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Becker, Stefan (2010): Dynamics and Transport of Laser-Accelerated Particle Beams. Dissertation, LMU München: Fakultät für Physik



The subject of this thesis is the investigation and optimization of beam transport elements in the context of the steadily growing field of laser-driven particle acceleration. This cumulative thesis introduces to the theoretical framework of the elements and presents the results via corresponding publications. The first topic is the examination of the free vacuum expansion of an electron beam at high current density. Unlike in the case of conventional acceleration, laser acceleration yields charge densities which are comparatively high at lower energies. It could be shown that particle tracking codes which are commonly used for the calculation of space charge effects will generate substantial artifacts in the regime considered here. The artifacts occurring hitherto predominantly involve insufficient prerequisites for the Lorentz transformation, the application of inadequate initial conditions and non negligible retardation artifacts. A part of this thesis is dedicated to the development of a calculation approach which uses a more adequate ansatz calculating space charge effects for laser-accelerated electron beams. It can also be used to validate further approaches for the calculation of space charge effects. The next elements considered are miniature magnetic quadrupole devices for the focusing of charged particle beams. Invented in 1980 by Halbach, miniature permanent magnet quadrupoles yield field gradients at least a factor two higher than superconducting quadrupole devices. General problems involved with their miniaturization concern distorting higher order field components. If these distorting components cannot be controlled, the field of applications is very limited. In this thesis a new method for the characterization and compensation of the distorting components was developed, which might become a standard method when assembling these permanent magnet multipole devices. Consequently, the field where these devices are applicable could be broadened. The newly developed characterization method has been validated at the Mainz Microtron (MAMI) electron accelerator. Now that we can ensure optimum performance, the first application of permanent magnet quadrupole devices in conjunction with laser-accelerated ion beams is presented. The experiment was carried out at the Z-Petawatt laser system at Sandia National Laboratories. A Free Electron Laser (FEL) delivers coherent photon beams at higher energies than what can be reached by conventional laser systems. A promising application for laser-accelerated electron beams is the FEL in a university-scale size. The first discussion of all relevant aspects concerning a laser driven FEL is presented. The operation of an FEL depends on many factors, among which is the average electron beam size while propagating through the undulator. The undulator length could be reduced significantly if the average beam size can be reduced. This goal motivates the development of a new undulator concept, based on miniature magnetic quadrupoles, which is presented here. This quadrupole undulator yields strong intrinsic focusing properties which allow to keep the electron beam at a comparatively small and constant size over a long propagation range. The experimental realization of a compact FEL involves the first step of building a test undulator with a short undulator period length. This undulator device was assembled and experiments aiming at undulator radiation have been carried out at the MAMI electron accelerator facility in the course of this thesis. The investigations presented in this thesis mark important development steps on the route towards many applications of laser-accelerated particle beams. Especially laser-driven compact Free-Electron-Lasers are an attractive alternative to costly large-scale conventional facilities.