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Title: Creating and probing warm dense matter and high energy density blast waves
Author: Doyle, Hugo William
ISNI:       0000 0004 2712 8717
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Non-ideal plasmas are difficult to model numerically and achieve experimentally. Here I focus on reaching the warm dense matter (WDM) regime at one end of the energy scale and the high energy density (HED) regime at the other. Both regimes access common, yet hard to observe, features in planetary core physics and astrophysics respectively. We have implemented several experiments developing both ionic, isochoric heating of matter to HED states, and probing the release isentrope through the WDM regime. Using sub-picosecond, ~ 100 J laser pulses, ion beams were produced in a thin foil interaction and then used to rapidly and uniformly heat ~ 20 µm wires to ~15 eV temperatures before hydrodynamic expansion could occur. Thus the partially ionised, strongly coupled WDM regime was accessed and then explored using streaked XUV and UV imaging of the expansion into vacuum, together with measurement of the ion spectra deposited in the sample. The calibrated ion spectra indicates the energy deposition occurs over ~ 400 ps and as such further investigation of the stopping power of warm dense matter is required. The high absorption of these laser pulses in cluster gases (> 90%) was used to create HED blast waves. Under hydrodynamic scaling laws these blast waves can be used to model processes occurring within astrophysical phenomena. Schlieren, interferometry and ion probing methods have been used to spatially and temporally resolve the blast wave profiles. We describe high energy scaling experiments in the search for the thermal cooling instability, in which radiation from the blast wave modi es both its density profile and propagation dynamics. A unique perpendicular, time delayed colliding blast wave geometry has been used to identify up-stream characteristics of the front propagation and to pre-heat material leading to shock front acceleration. We show that ions of an energy greater than ~ 200 keV are required to probe the transient electromagnetic fields believed to occur at the shock front. The development and characterisation of low energy (0.1 - 10 MeV) proton beams was necessary for studies of both non-ideal plasma regimes, particularly for probing high density media and transient electromagnetic fields. The application of ions to recover stopping power is discussed for WDM and HED plasmas.
Supervisor: Smith, Roland Sponsor: AWE
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral