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Title: Fast electron energy transport in high intensity laser-plasma interactions
Author: Green, James Simon
ISNI:       0000 0001 3516 1419
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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This thesis presents experimental measurements of fast electron energy transport made using optical probing, x-ray and XUV imaging techniques. Hydrodynamic and hybrid particlein- cell (PIC) simulations were used to interpret the results. Measurements of fast electron heating patterns were made using the Vulcan 100 Terawatt (TW) and Petawatt (PW) lasers. For the first (100 TW) experiment the laser power was increased from 10 TW to 70 TW and a transition was observed between collimated electron flow and an annular transport pattern. Hybrid modelling showed that a form of beam hollowing accounted for this. Using the PW laser, a comparison was made of different diagnostic techniques for measuring the fast electron beam divergence. Cu K-alpha and optical probing measurements were found to be consistent, with both measuring a divergence angle significantly larger than that measured before at lower intensities. Several different target geometries were used to investigate how energy coupling from the laser into the fast electron beam is affected by the presence of a laser guide cone. Using the Vulcan PW laser, a significant decrease in energy coupling was observed when using metallic cone-slab targets. The addition of a cone assembly to plastic I AI sandwich targets acted to reduce the fast electron heating pattern. Novel cone-wire target geometries revealed that heating of a cone-guided wire plasma is maximised close to the wire surface. Computational modelling revealed that this is due to enhanced Ohmic heating. Finally, measurements were made of the dependence of laser intensity on the fast electron beam divergence. Data taken at intensities relevant to fast ignition was combined with previous published measurements. It was found that the divergence angle increased with laser intensity and had little dependence on pulse duration. PIC modelling was performed to analyse the data and possible explanations for the intensity dependence are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available