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ABSTRACT: X-ray emission has been detected occasionally during the streamer-corona propagation in a wire-plate corona reactor open to ambient air. A 65 kV pulse with 15 ns rise time is applied to the wire anode superimposed on a 20 kV dc bias. The duration of the driving voltage pulse (110 ns) is less than 2.5 times the primary streamer transit time. Under this condition no arc discharge occurs between the wire and the cathode plates separated by 6 cm air. The onset of x-ray emission coincides with the initiation of the primary streamers near the wire anode. No x-rays were detected later, during or after the primary or secondary streamer development. X-ray energies ranged between 10 and 42 keV, as detected by a LaBr3 (Ce) scintillator–photomultiplier combination. Time resolved imaging of the streamer propagation highlights the different stages in the streamer discharge process. The energetic electrons originate near the anode, at the moment of streamer initialization.
Journal of Physics D Applied Physics 12/2009; 43(2):025202. · 2.54 Impact Factor
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ABSTRACT: This paper describes an efficient, repetitive nanosecond pulsed power generator using a transmission-line-transformer (TLT) based multiple-switch technology. Within this setup, a 10-stage TLT and ten high-pressure spark-gap switches are adopted. At the input side, ten spark-gap switches are interconnected in series via the TLT, so that all the spark-gap switches can be synchronized automatically. At the output side, all the stages of the TLT are connected in parallel, thus a low output impedance (5 ¿) is obtained, and a large output current is realized by adding the currents through all the switches. Experimental results show that 10 spark-gap switches can be synchronized within about 10 ns. The system has been successfully demonstrated at repetition rates up to 300 pps (Pulses Per Second). Pulses with a rise-time of about 11 ns, a pulse width of about 55 ns, an energy of 9-24 J per pulse, a peak power of 300-810 MW, a peak voltage of 40-77 kV, and a peak current of 6-11 kA have been achieved with an energy conversion efficiency of 93-98%.
IEEE Transactions on Dielectrics and Electrical Insulation 09/2009; · 1.09 Impact Factor
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ABSTRACT: Gas-cleaning techniques using nonthermal plasma are slowly introduced into industry nowadays. In this paper, we present a novel power modulator for the efficient generation of large-volume corona plasma. No expensive high-voltage components are required. Switching is done at an intermediate voltage level of 1 kV with standard thyristors. Detailed investigations on the modulator and a wire-plate corona reactor will be presented. In a systematic way, modulator parameters have been varied. Furthermore, reactor parameters, such as the number of electrodes and the electrode-plate distance, have been varied systematically. The yield of O radicals was determined from the measured ozone concentrations at the exhaust of the reactor.
IEEE Transactions on Plasma Science 07/2009; · 1.17 Impact Factor
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ABSTRACT: Streamer properties such as their velocity, diameter, intensity and density, can be obtained by analysis of temporal and spatial resolved ICCD imaging. In this paper, experimental results on streamer generation and propagation as a function of several high-voltage pulse and reactor parameters are described. Experiments were performed on a large scale wire–plate reactor in ambient air. The set-up allows for independent variation of the parameters over wide ranges. The minimum gate time of the ICCD camera is 5 ns, allowing for a high temporal resolution. The camera can be triggered with a precision of 1 ns. Both negative and positive polarity pulses are investigated. The most important conclusions are as follows. (1) The streamer velocity ((0.5–2.5) × 106 m s−1) increases if the applied electric field and/or the voltage rise rate is increased. (2) The same is true regarding the velocity ((0.2–1.2) × 105 m s−1) with which the streamer diameter (0.7–3.0 mm) increases during propagation. (3) Typical properties (velocity, diameter, etc) of negative and positive polarity streamers vary less than 25%, especially when the applied electric field is high. (4) As long as the dc bias voltage is below the dc corona onset value it does not have a separate effect on the visual streamer properties. Only the total voltage (peak voltage + dc) is of importance. (5) A simple model was used to determine the electric field in the secondary streamer channel. It was found that in the light emitting part of the secondary streamer the electric field is approximately 21.5 kV cm−1. In the remainder (dark part) of the channel the electric field is around 6.5 kV cm−1. This paper shows mainly experimental findings. Not all observed relations and phenomena could be explained. This is partly caused by the fact that current theoretical and numerical models are not yet able to describe the experimental situation as used during this study.
Journal of Physics D Applied Physics 11/2008; 41(23):234001. · 2.54 Impact Factor
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ABSTRACT: The production of O* radicals in air by a pulsed streamer plasma is studied by integration of a large set of precise experimental data and the chemical kinetics of ozone production. The measured data comprise ozone production, plasma energy, streamer volume, streamer length, streamer velocity, humidity and gas-flow rate. Instead of entering input parameters into a kinetic model to calculate the end products the opposite strategy is followed. Since the amount of end-products (ozone) is known from the measurements the model had to be applied in the reverse direction to determine the input parameters, i.e. the O* radical concentration.
Journal of Physics D Applied Physics 11/2008; 41(23):234015. · 2.54 Impact Factor
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ABSTRACT: Streamer plasmas can be used to remove pollutants from gases. As a result of the complex mechanisms involved during streamer initiation and propagation, the related knowledge is incomplete. During the last few years, extensive research was performed to determine typical streamer properties (such as velocity and dimensions) as a function of various pulse parameters. During the study, as presented in this paper, typical streamer velocities and diameters in the range of 10<sup>5</sup>-10<sup>6</sup> m/s and 0.5-3.0 mm, respectively, were found.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
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ABSTRACT: This paper presents a circuit topology to obtain current multiplication by using multiple thyristors. To gain insight into this technique, an equivalent circuit model is introduced. Proper operation of the topology was demonstrated by experiments on a small-scale setup including three thyristors. One thyristor is triggered by a trigger circuit; the other two are autotriggered and require no external trigger circuit. The three thyristors could be synchronized automatically in sequence. During the closing process, the discharging of the energy storage capacitors via the thyristors is prevented. The discharging starts when all thyristors are closed, and the currents through each thyristor are simultaneous and identical. The output current is exactly three times the switching current.
Review of Scientific Instruments 08/2008; 79(7):075101. · 1.37 Impact Factor
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ABSTRACT: In this paper, the matching between a pulsed-power modulator and a streamer plasma reactor is discussed. The total process of energizing the reactor is divided into three different steps: before, during, and after plasma generation. Equivalent circuit models are used to obtain insight in the relevant mechanisms. Experiments are used to validate the results of the modeling. Based upon the results, design criteria are derived that can be used to design energy efficient streamer plasma systems.
IEEE Transactions on Plasma Science 03/2008; · 1.17 Impact Factor
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ABSTRACT: A high ratio (winding ratio of 1:80) pulse transformer with a modular ferrite core was developed for a repetitive resonant charging system. The magnetic core is constructed from 68 small blocks of ferrites, glued together by epoxy resin. This allows a high degree of freedom in choosing core shape and size. Critical issues related to this modular design are the size tolerance of the individual ferrite blocks, the unavoidable air gap between the blocks, and the saturation of the core. To evaluate the swing of the flux density inside the core during the charging process, an equivalent circuit model was introduced. It was found that when a transformer is used in a resonant charging circuit, the minimal required volume of the magnetic material to keep the core unsaturated depends on the coupling coefficient of the transformer and is independent of the number of turns of the primary winding. Along the flux path, 17 small air gaps are present due to the inevitable joints between the ferrite blocks. The total air gap distance is about 0.67 mm. The primary and secondary windings have 16 turns and 1280 turns, respectively, and the actually obtained ratio is about 1:75.4. A coupling coefficient of 99.6% was obtained. Experimental results are in good agreement with the model, and the modular ferrite core works well. Using this transformer, the high-voltage capacitors can be charged up to more than 70 kV from a low-voltage capacitor with an initial charging voltage of about 965 V. With 26.9 J energy transfer, the increased flux density inside the core was about 0.23 T, and the core remains unsaturated. The energy transfer efficiency from the primary to the secondary was around 92%.
Review of Scientific Instruments 02/2008; 79(1):015104. · 1.37 Impact Factor
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ABSTRACT: Long lifetime heavy duty pulsed power sources become more and more attractive for industrial applications such as gas/water cleaning, etc. One critical issue associated with such kind of source is the heavy switching duty. This paper describes a multiple switches based large scale prototype setup. It consists of ten high-pressure spark gap switches and a ten-stage transmission-line-transformer (TLT). By means of the TLT, the ten spark gap switches are able to share the heavy switching duty identically and simultaneously. At the switching side, the ten spark gap switches are interconnected via the TLT, and are put into one cavity. At the output side the TLT is put in parallel, thus it has very low output impedance, i.e. 5 ohm. This prototype has been successfully demonstrated. In this paper, the development and experimental results will be presented.
Pulsed Power Conference, 2007 16th IEEE International; 07/2007
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ABSTRACT: In this paper, the matching between the a pulsed power modulator and a corona plasma reactor is discussed. The matching is expressed as the energy transfer efficiency between the modulator and the reactor. The criterion for optimal matching between a source and a load is that the output impedance of the source is equal to the load impedance. When trying to match a pulsed power modulator to a plasma reactor this criterion is difficult to obey since the load impedance changes rapidly before, during and after plasma generation. To simulate the response of the load as function of the voltage pulse, an equivalent circuit is used. Measurements will be presented to verify the derived model. Guidelines to optimize the matching between the modulator and reactor are derived.
Pulsed Power Conference, 2007 16th IEEE International; 07/2007
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ABSTRACT: An experimental set-up for pulsed corona discharges is presented that offers a much wider parameter range than usual. The discharge is created in a large stainless steel vessel that allows point-plane gaps to vary from 10 to 160 mm. The gas pressure in the vessel can be the standard 1 bar, but it can also be decreased down to 13 mbar. The operating gas is usually ambient air, but pure N2 from cylinders is also available. Two pulsed power supplies are constructed that permit pulse amplitudes between 2 and 90 kV, voltage rise times between 15 and 180 ns and pulse durations from 100 ns up to many microseconds. Furthermore, both supplies operate with both pulse polarities. Examples of photographs with an intensified CCD camera are shown.
Journal of Applied Physics - J APPL PHYS. 01/2007;
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ABSTRACT: For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications: rise time of 10-25 ns, pulsewidth of 50-150 ns, pulse repetition rate of up to 1000 pulses per second, peak voltage pulse of 70 kV, peak current of 3.5 kA, dc bias voltage of 10-35 kV, and energy per pulse of up to 30 J. Sixteen parallel wire cylinder reactors are used to match the source. Gas and reactor temperatures can be controlled individually with water flow around the outside of those cylinders. The system is designed for gaseous oxidation and electrostatic dust precipitation. The system has been used for up to 17 kW in average power. This paper reports the system in detail, discusses issues related to the matching between the source and the reactor, and presents an example of industrial demonstrations on odor abatement at 1000 m<sup>3</sup>/h. Finally, this paper also gives a general guideline for design of corona plasma systems
IEEE Transactions on Plasma Science 11/2006; · 1.17 Impact Factor
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ABSTRACT: In this paper a large-scale pulsed corona system is described in which pulse parameters such as pulse rise-time, peak voltage, pulse width and energy per pulse can be varied. The chemical efficiency of the system is determined by measuring ozone production. The temporal and spatial development of the discharge streamers is recorded using an ICCD camera with a shortest exposure time of 5 ns. The camera can be triggered at any moment starting from the time the voltage pulse arrives on the reactor, with an accuracy of less than 1 ns. Measurements were performed on an industrial size wire-plate reactor. The influence of pulse parameters like pulse voltage, DC bias voltage, rise-time and pulse repetition rate on plasma generation was monitored. It was observed that for higher peak voltages, an increase could be seen in the primary streamer velocity, the growth of the primary streamer diameter, the light intensity and the number of streamers per unit length of corona wire. No significant separate influence of DC bias voltage level was observed as long as the total reactor voltage (pulse + DC bias) remained constant and the DC bias voltage remained below the DC corona onset. For those situations in which the plasma appearance changed (e.g. different streamer velocity, diameter, intensity), a change in ozone production was also observed. The best chemical yields were obtained for low voltage (55 kV), low energetic pulses (0.4 J/pulse): 60 g (kWh)−1. For high voltage (86 kV), high energetic pulses (2.3 J/pulse) the yield decreased to approximately 45 g (kWh)−1, still a high value for ozone production in ambient air (RH 42%). The pulse repetition rate has no influence on plasma generation and on chemical efficiency up to 400 pulses per second.
Journal of Physics D Applied Physics 06/2006; 39(14):3010. · 2.54 Impact Factor
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ABSTRACT: The area of pulsed-power technology covers a broad range of voltages and pulse durations. State of the art systems have voltages up to a few hundred kilovolts at pulse lengths down to the nanosecond range. Special applications require extreme field strengths in the range of 1 GV/m. The design of a compact source meeting the above requirement aims for 1 MV, 1 ns pulses. In this paper, we propose a concept for a novel compact transmission line transformer. To verify theoretical analyses and understanding, a model of the transmission line transformer has been simulated by time domain electromagnetic field solver. An optimized transmission line transformer has been built and first measurements have been performed. The equivalent simulation model agrees with the experimental results. The effect of secondary mode suppression by means of ferrite has been studied. Both simulations and experiments showed that ferromagnetic cores around each individual transmissions line in our design can be omitted
Power Modulator Symposium, 2006. Conference Record of the 2006 Twenty-Seventh International; 06/2006
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ABSTRACT: A repetitive four spark gap switches and transmission line based pulsed power generator has been developed to study the multiple switching technology. It includes 16 1.5m-long coaxial cables, four cables in parallel per switch. By means of transmission lines, the four switches can be synchronized in nanoseconds. It can produce a pulse at a high voltage or a large current. Combined with the LCR (inductor-capacitor-resistor) trigger method, the setup can be operated repetitively and very stably. The detailed experimental results will be discussed in this paper
Power Modulator Symposium, 2006. Conference Record of the 2006 Twenty-Seventh International; 06/2006
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ABSTRACT: The Blumlein generator has been one of the most popular pulsed-power circuits. The pulse forming lines are charged simultaneously, and then discharged via a single switch, such as a spark gap. The generator can be used for single pulse or at a high repletion rate. However, for large pulsed power generation, one critical issue for such a single-switch based circuit topology is related to large switching currents. In this article, we propose a novel Blumlein circuit topology based on multiple switches. The pulsed forming lines are charged in parallel and then are synchronously commutated via multiple switches. No special synchronization trigger circuit is needed for the proposed circuit topology; this robust circuit topology is simple and very reliable. A prototype multiple-switch Blumlein generator with two spark-gap switches has been experimentally evaluated with both resistive and corona plasma loads. In terms of the switching currents, it is observed that the two switches can be synchronized within 2–3 ns. The energy conversion efficiencies are 82% and 76.8% for a matched resistive load and a plasma reactor, respectively.
Review of Scientific Instruments 03/2006; 77(3):033502-033502-5. · 1.37 Impact Factor
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ABSTRACT: A transmission line transformer (TLT)-based multiple-switch circuit topology was recently proposed for pulsed-power generation. By means of a TLT, multiple spark-gap switches can be synchronized in a short time (ns). It is attractive to be used to design a long-lifetime repetitive large pulsed-power source ( 100 kW , 1 kHz ) for various kinds of applications, such as corona plasma-induced gas cleaning. To gain insight into the synchronization principle and switching behavior of the individual switch, an equivalent circuit model was developed and an experimental setup with two spark-gap switches and a two-stage TLT has been constructed. We observed that in terms of switching currents, the two switches can be synchronized within 2–3 ns . The equivalent circuit model approximately fits the experimental results.
Review of Scientific Instruments 12/2005; · 1.37 Impact Factor
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ABSTRACT: This paper discusses some critical issues when developing industrial corona plasma systems. Based on streamer generation and interaction between power sources and reactors, the power conditions for streamer corona plasma generation can be basically divided into two groups, namely ultra-short and high-frequency oscillation DC/AC sources. Today, single- and multiple-switch circuit topologies become available to scale the ultra-short pulsed-power system up. DC/AC sources are being introduced into the market. With regard to processing conditions and costs of the power sources, this paper presents their advantages and drawbacks. In order to develop very large scale plasma systems, a new energization technique to integrate the power source and the reactor has been developed for energization of multiple reactors. Today, various options are available for industrial plasma applications, and the data available would be sufficient enough to carry out commercial-scale designs for both odour emission control and exhaust gas cleaning.
Industry Applications Conference, 2005. Fourtieth IAS Annual Meeting. Conference Record of the 2005; 11/2005
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ABSTRACT: A critical component for pulsed power sources is the switch. Main related issues are life-time, stability, cost, repetition rate, hold-off voltage and current ratings. This paper discusses these problems, presents a high repetition rate (1-1000 pps), large average power (1-10 kW), and long-life time spark-gap switch. Due to its coaxial design, the inductance of the switch is low, enabling fast switching, i.e. less than 5 ns voltage rise-time. The switch is used with a LCR trigger circuit. It is observed that the switch has a good stability, and its lifetime is estimated to be in the order of 4·10<sup>10</sup> shots.
Pulsed Power symposium, 2005. The IEE (Reg. No. 2005/11070); 10/2005
