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Plasma Science, IEEE Transactions on

Issue 4 • Date April 2013

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Displaying Results 1 - 25 of 35
  • Table of contents

    Page(s): C1 - 825
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  • IEEE Transactions on Plasma Science publication information

    Page(s): C2
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  • Observation of Positive Self-Bias in Radio Frequency Atmospheric Pressure Microplasmas

    Page(s): 826 - 828
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    Negative self-bias is well known at the powered small-sized electrode in low-pressure capacitive-coupled discharge plasmas. In this paper, however, the self-bias at the powered electrode observed in an RF atmospheric-pressure microplasma demonstrates either a positive or negative sign depending on the supplied power and interelectrode gap. View full abstract»

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  • Effects of Increasing Magnetic Field and Decreasing Pressure on Asymmetric Magnetron Radio Frequency {\rm Ar}/{\rm O}_{2} Discharges

    Page(s): 829 - 838
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    The aim of this paper is to define the optimal couple of the total pressure and the magnetization of the permanent magnets for self-maintaining under optimal conditions an asymmetric magnetron radio frequency (RF) discharge. Electro-dynamics discharge simulations are based on a self-consistent particle model using Monte Carlo method for the treatment of collisions between charged particle and background gas. The simulations are performed at a fixed mixture of 90% Ar/10% O2 by simultaneously decreasing the total pressure P and increasing the magnetization σ. In the case of a sinusoidal RF power supply with 200 V for peak voltage and 13.56 MHz for frequency, the magnetization of the permanent magnets varies between 500 Gauss at 25 mTorr to 1400 Gauss at 5 mTorr. We use a semianalytical method for calculating the applied magnetic field generated by two permanent magnets that are composed of concentric rings. This enables generating, in a specific region of the interelectrode gap near the cathode, an optimal magnetic field crossing the RF electric field for application to magnetron discharges. The simulation results of RF magnetron discharge shown that, in the case of the lowest considered pressure (5 mTorr), a high magnetization of 1400 Gauss is the most favorable for self-maintaining the discharge and generating a quasi-ion beam energy distribution near the cathode that is interesting for cathode sputtering processes. View full abstract»

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  • Insights Into Sustaining a Plasma Jet: Boundary Layer Requirement

    Page(s): 839 - 842
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    In this paper, we investigate the effects of various background gases on the formation and sustenance of a plasma jet. A helium plasma is ignited inside a dielectric tube and introduced into a vacuum chamber where the gas composition and pressure can be controlled. The gas composition inside the chamber is altered by separately injecting various background gases, such as air, nitrogen, and argon. Here, we report that, in order to sustain a plasma jet, there needs to be a physical boundary layer around the helium flow. This boundary can be in the form of a solid surface that encapsulates the flow, or a background gas other than helium. If only helium is present inside the chamber, no propagating jet is created; rather a diffuse plasma fills the chamber. If another gas is introduced, then the diffuse plasma reverts into a jet. Additionally, we discovered what can be considered as the signature emission line from a plasma jet operating with helium. This emission line is at 587.4 nm (He). This line appears in the emission profile only in the presence of a plasma jet, and disappears as the plasma transitions to a diffuse state at the same applied power parameters and pressure. View full abstract»

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  • New Solutions of the Corona Discharge Equation for Applications in Waveguide Filters in SAT-COM

    Page(s): 843 - 846
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    The microwave device designers in the industry of satellite communications systems use analytical solutions of the corona discharge equation, employing the concept of characteristic diffusion length, to determine whether its intensity in a particular device, such as waveguides and filters, is within established margins. The analytical solutions provide the lowest possible breakdown threshold. Until now, the difference of the gap between the electrical breakdown values obtained experimentally and provided by analytical solutions has not yet been explained sufficiently. This paper shows how it is inappropriate to use the characteristic diffusion length (Λ) rather than the effective diffusion length (Λeff), although in principle electric fields are considered in terms of its geometry. The presence of an ionic space charge generated during the time evolution of the electron avalanche alters the medium properties in waveguide filters, occasioning signal absorption and reflection anomalies that modify the condition of homogeneous fields in inhomogeneous fields. View full abstract»

