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Title: The dynamics of strong laser-driven shocks in cluster media
Author: Hohenberger, Matthias
ISNI:       0000 0004 2688 2750
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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Shocks and blast waves are ubiquitous features observed in plasma physics and in astrophysical phenomena and, as such, have long been the subject of experimental and theoretical studies. This thesis describes experimental and numerical investigations of the dynamics of laser driven shocks in cluster media. Target gases of atomic clusters have been shown to exhibit e cient absorption of high-intensity laser radiation, allowing to use `table-top' scale laser systems to drive high Mach-number shock waves. By applying hydrodynamic scaling laws, these systems can provide insight into the physics governing much larger astrophysical phenomena, such as supernova remnants. Experiments were conducted to investigate the structure and propagation dynamics of cylindrical blast waves in radiative and non-radiative gases. Shock pro ling studies performed at Imperial College London are presented, that highlight the need for non-LTE calculations of the shock physics. Investigations into the onset of the radiation driven thermal cooling instability (TCI) were performed by means of a streaked Schlieren technique, developed to obtain single-shot shock trajectory measurements, while removing any ambiguities imposed by shot-to-shot uctuations. In order to scale previous results to higher drive energies, experiments were performed using the Vulcan laser facility at the Rutherford Appleton Laboratory. The resulting cluster absorption and shocked gas comparison data is discussed in detail, including data indicating the rst experimental observation of TCI. To study shock collisions, a unique focal geometry has been employed, creating two near-parallel cylindrical shocks. By means of an interferometric tomography technique, the full 3D electron density pro le was reconstructed, showing complex material transport and Mach stem formation at the oblique shock collision interface, con rmed by 3D hydrodynamics simulations. To investigate this feature further, shock interactions with an obstruction were also performed, showing interesting propagation features through density steps imposed by the obstruction in the cold gas stream.
Supervisor: Smith, Roland Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral