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Surface-dielectric-barrier discharges (SDBDs) can be applied for a wide range of applications, such as ozone generation, surface treatments, and air-pollutants removal. An important advantage of the SDBD plasma is that relatively low high-voltage (HV) pulses (<10 kV) are needed to generate the plasma. They are effective in removing a wide range of pollutants. Despite their high energy efficiency, plasma decomposition generally results in the reaction by-products and the formation of ozone and nitrogen oxides. This drawback can be overcome by combining the SDBD plasma with catalysis. In this paper, a novel plasma-catalytic topology is proposed for the purpose of on-demand air purification. The main idea of the plasma-catalytic reactor is that both the plasma and the catalytic function are configured as planar structures which are positioned in parallel to each other. The plasma is generated along a planar dielectric structure. We use an SDBD for this purpose. Plates coated with the catalytic material are positioned in parallel to the SDBD plates. The air to be treated is flushed along the plates. There are no restrictions to the type or combination of catalysts used; the catalysts and their specifications can be chosen freely. We have developed a modular plasma-catalytic SDBD reactor to handle large flows, which can be scaled up and scaled down easily. To energize the plasma, an SDBD power modulator was developed. The modulator is able to generate a HV output pulse over an SDBD plasma load with a magnitude adjustable from 4.78 to 6.95 kV. The pulse rise time is about $1~\mu \text{s}$ and its ramp is about 6 kV/ $\mu \text{s}$. The energy per pulse then ranges from 1.1 to 17.4 mJ. The output power can be adjusted up to 48 W at a repetition rate of 5.5 kHz. The maximum possible pulse repetition rate is 22 kHz, but it is limited to 5.5 kHz due to the limited current rating of the available dc power supply. The total energy efficiency of the power modulator is 68%. A single modulator unit can power up to two SDBD reactor plates of $100\times 150$ mm size, having plasma at both sides of the plate. The operational efficiency of the developed SDBD catalytic reactor has been investigated by studying the removal of NOx and ethylene. The removal efficiency of NOx and ethylene is determined as a function of energy density and operational parameters, such as their initial concentrations and the gas flow rate. [ABSTRACT FROM AUTHOR]

Water can be activated by applying plasma to water, for instance, by creating plasma inside (bubbles in) the water, or along a water surface. Plasma-activated water (PAW) typically contains hydrogen peroxide, nitrates, nitrites, and peroxynitrite, and typically has a pH ranging from 2 to 4. The components of PAW and the low pH have proven synergistic antimicrobial effects against bacteria, biofilms, yeasts, and other microorganisms. This paper describes a power modulator and a plasma reactor system for high-yield production of PAW at high production rate. A compact and solid-state dual resonant system has been realized and successfully demonstrated for industrial PAW production. The system generates up to 80-kV (theoretical 120 kV is possible) dual-resonant high-voltage pulses with an oscillation frequency up to 2 MHz, pulse repetition rate > 20 kHz, and an average power of 800-W continuous. In addition to the power modulator, the PAW production system consists of a transient arc plasma reactor and a loop system. Depending on the application, the system is able to activate 10–100 L/h. The disinfecting properties of the PAW production system have been verified by experiments on the reduction of Staphylococcus Epidermidis. Directly after its production, the log reduction of S. Epidermidis can be as high as >8 log. During a period of at least 40 min after its production, the PAW has “mild” disinfecting properties, being able to deactivate S. Epidermidis by 3–4.1 log. [ABSTRACT FROM PUBLISHER]

The influence of SF6-admixtures to N2 on electrodeless streamer inception at the surface of a dielectric solid (epoxy resin) is investigated for different SF6/N2 ratios and gas pressures, with focus on the lower pressure region (below 1 bar) which is only sparsely discussed in literature. For this purpose, we use a special set-up with cylindrical electrodes embedded out of axis in a cylindrical epoxy rod. The influence of the dielectric surface on streamer development is analyzed by estimating the ionization rate. Ionization rates obtained from experimental measurements seem to be higher than those available for discharges in bulk gas under similar conditions. The main influence on the inception voltage, however, seems to come from the change in the field distribution due to the presence of the dielectric solid. Furthermore, it turns out that the streamer inception voltage increases with gas pressure for a constant SF6/N2 ratio, increases rapidly as a function of the SF6/N2 ratio at small amounts of SF6 (∼ 5%), and increases at lower rates for higher amounts. The total duration of the discharge decreases almost by a factor of 10, i.e., from tens of nanoseconds to several nanoseconds for pure nitrogen and 5% SF6-admixture, respectively. Overall, it is shown, that the major inception parameters (critical voltage, rise and fall times, current shapes) of streamer discharges on a gas-solid dielectric interface change considerably starting already with a small (5%) admixture of SF6 to nitrogen. [ABSTRACT FROM PUBLISHER]

