<p>The state of matter at extremely high pressures and densities is of fundamental interest to many branches of research, including planetary science, material science, condensed matter physics, and plasma physics. Matter with pressures, or energy densities, above 1 megabar (100 gigapascal) are defined as High Energy Density (HED) plasmas. They are directly relevant to the interiors of planets such as Earth and Jupiter and to the dense fuels in Inertial Confinement Fusion (ICF) experiments. To create HEDP conditions in laboratories, a sample may be compressed by a smoothly varying pressure ramp with minimal temperature increase, following the isentropic thermodynamic process. Isentropic compression of aluminum targets has been done using magnetic pressure produced by megaampere, pulsed power currents having ~ 100 ns rise times. In this research project, magnetically driven, cylindrical isentropic compression has been numerically studied. In cylindrical geometry, material compression and pressure become higher than in planar geometry due to geometrical effects. Based on a semi-analytical model for the Magnetized Liner Inertial Fusion (MagLIF) concept, a code called ?SA? was written to design cylindrical compression experiments on the 1.0 MA Zebra pulsed power generator at the Nevada Terawatt Facility (NTF). To test the physics models in the code, temporal progresses of rod compression and pressure were calculated with SA and compared with 1-D magnetohydrodynamic (MHD) codes. The MHD codes incorporated SESAME tables, for equation of state and resistivity, or the classical Spitzer model. A series of simulations were also run to find optimum rod diameters for 1.0 MA and 1.8 MA Zebra current pulses. For a 1.0 MA current peak and 95 ns rise time, a maximum compression of ~ 2.35 (~ 6.3 g/cm</p><p>3) and a pressure of ~ 900 GPa within a 100 ?m radius were found for an initial diameter of 1.05 mm. For 1.8 MA peak simulations with the same rise time, the initial diameter of 1.3 mm was optimal with ~ 3.32 (~ 9.0 g/cm</p><p>3) compression.

A laser ion source was investigated for a laser produced spatially bound plasma and the production of cluster ions. The design of a unique geometry for the target was fabricated to have a hollow cylindrical structure where the plasma is ignited inside the narrow volume. The study clarified the difference in the plasma dynamics of the laser ion source operation using the hollow cylinder target as the plasma was allowed to interact with the target surface. The proposed scheme, aiming to produce a low plasma temperature condition, was observed to the increase the probability for agglomeration and generated cluster ions. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

We consider strong wave propagation in the generalized compressible Euler equations. Our results include pairwise interactions of nonlinear waves, smooth wave propagation, formation of gradient blowup and several exact examples. In particular, we directly generalize P.Lax’s gradient blowup results for conservation laws with two variables to the generalized compressible Euler equations.

The results of nuclear magnetic resonance (NMR) on thin $\sp3\rm{He}$-$\sp4$He mixture films at temperatures 24mK $\leq T \leq$ 650mK which are adsorbed to Nucleopore are reported. The nuclear magnetic susceptibility, the relaxation times T$\sb1$ and T$\sb2$, and the spin diffusion coefficient, D, were measured used pulsed NMR techniques in a 2 Tesla field. The $\sp4$He coverages investigated ranged from 0.137 $\leq n\sb4\leq$ 0.534 atoms A$\sp2$ with a fixed submonolayer $\sp3$He coverage of 0.00746 $\leq n\sb3 \leq$ 0.00749 atoms A$\sp2.$ At $n\sb4$ = 0.391 atoms/A$\sp2$ measurements were taken with the $\sp3$He coverage ranging 0.00749 $\leq n\sb3 \leq$ 0.0179 atoms/A$\sp2$. We present the $\sp3$He magnetization as a function of the $\sp4$He coverage. The magnetization is degenerate for temperatures below the Fermi temperature, T$\sb{F}$, and from the degenerate magnetization the hydrodynamic mass over a range of $\sp4$He coverages is obtained. Variational and density functional descriptions of the film are considered. The diffusion data are seen to rise rapidly, from 10$\sp{-8}$ to 10$\sp{-3}\ \rm{cm}\sp2$/sec, as the $\sp4$He coverage is increased from 0.19 to 0.39 atoms/A$\sp2$, a range of just 2.5 layers. For $T < T\sb{F}$ the temperature dependence of a degenerate Fermi gas is not seen; $D \not= T\sp{-2}$. For all coverages T$\sb1$ is two orders of magnitude larger than T$\sb2$. Two regimes are seen. For coverages $n\sb4 <$ 0.23 the temperature dependence of T$\sb1$ and T$\sb2$ are consistent with $\omega\tau\sb{c} \gg$ 1. A signature of the completion of the second layer of the $\sp4$He is seen in T$\sb{1}$. For coverages $n\sb4 >$ 0.23, $\omega\tau\sb{c} \ll$ 1 and the temperature dependence correlates with the superfluid areal density. Activated behavior is seen which probes higher bound states of the $\sp3$He in the $\sp4$He film.

