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Plasma Science, IEEE Transactions on

Issue 2  Part 3 • Date April 2005

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Displaying Results 1 - 21 of 21
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - 857
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  • IEEE Transactions on Plasma Science publication information

    Publication Year: 2005 , Page(s): c2
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  • The design of a high-power, high-gain, frequency-doubling gyroklystron

    Publication Year: 2005 , Page(s): 858 - 865
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We present a theoretical comparison of multicavity gyroklystron circuits which are designed to optimize the beam-microwave interaction efficiency given a set of physical constraints imposed by the experimental system. The restrictions considered in this work are representative of realistic systems and include a cap on the maximum input power available, as well as a magnetic field defined by preexisting field coils and power supplies. The frequency doubling circuits all have input cavities which operate near the fundamental cyclotron frequency and all have output cavities which operate near the second-harmonic. Intermediate bunching cavities can be operated in either the first or second-harmonic. It was found that to maximize gain it is best to have initial buncher cavities at the fundamental harmonic and that to optimize efficiency, it is best to have the final buncher cavities at the second-harmonic. It was also found that diminishing returns are found for enhanced gain with increasing numbers of cavities, and that for the parameters of this study, a six cavity tube with three first-harmonic and three second-harmonic cavities appears to be optimal. View full abstract»

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  • A large-scale Ar plasma source excited by a TM330 mode

    Publication Year: 2005 , Page(s): 866 - 875
    Cited by:  Papers (9)
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    This paper reports a theoretical and experimental study on the spatial structure of a large-scale, slot-antenna excited plasma source operating in Ar. The overdense plasma (with a plasma frequency ωpl higher than stimulating frequency ω) close to the wave energy source sustained by the TM330 surface mode is analyzed. A self-consistent theoretical model based on a set of coupled equations is developed, which includes the electron Boltzmann equation, the rate balance equations for the most important excited species and charged particles, the gas thermal balance equation, and the wave mode electrodynamic equations. The principal collisional and radiative processes that determine the populations in the Ar(3p54s) and Ar(3p54p) levels are accounted for. The model determines the three-dimensional discharge structure, i.e., the radial, azimuthal and axial variations of the main discharge quantities. An experimental validation of the model predictions is achieved using probe techniques and radiophysics methods. Strong correlations are shown to exist between the density distributions of plasma electrons, positive ions, and electronically excited states of Ar atoms and the electric field intensity distribution in the discharge zone of the plasma source. View full abstract»

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  • Ion acceleration in a radio frequency driven ferroelectric plasma source

    Publication Year: 2005 , Page(s): 876 - 881
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    Ion emission from ferroelectric plasma sources driven by radio frequency (RF) applied voltage is studied. An experimental investigation of particle emission from lead zirconate titanate ferroelectric ceramics driven by bursts of seven cycles of RF voltage at 248 kHz has revealed significant ion current emission. Measured electron to ion peak current ratios ranged from 11 to 19, which is much lower than the expected thermal current ratio. These results indicate that the ions are being preferentially accelerated. An analysis of the ponderomotive force on the ions and electrons reveals that it may be responsible for acceleration of the ions. The ferroelectric plasma is examined as a possible micropropulsion thruster. Performance estimates based on the ponderomotive acceleration calculations predict specific impulse of 2000-3000 s, thrust of 0.1-1 mN, and specific power of 15 W/mN. These estimates are compared to existing micropropulsion concepts, revealing the attractiveness of ferroelectric plasma sources. View full abstract»

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  • Focusing of high-perveance planar electron beams in a miniature wiggler magnet array

    Publication Year: 2005 , Page(s): 882 - 891
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1536 KB) |  | HTML iconHTML  

    The transport of planar electron beams is a topic of increasing interest for applications to high-power, high-frequency microwave devices. This paper describes two- and three-dimensional simulations of electron-beam transport in a notched wiggler magnet array. The calculations include self-consistent effects of beam-generated fields. The simple notched wiggler configuration can provide vertical and horizontal confinement of high-perveance sheet electron beams with small transverse dimensions. The feasibility calculations address a beam system to drive a 95-GHz traveling-wave tube experiment under construction at Los Alamos National Laboratory, Los Alamos, NM. View full abstract»

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  • Initial electron-beam results from the DARHT-II linear induction accelerator

