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Ion beams accelerated by laser irradiation of thin foils and their applications

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Title: Ion beams accelerated by laser irradiation of thin foils and their applications
Authors: Hicks, George
Item Type: Thesis or dissertation
Abstract: This thesis presents experimental measurements, supported by particle-in-cell simulations, of ion beams accelerated from ultra thin plastic foils by high intensity laser plasma interactions in the sheath acceleration and relativistic transparency regimes. An application of accelerated proton beams is radiography, which can be used to image the fields in high intensity laser plasma interactions. Experimental measurements are presented of observations of strong electromagnetic fields associated with plasma instabilities. The use of thin foils in high intensity laser experiments is attractive, because for thin foils the radiation pressure acceleration and relativistic transparency regimes begin to dominate. For intensities 1e20 W/cm^2, and target thicknesses <0.5 microns, laser heating causes the target to expand so that it becomes transparent to the laser. It has been postulated that targets that are transparent during the peak of the laser pulse, will experience increased electron heating and efficient proton acceleration. Optimum acceleration conditions were observed for target thicknesses, 100<d<250 nm. The control of plasma instabilities is one of the ultimate prizes in high energy density physics. These effects can limit the energy absorption into a plasma, which is of interest in all areas of plasma physics. However, control of these effects could lead to the amplification of laser pulses to very high powers. In this work, a ~15 ps laser pulse with intensity 1e18 W/cm^2 was focussed onto a near critical density argon gas jet. Transverse proton probing was enabled by focussing a ~1 ps laser pulse with intensity 1e19 W/cm^2 onto a 20 micron gold foil. The protons imaged the electromagnetic fields and revealed a strong, low frequency, oscillatory field. Experimental evidence suggests this field is due to an ion acoustic wave driven by stimulated Brillouin scattering.
Content Version: Open Access
Issue Date: Sep-2015
Date Awarded: May-2016
URI: http://hdl.handle.net/10044/1/33316
DOI: https://doi.org/10.25560/33316
Supervisor: Najmudin, Zulfikar
Sponsor/Funder: Engineering and Physical Sciences Research Council
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses



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