Physical Sciences and Mathematics Commons^™

Dual Energy Electron Storage Ring Cooler Design For Relativistic Ion Beams, Bhawin Dhital

Physics Theses & Dissertations

Collider experiments demand small beam emittances in order to achieve high luminosity. For light particles such as electrons, there exists a natural synchrotron radiation damping resulting in low emittance beams at equilibrium. In the case of heavy particle beams such as proton or ion beams, there is no significant synchrotron radiation damping effect and some cooling mechanism is needed to get to low emittance beams. A dual energy storage ring cooler is a novel concept proposed to cool hadron beams at higher energies. The design consists of two rings: a low energy ring and a high energy ring connected by …

Pulse Power Effects On Transient Plasma Ignition For Combustion, David Wayne Alderman Ii

Electrical & Computer Engineering Theses & Dissertations

Transient plasma ignition (TPI) uses highly non-equilibrium plasmas, driven by less than 100 nanosecond, high-voltage pulses, to initiate combustion. The effects of pulse repetition frequency (PRF) and ultrashort nanosecond rise times on TPI are investigated in this work using lean, stoichiometric, and rich air-fuel mixtures at atmospheric pressure. Experimental data show the transient plasmas driven by ultrashort rise time, high voltage pulses at high PRF’s enhance the combustion of lean or stoichiometric air-methane mixtures in a static chamber. In particular, increasing PRF enhances the combustion performance by means of reduced delay times independent of the equivalence ratio of the air-fuel …

Characterization Of Argon And Ar/Cl2 Plasmas Used For The Processing Of Niobium Superconducting Radio-Frequency Cavities, Jeremy J. Peshl

Physics Theses & Dissertations

The plasma processing of superconducting radio-frequency (SRF) cavities has shown significant promise as a complementary or possible replacement for the current wet etch processes. Empirical relationships between the user-controlled external parameters and the effectiveness of Reactive Ion Etching (RIE) for the removal of surface layers of bulk niobium have been previously established. However, a lack of a physical description of the etching discharge, particularly as the external parameters are varied, limits the development of this technology. A full understanding of how these external parameters affect both the amount of material removed and the physical properties of the plasma would aid …

Generation Of Large-Volume Diffuse Plasma By An External Ionization Wave From A Single-Electrode Plasma Jet, Seyed Hamid Razavi Barzoki

Electrical & Computer Engineering Theses & Dissertations

A non-thermal transient diffuse plasma can be generated remotely in a nonconductive reduced pressure chamber by an external guided fast ionization wave (FIW). We found that an atmospheric-pressure low-temperature plasma jet (APPJ) can be a source of FIW which transfers an enhanced electric field at the wave front across a reduced pressure Pyrex glass chamber with no electrical connection to the chamber. Here, we studied the formation and propagation of the APPJ plasma, the interaction of atmospheric-pressure guided FIW with a dielectric surface which forms the wall of the reduced-pressure system, and the formation and propagation of the reduce-pressure FIW …

Instrument Design Optimization With Computational Methods, Michael H. Moore

Physics Theses & Dissertations

Using Finite Element Analysis to approximate the solution of differential equations, two different instruments in experimental Hall C at the Thomas Jefferson National Accelerator Facility are analyzed. The time dependence of density fluctuations from the liquid hydrogen (LH2) target used in the Q_weak experiment (2011-2012) are studied with Computational Fluid Dynamics (CFD) and the simulation results compared to data from the experiment. The 2.5 kW liquid hydrogen target was the highest power LH2 target in the world and the first to be designed with CFD at Jefferson Lab. The first complete magnetic field simulation of the Super High Momentum …

Low Temperature Plasma For The Treatment Of Epithelial Cancer Cells, Soheila Mohades

Electrical & Computer Engineering Theses & Dissertations

Biomedical applications of low temperature plasmas (LTP) may lead to a paradigm shift in treating various diseases by conducting fundamental research on the effects of LTP on cells, tissues, organisms (plants, insects, and microorganisms). This is a rapidly growing interdisciplinary research field that involves engineering, physics, life sciences, and chemistry to find novel solutions for urgent medical needs. Effects of different LTP sources have shown the anti-tumor properties of plasma exposure; however, there are still many unknowns about the interaction of plasma with eukaryotic cells which must be elucidated in order to evaluate the practical potential of plasma in cancer …

