また、この研究は、特定の動作条件で生成されたシートプラズマで、プラズマやシートプラズマの寸法を決定する動作パラメータなどのプラズマ条件を理解し、最適化パラメータと将来の産業用アプリケーションの条件を導き出すことも目的としています。 そのため、この研究は、表面技術アプリケーション用のシートプラズマデバイスの開発と理解に貢献することを試みています。 / Sheet plasmas have the advantage of producing thin films and functional surfaces by generating localized high-density and temperature gradient regions suitable for specific reactions. A stream of high energy electrons from a plasma cathode efficiently excites and/or ionizes atomic and molecular species which are confined in a linear magnetic field. An electron cyclotron resonance (ECR) sheet plasma device employing a 2.45 GHz microwave source and combination of permanent magnets and field coils was designed and operated. The combined field realized a linear magnetic field that sustained a rectilinear confinement of the plasma. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

A wide range of laboratory and naturally occurring plasmas are frequently attributed a fluid description and as such, demonstrate turbulent flows. We will investigate a variety of forms which may be taken by the correlation functions of these turbulent flows. The most commonly discussed isotropic symmetry is not generally applicable since most systems of interest have been shown to be strongly anisotropic. This thesis will develop an axi-symmetric description from which the magnetic helicity may be extracted together with its spectrum. This description will be compared to the form taken by axi-symmetric, helical Navier Stokes turbulence which will also be derived here. The microscales for this geometry will be tabulated and for completeness, the Von Karman Howarth equations will be derived.

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic (MHD) turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.;The statistical structure of two-dimensional MHD turbulence is also considered. It is shown that the three known rugged invariants of the isotropic case reduce to two for the anisotropic case. Randomness and ergodicity are also briefly discussed.

The stability and transition properties of a bounded, current carrying magnetofluid are explored, using the hydrodynamic theory developed for plane shear flows as a guide. A driven magnetohydrodynamic sheet pinch equilibrium is employed. A sixth order, complex eigenvalue equation which governs the normal modes of small oscillations is derived, and solved numerically by the Chebyshev tau method. Eigenfunctions are shown, as well as the curve of neutral stability. The locus of critical Lundquist numbers has the form of a hyperbola. The nonlinear stability of a primary disturbance of the system is considered. For regions in parameter space close to criticality, a nonlinear stability equation of the Landau type is derived. These regions are characterized by low values of the Lundquist numbers, in contrast with the inviscid, highly conducting limit considered by Rutherford (1973). Amplitude phase planes for these disturbances are exhibited. The full set of two dimensional magnetohydrodynamic equations is solved numerically by a semi-implicit, mixed Fourier pseudospectral-finite difference algorithm. Both linear and random perturbations of the system are followed numerically into the nonlinear regime. Current sheets and deflection currents are nonlinear structures found to be significant to the evolution of the system. A secondary instability mechanism, the dynamic rupturing of the current density sheet, is also observed.

This dissertation addresses the general problem of transport in chaotic systems. Typical fluid problem of the kind is the advection and diffusion of a passive scalar. The magnetic field evolution in a chaotic conducting media is an example of the chaotic transport of a vector field. In kinetic theory, the collisional relaxation of a distribution function in phase space is also an advection-diffusion problem, but in a higher dimensional space.;In a chaotic flow neighboring points tend to separate exponentially in time, exp({dollar}\omega t{dollar}) with {dollar}\omega{dollar} the Liapunov exponent. The characteristic parameter for the transport of a scalar in a chaotic flow is {dollar}\Omega\ \equiv\ \omega L\sp2/D{dollar} where L is the spatial scale and D is the diffusivity. For {dollar}\Omega\ \gg\ 1{dollar}, the scalar is advected with the flow for a time {dollar}t\sb{lcub}a{rcub}\ \equiv{dollar} ln(2{dollar}\Omega{dollar})/2{dollar}\omega{dollar} and then diffuses during the relatively short period 1/{dollar}\omega{dollar} centered on the time {dollar}t\sb{lcub}a{rcub}{dollar}. This rapid diffusion occurs only along the field line of the {dollar}\rm \ s\sb\infty{dollar} vector, which defines the stable direction for neighboring streamlines to converge. Diffusion is impeded at the sharp bends of an {dollar}\rm \ s{dollar} line because of a peculiarly small finite time Lyapunov exponent, hence a class of diffusion barriers is created inside a chaotic sea. This result comes from a fundamental relationship between the finite time Lyapunov exponent and the geometry of the {dollar}\rm \ s{dollar} lines, which we rigorously show in 2D and numerically validated for 3D flows.;The evolution of a general 3D magnetic field in a highly conducting chaotic media is also related to the spatial-temporal dependence of the finite time Lyapunov exponent. The Ohmic dissipation in a chaotic plasma will become a dominate process despite a small plasma resistivity. We show that the Ohmic heating in a chaotic plasma occurs in current filaments or current sheets. The particular form is determined by the time dependence of spatial gradient of the finite time Lyapunov exponent along a direction in which neighboring point neither diverge nor converge.

