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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]

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 generated by nanosecond high-voltage pulses have gained attraction for a variety of reasons, but mainly because they are very efficient for a number of plasma-processing applications. More specifically, researchers have noted that the pulse duration and the rise time of the applied high-voltage pulse have a significant influence on the radical yield of the transient plasmas generated with these pulses; shorter pulses result in higher yields. With the need to study transient plasmas generated by these short pulses comes the need to understand how to generate those pulses and to understand the interaction between the pulse source and the discharge. In this topical review, we will explore the different methods with which to generate nanosecond high-voltage pulses, how the interaction between the pulse source and the discharge may influence the source and the discharge and how to optimize the energy transfer from the pulse source to the discharge. [ABSTRACT FROM AUTHOR]

Transient plasma generated by high-voltage nanosecond pulses in a pulsed corona configuration has proven to be an efficient medium for e.g., air purification applications. In this article, we present a study on boosting the energy efficiency of such a system by using a special type of plasma reactor: the multiple-wire plasma reactor. The basic principle of such a reactor is that it has a lower transmission-line impedance than a normal wire-cylinder reactor while at the same time still producing the required high electric fields necessary for plasma generation. The lower impedance of the reactor results in a smaller impedance mismatch between the high-voltage pulse source and the reactor, thereby minimizing pulse reflections on the source-reactor interface, increasing the energy efficiency of the system. We calculate the impedance of the multiple-wire reactor and assess both the electrical energy efficiency as well as the chemical efficiency of the plasma by measuring electrical energies and ozone concentrations generated by the plasma when energized by a fast solid-state nanosecond pulse source (with 7-ns rise time pulses of up to 20kV) for a range of multiple-wire plasma reactor parameters. We show that with the multiple-wire reactor we can almost double the energy efficiency of the reactor (from 45% to 85%), reduce the voltage stress in the system by 29%–31% and increase the system efficiency by 95%–98% when using a multiple-wire electrode geometry (as compared to a single-wire system). [ABSTRACT FROM AUTHOR]

In this article, we present the concept, design, and first implementation of a new solid-state pulse topology: the solid-state impedance-matched Marx generator (IMG). This new topology can bring fast, adjustable pulse generation to a wide range of pulsed power applications. Where the original IMG is a high-power device (using spark gaps) for relatively low-repetition-rate, high-energy-density physics, we require a pulse source with a (sub)nanosecond rise time at moderate voltages of tens of kilovolts at high repetition rates for transient plasma generation. To achieve this, we adapted the IMG pulse source concept to a solid-state concept with additional transmission lines and metal–oxide–semiconductor field-effect transistor (MOSFET) switches. In this article, we present the general concept, a 20-stage design (with 3-D transient electromagnetic simulations), and a first 5-stage, 5-kV prototype. The prototype achieves 5–6-ns rise time pulses at voltages up to 2.5 kV into a matched 50- $\Omega $ load (due to an oscillation in the drive circuit, the pulse was somewhat distorted at higher voltages) and can generate flexible pulse waveforms. Finally, improvements are suggested to achieve the desired pulse specifications. [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]

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, 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]

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]

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, 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]

Due to their fast switching capabilities, silicon carbide (SiC) MOSFETs are increasingly used in high-voltage pulsed-power circuits where fast and flexible high-voltage pulses are required (e.g. for plasma-processing applications), such as in our solid-state Impedance-matched Marx generator. The turn-on time of SiC MOSFETs mainly depends on the gate-driving technique and its implementation. Therefore, many studies focus on SiC MOSFET gate-driving methods. In this article, a gate-boosting driving method that was previously proposed for IGBTs is optimized for SiC MOSFETs and applied to a very fast MOSFET to reduce turn-on time as much as possible. A prototype of the optimized gate-boosting driver was built and tested to assess its performance. The test results validate the effectiveness of the optimized gate-driving method and showed that a MOSFET turn-on time of below 2 ns is achievable at a high operating voltage and moderate current and below 3 ns for a wider range of load-current and operating-voltage conditions. Furthermore, current rise rates of 38.7 kA/ $\mu \text{s}$ at 356-A load current are possible. All these results are considerably faster than ever demonstrated before. [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]

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]

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]

The object of this study is the investigation of spark discharges ignited by unipolar positive rectangular high voltage (HV) pulses with 200 ps rise time and (15 ± 2) kV amplitude with 3 ns duration full width at half maximum in synthetic air in a 1.2 mm pin-to-pin gap (tungsten electrodes) at atmospheric pressure. The discharge development was recorded by synchronised iCCD and streak camera measurements in single-shot operation, revealing a two-stage propagation mode. The discharge started with a fast initial breakdown across the entire gap (∼10 mm ns−1) during the HV slope, followed by a much slower (∼0.1 mm ns−1) propagation originating from both electrodes towards the gap centre. The combination of high-resolution diagnostics with numerical modelling indicated that the initial breakdown phase is caused by the rapid increase of electric field strength during the steep HV slope, which leads to the simultaneous fast propagation of a positive and a negative streamer. [ABSTRACT FROM AUTHOR]

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]