Abstract
The main goal of this work is the numerical investigation of the plasma dynamic evolution of Z-pinch and X-pinch devises. A more thorough investigation of the jet formation mechanisms and dynamic evolution of a two-wire tungsten X-pinch formation along with experimental validation is presented. Additionally a possible correlation to astrophysical jets of YSO and HH objects is discussed. Specifically this study contributes to the estimation of the scalability factors and all the relevant numbers and parameters for a low current X-pinch tungsten plasma configuration. In order to achieve robust, flexible and realistic computational simulation models, a variety of different numerical and physical schemes is needed. An extra study for this dissertation, is the synthesizing process of extracting physical formulas for all the dissipative terms for all density and temperature regimes. The synthesis of different physical formulas for piece-wise functions or correction factors to already known f ...
The main goal of this work is the numerical investigation of the plasma dynamic evolution of Z-pinch and X-pinch devises. A more thorough investigation of the jet formation mechanisms and dynamic evolution of a two-wire tungsten X-pinch formation along with experimental validation is presented. Additionally a possible correlation to astrophysical jets of YSO and HH objects is discussed. Specifically this study contributes to the estimation of the scalability factors and all the relevant numbers and parameters for a low current X-pinch tungsten plasma configuration. In order to achieve robust, flexible and realistic computational simulation models, a variety of different numerical and physical schemes is needed. An extra study for this dissertation, is the synthesizing process of extracting physical formulas for all the dissipative terms for all density and temperature regimes. The synthesis of different physical formulas for piece-wise functions or correction factors to already known formulas or combination formulas, provide flexibility for any MHD numerical scheme and also, for any Z or X-pinch configuration at any density, thermal pressure and plasma temperature regime. The graphic presentation of these formulas, as a comparison evaluation tool with experimental/semi-empirical or other studies data, is provided and estimated by the author.The mathematical transformation of any Local plasma configuration to the Global coordinate system is a supplementary and necessary study, as it provides the appropriate spatial profiles for all the physical variables and assisting for the best spatial resolution that can be computationally executable. Moreover, the mathematical transformations through rotation and displacement matrices are presented correlating the mass density, thermal pressure and magnetic field Local components to the Global ones. The latter is important due to the novelty of the initial condition spatial implementation of the magnetic field. Examples of Z and X-pinch configurations are discussed according to these transformations. Information over the physical, mathematical and numerical implementation procedure of the new modifications to the code and the significance they have along the simulation run, is presented and discussed. The choice of the appropriate Riemann solver, the radiation transport module, the appropriate boundary conditions for the computational box, the magnetic field initial topology and the correct updating along the simulation run are, among others, subjects of this thesis analysis! Two specific simulation applications of these transformations are preliminary tested and evaluated, through the experimental and other simulation studies bibliographic data. The first is a "cold" start X-pinch configuration using two unmerged metallic tungsten wires, starting just before the ablation phase and the merging in a denser cross-point area. The focus of this simulation is at the cross-point area. The study ends when the merging is succeeded and the formation of the axial jets is initiated. Similarities with astrophysical jet mechanisms, are discussed. The second is a four tungsten, thin wire, low current Z-pinch array configuration study till the stagnation phase. Both studies present novel and very promising results for future work.The computational results study presents the dynamic behavior of 1/4 spatial model of a single tungsten Z-pinch wire evaluating the contribution of the radiation transport module to the appropriate plasma evolution. A 1/16 spatial model, of an X-pinch tungsten plasma configuration for a wide wire angle, is subsequently studied. The spatiotemporal plasma jet formation and evolution is presented and discussed. The simulated areal mass density is compared with the experimentally measured dense opaque region to enlighten the dense plasma evolution. In addition, the measured experimental areal electron density is compared to the simulation results. The main jet formation mechanisms are analyzed and discussed in relation to the influence of the J×B force and the mass momentum density.The physical and numerical modeling differences of GORGON and PLUTO and their influence on the simulation results are demonstrated and analyzed, for a sharp two-wire tungsten load X-pinch geometry. Six different computational MHD schemes are presented at a specific spatial moment only for PLUTO. The model comparison provides valuable information on the improvement of flexible and efficient X-pinch models according to the experimental data and offer crucial insights on the mechanisms of plasma evolution and jet formation.The scalability and jet astrophysical relevancy estimation, for the wide wire angle X-pinch pulsed power configuration, is attempted. All relevant dimensionless numbers are calculated for the X-pinch plasma and compared to the ones of other laboratory astrophysics experiments and to the ones of YSOs, HHs and other astrophysical objects.Keywords: MHD, plasma, Astrophysical jets, YSO, Laboratory Astrophysics, PLUTO code, GORGON code
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