When charged particles impact the surface of a solid material, they can be backscattered from that surface or cause secondary electrons to be emitted. The ratio of the number of emitted electrons (secondary and backscattered) to the incident electrons number is known as the total electron emission yield. Knowledge of this total electron emission yield (TEEY) is highly required in various modern technologies, and several experimental techniques were developed with the purpose of its determination. However, experimental data, obtained with different methods are not in good agreement and sometimes are even contradictive. The purpose of this paper is to review the existing experimental methods of investigating electron emission (EE) from dielectric surfaces, as well as to analyze their accuracy and reliability. The focus is on the processes of the emission from thick layers of insulators which is the case for modern high voltage technologies. [ABSTRACT FROM AUTHOR]

In this paper we investigate temperature and pressure effects on the properties of a positive pulsed streamer plasma. We use a corona plasma setup in which we vary the temperature between 303 and 773K at atmospheric pressure and the pressure between 37.9 and 100 kPa at room temperature to achieve the same neutral gas density and compare electrical and optical (ICCD imaging) measurements carried out in both experiments. From the measurements we found that the dissipated plasma energy and the average streamer propagation velocity are both higher for the temperature experiments at the same neutral gas densities as in the pressure experiments. This suggests the existence of a specific temperature effect. A possible explanation for this effect is a higher streamer conductivity at high temperatures, as was previously found in the literature. [ABSTRACT FROM AUTHOR]

In this paper, we describe a novel multiple-switch pulsed-power technology. The basic idea is that the heavy switching duty is shared by multiple switches. The multiple switches are interconnected via a transmission line transformer, in such a way that all switches can be synchronized automatically and no special external synchronization trigger circuit is required. It can produce either exponential or square pulses, with various voltage and current gains and with a high degree of freedom in choosing output impedances. The topology has been implemented on a prototype with ten spark-gap switches. Pulses with a rise time of 10 ns, a width of 55 ns, a peak power up to 810 MW, a peak voltage of 77 kV, and a peak current of 11 kA have been achieved at a repetition rate of 300 pps. The energy efficiency of the circuit is about 93%. In addition to spark gaps, any overvoltage-controlled switch can be applied in this topology. As an example, we demonstrate the synchronous switching of multiple thyristor switches for current multiplication. The proposed multiple-switch topology can also be applied in a Blumlein configuration for an inductive voltage adder and a linear transformer driver. [ABSTRACT FROM AUTHOR]

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 Ω) 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%. [ABSTRACT FROM AUTHOR]

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 0 radicals was determined from the measured ozone concentrations at the exhaust of the reactor. [ABSTRACT FROM AUTHOR]

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 Ω) 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%. [ABSTRACT FROM AUTHOR]

We studied the propagation of partial discharge pulses in a stator winding by means of measurements on a dismantled 35-MW generator and found that a stator winding acts as a transmission line. Therefore, a partial-discharge (PD) signal manifests itself at the generator terminals after a transit time that depends on the location of the discharge. Due to capacitive and inductive couplings in the end-winding region, a second propagation mode is present for higher frequencies. This ‘fast mode’ manifests itself at the terminals without appreciable time delay. The capacitive and inductive couplings also cause crosstalk between the phases. As a consequence, a signal measured in one phase does not necessarily originate from a discharge in that phase. The amplitudes of the fast mode and, to a lesser extent, the slow mode (or transmission-line mode) are heavily damped when the discharge occurs further away from the measuring terminal. The consequence is that only discharges close to the measuring terminal can be observed. The propagation of a PD signal is not only influenced by the construction of the generator but also by its external connections. [ABSTRACT FROM AUTHOR]

To supply combustion engines or gasturbines with fuel gas obtained from biomass gasification, it is necessary to clean the fuel gas. Also the production of chemicals by processes such as Fisher-Tropsch requires a high gas quality. Especially heavy aromatic hydrocarbons (“tars”) must be removed. In this work, we give an overview of our investigations on tar removal by pulsed corona discharges as an alternative approach to catalytic or thermal tar cracking. Experimental results (at a gas temperature of 200°C) are reported for the removal of various model tar components in synthetic fuel gas. In order to identify the major reaction pathways, experiments were also done on tars in individual fuel gas components. The results show that tar removal by pulsed corona processing is possible. The process for tar removal is mainly via oxidation. Also termination reactions by CO play an important role. [ABSTRACT FROM AUTHOR]

A promising pollution control technology is cold plasma driven chemical processing. The plasma is a pulsed electric gas discharge inside a near atmospheric-pressure-temperature reactor. The system is energized by a continuous stream of very short high-voltage pulses. The exhaust gas to be treated flows through the reactor. The methods applied involve the development of robust cold plasma systems, industrial applications and measuring technologies. Tests of the systems were performed at many industrial sites and involved control of airborne VOC (volatile organic compound) and odor. Electrical, chemical and odor measuring data were collected with state-of-the-art methods. To explain the test data an approximate solution of global reaction kinetics of pulsed plasma chemistry was developed. It involves the Lambert function and, for convenience, a simple approximation of it. The latter shows that the amount of removal, in good approximation, is a function of a single variable. This variable is electric plasma power divided by gas flow divided by input concentration. In the results sections we show that in some cases up to 99% of volatile pollution can be removed at an acceptable energy requirement. In the final sections we look into future efficiency enhancements by implementation of (sub)nanosecond pulsed plasma and solid state high-voltage technology and by integration with catalyst technology. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Industrial application of nanosecond pulsed corona technology for air purification requires high volume, high-power plasma reactors. Cylinder-wire type reactors require multiple cylinders to meet these demands. Variations in pulse waveforms per cylinder, misalignment of wires, and jitter in streamer inception could lead to an uneven energy distribution over the cylinders. Nanosecond ICCD imaging is applied to a semi-industrial scale pulsed corona reactor to study streamer inception and propagation of the streamer plasma simultaneously in 16 cylinders. The images show streamer inception of all cylinders within 9 ns. Streamer propagation and intensities are very similar for all cylinders. [ABSTRACT FROM PUBLISHER]

Industrial application of nanosecond pulsed corona technology for air purification requires high volume, high power plasma reactors. Cylinder-wire type reactors require multiple cylinders or very long reactors to meet these demands. In this article, we focus on the characterization of a pulsed corona plasma in a long (4.5 m) plasma reactor. The reactor cylinder acts as a coaxial transmission line wherein high-voltage pulses propagate with close to the speed of light. Interactions between plasma generation and reflection behavior inside the reactor are expected and therefore investigated. A 4.5-m-long corona reactor is constructed and equipped with voltage and current sensors at multiple positions along the reactor length. A lumped element SPICE model is developed to simulate the reflection behavior. Strong reflections at the end of the reactor are observed for pulse rise times which are shorter than the transient time of the reactor. Plasma generation and energy distribution in the reactor, as well as impedance matching between source and reactor, are affected by these reflections. We investigate the role of the input voltage and rise time and analyze the electrical characterization, impedance characterization, and reactor efficiency. [ABSTRACT FROM AUTHOR]

Streamer discharges are efficient non-thermal plasmas for air purification and can be generated in wire-cylinder electrode structures (the plasma reactor). When (sub)nanosecond high-voltage pulses are used to generate the plasma, components like a plasma reactor behave as transmission lines, where transmission times and reflections become important. We want to visually study the influence of these transmission-line effects on the streamer development in the reactor. Therefore, we need a unique experimental setup, which allows us to image the streamers with nanosecond time resolution over the entire length of the plasma reactor. This paper describes the setup we developed for this purpose. The setup consists of a large frame in which a specially designed plasma reactor can be mounted and imaged from below by an intensified charge-coupled device (ICCD) camera. This camera is mounted on a platform which can be moved by a stepper motor. A computer automates all the experiments and controls the camera movement, camera settings, and the nanosecond high-voltage pulse source we use for the experiments. With the automated setup, we can make ICCD images of the entire plasma reactor at different instances of time with nanosecond resolution (with a jitter of less than several hundreds of picoseconds). Consequently, parameters such as the streamer length and width can be calculated automatically. [ABSTRACT FROM AUTHOR]

In this paper, we present the final implementation of our 0–50-kV picosecond rise time 0.5–10-ns pulse generator. The pulse generator will be used in future work to generate a (sub)-nanosecond streamer plasma for air purification research. The pulse generator is a single-line pulse generator with an oil spark-gap (SG), which generates 0.5–10-ns pulses with a 200-ps rise time and can operate at repetition rates of over 1 kHz into a 50- \Omega load. It is an improvement over the first implementation of our nanosecond pulse generator that we designed and verified experimentally in previous work. In this paper, we evaluate the performance of the final design. Furthermore, we present 3-D electromagnetic simulations of the nanosecond pulse generator and show that the simulations are in good agreement with the measurements. A variation in pulse duration from 0.5 to 10 ns is possible and the output pulses are square shaped without the large plateau behind the main pulse that was present in the pulses from the first implementation of the nanosecond pulse generator. At high voltages, the pulse top becomes less flat due to a time-dependent mismatch in the spark-gap. Furthermore, investigation of electrode erosion of the oil spark-gap shows that the erosion rate of the electrodes is in the range of 200–600 \mu \mathrmcm^3 \cdot \mathrmC^-1 for the electrode that is mainly the cathode and 100–300 \mu \mathrm{cm}^{3} \cdot \mathrm{C}^{-1}$ for the electrode that is mainly the anode, respectively. This is almost an order of magnitude higher than most gas spark-gap studies show for brass electrodes. Therefore, electrode erosion in the oil spark-gap will be a limiting factor on the lifetime of the system. We designed a new electrode with a stainless steel head to increase this lifetime. [ABSTRACT FROM PUBLISHER]

Although removal of NOx by (pulsed) corona discharges has been thoroughly investigated for high concentrations of NOx in flue gas, removal of low levels in ambient air proves to be a difficult task. (Sub) ppm NOx levels exist in traffic tunnels due to accumulation of exhaust gases. The application of pulsed corona technology for purification of traffic tunnel air is studied during a series of lab and field experiments. An industrial pilot scale wire-cylinder type corona reactor has been utilized. Lab tests have been carried out using a diesel generator as NOx source. NOx conversion levels have been determined by applying two Recordum Airpointers (chemiluminescence-based detection). The detector appeared to be cross-sensitive for HNO3 and high levels of O3. NOx removal rates of 60-80% were obtained for inlet levels of 2-10 ppm. The SIE value of 10 ppm NOx removal is 7 J l-1. The corona discharges produce ppm level NOx at high energy densities. This intrinsic NOx production limits removal of inlet levels due to equilibrium between production and oxidation. [ABSTRACT FROM AUTHOR]

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J-1 at 74% conversion of 70 ppm toluene and 181 nmol J-1 at 81% conversion of 10 ppm limonene [ABSTRACT FROM AUTHOR]

The area of pulsed-power technology covers a broad range of powers (up to 1014 W), voltages (up to 106-107 V), currents (as high as 106 A or higher) and pulse durations (below 10-8 s). 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 present a novel compact TLT (Transmission Line Transformer). The TLT consists of 10 coaxial transmission lines which are connected in parallel at the input and in series at the output. To verify the theoretical analysis a model of the transmission line transformer has been simulated by a time domain electromagnetic field solver. An optimized transmission line transformer has been built and first measurements have been performed. The equivalent circuit model and the simulations agree with the experimental results. The effect of secondary mode suppression by means of ferrite has been investigated. Both simulations and experiments showed that ferromagnetic cores around each individual transmissions line in our design can be omitted. [ABSTRACT FROM AUTHOR]

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 as, pulsewidth of 50-150 as, 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 m³/h. Finally, this paper also gives a general guideline for design of corona plasma systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this article a critical component for pulsed power applications is described: the heavy-duty switch. The design of a coaxial, high repetition rate, large average power, and long lifetime spark-gap switch is discussed. The switch is used with a fail-free LCR trigger circuit. Critical issues for switch design are presented together with experimental results. It is observed that the switch has a good stability, and its lifetime is estimated to be in the order of 1010 shots (∼106 C) at 10 J/pulse, 60 kV and 100 ns pulses. Measurements were performed with 20 and 34 kV average switching voltage (100 ns pulses, energy per pulse 0.4 and 0.75 J, respectively). For up to 450 pulses/s (pps), pre-firing can be prevented by increasing the gap pressure (up to 2.5 and 7 bars, respectively), no gas flush is required. Above 450 pps, up to 820 pps, a forced gas flow of maximal 35 Nm3/h, is required for stable operation. Measurements on the time delay and jitter of the switch demonstrate that these values are influenced by pressure, flow, and pulse repetition rate. For 34 kV average switching voltage the time delay and time jitter vary between 35 and 250 and 10 and 80 μs, respectively. For 20 kV average switching voltage these values are: 30–160 and 4–50 μs. During a test run of 2.5 h (at 100 Hz, 0.75 J/pulse) the feasibility of the switch was proved, and the switching voltage jitter was less than 0.7%. [ABSTRACT FROM AUTHOR]

Breakdown strength in uniform electric fields of N 2 O mixtures with CO 2 , N 2 , and O 2 is measured under AC voltage stress, 300 kPa pressure, and electrode separation of 5 mm. The obtained results show the best synergism of 115% for N 2 O/CO 2 30/70 mixture. For high electric strength of mixtures, a high fraction of N 2 O is beneficial, but is limited by the oxidizing power. Considering this limit, a N 2 O/CO 2 49.1/50.9 mixture can be used with the electric strength 135% of synthetic air and 45% of SF 6 , respectively. [ABSTRACT FROM AUTHOR]

Presents a study which described the high-power repetitive pulse generation technology sources for power transmission. Reliability of the generators; Electric generation procedures in high-voltage circuits; Performance of a spark-gap switch.

In this article we discuss a 10 kW high-voltage pulse generator for producing corona-induced plasma. The generator mainly consists of a three-step resonant charging circuit switched by thyristors, a transmission line transformer, and a triggered spark-gap switch. Voltage pulses of 30-100 kV with a rise time of about 20 ns, a pulse duration of 50-250 ns, pulse repetition rate of 1-900 pulses per second, energy of up to 12 J/pulse, and an average power of up to 10 kW have been achieved with a total energy transfer efficiency of about 80%-90%. At each frequency, the deviation of the energy per pulse is around 1.0%. Moreover, the generator has been tested for more than 100 h for both industrial demonstrations and laboratory investigations at an average output power of 1-10 kW. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper introduces the work undertaken to reliably use off-the-shelf differentiating voltage probes attached to coaxial transmission lines. The results obtained prove that indeed such probes are a valid and simple instrument for measuring nanosecond and subnanosecond voltage impulses. As a bonus, this paper also highlighted an important challenging phenomenon that appears whenever an attempt is made to measure fast voltage impulses with a differentiating probe positioned too close to the closing switch of a pulse forming line generator. [ABSTRACT FROM AUTHOR]

A compact magnetic pulse compression (MPC) topology with only two magnetic cores and a continuous repetition rate of 20 kHz is presented. The demand for higher average output powers of pulsed power systems can be achieved by an increase of the pulse rate frequency (PRF). The PRF is often limited by the switching speed or recovery of the main switch and also the complex behavior of the magnetic materials. With the advent of insulated gate bipolar transistors and the nanocrystalline soft magnetic material, PRFs of tens of kilohertz are feasible if a suitable MPC topology is applied. The presented MPC is based on an existing topology that has been significantly improved to enable high-frequency pulse generation. A design method using 3-D magnetostatic and transient magnetic simulations is introduced to enable optimization of the magnetic switching components. A 20 kHz, 60 kV, and 52 ns full width at half maximum (FWHM) MPC generator is designed, built, and tested for a $100~\Omega $ load. Simulations suggest that a PRF up to 50 kHz is achievable, but continuous operation will likely be limited by thermal management. [ABSTRACT FROM AUTHOR]

