Effects of electrical resistivity on fast electron transport in relativistic laser-solid interactions

This thesis reports on experimental and numerical investigations of relativistic electron transport in solids irradiated by intense (i.e. IL > 10¹⁹ Wcm⁻²) laser pulses. Specifically, the effect of electrical resistivity on fast electron transport is explored. The first investigation explores fast electron transport in allotropes of carbon by measuring the spatial-intensity distribution of the beam of protons accelerated from the target rear-surface. An analytical model is developed which accounts for the rear-surface fast electron sheath dynamics, ionisation and projection of the resulting beam of protons, and is used (in conjunction with the experimental measurements) to infer annular fast electron beam transport with lamentary structure in 200 um-thick diamond targets. The important role that material lattice structure has in defining electrical resistivity, which in turn defines the fast electron transport properties, is established utilising three-dimensional hybrid particle-in-cell (3D hybrid-PIC) simulations together with an analytical model of the resistive lamentation instability. The second investigation explores fast electron transport in silicon utilising both experimental measurements and 3D hybrid-PIC simulations. Annular fast electron transport is demonstrated and explained by resistively generated magnetic fields. The results indicate the potential to completely transform the beam transport pattern by tailoring the resistivity-temperature profile at temperatures as low as a few eV. Additionally, the sensitivity of annular fast electron beam transport is explored by varying the drive laser pulse parameters (i.e. energy, focal spot radius and pulse duration) and is found to be particularly sensitive to the peak laser pulse intensity. An ability to optically 'tune' the properties of an annular fast electron transport pattern may be important for applications. In the final investigation the effect that initial target temperature, and thus lattice melt, has on fast electron transport properties is demonstrated. Laser-accelerated proton beams are used to isochorically heat silicon for several tens-of-picoseconds prior to the propagation of fast electrons through the pre-heated target. This enables the influence of resistivity gradients, generated by proton-induced lattice melt, on fast electron transport properties to be explored. The experimental observation of an annular proton beam after t heat = 30 ps of proton pre-heating, which corresponds to annular electron transport within the target, is in excellent qualitative agreement with 3-D hybrid-PIC simulations of fast electron transport in a target containing an initial temperature (and thus, resistivity) gradient.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2014

Author dc:creator

• MacLellan, David Andrew

DOI

10.48730/fvk5-cs49

Identifier

T13849

OAI identifier oai:identifier

oai:strathclyde:xk81jk44d