Browsing by Subject "Plasma"
Now showing 1 - 20 of 29
Results Per Page
Sort Options
Item A high density plasma source(Texas Tech University, 1978-05) Gordon, Lloyd B.A high density, low temperature plasma source has been designed and built for COp laser propagation and plasma heating studies. The plasma is produced in a hydrogen filled Pyrex tube by a high current linear discharge in a strong axial magnetic field. A density minimum on the axis is produced by using ring-shaped discharge electrodes. The discharge current is crowbarred at the first current zero to improve the plasma stability. The major plasma parameters are measured using image converter camera photography,spectroscopy, and interferometry. An unfocused CO^ laser beam is sent through the plasma to illustrate a simple laser-plasma interaction.Item A MULTI-STAGE DISTRIBUTED ENERGY PLASMA ARC RAILGUN(2010-12) Karhi, Ryan W.; Mankowski, John J.; Giesselmann, Michael G.; Bayne, Stephen B.; Rasty, Jahan; McNab, Ian; Wetz, David A.The development process pertaining to the design, fabrication, coding, and testing of multi-stage distributed energy plasma arc railguns are presented. In collaboration on an Air Force Office of Scientific Research (AFOSR) funded Multidisciplinary University Research Initiative (MURI) project, the Center for Pulsed Power and Power Electronics (P3E) at Texas Tech University is responsible for developing and investigating a functional scale model of a multi-stage distributed energy store (DES) railgun to analyze its effectiveness to suppress a restrike phenomenon and increase plasma armature railgun performance [1]. The term “restrike” denotes the formation of an electrical breakdown in the railgun bore some distance behind a traveling plasma armature. The formation of this secondary arc reduces the driving force on the primary armature and has led to a velocity ceiling of approximately 6 km/s on all breech-fed plasma armature railguns. Numerous solutions have been theorized as viable methods of restrike prevention but lack experimental verification. The primary objective of our research team within the MURI effort is to experimentally test Dr. Jerry Parker’s theoretical restrike suppression technique [2] that was developed at Los Alamos National Laboratory in the 1980’s. The project tasks are organized to identify potential problematic issues and verify theoretical concepts before implementation of a full scale system.Item Abatement of perfluorocompounds and chlorofluorocarbons using surface wave plasma technology(Texas A&M University, 2007-04-25) Frantzen, Michelle E. GunnApplication of surface wave plasma technology for effective abatement of environmentally harmful gases such as perfluorocompounds and chlorofluorocarbons is investigated. Perfluorocompounds (PFCs) are gases that contribute to forced global warming and have been favored for wafer etch and chamber clean applications in the semiconductor industry. Chlorofluorocarbons (CFCs) are ozone depleting gases that were used as refrigerants for commercial and domestic condensers and air conditioners, but current reserves still pose threats to environmental sustainability. Increased average global temperatures and further destruction of the ozone layer have prompted proposal of international initiatives such as the Montreal Protocols and the Kyoto Agreement to curtail emissions of such fugitive gases into the environment. These have increased the need for effective abatement technologies to control such emissions and include surface wave plasma abatement, the subject of this dissertation. Surface wave plasmas are considered high frequency non-equilibrium traveling wave discharges in contrast to the more frequently used standing wave discharges. The use of surface wave plasmas have the advantages of a variety of discharge vessel shapes, reproducibility of application, numerous operating conditions and large plasma volumes which ultimately produce low, molecular weight byproducts that are associated with high effective electron temperatures but low heavy particle temperatures. For these reasons, surface wave plasma abatement technology was developed for the destruction and removal of PFCs and CFCs. Results include final destruction and removal efficiencies (DREs) for octafluorocyclobutane greater than 99.8%, dichlorodifluoromethane greater than 99.995% and trichlorofluoromethane greater than 99.999% using moderate applied microwave powers of less than 2000 watts with the production of low molecular weight byproducts, such as CO2, CO, HF and HCl, that prevent environmentally harmful process emissions from entering the atmosphere. Characterizations of the initial and final products were accomplished by the use of Fourier transform infrared spectroscopy and quadrupole mass spectrometry to provide independent quantitative analyses of plasma processes. In addition to these analytical methods, Global_Kin a kinetic model, of plasma reactions were conducted and compared to all the experimental data determined in order to facilitate understanding of the chemistry involved in the surface wave plasma abatement applications studied. Basic plasma reaction mechanisms were determined for the abatement of octafluorocyclobutane and dichlorodifluoromethane.Item Beam diagnostics for the Texas Petawatt Laser Wakefield Acceleration Project(2009-12) Bedacht, Stefan; Downer, Michael Coffin; Fink, ManfredAn overview of the beam diagnostics for the laser wakefield acceleration project at the Texas Petawatt Laser facility is presented. In this experiment, short and intense laser pulses of 165 fs and up to 190 J will be used to accelerate electrons up to the GeV energy range using laser wakefield acceleration. The density variation of the plasma generated in a helium gas cell will be measured with different optical detection systems such as frequency domain holography. Spectra of the transmitted laser beam and optical transition radiation will yield information about the energy transfer to the plasma and the energy of the electrons, respectively. In addition, a calorimeter will measure accelerated electron energies. Prior to the final experiment, preliminary frequency shift measurements and simulations on optical transition radiation were performed.Item COb2s laser refraction and heating effects in a magnetized plasma column(Texas Tech University, 1974-05) Molen, George MarshallRecent developments in the area of high intensity lasers have caused an increased interest among researchers in applying various new techniques to heating gaseous plasmas to thermonuclear ignition temperatures. Lasers should be ideally suited for such an application because of their ability to deposit large bursts of energy in extremely short time durations. The basic requirements are that the plasma be heated to temperatures of several hundred million degrees to overcome the Coulomb barrier through energetic collisions and be confined long enough to get a net energy gain from the fusion reactions. Two different approaches have been proposed to attain these conditions using lasers. One approach, inertial confinement, would use nanosecond or less duration laser pulses in the tens of kilojoules to irradiate a small pellet fabricated (for example) of solid deuterium-tritium. The material would be vaporized be the focused laser and further heated by absorption of laser light in the blowoff material. Compression resulting from an implosion due to thermal pressure and the recoil from the plasma's expansion would heat the pellet. The plasma would be allowed to expand freely, thus giving rise to the term inertial confinement as only the inertia of the particles would determine the time scale.Item Design of a Plasma Abatement System for Perfluoronated Compounds(2011-08-08) Butler, MatthewThe plasma abatement system co-developed by Rf Environmental, Inc. and Texas A & M University has been effective at destroying the global warming gases CF4 and C4F8. The destruction of greenhouse gases, specifically perfluorocompounds, hydrofluorocompounds, chlorofluorocompounds (PFCs, HFCs, CFCs) and SF6, is paramount to significantly affecting atmospheric pollution. The premise of this study was to examine the design of the plasma abatement system for Global Warming Gases (GWGs) and its abatement potential for these gases. The first goal was to reduce the cost of ownership by examining the cooling system. The cost of an air cooling design was $1400/yr. The intent was to reduce the amount of air used or use a different medium that would produce the same amount of heat transfer. A liquid cooling system design had a cost of only $150/yr. A C4F8 abatement experiment was run on the liquid cooling design. The abatement process resulted in a destruction removal efficiency (DRE) of C4F8 of 97.5 percent. A lower operational cost unit was developed, but the operational performance was less than previous investigations. The second goal was to simulate the semiconductor radio frequency etching process and abate the output gases of the C4F8 and SiO2 reaction. The outcomes of this experiment included a microwave simulation of the radio frequency etching reaction and an abatement that resulted in a 99.98 plus/minus .05 percent DRE for C4F8 with no formation of any other CFC gases. The third goal was to simulate the etching process and abate the output gas, CF4 using H2O vapor as the additive gas. The outcomes of this experiment included a microwave simulation of the radio frequency etching reaction and an abatement that resulted in a 99.96 plus/minus .05 percent DRE for CF4 with no formation of any other CFC gases. A low cost of ownership and effective abatement levels will make this system viable for commercial use. The latest data shows the amount of PFC emissions from the semiconductor industry was 3.6 Tg CO2 Eq. The use of this or a similar abatement technology will have a significant impact on reducing environmental pollution.Item Electostatic plasma edge turbulence and anomalous transport in SOL plasmas(2014-08) Meyerson, Dmitry; Gentle, Kenneth W.; Waelbroeck, F.Controlling the scrape-off layer (SOL) properties in order to limit divertor erosion and extend component lifetime will be crucial to successful operation of ITER and devices that follow, where intermittent thermal loads on the order of GW/m² are expected. Steady state transport in the edge region is generally turbulent with large, order unity, fluctuations and is convection dominated. Owing to the success of the past fifty years of progress in magnetically confining hot plasmas, in this work we examine convective transport phenomena in the SOL that occur in the relatively "slow", drift-ordered fluid limit, most applicable to plasmas near MHD equilibrium. Diamagnetic charge separation in an inhomogeneous magnetic field is the principal energy transfer mechanism powering turbulence and convective transport examined in this work. Two possibilities are explored for controlling SOL conditions. In chapter 2 we review basic physics underlying the equations used to model interchange turbulence in the SOL and use a subset of equations that includes electron temperature and externally applied potential bias to examine the possibility of suppressing interchange driven turbulence in the Texas Helimak. Simulated scans in E₀×B₀ flow shear, driven by changes in the potential bias on the endplates appears to alter turbulence levels as measured by the mean amplitude of fluctuations. In broad agreement with experiment negative biasing generally decreases the fluctuation amplitude. Interaction between flow shear and interchange instability appears to be important, with the interchange rate forming a natural pivot point for observed shear rates. In chapter 3 we examine the possibility of resonant magnetic perturbations (RMPs) or more generally magnetic field-line chaos to decrease the maximum particle flux incident on the divertor. Naturally occurring error fields as well as RMPs applied for stability control are known to cause magnetic field-line chaos in the SOL region of tokamaks. In chapter 3 2D simulations are used to investigate the effect of the field-line chaos on the SOL and in particular on its width and peak particle flux. The chaos enters the SOL dynamics through the connection length, which is evaluated using a Poincaré map. The variation of experimentally relevant quantities, such as the SOL gradient length scale and the intermittency of the particle flux in the SOL, is described as a function of the strength of the magnetic perturbation. It is found that the effect of the chaos is to broaden the profile of the sheath-loss coefficient, which is proportional to the inverse connection length. That is, the SOL transport in a chaotic field is equivalent to that in a model where the sheathloss coefficient is replaced by its average over the unperturbed flux surfaces. Both fully chaotic and the flux-surface averaged approximation of RMP application significantly lower maximum parallel particle flux incident on the divertor.Item Electrode degradation in micro-hollow cathode discharge reactors(2015-05) Pinero, Daniel III; Berberoglu, Halil; Taylan, OnurThis thesis presents an experimental study to understand the effects of different working fluids, flow rate, reactor hole diameter and dielectric thickness on the electrode degradation rate and total reactor lifetime of micro-hollow cathode discharge reactors. Oxidizing mediums such as air and carbon dioxide tend to degrade the reactors at a higher rate than non-oxidative mediums. Furthermore, larger dielectric thicknesses and smaller working fluid rates serve to decrease degradation. The overall longest reactor lifetime was accomplished at maximum diameter, thickness and minimum flowrate, resulting in a total lifetime of 14 hours 42 minutes. Additionally, creation of favorable magnetic fields through the use of nickel mesh electrodes was investigated in an attempt to increase the reactor lifetime. The results showed that the use of mesh electrodes decreased the total lifetime due to the higher energy plasma regime of the experimental reactors when compared to reactors found in the literature. Finally, the feasibility of utilizing MHCD reactors for oxygen production on a sample return mission to Mars was conducted. The study indicated that production quotas can be met but reactor lifetimes and power efficiency needed