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Title: Particle interactions in high temperature plasmas
Author: Pike, Oliver
ISNI:       0000 0004 5367 6688
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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High temperature plasmas are ubiquitous in high energy astrophysics and are becoming increasingly accessible in the laboratory. This thesis is concerned with two interactions that are important in these systems. The first is the Coulomb interaction, which influences phenomena in systems ranging from controlled fusion experiments to catastrophic astrophysical events. In many of these cases, the motion of the electrons is relativistic. To account for this we extend Spitzer's famous work on dynamical friction in a plasma to relativistic interactions, deriving the Fokker-Planck coefficients and test particle relaxation rates in the same analytical form as Trubnikov's classical results. Following this, we present a self-consistent transport theory for a relativistic, magnetised plasma, including simple polynomial fits to the transport coefficients for various values of atomic number. This is the relativistic generalisation of the work of Braginskii and, within the confines of linear transport theory, is valid for all temperatures and field strengths of interest. These results are subsequently verified using Monte Carlo simulations, and the effects of non-Gaussian multiple scattering on transport in a plasma are shown to be small. Beyond relativistic corrections, high temperature plasmas are fundamentally different to their classical counterparts due to the possibility of pair production. One of the primary mechanisms for this and the second interaction we consider is the Breit-Wheeler process: the formation of an electron-positron pair in the collision of two photons. Despite being the simplest way in which light can be converted into matter, this process has never been directly observed in the laboratory. Here, we present a new design of photon-photon collider, in which a laser wakefield-driven gamma-ray beam is fired into the high temperature radiation field of a laser-heated hohlraum. On matching experimental parameters to current facilities, Monte Carlo simulations suggest this is capable of producing over 10^5 Breit-Wheeler pairs per shot.
Supervisor: Rose, Steven Sponsor: Engineering and Physical Sciences Research Council ; Atomic Weapons Establishment
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral