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Studies of Photoemission from Metal Cathodes with Micro-Rough Surface: Schottky Effect and Plasma Production Influence

In this work the photoemission performance of rough and smooth cathodes is presented. The cathodes made of by pure yttrium metal bulk. For evaluation of the cathodes a KrF excimer laser, operating at 248 nm wavelength, 5 eV photon energy and 23 ns FWHM was used. The targets were tested in a vacuum photodiode cell at 10-7 mbar; they were irradiated at normal incidence and the anode-cathode distance was set to 5 mm. The measurements were performed after a series of electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was made in order to increase the surface roughness. For the rough cathode the maximum output current was 10.5 A, reached at 25 kV and 12 mJ laser energy; the maximum quantum efficiency (QE) value was 1.3×10-4, while, for the smooth cathode the maximum output current was 8.4 A, and the maximum quantum efficiency (QE) value was 7.0×10-5,calculated in the same conditions. The temporal behavior of photoemission from these cathodes was studied. Plasma production and Schottky effect played a fundamental role in this process.

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Ph. D. Thesis – G. Caretto PREFACE The present work, performed since 2005 to 2007, has been dedicated to the development of a “good” system of electron photoemission that uses metal targets irradiated by excimer lasers. This research project has been mainly realized in the Applied Electronics Laboratory, at the Department of Physics of the University of Salento. The attention has been focused on the techniques to enhance the electron emission efficiency, in order to obtain electron beams of high intensity. Low angular divergence and short time duration of the extracted beams are other objectives of this work. In particular, this study wishes to lead to the optimization, for the realization of new and versatile accelerators, useful for application in the fields of: - new scientific devices such as free-electron lasers (FEL) - X-ray machines - electron beam therapy machines - high power microwave generators - controlled thermonuclear fusion reactors - collective ion accelerators for basic physics studies and medical therapies. Therefore, the photo-extraction process under different experiment conditions has been carefully investigated. Namely we studied the electron emission of a sample as a 3

Tesi di Dottorato

Dipartimento: fisica

Autore: Giuseppe Caretto Contatta »

Composta da 111 pagine.

 

Questa tesi ha raggiunto 266 click dal 18/11/2008.

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