to be improved.Item Emission spectra of simple hydrocarbons excited in a radio-frequency plasma(Texas Tech University, 1965-08) Mercer, Howard NicholasBeginning with an elementary discussion of the theory of atomic and molecular spectra and continuing with a discussion of the plasma state and other methods of excitation, a description of the apparatus used as well as the procedure followed in obtaining the results is given. The results of the analysis of the spectra will be introduced In tabular form. Generally, these results will be discussed In terms of the various methods of excitation.Item Experimental measurement of energy transport in tokamak plasmas(2010-08) Meyerson, Dmitry; Gentle, Kenneth W.; Horton, WendellA tokamak plasma near equilibrium can be perturbed with modulated power sources, such as modulated electron cyclotron heating, or repeated cold pulse application. Temperature response to cyclical changes in profiles parameters that are induced by modulated power deposition can be used to test theoretical transport models as well as improve experimental phenomenology used to optimize tokamak performance. The goal of this document to discuss some methods of analyzing electron temperature data in the context of energy transport. Specific experiments are considered in order to demonstrate the methods discussed, as well as to examine the electron energy transport properties of these shots. Electron cyclotron emission provides a convenient way to probe electron temperature for plasmas in thermal equilibrium. We can show that in tokamak devices,barring harmonic overlap, we can associate a particular frequency with a particular location in a tokamak, by carefully selecting the detection frequency and line of sight of the responsible antenna. ECE radiometers typically measure temperature at tens of locations at a time with a spatial resolution on the order of a few centimeters. Tracking the evolution of electron energy flux depends on careful analysis of the resulting data. The most straightforward way to analyze temperature perturbations is to simply consider various harmonics of the driving source and consider the corresponding harmonics in the temperature. We can analyze the phase and amplitude of the response to find the effective phase velocity of the perturbation which can in turn be related to parameters in the selected heat flux model. The most common example is to determine , the diffusion coefficient that appears in the linearized energy transport equation. The advantages and limitation of this method will be discussed in detail in Section 3. A more involved approach involves using the perturbed temperature data to compute modulated heat flux at any given point in the perturbation cycle, rather than using the temperature data directly. As before the heat flux can then be related to measured profile parameters and theoretical predictions. The advantages and limitations of this approach will be discussed in more detail. Both of the mentioned analysis methods are used to probe electron energy transport in a quiescent H mode (QH mode) shot conducted at DIIID. The nature of the internal transport barrier that is present in the shot is considered in light of the results.Item Fast wave resonances near the ion cyclotron frequency(Texas Tech University, 1976-12) Dollinger, Richard E.The original goal of the research reported here was to use "turbulent heating" to obtain a hotter plasma so that the damping of the fast wave at 2. fi would be enhanced. The advantages and the disadvantages of this plasma source are described in Ch. II along with the experimental arrangement. After much trial and error, the repeatability was finally improved by careful pre-ionization of the plasma.Item Glow Discharge Characteristics of Non-thermal Microplasmas at above Atmospheric Pressures and their Applications in Microscale Plasma Transistors(2013-07-25) Wakim, Dani GhassanA microscale plasma transistor capable of high speed switching was manufactured using microfabrication techniques and operated using microplasma discharges. Such a device has feature sizes on the order of 25 ?m, is robust against spikes in power, high temperatures, as well as electromagnetic interference and capable of low cost production through microfabrication. In this work two aspects of the Microscale Plasma Device development were investigated; (1) the microplasma properties and (2) the manufacturing of the MPD. To study the required plasma discharges and develop them to become better suited for the task at hand, Direct Current (DC) plasma discharge characteristics were investigated under pressures from atmospheric to 1.65 MPa while varying current from 0.1 mA to 4.5 mA and gap length from 5 ?m up to 250 ?m. This testing was carried out in a high pressure test