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Title: Self-generated magnetic fields in intense laser-solid interactions relevant to relativistic plasma astrophysics
Author: Butler, Nicholas Mark Henry
ISNI:       0000 0004 7226 4398
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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This thesis reports on self-generated magnetic fields in ultra-intense laser interactions with dense plasma and the role that these play in the dynamics of relativistic electrons, and, subsequently, ion acceleration. This includes an investigation of resistive magnetic fields generated within solids and their influence on the transport of multi-mega-Ampere currents of energetic electrons. It also includes investigations of magnetic fields in foils expanded to near-critical density, produced by the Biermann battery and Weibel instability mechanisms. The first part of the thesis explores the transport of relativistic electrons in relatively thick solids, specifically, different allotropes of lithium, silicon and carbon. This is initially explored numerically. Simulations, performed using a three-dimensional hybrid-particle-in-cell codes are used to investigate how the material resistivity-temperature profile affects fast electron transport via self-generated magnetic fields. The degree of lattice order in the material strongly affects electrical resistivity at low temperatures. By considering resistivity-temperature profiles intermediate to those of ordered and disordered arrangements of ions, it is shown that the magnitude and shape of the resistivity-temperature profile at low temperatures strongly affects the growth of self-generated resistive magnetic fields and the onset of resistive transport instabilities. The scaling of these effects to scenarios relevant to the fast ignition scheme for inertial confinement fusion is also discussed. Following this, the influence of the low temperature electrical resistivity on the onset of the resistive filamentation instability is investigated, both experimentally and numerically, in targets consisting of layers of ordered and disordered forms of carbon. It is demonstrated that the thickness of the disordered carbon layer influences the degree of filamentation of the fast electron beam, with strong filamentation produced for thickness of the order of 60μm or greater. Furthermore, it is also shown that the position of the disordered carbon layer (within the layered target) has a minimal influence on the growth of the resistive filamentation instability. The second part of the thesis explores the influence of self-generated magnetic fields on the dynamics of electron motion in ultrathin foil targets expanding to near-critical density and undergoing relativistic induced transparency. The generation of a plasma jet, supported by a self-generated azimuthal magnetic field is explored. The parameters of the jet and its sensitivity to the experimental parameters are characterised. Following this, the onset of Weibel instability-generated magnetic fields is investigated, as diagnosed by the formation of bubble-like structures in the beam of protons accelerated from the foil. The sensitivity of the Weibel-generated magnetic fields to the decompression of the target is explored. An analysis of the scaling of the relativistic plasma jet is presented, exploring the possibility of employing these laboratory-generated structures as analogues of astrophysical relativistic plasma jet phenomena.
Supervisor: McKenna, Paul Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral