner Schichten von Cs-K-Sb sowie die Messung der QE und chemischen Zusammensetzung erzielt werden. Dabei wurde mit der Ko-evaporation der Alkalimetalle eine neue Wachstumsmethode etabliert und hinsichtlich der Prozessstabilität und Qualität der erzeugten Proben mit der sequenziellen Methode verglichen. Schließlich beschreiben die Inbetriebnahme eines Prototyps des Photoinjektors und erste erfolgreiche Kathodentransfers im Vakuum einen wichtigen Schritt hin zum Betrieb eines Beschleunigers mit einer Cs-K-Sb Photokathode im supraleitenden Hochfrequenz-Injektor. Diese Kombination erlaubt die Erzeugung eines Elektronenstrahls mit niedriger Emittanz und hohem mittleren Strom. / For many disciplines in basic and applied research, medicine and industrial development accelerators are an important driving force. Especially electron accelerators as synchrotron sources are among the brightest sources of radiation from the infrared to the X-ray regime and thus fundamental to a broad range of analytical techniques. Photoinjectors as electron sources for accelerator applications are a key component for the development of light sources such as free electron lasers as well as new accelerator concepts like energy-recovery linacs. The photocathode and drive laser define the quantum efficiency (QE) and intrinsic emittance of the photoemission process and thus central figures of merit of the photoinjector. This work focuses on the development of alkali antimonide photocathodes for the application in a superconducting radio frequency photoinjector. Alkali antimonides generally exhibit a high QE and cesium potassium antimonide (Cs-K-Sb) specifically is expected to release electrons with a low intrinsic emittance as the photoemission threshold is close to the photon energy of common, green, drive laser wavelengths. A preparation and analysis system has been commissioned for the deposition of Cs-K-Sb thin film photocathodes and their analysis regarding QE and chemical composition. A new deposition technique, the alkali metal co-deposition, was established and compared to the sequential deposition in terms of process reliability and quality of the produced samples. The work concludes with a report of the commissioning of a prototype of the photoinjector and successful cathode transfers in ultra-high vacuum, which represents an important technological advancement towards the operation of an accelerator with the combination of Cs-K-Sb photocathodes and an SRF injector. This combination makes the generation of an electron beam with low emittance and high average current possible.