Quantum Cascade Lasers are a novel semiconductor light source with the unique property of wavelength tunability over the mid-infrared and terahertz range of frequencies. Advances since their first demonstration in 1994 have led to highly efficient designs capable of continuous room temperature operation. In lieu of increased advances in laser core efficiency, power scaling with broad area quantum cascade lasers has demonstrated enhanced continuous power. This initial work is used as a starting point for continuing advances in average brightness of quantum cascade lasers. A figure of merit calculation reliably predicts to within parts in thousands the qualitative beam profile of continuously driven and high duty cycle devices. Further, a model is developed to project performance not only in continuously driven conditions, but also in variable duty cycles. This is combined with the figure of merit calculation to guide designs for optimized average brightness.

A Hamiltonian treatment for the motion of a charged particle in a toroidal magnetic field is given. Assuming the plasma equilibrium, Boozer coordinates are used. The Hamiltonian of the exact trajectory is given in the guiding center coordinates. The higher order corrections to the standard drift Hamiltonian are derived. It is shown that the exact Hamiltonian depends on both the field strength and the shape of the magnetic surfaces (the metric of Boozer coordinates) while the standard drift Hamiltonian depends only on the field strength. The first order correction to the standard drift Hamiltonian, in gyroradius to system size, depends in a generic way on the shape of the magnetic surface, as does the exact Hamiltonian. Numerical calculations are done to compare the trajectories of the exact Hamiltonian, the standard drift Hamiltonian and the higher order drift Hamiltonian for a quasihelical symmetric vacuum field. The numerical results show that the difference in phase space structure between the exact and standard drift Hamiltonian can be predicted by the drift Hamiltonian with the first order correction.

Research conducted at Virginia Tech has examined plasma torch operational characteristics using a feedstock gas of mixed hydrocarbons representing a cracked JP-7 surrogate. The tests were part of a program to examine the torch as an igniter and flame-holder for hydrocarbon-fueled scramjet engines. Previous research has shown that the plasma torch has promise as a robust igniter and flame-holder using gaseous fuels such as methane, ethylene and propylene when combined with an aeroramp to assist with the combustion process. The present investigation tested the plasma torch with a feedstock mixture of gaseous hydrocarbons that simulates thermally cracked JP-7 jet fuel. This simulation of a cracked hydrocarbon fuel was studied to lay the foundation for work with liquid hydrocarbon fuel, which is of interest for today's aerospace vehicles. The cracked JP-7 surrogate consists of a 15/25/60 mixture of methane/ethane/ethylene. The research results include torch operational characteristics such as downstream plume temperatures and emission spectroscopy within the combustion plume, as well as the power supplied to the torch over a range of mass flow rates. Filtered photographs of the emissions plume were studied to aid torch plume diagnostics. Other observations made were erosion and alignment of the electrodes, which will help determine the potential lifespan of the torch using cracked JP-7 fuel. The results show successful operation over a range of powers with simulated cracked JP-7 feedstock flows. Measured spectra, current, and voltage are compared with similar results for other hydrocarbon feedstock gases. The torch operating on the JP-7 surrogate feedstock appears to be a satisfactory device for ignition, flame-holding, and combustion enhancement of cracked hydrocarbons in supersonic combustion. / Master of Science