Fast and repetitive switching in high-power circuits is a challenging task where the ultimate solutions still have to be found. We proposed a new approach. Supercritical fluids (SCFs) combine favorable properties of liquids - insulation strength, thermal behavior, and gases - self healing, high fluidity, and absence of vapor bubbles. That's why we start investigating the subject of plasma switches in SC media. First results indicate excellent switch recovery and very high insulation strength. We present the design of a SCF insulated switch (SC switch). Breakdown strength of the SCF is investigated and found to be high in comparison with most of the solid insulating media. The dielectric recovery inside the SC N2 switch is tested under a repetitive 30 kV, 200 ns pulse voltage at repetition rate up to 5 kHz. The recovery breakdown voltage across the SC switch achieves 80 % within 200 μs. The current interruption capability of SC N2 is investigated experimentally in a synthetic circuit generating a high-frequency arc of several hundreds of amperes and a transient recovery voltage of hundreds of volts. The results show that a SC N2 switch with fixed electrodes and an inter-electrode distance of mm range can successfully interrupt this current at approximately 2 ms after arc initiation. [ABSTRACT FROM PUBLISHER]

By the application of pulsed corona discharges in a carbon dioxide atmosphere over a water film, the formation of methane has been observed under mild reaction conditions, without the application of a dedicated catalyst. Methane is proposed to result from hydrogenation of carbon monoxide and possibly also carbon dioxide at the NiCr alloy high-voltage electrodes, the precursors being formed by plasma-induced decomposition of carbon dioxide and water. Applying energy densities up to 46 kJ/L has yielded methane levels of approximately 440 ppm at a production efficiency of 398 pmol/J. The observed plasma chemistry occurs at ambient pressure, while gas phase heat is cooled away by the water film, the latter being thermally nearly unaffected. [ABSTRACT FROM PUBLISHER]

Matching a pulse source to a plasma load is one of the main challenges to overcome to maximize the full potential of pulsed discharges for air purification applications. In this paper, we propose experiments that investigate the matching of a nanosecond pulse source to a corona plasma reactor that is aided by a high voltage on a tertiary electrode. The corona plasma reactor is a wire-cylinder reactor, as is commonly used in pulsed power plasmas. A tertiary electrode is situated on a dielectric layer against the cylinder of the reactor. On this tertiary electrode, we can apply a pulsed RF or dc voltage to provide an additional plasma and bias voltage in the corona plasma reactor. The pulse source that energizes the main corona plasma is the nanosecond pulse source of Kumamoto University, Japan. In this paper, we show the results of experiments with a dc voltage on the tertiary electrode. We varied the amplitude of the pulsed voltage as well as the dc voltage and investigated their effect on the corona plasma with energy and ozone measurements. The results show that the matching to the reactor increases with increasing dc voltages. However, the matching effect decreases with higher repetition rates. Furthermore, ozone measurements confirmed that a better matching also results in a higher ozone production, but in a lower ozone production energy yield. [ABSTRACT FROM PUBLISHER]

In this paper, a compact circuit topology is presented for pulsed power generation with a semiconductor opening switch (SOS). Such circuits require the generation of a fast forward current through the diode, followed by a reverse current that activates the recovery process. In general, magnetic switches are used to switch the diode current from forward to reverse. Therefore, adjustment of the output voltage of an SOS pulser is difficult. This paper introduces a circuit that allows an adjustable output voltage of the pulser. A solution is realized with a premagnetizing circuit on the primary winding of a pulse transformer (PT), so that a third winding is not needed. The primary capacitor voltage can now be varied while maintaining proper saturation of the PT. [ABSTRACT FROM PUBLISHER]

In this paper, we present the first implementation of our 0–60-kV picosecond rise time 1–10-ns pulse generator. The pulse generator will be used in future work to generate a (sub-)nanosecond streamer plasma for air purification research. The first implementation of the pulse generator is a single-line pulse generator with an oil spark-gap, which generates 5 ns pulses with a 200 picosecond rise time and can operate at repetition rates of over 1 kHz into a 50 \Omega load. In this paper, we evaluate its performance and describe how we measure the very short pulses with an integrated and calibrated D-dot sensor. Furthermore, we present 3-D EM simulations of the 5 ns pulse generator and show that the simulations are in good agreement with the measurements. We previously described methods to flexibly vary the pulse duration of the pulse source by (artificially) changing the length of the pulse forming line (PFL). Here, we test these methods and find that changing the length of the outer conductor of the PFL and inserting magnetic material at the end of the PFL is a suitable method to change the pulse duration. Finally, we measure the breakdown voltages of the oil spark-gap and discover that higher pulse repetition rates are possible at higher oil pressures and smaller gap distances. [ABSTRACT FROM AUTHOR]

In this paper, we present a design approach of a single-line nanosecond pulse source by using a thorough analytical investigation and by verification with CST MICROWAVE STUDIO. Through detailed analysis and simulation, we arrive at a design for a fast rise time variable pulse duration pulse source which is able to produce 1–10 ns pulses with tens of kilovolt amplitude and less than hundreds of picoseconds rise time. This variable pulse duration is achieved by using telescopic antennas and ferrites in the pulse-forming line of the pulse source. Finally, we present a first implementation of a 5-ns pulse source with an oil spark gap for fast switching. [ABSTRACT FROM AUTHOR]

In this paper, we present a solid state 0–120 kV microsecond pulse charger for our nanosecond pulse generator refid="ref1"/. The pulse-forming line (PFL) of our nanosecond pulse generator must be charged with microsecond pulses to prevent pre-firing of its oil spark gap. The pulse charger consists of two identical compact pulse charger modules with integrated electronics. The electronic circuits are mounted on a compact printed circuit board and consist mainly of a number of parallel connected insulated-gate bipolar transistors (IGBTs) that switch a primary capacitor bank into a pulse transformer. Each pulse charger module can generate 60 kV microsecond pulses at 1 kHz repetition rate. When connected in series, they are able to deliver up to 120 kV into a 100 pF load. This 100 pF load is the PFL of our nanosecond pulse generator at its maximum length of 1 m. The pulse charger is able to operate in a harsh electromagnetic interference environment as a result of its compact layout and optical triggering of the IGBTs. [ABSTRACT FROM PUBLISHER]

Although pulsed corona technology for air purification is widely investigated by the lab experiments, large-scale application has yet to be proven. Industrial systems require large flow handling and thus, high corona power. An autonomous semi-industrial scale pilot wire-cylinder type corona reactor has been constructed for air purification demonstrations. The reactor is powered by a 10-kW spark gap-based pulsed power supply, capable of generating 60-kV 100-ns wide pulses with 1-kHz repetition rate. The pulses are optionally superimposed on a 0–30-kV dc bias to enable electrostatic precipitation. The system has been successfully applied during several field and lab experiments. Conversion data as a function of energy density are presented for NOx, NH3, H2S, toluene, limonene, and fine dust removal. The system proves feasibility of large-scale air purification by pulsed corona. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed electric fields (nsPEFs) have been found to induce either cell death or cellular changes to a wide range of cells. However, for the current way of delivering the electric field to the cell (by electrodes contacting the cell culture), cells need to be placed in low-conductivity media unsuitable for maintaining cell growth. Here, we present a novel device for noncontact exposure of cells to nsPEF. The cells can be treated in their native cell culture medium and culture vessel. A single-turn loop antenna is designed that can contain a cylindrical cell culture vessel. The electric field within the loop is created by magnetic induction and depends on the time derivative of the current through the loop. To generate the required field strength of 10 kV/cm with duration of \sim6~ns, a fast high-voltage, low-inductance RLC circuit is developed. A fast rising current of 100 A/ns is achieved in this circuit. The developed method is used for the nsPEF treatment of either adherent [Chinese hamster ovary (CHO-K)] or suspension (CHO-S) cells in their native culture medium and vessel. We discovered that nsPEF enhances cell proliferation. This novel effect of nsPEF has significant applicability in improving the yield and lowering the cost of cell cultures and bioreactors. [ABSTRACT FROM AUTHOR]

In this paper, pulsed-power technology was applied to plasma printing, which is a maskless plasma patterning solution that is being developed for the fabrication process of printed electronics. A high-voltage pulse source was developed and applied to a high-speed plasma printer to improve the speed of plasma printing. Experiments on plasma printing were used to compare the performance of the pulse source with the currently used alternating-current source. From plasma experiments, an electrical plasma model was derived for the plasma printer. Different parameters were investigated, such as the plasma energy as a function of gap distance, applied voltage, and the total amount of plasma that was generated. From these experiments, a connection was made between the plasma energy and the print effectiveness to arrive at optimal parameter values for fast plasma printing. It was concluded that higher plasma energy leads to higher print effectiveness, which leads to an increase in plasma print speed by a factor of 10 when using the pulse source. Moreover, scaling the PlasmaPint technology to reach higher print speeds is achievable by using more print heads or print heads with more tips. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

A triggered multiple-gap spark gap switch has been developed and tested under atmosphere. By means of an LCR trigger circuit, the multiple-gap switch can be used very reliably. For the same switching voltage (35.5 kV), with increasing the number of gaps from 2 to 6, the switching current rise time is reduced from 13.5 to 6 ns, and the energy efficiency is increased from 87% to 92%. An eight-gap switch was also tested, and the switching current rise time is much smaller than the usable rise time of the current probe (3.5 ns). One interesting application of the multiple-gap switch is to improve the switching performance in the multiple-switch and transmission lines based pulsed power circuit. To verify this application, a six-gap switch was tested. In contrast to a single-gap switch, the output current rise time was improved from 21 to 11 ns by the six-gap switch. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A spark discharge generated by a 5-ns high-voltage pulse of 21 kV with a rise-time of 200 ps in a 1-mm gap between half-sphere steel electrodes was investigated in N2–O2 gas mixtures at atmospheric pressure. We compared short exposure and long exposure ICCD images of the discharge, as well as single shot images and accumulated images. At high repetition rates more discharge channels form due to higher background ionization. The influence of the O2 concentration between 0.1 and 10 vol% O2 in N2 is insignificant. [ABSTRACT FROM PUBLISHER]

Dielectric barrier discharges generated in a coaxial tip to cylinder configuration at atmospheric pressure by a 5-ns high-voltage pulse with sub-ns rise time were investigated with a fast intensified CCD camera. Different discharge characteristics were found for the breakdown during the pulse itself and in the subsequent reflections of the pulse. There is a transition from a complete diffuse regime to a breakdown in constricted channels, which finally cross the whole gap. [ABSTRACT FROM PUBLISHER]

Surface dielectric barrier discharges (SDBDs) provide homogeneous plasma over a large surface area. This allows surface treatments of foils, textiles, or fibers. In this paper, we present results of a study to characterize the pulsed performance of SDBD by fast imaging of the plasma development. [ABSTRACT FROM AUTHOR]

High current sparks are created in argon and air using a high-voltage pulse of 16-ns duration. Shadowgraphy is applied to image density fluctuations. Shock waves become visible \sim100 ns after the pulse; they expand with a velocity somewhat higher than the speed of sound. The filamentary core of the discharge shows heating that diffuses outward slowly and develops into microturbulences. They remain visible up to 3 ms. In air, the current remains lower than that in argon, and shocks only emerge from the electrodes. No indication of absorption is found; probably gas heating is observed near the electrodes. [ABSTRACT FROM AUTHOR]

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 105-106 m/s and 0.5-3.0 mm, respectively, were found. [ABSTRACT FROM AUTHOR]

Pulsed corona-induced partial oxidation of methane in humid oxygen or carbon dioxide atmospheres has been investigated for future fuel synthesis applications. The obtained product spectrum is wide, i.e. saturated, unsaturated and oxygen-functional hydrocarbons. The generally observed methane conversion levels are 6–20% at a conversion efficiency of about 100–250 nmol J−1. The main products are ethane, ethylene and acetylene. Higher saturated hydrocarbons up to C6 have been detected. The observed oxygen-functional hydrocarbons are methanol, ethanol and lower concentrations of aldehydes, ketones, dimethylether and methylformate. Methanol seems to be exclusively produced with CH4/O2 mixtures at a maximum production efficiency of 0.35 nmol J−1. CH4/CO2 mixtures appear to yield higher hydrocarbons. Carboxylic acids appear to be mainly present in the aqueous reactor phase, possibly together with higher molecular weight species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]