Plasma Processing Of Superconducting Radio Frequency Cavities, Janardan Upadhyay

Physics Theses & Dissertations

The development of plasma processing technology of superconducting radio frequency (SRF) cavities not only provides a chemical free and less expensive processing method, but also opens up the possibility for controlled modification of the inner surfaces of the cavity for better superconducting properties. The research was focused on the transition of plasma etching from two dimensional flat surfaces to inner surfaces of three dimensional (3D) structures. The results could be applicable to a variety of inner surfaces of 3D structures other than SRF cavities. Understanding the Ar/Cl₂ plasma etching mechanism is crucial for achieving the desired modification of Nb …

Characterization Of Microwave Discharge Plasmas For Surface Processing, Milka Nikolic

Physics Theses & Dissertations

We have developed several diagnostic techniques to characterize two types of microwave (MW) discharge plasmas: a supersonic flowing argon MW discharge maintained in a cylindrical quartz cavity at frequency ƒ = 2.45 GHz and a pulse repetitive MW discharge in air at ƒ = 9.5 GHz. Low temperature MW discharges have been proven to posses attractive properties for plasma cleaning and etching of niobium surfaces of superconductive radio frequency (SRF) cavities. Plasma based surface modification technologies offer a promising alternative for etching and cleaning of SRF cavities. These technologies are low cost, environmentally friendly and easily controllable, and present a …

Application Of Chebyshev Formalism To Identify Nonlinear Magnetic Field Components In Beam Transport System, Michael Spata

Physics Theses & Dissertations

An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a beam-based technique for characterizing the extent of the nonlinearity of the magnetic fields of a beam transport system. Horizontally and vertically oriented pairs of air-core kicker magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the beam orbit relative to the unperturbed reference orbit. Fourier decomposition of the position data at eight different points along the beamline was then used to measure the amplitude of these frequencies. For a purely linear transport system one expects to find solely the …

Case Studies In Many-Body Physics, Ana Samolov

Physics Theses & Dissertations

The many-body problem refers to any physical problem made of more than two interacting particles. With increasing number of particles in a system, their coupling and entanglement becomes more complex, and there is no general analytic solution even for a three-body classical or quantum systems. However, some of the most fascinating phenomena in nature are products of collective effects. Therefore, significant efforts have been made in both experiment and theory to unravel some specific many-body problems. If we look at still unanswered physics questions we see that for most of these problems addressing the many-body interactions is a key issue. …

Characterizations Of Atmospheric Pressure Low Temperature Plasma Jets And Their Applications, Erdinc Karakas

Electrical & Computer Engineering Theses & Dissertations

Atmospheric pressure low temperature plasma jets (APLTPJs) driven by short pulses have recently received great attention because of their potential in biomedical and environmental applications. This potential is due to their user-friendly features, such as low temperature, low risk of arcing, operation at atmospheric pressure, easy handheld operation, and low concentration of ozone generation. Recent experimental observations indicate that an ionization wave exists and propagates along the plasma jet. The plasma jet created by this ionization wave is not a continuous medium but rather consists of a bullet-like-structure known as "Plasma Bullet". More interestingly, these plasma bullets actually have a …

Experimental Investigation Of A Non-Thermal Atmospheric Pressure Plasma Jet, Asma Begum

Electrical & Computer Engineering Theses & Dissertations

The main objective of this dissertation is to understand the formation of the plasma jet from the plasma pencil, and the propagation of the plasma jet in the ambient atmosphere where the effect of the external electric field is almost zero. Before investigating the formation and propagation phenomenon of the plasma jet, common physical properties of plasma jets are determined by using the imaging technique and optical emission spectroscopy. The first goal of this dissertation is to establish the laminar helium gas flow channel through a plasma pencil.

The formation position, formation time, and the criterion of the plasma jet …

Characterization Of Microwave Cavity Discharges In A Supersonic Flow, Dareth Janette Drake

Physics Theses & Dissertations

A partially ionized gas is referred to as either a plasma or a discharge depending on the degree of ionization. The term discharge is usually applied to a weakly ionized gas, i.e. mostly neutrals, where as a plasma usually has a larger degree of ionization. To characterize a discharge the plasma parameters, such as the rotational temperature, vibrational temperature, and electron density, must be determined. Detailed characterization of supersonic flowing discharges is important to many applications in aerospace and aerodynamics. One application is the use of plasma-assisted hydrogen combustion devices to aid in supersonic combustion. In conditions close to the …

Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara

Mechanical & Aerospace Engineering Theses & Dissertations

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and unsteady solutions are obtained …