chamber fitted with a micrometer for variable electrode spacing and gas inlets and outlets for varying the working gas and pressure. Voltage and current measurements along with microscopic imaging and optical emission spectroscopy were taken for discharges in the varying gases to determine discharge V-I characteristics, sizes and temperatures. Data gathered was used to understand the microdischarge characteristics and tailor the plasma for application in the microtransistor. Discharges with diameters as small as 7 ?m have been achieved in Nitrogen and 16.7 ?m in Helium by operating at low current, 0.5mA, and at pressures of 1.65 MPa and 0.34 MPa respectively. Paschen type, Pd, scaling is observed both in breakdown voltages, steady state voltage, and discharge size from 0.1 MPa to 1.65 MPa. The discharges operated in a normal glow regime with near constant normalized current densities and relatively flat voltage current characteristics indicating normal glow discharge behavior in the microplasmas. During device development small diameter metal wires, 25 ?m and 50 ?m, were used to carry out experiments on the microscale device to aid in electrode and substrate material selection. Robust electrode and substrate materials were required to withstand high discharge temperatures in order to prolong the device life time. As material selection was narrowed down microfabrication techniques were utilized to achieve smaller electrode geometry and electrode gap spacing with greater consistency. Photolithography coupled with thin film deposition using metal evaporation and electroplating resulted in electrodes with features and electrode gap spacing on the order of 25 ?m and film thicknesses of 35 ?m. Aluminum, Nickel, Copper and Titanium were deposited onto Alumina (Al_(2)O_(3)) and Ceria Stabilized Zirconia (CSZ) ceramic substrates, where only the latter two electrode materials proved to be robust enough to withstand the discharge temperatures. Superficial oxide layers on the electrode surfaces provided a protective coating, prolonging electrode lifetime in atmospheric air from 360 seconds to greater than 400 seconds without metal evaporation occurring. The oxide coating also acted as a dielectric barrier and increasing the resistance of the electrode surfaces to the order of 300 M? in some cases thus acting as a ballast resistance, compensating for stray capacitance and helped stabilize the plasma discharge.Item Glow Discharge Enhanced Chemical Reaction: Application in Ammonia Synthesis and Hydrocarbon Gas Cleanup(2014-06-05) Ming, PingjiaTwo different plasma enhanced processing technologies were investigated in this study: ammonia synthesis from steam and nitrogen, and hydrocarbon gas clean up. Ammonia is a common sanitizer in swimming pool and fish tank, changing the pH of the water, which does not benefit bacteria. Also ammonia is used in various NOx reduction technologies, for example, selective catalytic reduction (SCR) methods have been studied for the cleaning of diesel engine exhaust. A small compact glow discharge was applied to investigate ammonia synthesis from steam and nitrogen. Ammonia was successfully detected via UV-VIS absorbance and through increasing pH value of treated water by product gas. Heavier hydrocarbon C3 to C5 are produced with natural gas, but cannot be used in sensitive energy conversion systems, like solid oxide fuel cell (SOFC). Utilizing small amount of energy to clean up and reform heavier hydrocarbon into synthesis gas is necessary when using hydrocarbon sources which contain heavier hydrocarbons mixture such as EPE (74.8% methane, 8% ethane, 8% ethylene, 2.1% propane and 1.1% Propene). Non-thermal plasmas, due to their unique non-equilibrium characteristics, offer advantages as method of reforming at lower temperature (100-150 ?C) and atmospheric pressure. For an EPE gas mixture, a high conversion and low specific energy cost is desirable. Variation in discharge power density, air and, water addition were tested, in order to find conditions which were energetically feasibility, efficiency and sufficiently reduced the higher hydrocarbon. High conversion efficiency was achieved, in propane and propene, which was more than 90%, without carbon deposition through air addition. For a 1 J/ml power density and 1.08 O2/C ratio condition, a process efficiency of 74% and 54% available output energy was achieved. At the same time, the concentration of ethane, ethylene, propane, propylene, and acetylene were cleaned-up to value of 1.01%, 1.67%, 0.08%, 0.00%, and 0.50%, respectively, less than 20% of their original input amount. Higher power density produced cleaner (less high hydrocarbons) in the products, and were still energetically feasible, but less efficient.Item Investigation of magnetohydrodynamic plasma actuators for aerodynamic flow control(2013-05) Pafford, Brent Joel; Sirohi, JayantThis thesis describes the analysis, fabrication and testing of a novel magnetohydrodynamic plasma actuator for aerodynamic flow control, specifically, retreating blade stall. A magnetohydrodynamic plasma actuator is comprised of two parallel rail electrodes embedded chord-wise on the upper surface of an airfoil. A pulse forming network generates a low-voltage, high-current repetitive pulsed arc. Self-induced electromagnetic fields force the pulsed arc along the length of the rail electrodes at high velocities, transferring momentum to the surrounding air, creating a high-velocity pulsed air wall jet. A systematic experimental investigation of the effect of plasma actuators on the surrounding air is conducted in stagnant air conditions to gain an understanding of the physical characteristics. These characteristics include voltage and current measurements, pulsed arc velocity measurements, and high speed video imaging. The results show typical pulsed arc velocities of about 100 m/s can be induced with discharge energies of about 300 J per pulse. Additional experimental studies are conducted to quantify the performance of the pulsed arc for potential use in subsonic flow control applications. To gain an estimate of the momentum transferred from the pulsed arc to the surrounding air the plasma actuator is placed in a subsonic open-circuit wind tunnel at a Reynolds number of 4.5 x 105. The induced velocity of the pulsed wall jet is measured using a Laser Doppler Anemometer. The measurements show that the pulsed arc creates a high-velocity pulsed wall jet that extends 40 mm above the airfoils surface and has an induced velocity of 15 m/s greater than the unaltered air flow over the airfoil, with peak velocities of 32 m/s. The magnetohydrodynamic plasma actuator proved to induce velocities an order of magnitude greater than the velocities attained by current state-of-the-art plasma actuators. Moreover, the RailPAc is found to posses the potential for alleviation of retreating blade stall. Future work will include experiments to gain a detailed understanding of the improvements to the static stall angle, the optimal actuator geometry, excitation duty cycle, magnetic field augmentation, and behavior of the plasma armature at high Mach/Reynolds numbers. Particle Image Velocimetry (PIV) will be utilized to improve the induced flow velocity measurements acquired with the LDA.Item Magnetofluid dynamics in curved spacetime : theory and application(2016-05) Bhattacharjee, Chinmoy; Hazeltine, R. D. (Richard D.); Mahajan, Swadesh M.; Berk, Herbert; Bohm, Arno; Yoshida, ZenshoA grand unified field tensor [Greek capital letter Mu] [Greek small letter mu] [Greek small letter nu] is constructed from Maxwell's field tensor and appropriately modified flow field, both nonminimally coupled to gravity, to analyze the dynamics of hot charged fluids in curved background space-time. With suitable 3+1 decomposition, this new formalism of hot fluid is then applied to investigate vorticity generation and a class of states known as the Beltrami-Bernoulli (BB) equilibria in the accretion disk around Schwarzschild and Kerr black holes. Of the two principle sources of vorticity i.e. baroclinic and relativistic, the relativistic drive peaks near innermost (isco) circular orbit for both black holes, whereas baroclinic drive dominates at larger distances. For General Relativity as well as modified gravity, the Kerr geometry leads to a ``stronger" vorticity generation than its Schwarzschild counterpart. On the other hand, modelling the disk plasma as a Hall MHD system, it has been shown that velocity/magnetic decay rate gets altered due to space time curvature, for example the velocity profile in BB states deviate substantially from the predicted geodesic velocity profiles. Moreover, these equilibrium states have their origin in the two helicity invariants which conspire to introduce a new oscillatory length scale into the system that is strongly influenced by relativistic and thermal effects. Consequences of this formalism are also discussed in several astrophysical settings.Item Mechanistic study of plasma damage to porous low-k : process development and dielectric recovery(2010-05) Shi, Hualiang; Ho, Paul S.; Niu, Qian; Shi, Li; Swift, Jack B.; Yao, ZhenLow-k dielectrics with porosity are being introduced to reduce the RC delay of Cu/low-k interconnect. However, during the O2 plasma ashing process, the porous low-k dielectrics tend to degrade due to methyl depletion, moisture uptake, and densification, increasing the dielectric constant and leakage current. This dissertation presents a study of the mechanisms of plasma damage and dielectric recovery. The kinetics of plasma interaction with low-k dielectrics was investigated both experimentally and theoretically. By using a gap structure, the roles of ion, photon, and radical in producing damage on low-k dielectrics were differentiated. Oxidative plasma induced damage was proportional to the oxygen radical density, enhanced by VUV photon, and increased with substrate temperature. Ion bombardment induced surface densification, blocking radical diffusion. Two analytical models were derived to quantify the plasma damage. Based on the radical diffusion, reaction, and recombination inside porous low-k dielectrics, a plasma altered layer model was derived to interpret the chemical effect in the low ion energy region. It predicted that oxidative plasma induced damage can be reduced by decreasing pore radius, substrate temperature, and oxygen radical density and increasing carbon concentration and surface recombination rate inside low-k dielectrics. The model validity was verified by experiments and Monte-Carlo simulations. This model was also extended to the patterned low-k structure. Based on the ion collision cascade process, a sputtering yield model was introduced to interpret the physical effect in the high ion energy region. The model validity was verified by checking the ion angular and energy dependences of sputtering yield using O2/He/Ar plasma, low-k dielectrics with different k values, and a Faraday cage. Low-k dielectrics and plasma process were optimized to reduce plasma damage, including increasing carbon concentration in low-k dielectrics, switching plasma generator from ICP to RIE, increasing hard mask thickness, replacing O2 by CO2 plasma, increasing CO addition in CO/O2 plasma, and increasing N2 addition in CO2/N2 plasma. By combining analytical techniques with the Kramers-Kronig dispersion relation and quantum chemistry calculation, the origin of dielectric loss was ascribed to the physisorbed water molecules. Post-ash CH4 plasma treatment, vapor silylation process, and UV radiation were developed to repair plasma damage.Item Megagauss 2.0 : a 10 capacitor system for production of megagauss fields for laser plasma experiments(2013-05) Lewis, Sean Matthew; Bengtson, Roger D.High magnetic fields greater than 100 Tesla applied to laser generated plasmas can generate unique and interesting conditions. High power laser systems at the University of Texas in the Center for Higher Energy Density Sciences readily produce short lived fusion plasmas in cluster targets. A strong magnetic field could increase fusion neutron yield and plasma confinement while providing a unique plasma physics environment. For this purpose, Sandia National Laboratories in collaboration with the University of Texas designed and constructed a pulsed power device to produce more than 2 megaamperes. This current produces strong magnetic fields in small coils with duration on the order of microseconds. At the University of Texas, tests with this device determined the operational characteristics. I will describe the behavior of this device with currents of approximately a megaamp and magnetic fields of more than 60 Tesla. Emphasis is placed on understanding the behavior of the fields and coils.Item A Neutral Beam Probe for the Helimak plasma experiment(2013-05) Garcia de Gorordo, Alvaro; Hallock, G. A.A Neutral Beam Probe (NBP) was developed for studying the Texas Helimak plasma experiment. The probe consisted of a beam of neutral sodium atoms that were injected into the magnetized plasma of the Helimak. After some fraction of the atoms underwent electron impact ionization, the resulting ion beam followed a path to an energy analyzer where the change of energy was detected along with the total ion current. The measurement of the change of energy implies a change of potential energy at the point of ionization since all the neutral beam particles enter the plasma with a well determined energy. The total current detected at the energy analyzer also implies a rate of electron impact ionization, which in turn implies an electron density and temperature. The NBP was developed based on the Elmo Bumpy Torus (EBT) Heavy Ion Beam Probe (HIBP), which was operated at Oak Ridge National Labs. In fact, the majority of the equipment that was used in this experiment was taken from that HIBP, and some of it was rebuilt. We generated an estimate of the radial electric field in the Helimak along with an estimate of density changes as a result of biasing experiments. Interestingly, when a bias voltage was applied inside the Helimak, the radial electric field did not change significantly at the sample region, but the electron density did vary. The probe data taken by the Helimak team agree with the density changes. The electric field derived from Langmuir probes is not trivial (especially in