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  • Field Distributions and Beam Coupling in the Low-Impedance Transit-Time Oscillator Without Foils

    Page(s): 847 - 852
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    The low-impedance transit-time oscillator (LITTO) without foils is a new high-power microwave generator. Its main operation mode is the coaxial transverse mode TM01 . This paper solves the field distributions and the corresponding beam coupling coefficients in the LITTO. As shown in this paper, the modulating electric field in the multicavity LITTO can be derived from a single-cavity theory; thus, its corresponding beam coupling coefficient can be easily obtained. View full abstract»

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  • Mode Selection and Coaxial Cavity Design for a 4-MW 170-GHz Gyrotron, Including Thermal Aspects

    Page(s): 853 - 861
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    Gyrotron oscillators are millimeter wave sources, capable of reaching megawatt power levels. Such high RF power is required for electron cyclotron resonance heating and current drive systems for current and future nuclear fusion facilities. With total heating system powers in the range up to about 100 MW, these installations call for unit powers above 1 M W, to reduce cost and complexity of the complete heating system. In this paper, a mode selection process for a 4-MW 170-GHz coaxial-cavity gyrotron is presented and stable operating parameters are elaborated. The employed formalism, based on normalized variables, suggests one mode, namely the TE-52,31, which is sufficiently separated from its competitors and supports an advanced two-beam quasi-optical mode converter . Through the utilization of time-dependent and self-consistent approaches, a coaxial cavity is optimized and stable single-mode operation at 4.35 MW of generated output power with an interaction efficiency of 33% is predicted. This paper discusses the mode selection process under consideration of realistic technical limitations, optimization of the cavity for stable operation with a pure output mode, and finally thermo-mechanical calculations on cavity cooling and surface temperature. View full abstract»

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  • Experimental Study of the Start-Up Scenario of a 1.5-MW, 110-GHz Gyrotron

    Page(s): 862 - 871
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    We present experimental results of the modes excited during the voltage rise of a 1.5-MW, 110-GHz gyrotron operating in the TE22,6,1 forward-wave mode. Results were obtained by two different experimental techniques: measurements with a time-gated heterodyne receiver and measurements during the flat-top portion of the voltage pulse with a sequence of increasing voltages. Two operating points were selected: a high-efficiency 1.2-MW power-level point at 4.38 T and a highly stable 600-kW point at 4.45 T. In the former case, the TE21,6,3 and TE21,6,4 backward-wave modes far from cutoff were excited during the voltage rise of the pulse before the desired TE22,6,1 operating mode was excited; in the latter case, the excitation of a TE22,6,2 backward-wave mode dominated the voltage rise before eventually exciting the desired operating mode. Analysis of the microwave output beam spatial pattern and the frequency and power levels recorded indicate that these modes are indeed excited within the cavity. Single-mode MAGY simulations provide further evidence that such modes can exist in the gyrotron during the voltage rise. Knowledge of the modes excited during start-up is important for achieving high efficiency and avoiding power at unwanted frequencies. View full abstract»

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  • Influence of Annular Beam Displacement on the Performance of a High-Power Gyrotron

    Page(s): 872 - 878
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    In this paper, we present the results of an experimental study on the influence of the lateral misalignment between the axes of the annular electron beam and the cavity on the performance of a 1-MW 140-GHz gyrotron. The subject of the study is of practical interest. On one hand, the discrepancy between numerical simulations of the gyrotron performance and experimental results could by partially attributed to the beam misalignment. On the other, it is in practice very difficult to reach the necessary tolerances in series production of high-power high-frequency (>100 GHz) gyrotrons. The problem actually will become more demanding with the increase of the operating frequency of the working mode because the required accuracy scales with the wavelength of the electromagnetic wave. It is shown that a large displacement of the annular beam from the cavity axis may lead to the excitation of a competing mod which is not excited under normal conditions. The excitation of the main mode is observed, however, at a beam-cavity displacement of up to 0.8 mm. View full abstract»

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  • HPM Formation in Air and SF6/Argon Mixture

    Page(s): 879 - 886
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    Using fast-rising voltage pulses, corona discharges are created on the helix. Investigations are carried out in atmospheric air and SF6/argon mixture. The corona discharges produce electron beams on the helix. High-power microwaves are obtained in the structure that has two microwave sources. The helix as the slow-wave structure with in situ generated electron beams is one source of microwave generation. The experimental data are presented. The analysis of the data related to the helix is based on the backward-wave oscillator. View full abstract»

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  • Improvement of Luminous Efficacy Using Short Sustain Pulsewidth and Long Off-Time Between Sustain Pulses in AC Plasma Display Panel

    Page(s): 887 - 891
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    This paper investigated the discharge characteristics driven by a short sustain pulsewidth according to the sustain pulsewidth and the off-time between the sustain pulses in an ac plasma display panel. As a result, the luminous efficacy was found to increase when decreasing the sustain pulsewidth due to a reduced ion heating loss. Furthermore, it was shown that the sustain discharge mode could be controlled by adjusting both the sustain pulsewidth and the off-time. It should be noted that the luminous efficacy was significantly improved when the sustain discharge was made to occur outside the sustain pulsewidth due to the minimized ion heating loss. Consequently, under this experimental condition, a sustain pulsewidth of 0.4 μs and an off-time of 10 μs produced the maximum luminous efficacy of 3 lm/W, which was almost double the value obtained with the conventional sustain pulsewidth of 2 μs and the off-time of 10 μs. View full abstract»

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  • Numerical Study on Propeller Flow-Separation Control by DBD-Plasma Aerodynamic Actuation

    Page(s): 892 - 898
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    The process of dielectric barrier discharge (DBD) plasma flow-separation control on screw propeller is numerically simulated based on the unsteady compressible Navier-Stokes equations loosely with DBD-plasma body force aerodynamic actuation mechanism. The effect and the mechanism of plasma flow control to enhance the propeller aerodynamic characteristics are discussed. The results show that the propeller aerodynamic characteristics will decrease as the altitude increase without plasma flow control, but it will first increase and then decrease as the altitude increases with plasma flow control. The effect of DBD-plasma flow control on the distribution of pressure is small at ground condition, and the difference of pressure distribution between general propeller and plasma efficiency-enhance propeller will be increased as the altitude increases. The effect of DBD-plasma flow-separation control will increase as the altitude increases. Mainly, the mechanism of the plasma flow control to enhance the propeller aerodynamic is obtained as follows. The flow separation on the propeller blade surface could be effectually controlled by DBD-plasma aerodynamic actuation, thereby increasing the efficiency of the propeller. The pressure of the windward surface of the blade will decrease by the plasma body force, which will increase the thrust of the propeller. View full abstract»

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  • Experimental and Numerical Investigation on the Interaction Between Ar Flow Channel and Ar Plasma Jet at Atmospheric Pressure

    Page(s): 899 - 906
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    In this paper, the interaction between Ar flow channel and atmospheric pressure plasma jet (APPJ) is investigated quantitatively by combining 3-D species transport simulation and optical schlieren observation together. The turbulence model, gravity force, and electrostatic force model are included into the Ar flow channel simulation. It is found that, with the increment of the Ar flow rate, the plasma plume reaches the maximum length at 3.5 L/min and then decreases sharply, which is corresponding to the Ar flow status. The simulations of the Ar flow channel show good agreement with the captured schlieren images. At small flow rates, the Ar flow channel bends downward due to the gravity. Under laminar flow, the high Ar mole fraction region near the axis of the Ar flow channel increases with the flow rate. However, the Ar flow presents as twist and radial diffusion, and the Ar mole fraction decreases rapidly when the Ar flow transits into turbulence, which leads the length of the Ar plasma plume to decrease sharply correspondingly. The plasma plume bestows the Ar flow channel a forward momentum, which decreases the curvature of bending downward and reinforces the twist and instability of the Ar flow channel under turbulence flow. By coupling the optical emission spectra and flow channel investigation together, it is revealed that Ar APPJ propagates along the core of the conelike flow channel. The Ar mole fractions at the head of the plasma plume are about 0.985 and 0.45 under laminar and turbulence flow, respectively. View full abstract»

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  • {\rm He}\hbox {-}{\rm H}_{2}{\rm O}_{2} Plasma Jet Irradiation of Tissue Surfaces: Study of Dominant Pathways For Plasma Chemical Tissue Removal

    Page(s): 907 - 914
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    Surface tissue-removal mechanisms, resulting from atmospheric He-H2O2 plasma jet fluxes impinging on tissue surfaces, were investigated. We employed primarily optical emission for cataloging relative concentrations of reactive plasma radicals versus plasma-jet conditions. The reactive radicals were then correlated with measured tissue-removal rates, under varying experimental conditions to determine the dominant role of OH radicals in the tissue removal. Fourier transform infrared (FTIR) molecular spectroscopy was employed to track molecular bond alterations at tissue surfaces, following the plasma irradiation of tissue surfaces. We studied three types of samples: 1) volatilized tissue fragments, filtered out of the effluent; 2) remaining solid-phase tissue samples in the incision region; and 3) nonprocessed contiguous tissue-surface regions. All surface bondings were compared and contrasted by FTIR analysis. In parallel, both the pure electro surgery (ES) with no added plasma radical fluxes and plasma-assisted ES were used as a dual baseline. This three-part study provides evidence that OH radicals drive the observed changes on tissue surfaces both within, and in bordering tissue regions in a He-H2O2 atmospheric plasma jet. Moreover, plasma-assisted ES as compared to pure ES reduces buildup of tissue char on the ES device electrodes, which is a practical advantage in ES surgery. FTIR measurement of the surgical margins (surrounding the removed tissue) is possible in pure plasma-jet tissue removal, via measuring changes in amide A bonds, which are indicators of the level of thermal damage to surrounding tissue, and may be a possible control means to achieve minimum collateral damage. View full abstract»

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  • Investigation of SF6 Arc Characteristics Under Shock Condition in a Supersonic Nozzle With Hollow Contact

    Page(s): 915 - 928
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    Arc-shock interaction and its influence on steady and dynamic characteristics of SF6 arcs in a supersonic nozzle with hollow contact, which is representative of switching arcs in a gas blast high-voltage circuit breaker, are computationally investigated using the magneto-hydro-dynamic theory with fixed inlet stagnation pressures and at five different exit pressure to inlet stagnation pressure ratios (referred to as pressure ratios). The significant quantity in determining the thermal interruption capability of a circuit breaker, i.e., the critical rate of rise of recovery voltage, was predicted and compared with available test results. The deterioration of thermal interruption capability of a supersonic nozzle under shock conditions, which was observed in previous tests is verified and discussed by current arc model. It was found that the close coupling between the shock and the surrounding gas flow can greatly influence the aerodynamic and electrical behavior of a nozzle arc and hence the thermal recovery behavior of current interruption. Additionally, the velocity deceleration caused by the shocks and the enhanced turbulent cooling brought by the sucked gas and arc interaction both pay a significant role in the determination of thermal interruption capability. View full abstract»

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  • Electron Beam Emission and Interaction in 0.3-THz Gyrotron for Second Harmonic, CW Operation

    Page(s): 929 - 934
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    This paper describes the design of a 0.3-THz gyrotron at second harmonic operation. The interaction cavity design and the beam-wave interaction computation are carried out for TE0,6 mode by using the particle-in-cell electromagnetic simulation approach. The simulation results confirm > 6-kW output power with efficiency ~ 17% by using an electron beam with accelerating voltage 20 kV and current 2.0 A. To achieve the required electron beam parameters, a triode magnetron injection gun is designed. The transverse-to-axial velocity ratio (α), 1.27 and the transverse velocity spread <; 4% are realized. Considering the fabrication and operation of the device, the parametric analysis is also performed. View full abstract»

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  • Study on Plasma Agent Effect of a Direct-Current Atmospheric Pressure Oxygen-Plasma Jet on Inactivation of E. coli Using Bacterial Mutants

    Page(s): 935 - 941
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    Biosensors of single-gene knockout mutants and physical methods using mesh and quartz glass are employed to discriminate plasma agents and assess their lethal effects generated in a Direct-Current atmospheric-pressure oxygen plasma jet. Radicals generated in plasma are determined by optical emission spectroscopy, along with the O3 density measurement by UV absorption spectroscopy. Besides, thermal effect is investigated by an infrared camera. The biosensors include three kinds of Escherichia coli (E. coli) K-12 substrains with their mutants, totalling 8 kinds of bacteria. Results show that oxidative stress plays a main role in the inactivation process. Rather than superoxide O2-, neutral reactive oxygen species such as O3 and O2(a1Δg) are identified as dominant sources for oxidative stress. In addition, DNA damage caused by oxidation is found to be an important destruction mechanism. View full abstract»

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  • Simulation of Expansion of Thermal Shock and Pressure Waves Inducaed by a Streamer Dynamics in Positive DC Corona Discharges

    Page(s): 942 - 947
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    This paper is devoted to the simulation of the thermal shock and the induced pressure-waves expansion, generated by a dc pin-to-plan corona discharge in the air at ambient temperatures and under atmospheric pressure. The positive dc voltage applied to the tip generates a monofilamentary streamer that crosses the gap from the tip toward the plan. The simulation models are based on the coupling of a 2-D dynamics streamer model with the hydrodynamics conservation equations of a compressible gas. The source term for the gas dynamics equations takes into account the fast-energy relaxation from excited molecules to the random thermal energy. The simulation shows that the streamers generate a thermal shock near the anodic tip, which induces high pressure gradients and finally the gas expansion. The thermal shock is located just in front of the anodic tip, where the injected energy density is the highest. After 0.3 μs, the mean gas temperature increases up to around 800 K in a small volume just in front of the anodic tip while the maximum temperature reaches 1200 K. In addition, two pressure waves, a spherical and a cylindrical one, are induced with a propagation velocity of 370 m s-1 i.e., close to the speed of sound in air. View full abstract»

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  • Development of Large-Area Switchable Plasma Device for X-Band Applications

    Page(s): 948 - 954
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    This paper demonstrates a large-area, lightweight, conformal plasma device that interacts with propagating X-band microwave energy. The active elements are rugged plasma-shells - hollow ceramic shells encapsulating a controlled-pressure gas that can be ionized to controlled plasma parameters. Plasma-shells are electrically excited by frequency selective surfaces that are transparent to the frequency band of interest. The result is equivalent to large-area free-space plasma confined in a discrete plasma slab. A novel structure is designed with the aid of full-wave simulation and fabricated as a 76.2-mm square array, and transmission performance is tested across different drive voltages and angles of incidence. Switchable attenuation of 7 dB is measured across the passband when driven with 1400 Vpp at 1 MHz. Plasma parameters are estimated from theory and full-wave simulation, with electron density estimated to be 3.6×1012 cm-3. The proposed structure has potential for use on mobile platforms. View full abstract»

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  • Measurement of Transient Electric Fields in Air Gap Discharge With an Integrated Electro-Optic Sensor

    Page(s): 955 - 960
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    The spatial electric field is a key parameter for gas discharge research. Based on the electro-optic effect, a small size (mm), wide measuring-amplitude (MV/m), mono-shield structure, integrated electro-optic sensor is designed and developed. The ns-level time domain calibration system of the sensor is established. The calibration result shows that the output electric field is linear with the input signal, and the dynamic response time of the sensor is less than 2 ns. Using the developed sensors, the spatial electric field of a 1-m rod-plane air gap discharge is tested and the sudden step of an electric field is detected. As the imposed voltage increases, the probability and amplitude of the electric field step increased as well. This step phenomenon is confirmed to be the inception and development of a streamer; the confirmation is made by means of simultaneously captured photos. The rise time and the amplitude of the electric field step are discussed. Accordingly, the integrated electro-optic sensor will be a powerful tool for studying the mechanism of air gap discharges. View full abstract»

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  • Pattern Formation in Electrical Exploding of Thin Metal Films

    Page(s): 961 - 966
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    We present the experimental results of the nanometer Zn films electrical explosion in the air. The film destruction is accompanied with the stratification; the strata are formed in the transverse direction to the applied electric field. The initial strata growth can be explained by the electro-thermal instability development. The strata propagation velocity reaches 50 km/s and depends on the current. The pattern is formed during ~60 ns and each stratum's voltage settles at the constant level limited by arc discharges. We found that strata fractal dimension D=1.55±0.02 for all experiments, which means that the patterns are determined by a certain universal mechanism. View full abstract»

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  • Influence of a Circuit Parameter for Plasma Water Treatment by an Inductive Energy Storage Circuit Using Semiconductor Opening Switch

    Page(s): 967 - 974
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    In this paper, we investigate a water treatment method that sprays waste water droplets into a pulsed discharge space. For this method, it is important to apply pulsed voltages with a short pulse width and a fast rise to the electrode to realize high energy efficiency. An inductive energy storage (IES) circuit using a semiconductor opening switch (SOS) outputs pulsed voltages similar to the above-mentioned voltage. We report the characteristics of the water treatment using the IES circuit. The capacitance and inductance in the IES circuit are varied. An increase in the inductance in the secondary circuit of the pulse transformer, results in the formation of pulsed voltages with a longer pulse width; thus, the ratio of the thermal loss to the discharge energy becomes high. However, the energy transfer efficiency improves. Additionally, we vary the maximum current of the SOS, keeping the pulse width constant, by adjusting the capacitance and the inductance. As a result, when the current in the SOS increased, pulsed voltages with a higher peak and a shaper rise are obtained. Further, the pulse width of the voltage and the energy transfer efficiency are not affected by the current in the SOS. Hence, the energy density of the discharge is higher. The increase in the secondary inductance and the forward current increased the energy efficiency of the water treatment system owing to the increase in the energy transfer efficiency and the discharge energy density. View full abstract»

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  • Fast Ignitron Trigger Circuit Using Insulated Gate Bipolar Transistors

    Page(s): 975 - 979
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    This paper describes a low cost, easy-to-implement circuit for triggering ignitrons in plasma physics experiments and other pulsed power applications. Using insulated gate bipolar transistors (IGBTs) for rapid switching, the circuit delivers >2 peak current from a 0.1-μF capacitor to the ignitron trigger pin with a rise time of ~ 0.6 μs. The trigger circuit is isolated from the ignitron by a pulse transformer. Details of the circuit design and practical considerations for working with IGBTs are discussed. Sources of inductance in the system are identified, and leakage inductance associated with the pulse transformer is shown to be the primary factor limiting the pulse rise time. View full abstract»

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  • Feasibility and Performance of a Tapered Helical Pulse-Forming Line-Based Pulse Transformer

    Page(s): 980 - 984
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    Conventional pulsed power devices such as Marx generators, Tesla transformers, and cable-based generators are usually bulky and occupy a large volume when used for generating high-voltage pulses of duration longer than 100 ns. Cable-based generators also have the limitation of generating half the charging voltage when delivering the entire energy into a matched load. Inductive energy storage systems provide an alternate and effective scheme to overcome these issues. However, their efficiency depends upon the performance of opening switches. Also, inductive energy storage systems do not typically generate flat-top voltage pulses that are desirable for driving various pulsed power loads. In this paper, a new device, named the tapered helical pulse-forming line-based pulse transformer (THPFL-PT), is designed to overcome the above-mentioned drawbacks. The device performs two actions at the same time, i.e., it steps up the input charging voltage, and it generates a flat-top nanosecond voltage pulse. It is developed and characterized at low voltages to verify the feasibility of the concept developed and design parameters. The entire device is compact, with length of about 330 mm. It is capable of generating a voltage pulse of magnitude higher than the charging voltage with a duration of about 100 ns and almost a flat-top profile. View full abstract»

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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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