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Title: Ion acceleration driven by ultra-short ultra-intense laser pulses
Author: Prasad , Rajendra
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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Laser driven ion sources are being foreseen as promising candidate for many potential applications. This thesis presents the results of ion acceleration investigated in the regime of ultra-high intensity (>1020 W/cm2). ultra -short (50 fs) and ultra-high contrast laser pulse interaction with solid density targets. The efficiency of ion acceleration in this unique condition was studied by varying various laser and target parameters. The energy scaling and spectral features were investigated at oblique and normal laser incidence. Under oblique incidence, the dependence of maximum cut-off energy of the protons and ion flux of the accelerated particles on the target thickness (50 nm- 6pm) were investigated. A comparison of ion flux at oblique incidence with ion flux at normal incidence was performed. The conversion efficiency of laser energy into proton energies was estimated. At normal incidence, with ultra-thin so lid targets (10-100 nm), a possible emergence of the radiation pressure acceleration scenario was observed. In the proton spectra, quasimonoenergetic peak centred around 10 MeV was observed. The energy of the protons at peak followed the energy scaling of the RPA process in the non-relativistic limit. These features were corroborated by 20 PIC simulations. The maximum cut-off energies dependence of the accelerated ions was investigated by varying target thickness for linear and circular polarisations. Cut-off energies of 20 MeV/u for both the protons and (6+ were obtained. The interaction of ultra-short, intense laser pulses with spray targets was studied. In the previous experiments using water spray, observation of negative ions was explained by electroncapture an~ loss processes, and acceleration of neutral oxygen atoms with similar energies was also suggested. The neutrals were measured employing a time of flight technique. The concept of generation of negative ions was verified by a novel method where positive ions produced from foil target propagated through the cold spray medium, producing negative ions. A new ethanol spray was also characterised. The irradiation of this new spray target with intense laser produced negative carbon ions in addition to the negative oxygen ions. Moreover, negative hydrogens were also observed. The acceleration of quasi-monoenergetic protons with energy, 2.8t,O.3 MeV observed from water spray is also discussed simulations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available