The H-mode plasma edge is a region of steep gradients in density and temperature known as the “pedestal” which greatly increases energy confinement. The complex links between neutral-plasma interactions and both diffusive and convective transport in the pedestal must be understood to model, predict, and achieve the high performance required for a fusion power plant. This dissertation explores the effects of different hydrogenic isotope neutral particles and plasma transport from the edge pedestal region into the Scrape-Off Layer. Current experiments typically use deuterium (H with amu=2 or D), however future fusion power plants may startup with hydrogen (H), and eventually burn a mixture of deuterium and tritium (H with amu=3 or T). As isotope mass increases, energy confinement also increases in direct contradiction to the predicted scaling from diffusive theory, a phenomenon known as the “isotope effect”. Using a database of H and D pedestals on the DIII-D tokamak, we show indications that both species pedestals are in electron-dominant turbulence regimes, where increased outwards convection for hydrogen contributes to lower electron density pedestals consistent with gyrokinetic theory. However, this is complicated by indications of fueling differences between the isotopes. To isolate the effect of fueling, we conducted an experiment on DIII-D to match electron density (ne) and temperature (Te) profiles between hydrogen and deuterium, where neutral particle ionization profiles were measured with the newly available Lyman-α LLAMA diagnostic. On the High Field Side (HFS), neutral penetration lengths (λn0 ) across the pedestal are 40% longer for hydrogen compared to deuterium, consistent with the thermal velocity ratio between the isotopes (v_{H_{th}}/v_{D_{th}} = √2), while measurements on the Low Field Side (LFS) suggest a transport effect. The influence of neutral penetration on electron density pedestal width (∆ne) diminishes with increasing opaqueness (η ≡ ∆ne /λn0 ), shown by low opaqueness pedestals (η ∼ 0.9) in hydrogen being ∼ 40% wider than their deuterium counterparts. Higher opaqueness η ∼ 2 more effectively shields the pedestal from neutrals, as indicated by hydrogen and deuterium having nearly identical ∆ne . Moving across the separatrix into the Scrape-Off Layer, we conducted a diagnostic validation exercise using the ELZAR analysis method with stereoscopic fast cameras on MAST to detect field-aligned turbulent transport events known as “filaments”. Comparisons between the cameras show similar data in individual frames, inversion maps, and statistical distributions of located blobs. The two most important parameters for the framework connecting the statistics to SOL steady-state profiles are the lognormal distributions for filament radial position and major axis width which are within error between the cameras. The remaining distributions are unimportant to the statistical framework and we systematically attribute their differences to the experiment setup.

Charged particles constantly stream outward from the Sun to fill the solar system. These particles, consisting mainly of protons and electrons, form a plasma called the solar wind. The solar wind interacts with every celestial body in the solar system, giving rise to different phenomena, such as the auro- ras observed at high latitudes on Earth or disruption of the systems onboard artificial satellites.  The general structure of the solar wind has been established several decades ago, however we still do not fully understand how the solar wind properties, like temperature and velocity distribution, evolve as it propagates outward in the solar system. Observations of these properties cannot be explained from a conventional fluid description. In a system approximated as a fluid, particle collisions dictate its thermodynamic state. However, the solar wind is a weakly collisional plasma that deviates from thermodynamic equilibrium. Therefore, the radial evolution of the solar wind properties must be driven by different processes. In particular, wave-particle interactions are an important regulator of the solar wind properties, because of the strong connection between the electromagnetic fields and the charged particles.  In this thesis, we probe how the velocity distribution of solar wind par- ticles evolves as it travels from the Sun to the Earth. Specifically, we study the contribution of waves on the observed solar wind properties at different distances and how these waves can affect the interplanetary environment. We focus on two types of plasma waves frequently observed in the solar wind, Langmuir and ion-acoustic waves. We present their occurrence rates at differ- ent heliocentric distances and suggest wave generation mechanisms based on Solar Orbiter observations. We show that Langmuir waves in the unperturbed solar wind are more commonly observed in regions where the magnetic field magnitude is lower than the background value. Furthermore, we also find that the occurrence rate of ion-acoustic waves is increased in the ramp regions of interplanetary shocks observed at different heliocentric distances, compared to the ion-acoustic wave occurrence rate in the unperturbed solar wind.