Browsing by Subject "Electrons"
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Item An experimental and theoretical investigation of nonequilibrium behavior of electrons in gases(Texas Tech University, 1984-05) Young, Chris MorrowNot availableItem An investigation of non-equilibrium electron kinetics in nitrogen(Texas Tech University, 1983-12) Tzeng, YonhuaThe kinetic behavior of electrons immersed in a background gas or gas mixture under the action of an externally applied electric field with or without the influence of the space charge induced electric fields have been investigated. Novel Monte Carlo techniques have been developed and applied to study the evolution of the electrons self-consistently , that is, including the effects of the electric field generated by the space charge and the effects of boundaries. Statistical fluctuations of the macroscopic variables describing the evolution of the electron assembly have been studied. This is important when the total number of electrons is less than about 100. Ensemble averaged descriptions, kinetic in nature, have been used to study the development of an avalanche and the formation and propagation of a streamer. The results from this research program have provided key fundamental knowledge necessary for the explanation of the approach to equilibrium of an assembly of electrons, the effects of scattering processes on the electron velocity distribution, prebreakdown phenomena and manipulating the dielectric properties of gas mixtures used in insulating and switching applications.Item Hylleraas correlation in two-electron spectra(Texas Tech University, 1967-05) Minor, James MarshallElectron correlation is a method of obtaining a more accurate solution of the two-electron Schrodinger equation. In the Hylleraas type correlation method, the relative electronic coordinates are introduced into the wave function, and the variation principle is used to determine some adjustable parameters. Lennard-Jones and Pople and Brickstock and Pople have developed electron correlation in twoelectron systems in a more general way for both the ground states and excited states. The Hylleraas correlation is actually a special case of the general development. In this work, a Hylleraas-type correlation function is used to modify multiplet wave functions constructed from 2 hydrogenic orbitals of the (n, n - 1) configuration outside of closed shells. The effect upon the multiplet energy spacings of a two parameter correlation function is important to determine the feasibility of similar calculations involving a more sophisticated but more accurate basis set of functions, such as the Hartree-Fock orbitals.Item Laboratory visualization of laser-driven plasma accelerators in the bubble regime(2010-08) Dong, Peng; Downer, Michael Coffin; Becker, Michael; Ditmire, Todd; Lang, Karol; Shvets, GennadyAccurate single-shot visualization of laser wakefield structures can improve our fundamental understanding of plasma-based accelerators. Previously, frequency domain holography (FDH) was used to visualize weakly nonlinear sinusoidal wakes in plasmas of density n[subscript e] < 0.6 × 10¹⁹/cm³ that produced few or no relativistic electrons. Here, I address the more challenging task of visualizing highly nonlinear wakes in plasmas of density n[subscript e] ~ 1 to 3× 10¹⁹/cm³ that can produce high-quality relativistic electron beams. Nonlinear wakes were driven by 30 TW, 30 fs, 800 nm pump pulses. When bubbles formed, part of a 400 nm, co-propagating, overlapping probe pulse became trapped inside them, creating a light packet of plasma wavelength dimensions--that is, an optical "bullet"--that I reconstruct by FDH methods. As ne increased, the bullets first appeared at 0.8 × 10¹⁹/cm³, the first observation of bubble formation below the electron capture threshold. WAKE simulations confirmed bubble formation without electron capture and the trapping of optical bullets at this density. At n[subscript] >1× 10¹⁹/cm³, bullets appeared with high shot-to-shot stability together with quasi-monoenergetic relativistic electrons. I also directly observed the temporal walk-off of the optical bullet from the beam-loaded plasma bubble revealed by FDH phase shift data, providing unprecedented visualization of the electron injection and beam loading processes. There are five chapters in this thesis. Chapter 1 introduces general laser plasma- based accelerators (LPA). Chapter 2 discusses the FDH imaging technique, including the setup and reconstruction process. In 2006, Dr. N. H. Matlis used FDH to image a linear plasma wakefield. His work is also presented in Chapter 2 but with new analyses. Chapter 3, the main part of the thesis, discusses the visualization of LPAs in the bubble regime. Chapter 4 presents the concept of frequency domain tomography. Chapter 5 suggests future directions for research in FDH.Item Substorm induced electron energization(2005) Mithaiwala, Manish Jay, 1977-; Horton, C. W. (Claude Wendell), 1942-Item Two-electron correlation effects in Hartree-Fock atomic systems(Texas Tech University, 1969-05) Minor, James MarshallNot available