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Articles 151 - 180 of 218

Full-Text Articles in Plasma and Beam Physics

Plasma Treatment Of Bulk Niobium Surface For Superconducting Rf Cavities: Optimization Of The Experimental Conditions On Flat Samples, M. Rašković, J. Upadhyay, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips Jan 2010

Plasma Treatment Of Bulk Niobium Surface For Superconducting Rf Cavities: Optimization Of The Experimental Conditions On Flat Samples, M. Rašković, J. Upadhyay, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips

Physics Faculty Publications

Accelerator performance, in particular the average accelerating field and the cavity quality factor, depends on the physical and chemical characteristics of the superconducting radio-frequency (SRF) cavity surface. Plasma based surface modification provides an excellent opportunity to eliminate nonsuperconductive pollutants in the penetration depth region and to remove the mechanically damaged surface layer, which improves the surface roughness. Here we show that the plasma treatment of bulk niobium (Nb) presents an alternative surface preparation method to the commonly used buffered chemical polishing and electropolishing methods. We have optimized the experimental conditions in the microwave glow discharge system and their influence on …

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Coupled Ray-Tracing And Fokker-Planck Ebw Modeling For Spherical Tokamaks, Jakub Urban, Joan Decker, Y. Peysson, Josef Preinhaelter, Gary Taylor, Linda L. Vahala, George Vahala Nov 2009

Coupled Ray-Tracing And Fokker-Planck Ebw Modeling For Spherical Tokamaks, Jakub Urban, Joan Decker, Y. Peysson, Josef Preinhaelter, Gary Taylor, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The AMR (Antenna—Mode-conversion—Ray-tracing) code [1, 2] has been recently coupled with the LUKE [3] Fokker-Planck code. This modeling suite is capable of complex simulations of electron Bernstein wave (EBW) emission, heating and current drive. We employ these codes to study EBW heating and current drive performance under spherical tokamak (ST) configurations—typical NSTX discharges are employed. EBW parameters, such as frequency, antenna position and direction, are varied and optimized for particular configurations and objectives. In this way, we show the versatility of EBWs.

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Characterization Of Microwave Cavity Discharges In A Supersonic Flow, Dareth Janette Drake Apr 2009

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 …

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Beam-Energy And System-Size Dependence Of Dynamical Net Charge Fluctuations, B. I. Abelev, M. M. Aggarwal, Z. Ahammed, B. D. Anderson, D. Arkhipkin, G. S. Averichev, Y. Bai, J. Balewski, S. Bueltmann, Star Collaboration Jan 2009

Beam-Energy And System-Size Dependence Of Dynamical Net Charge Fluctuations, B. I. Abelev, M. M. Aggarwal, Z. Ahammed, B. D. Anderson, D. Arkhipkin, G. S. Averichev, Y. Bai, J. Balewski, S. Bueltmann, Star Collaboration

Physics Faculty Publications

We present measurements of net charge fluctuations in Au+Au collisions at √sNN=19.6, 62.4, 130, and 200 GeV, Cu+Cu collisions at √sNN=62.4 and 200 GeV, and p+p collisions at √s=200GeV using the dynamical net charge fluctuations measure ν+−,dyn. We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/Nch scaling but display approximate 1/Npart scaling. We also study the azimuthal and …

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Photodisintegration Of 4He Into P+T, Clas Collaboration, M. J. Amaryan, S. L. Careccia, G. E. Dodge, C. E. Hyde, S. E. Kuhn, M. Mayer, C. S. Nepali, M. R. Niroula, H. Seraydaryan, S. Tkachenko, L.B. Weinstein, J. Zhang Jan 2009

Photodisintegration Of 4He Into P+T, Clas Collaboration, M. J. Amaryan, S. L. Careccia, G. E. Dodge, C. E. Hyde, S. E. Kuhn, M. Mayer, C. S. Nepali, M. R. Niroula, H. Seraydaryan, S. Tkachenko, L.B. Weinstein, J. Zhang

Physics Faculty Publications

The two-body photodisintegration of 4He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid 4He target. This is the first measurement of the photodisintegration of 4He above 0.4 GeV. The differential cross sections for the γ 4He →pt reaction were measured as a function of photon-beam energy and proton-scattering angle and are compared with the latest model calculations by J.-M. Laget. At …

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New Compact Tem-Type Deflecting And Crabbing Rf Structure, J. R. Delayen, H. Wang Jan 2009

New Compact Tem-Type Deflecting And Crabbing Rf Structure, J. R. Delayen, H. Wang

Physics Faculty Publications

A new type of rf structure for the deflection and crabbing of particle beams is presented. The structure is comprised of a number of parallel TEM resonant lines operating in opposing phase from each other. One of its advantages is its compactness compared to conventional crabbing cavities operating in the TM110 mode, thus allowing low frequency designs. This geometry would also be effective for the deflection of beams propagating at velocities substantially less than that of light.

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Search For The Photoexcitation Of Exotic Mesons In The Π+Π+Π- System, Clas Collaboration, M. J. Amaryan, H. Bagdasaryan, S. Bektasoglu, S. Bültmann, G. E. Dodge, G. Gavalian, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, S. E. Kuhn, J. Lachniet, M. R. Niroula, L. M. Qin, S. Tkachenko, L. B. Weinstein, J. Zhang Jan 2009

Search For The Photoexcitation Of Exotic Mesons In The Π+Π+Π- System, Clas Collaboration, M. J. Amaryan, H. Bagdasaryan, S. Bektasoglu, S. Bültmann, G. E. Dodge, G. Gavalian, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, S. E. Kuhn, J. Lachniet, M. R. Niroula, L. M. Qin, S. Tkachenko, L. B. Weinstein, J. Zhang

Physics Faculty Publications

A search for exotic mesons in the π+π+π− system photoproduced by the charge exchange reaction γp→π+π+π−(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the …

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Cold Atmospheric Pressure Air Plasma Jet For Medical Applications, Juergen Friedrich Kolb, A.-A H. Mohamed, R. O. Price, R. J. Swanson, A. Bowman, R. L. Chiavarini, Michael W. Stacey Jan 2008

Cold Atmospheric Pressure Air Plasma Jet For Medical Applications, Juergen Friedrich Kolb, A.-A H. Mohamed, R. O. Price, R. J. Swanson, A. Bowman, R. L. Chiavarini, Michael W. Stacey

Bioelectrics Publications

By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2 cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.

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Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara Jan 2008

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 …

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Sublethal And Killing Effects Of Atmospheric-Pressure, Nonthermal Plasma On Eukaryotic Microalgae In Aqueous Media, Ying Zhong Tang, Xin Pei Lu, Mounir Laroussi, Fred C. Dobbs Jan 2008

Sublethal And Killing Effects Of Atmospheric-Pressure, Nonthermal Plasma On Eukaryotic Microalgae In Aqueous Media, Ying Zhong Tang, Xin Pei Lu, Mounir Laroussi, Fred C. Dobbs

OES Faculty Publications

In-depth studies on the interaction of nonthermal plasmas with microorganisms usually focus on bacteria; only little attention has been given to their effects on more complex eukaryotic cells. We report here nonthermal plasma's effects on cell motility, viability staining, and morphology of eukaryotic microalgae, with three marine dinoflagellates and a marine diatom as major targets. The effects on motility and viability staining depended on the time of exposure to plasma and the species of microalgae. We observed a strong pH decrease in aqueous samples (marine and freshwater algal cultures, their culture media, and deionized water) after exposure to plasma, and …

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Electron Density And Temperature Measurement Of An Atmospheric Pressure Plasma By Millimeter Wave Interferometer, Xinpei Lu, Mounir Laroussi Jan 2008

Electron Density And Temperature Measurement Of An Atmospheric Pressure Plasma By Millimeter Wave Interferometer, Xinpei Lu, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

In this paper, a 105 GHz millimeter wave interferometer system is used to measure the electron density and temperature of an atmospheric pressure helium plasma driven by submicrosecond pulses. The peak electron density and electron-neutral collision frequency reach 8 X 1012 cm-3 and 2.1 X 1012 s-1, respectively. According to the electron-helium collision cross section and the measured electron-neutral collision frequency, the electron temperature of the plasma is estimated to reach a peak value of about 8.7 eV.

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Plasma Medicine, Mounir Laroussi, Alexander Fridman Jan 2008

Plasma Medicine, Mounir Laroussi, Alexander Fridman

Electrical & Computer Engineering Faculty Publications

Recent demonstrations of plasma technology in the treatment of living cells, tissues, and organs are creating a newfield at the intersection of plasma science and technology with biology and medicine - Plasma Medicine.

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Bactericidal Effects Of Cold Plasma Technology On Geobacillus Stearothermophilus And Bacillus Cereus Microorganisms, Angela D. Morris, Gayle B. Mccombs, Susan L. Tolle, Mounir Laroussi, Wayne L. Hynes Oct 2007

Bactericidal Effects Of Cold Plasma Technology On Geobacillus Stearothermophilus And Bacillus Cereus Microorganisms, Angela D. Morris, Gayle B. Mccombs, Susan L. Tolle, Mounir Laroussi, Wayne L. Hynes

Dental Hygiene Faculty Publications

Cold plasma is a state of matter that contains a large number of particles that are electrically charged. Plasmas generate chemically reactive species and ultraviolet radiation making them useful in decontamination applications (Kong & Laroussi, 2003). Research regarding the inactivation of gram-positive bacteria by cold plasma has been studied by Laroussi et al (2003); however, there is limited research regarding the germicidal effectiveness of cold plasma on Geobacillus stearothermophilus and Bacillus cereus microorganisms. The purpose of this study was to determine if cold plasma technology inactivates Geobacillus stearothermophilus and Bacillus cereus vegetative cells and spores. This study consisted of 981 …

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Self-Organization In Cathode Boundary Layer Discharges, Nobuhiko Takano Oct 2007

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 …

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Reactive Oxygen Emission From Microwave Discharge Plasmas, S. Popovic, M. Rašković, S. P. Kuo, L. Vuskovic Jan 2007

Reactive Oxygen Emission From Microwave Discharge Plasmas, S. Popovic, M. Rašković, S. P. Kuo, L. Vuskovic

Physics Faculty Publications

Metastable oxygen atoms and molecules have received increased interest because of their function in surface modification, bio-decontamination and many other industrial applications, in addition to the role in the upper atmospheric layer chemistry. We review work on production and detection of metastable oxygen and we describe our experiments, including the development of techniques for measurement of metastable molecular oxygen. We show that either metastable oxygen molecules or metastable oxygen atoms can be produced in large quantities in electrical discharges, carefully tailored to promote the required kinetics. Although the two species may coexist, colder discharge regimes favor production of molecules, while …

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Plasma Treatment Of Bulk Nb Surface In The Ar/Cl2 Discharge, M. Rašković, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips Jan 2007

Plasma Treatment Of Bulk Nb Surface In The Ar/Cl2 Discharge, M. Rašković, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips

Physics Faculty Publications

The preparation of the cavity walls has been one of the major challenges in the superconducting radio-frequency (SRF) accelerator technology. Therefore, constant research and development effort is devoted to develop surface preparation processes that will improve roughness and lower the level of impurities, like hydrogen or oxygen, embedded in bulk Nb, having in the same time reasonable etching rates. Plasma based surface modification provides an excellent opportunity to achieve these goals. We present Ar/Cl2 discharge treatment of bulk Nb where we achieved etching rates comparable to the rates obtained with the electropolishing method without introducing impurities in Nb. The …

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Dynamics Of An Atmospheric Pressure Plasma Plume Generated By Submicrosecond Voltage Pulses, Xinpei Lu, Mounir Laroussi Jan 2006

Dynamics Of An Atmospheric Pressure Plasma Plume Generated By Submicrosecond Voltage Pulses, Xinpei Lu, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, "the plasma pencil," is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the …

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Electron Bernstein Wave Simulations And Comparison To Preliminary Nstx Emission Data, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Gary Taylor, Steffi Diem, Linda L. Vahala, George Vahala Jan 2006

Electron Bernstein Wave Simulations And Comparison To Preliminary Nstx Emission Data, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Gary Taylor, Steffi Diem, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