plasmas with flows) and was not computed for this thesis.Item New biomedical applications of near-infrared femtosecond laser ablation(2010-12) Qiu, Jinze; Milner, Thomas E.; Neev, Joseph; Teichman, Joel M.; Tunnell, James; Dunn, Andrew; Downer, Mike; Chan, Kin F.The main purpose of this research was to investigate new medical applications of femtosecond laser ablation. A near-infrared femtosecond laser was tested and proved to be able to overcome the existing limitations and outperform the conventional long-pulse lasers in the areas of human urinary calculus (kidney stone) lithotripsy and skin treatment. The two primary objectives of my research are: 1) to investigate the feasibility of using femtosecond pulsed laser radiation to ablate urinary calculus of various compositions. The laser-calculus interaction mechanism was characterized using pump probe imaging and fast flash imaging. A novel fiber delivery system was developed to transmit and focus high energy femtosecond pulses for urinary calculus lithotripsy. The successful demonstration of the femtosecond laser lithotripsy provided a promising treatment method better than the existing long-pulse laser lithotripsy in a few different aspects, including less collateral damage to surrounding tissue, small-size debris and more controlled experimental condition. 2) to investigate the depth limitation of femtosecond subsurface ablation in scattering skin sample and develop a prototype tissue optical clearing device to enhance femtosecond beam penetration for deeper subsurface cavitation production in the skin. The successful demonstration of the device has potential benefits to new femtosecond-based therapies for reshaping or removing subcutaneous tissues.Item Plasma damaging process of porous ultra-low-k dielectrics and dielectric repair(2012-08) Huang, Huai, Ph. D.; Ho, P. S.; Tsoi, Maxim; Shih, Chih-Kang; Huang, Rui; Yao, ZhenThe Ultra-low-k material is required to reduce the RC time delay in the integrated circuits. However, the integration of the porous low-k material into the on-chip interconnects was impeded by the plasma induced damage during etching and photoresist stripping processes. This dissertation aims to study the mechanism of plasma damage to porous ultra-low-k dielectrics with the objective to minimize the damage and to develop methods and processes to restore the low-k dielectric after the plasma damage. First, the plasma etching induced surface roughening was studied on blanket porous SiCOH films in the fluorocarbon based plasma. Substantial surface roughening was found in the low polymerization region, where the surface roughening process was initiated by the unevenly distribution of surface fluorocarbon polymers in the pore structure and enhanced by ion induced surface densification. With oxygen addition, the surface densification layer increased the radial diffusion rate difference between the top and the bottom of the pits, resulting in further increase of the surface roughness. The best process optimization was found at a "threshold point" where the surface polymerization level is just high enough to suppress the roughness initiation. The second part of this dissertation investigates the mechanism of the oxygen plasma damaging process. The roles of plasma constituents (i.e. ions, radicals and photons with different wavelengths) were differentiated by an on-wafer filter system. Oxygen radical was identified as the most critical and its damage effect was enhanced by photons with wavelength smaller than 185nm. The oxygen radical kinetics in the porous structure of low-k, including diffusion, reaction and recombination, was described analytically with a plasma altered layer model and then simulated with a Monte Carlo computational method, which give guidelines to minimize the damage. The analytical model of oxygen radical kinetic process is also used to investigate the oxygen plasma damage to patterned low-k structure, which is confirmed by experiments. Finally, the dielectric recovery was studied using silylation and UV broadband thermal treatment, both individually and in combination. After both vapor and supercritical CO₂ silylation, surface carbon and hydrophobicity were partially recovered. However, the recovery effect was limited to the surface. In comparison, UV treatment can effectively remove water from the bulk of the damaged film and consolidate the silanol bonds with the help of thermal activation. The combination of UV and silylation treatments is more effectively for dielectric recovery than UV or silylation alone. The "UV first" treatment provided a better recovery in sequential processes. Under the same conditions, simultaneous treatments by silylation and UV irradiation achieved better bulk and surface recovery than the sequential process.