Self-Organization In Cathode Boundary Layer Discharges, Nobuhiko Takano

Electrical & Computer Engineering Theses & Dissertations

Cathode boundary layer (CBL) discharge, which has been developed as a UV light source, operates in a direct current between a planar cathode and a ring-shape anode that are separated by a dielectric with an opening of the same diameter as the anode. The nonthermal CBL discharges operate in a medium pressure range down to 30 Torr, emitting excimer radiation when operated with noble gases. The radiant excimer emittance at 172 nm in xenon reaches 1.7 W/cm², and a maximum excimer efficiency of 6 % has been obtained. The high excimer radiant emittance, in addition to low cost …

Scaling And Characterization Of Direct Current Glow Discharge Plasma In Atmospheric Air, Abdel-Aleam Hefney Mohamed

Electrical & Computer Engineering Theses & Dissertations

A microhollow cathode discharge was used as a plasma cathode to sustain a stable direct current glow discharge in atmospheric pressure air. The volumetric scale of glow discharge increased from the millimeter to the centimeter range by extending the plasma in lateral and axial directions. In the axial direction, the length of the glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with the glow discharge column length. Extension in the lateral direction was obtained by operating discharges in parallel. The glow discharge plasma of the parallel discharge columns was found to …

Microdischarge Arrays, Wenhui Shi

Electrical & Computer Engineering Theses & Dissertations

Microhollow cathode discharges (MHCDs) are DC or pulsed gas discharges between two electrodes, separated by a dielectric, and containing a concentric hole. The diameter of the hole, in this hollow cathode configuration, is in the hundred-micrometer range. MHCDs satisfy the two conditions necessary for an efficient excimer radiation sources: (1) high energy electrons which are required to provide a high concentration of excited or ionized rare gas atoms; (2) high pressure operation which favors excimer formation (a three-body process). Flat panel excimer sources require parallel operation of MHCDs. Based on the current-voltage characteristics of MHCD discharges, which have positive slopes …

Decomposition Of Carbon Dioxide In A Capacitively Coupled Radio Frequency Discharge, Thao Hoang Dinh

Physics Theses & Dissertations

Decomposition of CO₂ was studied in a capacitively coupled radio frequency discharge using Martian Simulant Gas mixture that contains 95% CO₂. The discharge was operated at a gas pressure of 3 to 6 Torr and a discharge power density of less than 2.0 W/cm³. The main mechanism of the CO₂ decomposition process is the electron impact dissociation and the rate of the process depends on the electron density, Ne, the concentration of CO₂, and the reduced electric field, E/N. A self-consistent model was established to describe the CO …

High Resolution Laser Absorption Spectroscopy Of Ozone Near 1129.4 Cm-1, Lawrence N. Majorana

Physics Theses & Dissertations

A Beer's Law experiment was performed with a tunable laser to determine self broadened line shape parameters of one infrared absorption ozone line in the v1 band for ten pressures from 0.26 to 6.29 Torr at 285K. SO₂ line positions were used for wavelength calibration. Line shapes were iteratively fitted to the Voigt function at a Doppler width of 29.54 MHz (HWHM) resulting in values for the integrated line• strength, ( S), of (0.144 +/- 0.007 ) x ·10^-20 cm-1/molecule cm-2, line center frequency, (υ_ο) of 1129.426 cm-1 and the Lorentzian contributions to half width, (α …

The Effects Of Electron Irradiation On Mosfets, Mark D. Skeldon

Physics Theses & Dissertations

The characteristics of n and p-channel MOSFETs have been investigated while irradiated with electron radiation from Strontium 9Ø. The drain current vs. gate voltage of the p-channel MOSFET and the threshold voltage changes in n and p-channel MOSFETs have been studied with and without aluminum shielding. The switching characteristics and threshold voltage changes of COS/MOS dual input NAND gates have been investigated while exposed to electron radiation. Various methods of annealing the radiation damage to these devices is discussed.

Spectroscopic Measurement Of The Electron Temperature In The Tenuous Argon Ion Laser Plasma, Dane Danijel Bicanic

Physics Theses & Dissertations

The validity of the line intensity ratio technique for measuring the electron temperature was examined for an argon plasma with a "population inversion" i.e., the number of ions with electrons in the upper 4p levels was greater than in the lower 4s levels. The line intensities from these levels, the argon ion lasing transitions, were measured in a pulsed tenuous plasma at 110μ Hg produced by discharging a capacitor through a tube 2m long and 7mm inside diameter. The electron impact cross sections for simultaneous excitation and ionization as measured by Latimer and St. John were used and averaged over …