Simulations indicate that during flattop current discharges the optimal angles for the aiming of the National Spherical Torus Experiment (NSTX) antennae are quite rugged and basically independent of time. The time development of electron Bernstein wave emission (EBWE) at particular frequencies as well as the frequency spectrum of EBWE as would be seen by the recently installed NSTX antennae are computed. The simulation of EBWE at low frequencies (e.g., 16 GHz) agrees well with the recent preliminary EBWE measurements on NSTX. At high frequencies, the sensitivity of EBWE to magnetic field variations is understood by considering the Doppler broadened electron …

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Plasma Emission Redistribution In A Single Cylce Of A Pulsed Dc Magnetron, W. Zhu, G. Buyle, J. Lopez, S. Shanmugmurthy, A. Belkind, K. Becker, R. De Gryse Jan 2006

Plasma Emission Redistribution In A Single Cylce Of A Pulsed Dc Magnetron, W. Zhu, G. Buyle, J. Lopez, S. Shanmugmurthy, A. Belkind, K. Becker, R. De Gryse

Physics Faculty Publications

Time-resolved images of the optical emissions from a pulsed dc titanium target planar rectangular sputtering magnetron plasma were taken using Argon spectral filters and a Roper Scientific ICCD camera with a time resolution of 0.05-0.2 μs. At the beginning of the 'on-time', when the power is turned on, the discharge initially starts preferentially in two opposite curved sections ('cross corners') of the magnetron race track, where it exhibits the most intense plasma emissions. During the rest of the 'on-time', the emissions from the straight sections of the race track of the magnetron are always slightly more intense than the emissions …

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Plasma Treatment Of Bulk Niobium Surfaces For Srf Cavities, M. Rašković, L. Vuškovic, S. Popović, L. Phillips, A. -M. Valente-Feliciano, S. B. Radovanov, L. Godet Jan 2006

Plasma Treatment Of Bulk Niobium Surfaces For Srf Cavities, M. Rašković, L. Vuškovic, S. Popović, L. Phillips, A. -M. Valente-Feliciano, S. B. Radovanov, L. Godet

Physics Faculty Publications

Two types of electric discharges were used to demonstrate the validity of plasma surface treatment for superconducting radio-frequency (SRF) cavities. The experiments were performed on disc-shaped Nb samples and compared with identical samples treated with buffer chemical polishing (BCP) techniques. Surface analysis indicates comparable or superior properties of plasma-treated samples. These promising results are still preliminary and additional work is in progress.

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Design And Fabrication Of A Prototype Fabry-Perot Cavity For The Compton Polarimeter Upgrade At Jefferson Lab, Deepa Deepa Jul 2005

Design And Fabrication Of A Prototype Fabry-Perot Cavity For The Compton Polarimeter Upgrade At Jefferson Lab, Deepa Deepa

Mechanical & Aerospace Engineering Theses & Dissertations

Upcoming experiments at Hall A at Jefferson lab require 1 % absolute accuracy of the electron beam polarization measurement at 0.85 Ge V energy. The Compton polarimeter at Hall A is capable of measuring beam polarization with 3 - 4 % accuracies at this beam energy. Hence it was proposed to upgrade the present Compton by doubling the laser frequency [2]. The present Compton polarimeter operates with a 1064 nm, continuous wave laser at 200 mW. This power is enhanced to 1.5 kW using a 0.85 m long Fabry-Perot Cavity. Changing to 532 nm laser with the same power would …

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Predicted Properties Of Microhollow Cathode Discharges In Xenon, J. P. Boeuf, L. C. Pitchford, K. H. Schoenbach Jan 2005

Predicted Properties Of Microhollow Cathode Discharges In Xenon, J. P. Boeuf, L. C. Pitchford, K. H. Schoenbach

Bioelectrics Publications

A fluid model has been developed and used to help clarify the physical mechanisms occurring in microhollow cathode discharges (MHCD). Calculated current-voltage (I-V) characteristics and gas temperatures in xenon at 100 Torr are presented. Consistent with previous experimental results in similar conditions, we find a voltage maximum in the I-V characteristic. We show that this structure reflects a transition between a low-current, abnormal discharge localized inside the cylindrical hollow cathode to a higher-current, normal glow discharge sustained by electron emission from the outer surface of the cathode. This transition, due to the geometry of …

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Optimization Of Ultraviolet Emission And Chemical Species Generation From A Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, Xinpei Lu, Mounir Laroussi Jan 2005

Optimization Of Ultraviolet Emission And Chemical Species Generation From A Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, Xinpei Lu, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

One of the attractive features of nonthermal atmospheric pressure plasmas is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. This attractive characteristic recently led to their extensive use in applications that require low temperatures, such as material processing and biomedical applications. The agents responsible for the efficient plasma reactivity are the ultraviolet (UV) photons and the chemically reactive species. In this paper, in order to optimize the UV radiation and reactive species generation efficiency, the plasma was generated by a dielectric barrier discharge driven by unipolar submicrosecond square pulses. To keep the discharge …

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Cluster Issue On Microplasmas, Kurt H. Becker, J. Gary Eden, Karl H. Schoenbach Jan 2005

Cluster Issue On Microplasmas, Kurt H. Becker, J. Gary Eden, Karl H. Schoenbach

Bioelectrics Publications

Atmospheric-pressure diffuse discharge plasmas are susceptible to instabilities and, in particular, to arcing (the glow-to-arc transition). Some of the most promising approaches to ‘stabilizing’ atmospheric-pressure plasmas are based on the recognition that arc formation can be avoided when the plasmas are generated and maintained in spatially constricted geometries with dimensions from tens to hundreds of microns. Known as microplasmas or microdischarges, these weakly-ionized discharges represent a new and fascinating realm of plasma science in which several scientific issues, such as the potential breakdown of pd scaling and the role of boundary-based phenomena, come to the fore. In contrast to ‘macroplasmas’ …

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Room-Temperature Atmospheric Pressure Plasma For Biomedical Applications, Mounir Laroussi, Xinpei Lu Jan 2005

Room-Temperature Atmospheric Pressure Plasma For Biomedical Applications, Mounir Laroussi, Xinpei Lu

Electrical & Computer Engineering Faculty Publications

As low-temperature non-equilibrium plasmas come to play an increasing role in biomedical applications, reliable and user-friendly sources need to be developed. These plasma sources have to meet stringent requirements such as low temperature (at or near room temperature), no risk of arcing, operation at atmospheric pressure, preferably hand-held operation, low concentration of ozone generation, etc. In this letter, we present a device that meets exactly such requirements. This device is capable of generating a cold plasma plume several centimeters in length. It exhibits low power requirements as shown by its current-voltage characteristics. Using helium as a carrier gas, very little …

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Levitation Using Microwave-Induced Plasmas, R. J. Exton, S. Popovic, G. C. Herring, M. Cooper Jan 2005

Levitation Using Microwave-Induced Plasmas, R. J. Exton, S. Popovic, G. C. Herring, M. Cooper

Physics Faculty Publications

The levitation of objects above a microwave horn is demonstrated. High-power microwave pulses generate a low-temperature, diffuse plasma on the surface of the horn window. The thermal effect of the surface plasma brings about a localized increase in the pressure and results in a vertical flow of air, thus levitating the object.

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Scaling And Characterization Of Direct Current Glow Discharge Plasma In Atmospheric Air, Abdel-Aleam Hefney Mohamed Apr 2004

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 …

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Microdischarge Arrays, Wenhui Shi Apr 2004

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 …

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Excimer Emission From Cathode Boundary Layer Discharges, Mohamed Moselhy, Karl H. Schoenbach Jan 2004

Excimer Emission From Cathode Boundary Layer Discharges, Mohamed Moselhy, Karl H. Schoenbach

Bioelectrics Publications

The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 μm, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the “cathode boundary layer” plasma, in the 100 μm range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm2 for …

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Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala Jan 2004

Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The effect of the direction of the detected beam on the intensity of ECE is studied. It is found that the combined effects of the strong dependence of the conversion efficiencey of O mode at the plasma resonance on the direction of the incident wave and the partial screening of the beam waist by the MAST vessel wall, can be responsible for the weakening of ECE emission for some frequencies. The theoretical model for ECE data interpretation on MAST has been significantly improved. New features of the model are as follows: the quasioptical treatment of the receiving antenna, interference, polarization …

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