Chaotic mixing of viscous fluids in slow flows is pervasive in the chemical and polymer industries but poorly understood. However, relatively simple experiments provide a wealth of information regarding mixing mechanisms and indicate the need for complementary theoretical developments in dynamical systems. In this thesis, we present a versatile cavity flow apparatus, capable of producing a variety of two-dimensional velocity fields, and use it to conduct a detailed experimental study of mixing of Newtonian and viscoelastic fluids in low Reynolds number flows. Since the goal is detailed understanding, only two time-periodic cavity flows induced by tangential wall motions are considered: one continuous and the other discontinuous. In the Newtonian case, the two flows produce exponential growth of intermaterial area, as expected from chaotic flows, and a mixture of islands and chaotic regions. A procedure for identifying periodic points and determining their movements is presented as well as how to make meaningful comparisons between periodic flows. We observe that periodic points move very much as a planetary system; planets (hyperbolic points) have moons (elliptic points) with twice the period of the planets; furthermore the spatial arrangement of periodic points becomes symmetric at regular time intervals. Detailed analyses reveal complex behavior: birth, bifurcation, and collapse of islands; formation and periodic motion of coherent structures, such as islands and large scale folds. Experimental results show that the viscoelastic systems also exhibit regular and chaotic regions, and the large scale structures--folds and symmetry--in the viscoelastic systems are remarkably similar to that of the Newtonian systems. But, the islands in the viscoelastic systems are significantly larger than the Newtonian's, and the size of those islands increases monotonically with increasing Deborah number.

No description available.

This dissertation details the nature of subnanosecond laser-induced microplasma dynamics, particularly concerning the evolution of the electron temperature and concentration. Central to this development is the advent of a femtosecond four-wave mixing (FWM) spectroscopic method. FWM (in the form of coherent anti-Stokes Raman scattering (CARS)) measurements are performed on the fundamental oxygen vibrational transition. An analytical expression is provided that accounts for the resonant and nonresonant contributions to the CARS signal generated from the interaction of broadband pump and Stokes pulses. The inherent phase mismatch is also accounted for, resulting in quantitative agreement between experiment and theory. FWM is then used to measure the early-time electron dynamics in the noble gas series from He to Xe following irradiation by an intense (10^14 Wcm-2) nonresonant 80 fs laser pulse. An electron impact ionization cooling model is presented to determine the evolution of electron kinetic energies following ionization. Kinetic energies are predicted to evolve from &gt; 20 eV to &lt; 1 eV in the first 1.5 ns. The initial degree of ionization is determined experimentally via measurement of the Bremsstrahlung background emission, and modeled with a modified ADK theory based on tunnel ionization. Combined, these two descriptions account for the evolution of both the electron temperature and concentration and provide quantitative agreement with the FWM measurements. The model is further tested with measurements of the gas pressure and pump laser intensity on the electron dynamics. The FWM experiments are concluded with a qualitative discussion of dissociative recombination dynamics occurring in molecular microplasmas. The microplasma environment is used as a source for the generation of two-level systems in the excited state manifold of atomic oxygen and argon. These two-level systems are coupled using moderately intense ~1 ps near-infrared (and near-resonant) pulses, resulting in Rabi sidebands with unprecedentedly large shifts in excess of 90 meV. A time-dependent generalized Rabi-cycling model is developed to account for the time-dependence of the laser electric field and subsequently the Rabi frequency. The Rabi radiation is determined to be coherent and tunable (up to 200 meV), providing a new method for ultrashort pulse generation. The dependence of the spectral positions of the Rabi sidebands on laser intensity affords the opportunity to simultaneously determine the ratios of transition dipole moments for the states accessed. / Chemistry

Plasmas involving strong electron drift in crossed electric and magnetic fields are of great interest for a number of applications such as space propulsion and material processing plasma sources. Specific applications include Hall thrusters, which are high efficiency, low thrust propulsion systems used on many missions for satellite orbit corrections and for future planned interplanetary missions, as well as magnetrons of various configurations used in plasma deposition devices. Similar conditions also exist in the E-layer of the ionosphere and on the Sun. Despite many successful applications of Hall thrusters and other Hall plasma sources, some aspects of their operation are still poorly understood. A particularly important problem is the anomalous electron transport, which greatly exceeds classical collisional values. Hall plasma devices exhibit numerous turbulent fluctuations in a wide frequency range and it is believed that fluctuations resulting from plasma instabilities are likely one of the main causes of the observed anomalous transport. Plasma turbulence also affects many other important processes such as electron injection, location of the ionization region and wall erosion among others that influence the operation and efficiency of Hall thrusters. In Hall thrusters, the E0xB0 flow is made unstable due to gradients in the plasma density, temperature and magnetic field. The gradient drift instabilities are long wavelength instabilities that propagate in the azimuthal direction. A fluid theory of these unstable modes is proposed. It is shown that a full account of the compressibility of the electron flow in inhomogeneous magnetic field leads to quantitative modifications of the previously obtained instability criteria and characteristics of the unstable modes. The ExB drift also drives ion sound type instabilities in Hall thrusters. The reactive/dissipative response of the closure current to the thruster walls drives these negative energy modes. A model for this type of instabilities is proposed and analyzed for typical Hall thruster conditions. It is shown how wall parameters modify the characteristic growth rate and frequency of the unstable modes and the related anomalous transport. Nonlinear phenomena are important to understand different aspects of the Hall thruster plasma dynamics. A nonlinear fluid model for the typical Hall thruster plasma is proposed. The model takes into account electron inertia, electron collisions with neutrals, density gradients as well as various nonlinear terms that arise from the electron drift and nonlinear polarization that were included via the gyroviscous cancellation. The proposed model includes the long wavelength and the low hybrid modes destabilized by density gradients and collisions. This system of fluid equations was implemented using the computational framework BOUT++ from which a set of nonlinear simulations of plasma turbulence was performed. It is shown from these first principles nonlinear simulations that small scale low hybrid oscillations result in an anomalous electron current significantly exceeding the classical collisional current.

No description available.

No description available.