    Publication Year: 2005 , Page(s): 892 - 900
    Cited by:  Papers (11)
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    The DARHT-II linear-induction accelerator has been successfully operated at 1.2-1.3 kA and 12.5-12.7 MeV to demonstrate the production and acceleration of an electron beam. Beam pulse lengths for these experiments were varied from 0.5 μs to 1.2 μs full-width half-maximum. A low-frequency inductance-capacitance (LC) oscillation of diode voltage and current resulted in an oscillation of the beam position through interaction with an accidental (static) magnetic dipole in the diode region. There was no growth in the amplitude of this oscillation after propagating more than 44 m through the accelerator, and there was no loss of beam current that could be measured. The results of these initial experiments are presented in this paper. View full abstract»

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  • Gas evolution during operation of a CsI-coated carbon fiber cathode in a closed vacuum system

    Publication Year: 2005 , Page(s): 901 - 910
    Cited by:  Papers (13)
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    In order to quantify the gases generated during operation of an explosive emission cathode, residual gas analysis was performed on a closed vacuum system. Two different anode materials were tested using an identical CsI-coated carbon fiber cathode. For both the nearly transparent molybdenum mesh and the carbon fiber anode, the largest pressure increases were observed in hydrogen and carbon dioxide. Use of the molybdenum mesh resulted in the generation of approximately 0.38 neutrals per electron compared to 0.73 neutrals per electron while using the carbon fiber anode. While the background vacuum pressure was typically in the low 10-7 torr scale, it was found that gas generation during these explosive emission pulses led to local diode pressures of 0.5 mtorr up to several tens of mtorr. Such pressures are consistent with the ability to generate ion densities that can drastically effect the space charge-limited current. View full abstract»

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  • Stability problems in a conducting crossed-field diode

    Publication Year: 2005 , Page(s): 911 - 919
    Cited by:  Papers (1)
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    Current work on excess noise and chaos in the presence of a magnetic field justifies further inquiry into the more general question of stability of such systems. We have shown that the electron flow in a conducting, crossed-field diode is fundamentally unstable for certain values of the magnetic field and the injection current density. In the process, we have systematised some of the earlier investigations of electron flow stability in the absence of the magnetic field. View full abstract»

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  • Understanding of suspension DC plasma spraying of finely structured coatings for SOFC

    Publication Year: 2005 , Page(s): 920 - 930
    Cited by:  Papers (39)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3352 KB) |  | HTML iconHTML  

    Suspension plasma spraying was used to achieve a dense and thin (∼30 μm) yttria stabilized zirconia (YSZ) coating for the electrolyte of solid oxide fuel cells (SOFCs). A suspension of YSZ powder (d50∼1 μm) was mechanically injected in direct current (dc) plasma jets. The plasma jet acted as an atomizer and the suspension drops (d∼200 μm) were sheared, long before they started vaporizing, into many droplets (d∼2 μm). The solvent of the latters was then very rapidly (a few microseconds) evaporated and decomposed by the plasma jet. The solid particles enclosed in each droplet were then accelerated and melted before impacting on the substrate where they formed splats. The thermal inertia of particles with sizes below 1 μm being low, the standoff distance was much shorter than in conventional plasma spraying (40-60 against 100-120 mm). Thus, the heat flux from the plasma to the coating reached 20 MW·m-2 when spraying YSZ suspensions with Ar-H2 or Ar-H2-He plasma jets. It allowed keeping the whole pass (about 0.8-μm-thick) completely molten resulting after its solidification, for YSZ, in a fully dense coating (20-30-μm-thick) with a granular microstructure. View full abstract»

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  • Analysis of microdischarge characteristics induced by synchronized auxiliary address pulse based on cross-sectional infrared observation in AC plasma display panel

    Publication Year: 2005 , Page(s): 931 - 940
    Cited by:  Papers (6)
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    The microdischarge characteristics induced by an auxiliary address pulse with the synchronized application of sustain pulses are investigated based on cross-sectional infrared (IR) (823 nm) observations taken using an image-intensified charge-coupled device (ICCD) camera. The IR observations reveal that the application of an auxiliary short pulse with an optimal amplitude and width to the address electrode enhances the intensity of the IR emission. Furthermore, the cross-sectional IR observations demonstrate that the effective infrared emission region is extended toward the address electrode. In addition, a numerical analysis using a two-dimensional fluid simulation is also applied to investigate the discharge mechanism relative to the amplitude and width of the auxiliary address pulse. As a result, the improvement in the luminance and luminous efficiency was found to be caused by a face discharge between the address and the sustain (or scan) electrodes, where the face discharge plays an important role in supplying priming particles to the surface discharge and lengthening the discharge path, which in turn intensifies the surface discharge. View full abstract»

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  • Submillimeter dielectric barrier discharges at atmospheric pressure: edge effect

    Publication Year: 2005 , Page(s): 941 - 948
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1856 KB) |  | HTML iconHTML  

    Dielectric barrier discharges in atmospheric pressure helium, argon, nitrogen, oxygen, and air have been studied. Discharges were generated in short gaps (d≤1 mm) between two quartz plates with conducting coatings on their counter sides to strengthen the edge effect. It was found that a decrease in d leads to the degeneration of a volume barrier discharge into a barrier corona discharge. The role of this phenomenon in the formation of spatio-temporal patterns in short barrier discharges is discussed. View full abstract»

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  • Numerical simulation on mode transition of atmospheric dielectric barrier discharge in helium-oxygen mixture

    Publication Year: 2005 , Page(s): 949 - 957
    Cited by:  Papers (11)
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    A one-dimensional numerical simulation of a homogeneous dielectric barrier discharge has been carried out for a nonequilibrium helium-oxygen mixture plasma to understand the influences of oxygen additive on its discharge characteristics at atmospheric pressure. The numerical results obtained by solving continuity equations for plasma species and Poisson equation show that, depending on the amount of oxygen added, the homogeneous barrier discharge turns out to have two fundamental modes: glow and Townsend. When oxygen is rare, the discharge has similar characteristics to the direct current glow discharge at low pressure. As the oxygen additive increases, the discharge characteristics of the glow mode are destroyed and changed into the Townsend mode. The reason for this mode transition is due to the fact that oxygen plays an important role both in quenching helium metastables and in attaching electrons on it in the plasma. As a practical method of sustaining the glow mode even with high oxygen concentration in the discharge, adjustment of the frequency of applied driving voltage is introduced. The numerical simulation reveals that the glow mode recovers from the Townsend mode by increasing the frequency while the amount of oxygen is highly contained. Finally, discharge operation regimes for the glow and Townsend modes are numerically obtained, which are dependent on both oxygen additive and applied frequency. View full abstract»

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  • Decomposition of phosgene by microwave plasma-torch generated at atmospheric pressure

    Publication Year: 2005 , Page(s): 958 - 963
    Cited by:  Papers (13)
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    The microwave plasma-torch and its application for decomposition of chemical warfare agent using a moderate microwave power are investigated. Decomposition of chemical warfare agents is demonstrated for phosgene (COCl2) as a sample example. The main byproducts of phosgene decomposition are CO and Cl2. The Cl2 gas was completely converted to HCl by injecting NH3 into the microwave plasma-torch as an additive gas. The HCl is, in turn, eliminated by passing the exhaust gas through a wet-scrubber. Detailed decomposition properties of phosgene by microwave plasma-torch at the atmospheric pressure are also investigated by making use of Fourier transform infrared, mass spectroscopy, and ion chromatography. View full abstract»

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  • Characteristics of a wall voltage during sustain period in AC plasma display panels

    Publication Year: 2005 , Page(s): 964 - 968
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    According to the viewpoint of a driving scheme, the luminance and luminous efficiency is mainly determined during the sustain period. Therefore, it is very important to understand the characteristics of the wall voltage during the sustain period, which is essential to design the driving pulse scheme. In this study, the quantitative analysis of the wall voltage has been carried by the wall voltage measurement method during the sustain period. The initial difference of the wall voltage is sharply stabilized due to the sustain discharges and it is mainly determined by the sustain voltage. The wall voltage between the sustain electrodes is changed symmetrically for the reference voltage level, while the wall voltage between the address and sustain electrode is positively sustained which is roughly mean value of the total effective voltage. View full abstract»

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  • Compact power detection probe for the RF plasma heating waveguide array

    Publication Year: 2005 , Page(s): 969 - 975
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    Reduced height waveguide arrays are commonly used in fusion plasma radio frequency heating in the lower hybrid frequency range. In order to distinguish the incident wave and the reflected wave, power detection with high directivity in each reduced height waveguide is required. Due to the confined space in a stack of reduced height waveguides, power detection with high directivity in the reduced height waveguide is extremely difficult, especially from the wide side of the waveguide by using a conventional E probe. A new compact probe, which employs current loops, to monitor the incident and reflected wave from the narrow side of the reduced height waveguide has been developed. According to the test data, greater than 35 dB of directivity was measured with this compact probe at 4.6 GHz. View full abstract»

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  • A new optical technique for investigations of low-Voltage circuit breakers

    Publication Year: 2005 , Page(s): 976 - 981
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    The technique of broad-band optical absorption spectroscopy has been successfully used for investigations of transient media in low-voltage circuit breakers, thanks to an intense radiation source developed at our laboratory. It enabled the determination of the concentration of copper atoms and C2 molecules in hot gas behind a moving arc. The temperature of this gas was estimated using the molecular absorption spectrum of C2 Swan bands. Thanks to the high-spectral intensity of the auxiliary source, measurements were also performed in an electrical arc. The measurements allowed the determination of the population of excited levels for several metallic atoms in the arc. Assuming local thermodynamic equilibrium, the electron temperature of the arc and the total concentration of these metallic atoms, coming from contacts and splitters, were deduced. This temperature is in good agreement with the one deduced from optical emission spectroscopy. View full abstract»

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  • Fast discharge energy storage development for advanced X-ray simulators

    Publication Year: 2005 , Page(s): 982 - 989
    Cited by:  Papers (3)
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    Design studies have been completed to investigate the impact of improvements in fast energy storage systems on the designs of: larger future simulators (such as a 15-MA plasma radiation source (PRS) simulator), simulator upgrades of operational machines (such as Double-EAGLE), and for very compact, smaller simulators. The fast energy storage system that has been investigated and is presently under development is a fast Marx generator (FMG) with inductance capacitance (LC) 1/2=200 ns and LC 1/2=300 ns, depending on the capacitance per stage. This new fast Marx energy storage system uses newly developed, low-inductance rail switches and low-inductance capacitors. These components are configured in a low-inductance FMG stage and then stacked in series to form a unit for the voltage required and a number of units in parallel for the required system inductance and stored energy. A four-stage fast Marx prototype has been demonstrated with a total of 60-kJ energy stored and an output voltage of 680 kV. This new FMG technology will provide the capability to build X-ray machines in a significantly more compact configuration. The new FMG technology minimizes or eliminates the need for storing the energy in a large water transfer capacitor. A design sketch of a 15-MA PRS machine driven by a fast Marx will be presented. This generator would consist of 48 eight-stage FMG units and would drive the PRS directly without further pulse compression. We will also present the concept of a high voltage (2-3 MV), compact X-ray machine that uses a nine-stage fast Marx module to directly charge a vacuum inductive store. A plasma opening switch (POS) is used to switch the inductive store and deliver the electron beam to the load. View full abstract»

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  • Experimental study of X-pinch in a submicrosecond regime

    Publication Year: 2005 , Page(s): 990 - 996
    Cited by:  Papers (7)
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    X-pinch plasmas are known as point-like X-ray sources with the potential application for backlighting diagnostics. X-pinches are commonly driven by large pulsed power generators delivering high-voltage pulses with short rise-times, typically under 100 ns. When operating with slower capacitor banks, X-pinches become less reliable because of the arising X-ray pulse jitter and because of the appearance of two or more X-ray bursts coming from multiple hot spots. In this paper, a very compact inductance-capacitance (LC) generator with the current rise-time of 200 ns was used to drive molybdenum and tungsten wire X-pinches. A single peak, small shot-to-shot jitter emission of X-rays was obtained. Time-integrated penumbral imaging recorded the X-ray source dimension of less than 15 μm in the spectral region above 2.4 keV. The total yield of more than 80 mJ was registered with the radiation pulse duration as short as 1.5 ns. The appearance of single- or multiple-source core structures is discussed in correlation with used wire material and X-pinch torsion angle. The results confirm the possibility of using an X-pinch driven by a fast compact capacitor bank for backlighting applications. View full abstract»

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  • Three-dimensional numerical simulation on performance of nonequilibrium plasma MHD generator coupled with radio frequency electromagnetic field

    Publication Year: 2005 , Page(s): 997 - 1004
    Cited by:  Papers (3)
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    Three-dimensional numerical simulation has been carried out to investigate the performance of a large scale disk magnetohydrodynamics (MHD) generator coupled with radio frequency (RF) electromagnetic field. The RF technique is verified to be useful for the improvement of performance and widening the actual operating conditions even for a large scale MHD generator. The skin effect of plasma influences the distribution of RF electric field, however, under the present plasma condition in the MHD generator, this effect will not induce the failure of the RF application. When the plasma does not achieve the fully ionized seed condition only by self-induced Joule heating, the plasma is unstable and nonuniform three-dimensionally. Coupling with the RF power can stabilize the plasma and improve the performance of MHD generator. An optimal value of the RF power under which the plasma structure becomes completely uniform in azimuthal direction, and the performance of MHD generator can be most effectively improved is evaluated. The energy cost of RF Joule heating is smaller than the power output increased by coupling with the RF power. The improvement of MHD generator performance by the RF power is efficient. View full abstract»

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  • IEEE Transactions on Plasma Science Information for authors

    Publication Year: 2005 , Page(s): c3
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IEEE Transactions on Plasma Sciences focuses on plasma science and engineering, including: magnetofluid dynamics and thermionics; plasma dynamics; gaseous electronics and arc technology.

 

 

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