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Title: Magnetohydrodynamic modelling of supersonic jets and colliding blast waves for laboratory astrophysics investigation
Author: Marocchino, Alberto
ISNI:       0000 0004 2687 1015
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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The thesis is related to laboratory astrophysics, and investigates with this technique, the launching mechanism for young stellar object jets and the interaction of two supernovae remnant in the Sedov-Taylor regime. Recent experiments performed at Imperial College on the pulsed-power magpie facility have successfully shown the formation of magnetically driven radiatively cooled plasmas jets formed from radial wire arrays, which are relevant to studying the launching mechanisms of astrophysical jets [A. Ciardi, et al. Phys. Plasmas 14, p056501 (2007)]. The experiments have been now extended to study episodic mass ejection ( 25 ns [F. A. Suzuki-Vidal, et al. 49th Annual Meeting of the Division of Plasma Physics, UO4.00007 (2007)]) and the interaction of jets and magnetic bubbles with an ambient gas. The dynamics of the interaction is investigated through three-dimensional resistive magneto-hydrodynamic simulations using the code gorgon [A. Ciardi, et al. Phys. Plasmas 14, p056501 (2007) – J.P. Chittenden, et al. Plasma Phys. Control. Fusion 46 B457 (2004)]. In particular ablation of the cathode is investigated numerically to explain the periodicity and subsequent formation of multiple bubbles. Comparison with experiments is offered to validate the results. The complex structure of the magnetic field is investigated, the conservation of the magnetic flux is explained and the consequent confinement offered to the central jet. Furthermore the interaction of the plasma outflows with an ambient gas is investigated. The formation of shocks in the ambient gas, as well as the formation of three-dimensional Mach stems is analyzed. In addition, recent experiment at Imperial College performed by the QOLS group, by laser-heating a medium of atomic clusters [R. A. Smith, et al. 2007 Plasma Phys. Control. Fusion 49 B117-B124 (2007)], shows the capability to create plasmas with sufficiently high energy densities to launch strong shocks. Interactions between high-Mach number shock waves are believed to be responsible for many of the complex, turbulent structures seen in astrophysical objects including supernova remnants. The experiment of two colliding Sedov-Taylor regime blast-waves is modelled. Detailed 3D numerical modeling is performed in order to study the importance of thermal conduction, rarefaction waves, refractive shock waves and complex three-dimensional mach stem formation. The simulated data are benchmark against a three-dimensional tomography image (newly developed experimental technique). The collision of two blast-waves should reproduce the non uniform interstellar medium where supernovas normally expand.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral