Search

In this study, the effect of waveform control of pulsed discharge on ozone production for water treatment under atmospheric pressure is investigated and optimized. Using solid-state linear transformer driver (LTD) which has flexible waveform control capability, the applied voltage pulse has been separated into two parts, and each can be independently controlled while keeping the total input energy constant. The experimental results have shown that if the two parts are consecutive to each other without time interval, the second part of the discharge is inefficient for producing ozone. However, by introducing an interval between two voltage parts, making it effectively a double-pulse discharge, an increase in the energy yield of ozone production is observed. In addition, the ozone producing energy yield increases when the pulse interval is lengthened, up to 10 ms. Therefore, in conclusion, it has been observed that shorter pulsewidth and longer pulse interval lead to more efficient ozone production by pulsed discharge under atmospheric pressure. [ABSTRACT FROM AUTHOR]

The effect of sharpening capacitor on the rise time of pulsed power generator has been studied recently, suggesting that a capacitor connected in parallel to the resistive load may help in reducing the rise time of the output. In addition, a bias voltage applied on this capacitor may further reduce the rise time. In this article, a solid-state Marx generator has been used to demonstrate this effect. A ten-module Marx generator circuit using power MOSFETs was used. Experiments were carried out by comparing the output rise time, defined by the time between 10% and 90% of the peak voltage, obtained with and without the sharpening capacitor. With a charging voltage of 800 V, the Marx generates an output of ~7.8 kV on a 40 $\Omega $ load. Using a sharpening capacitor of 520 pF, the rise time is reduced from ~140 to ~120 ns. Furthermore, by applying a bias voltage of −2 kV, the rise time is shortened to ~83 ns, a ~41% reduction from that obtained without the sharpening capacitor. [ABSTRACT FROM AUTHOR]

'ETIGO.IV,' a new repetitive pulsed-power generator, has been developed. It is capable of delivering, to a matched load, an output pulse of 400 kV in peak voltage, 13 kA in peak current, and 120 ns in pulse length, at the repetition rate of 1 Hz. It is aimed at applications to material development, pulsed ion-beam acceleration, and high-power microwave generation. This paper reports the design details and operation results of 'ETIGO-IV,' as well as the initial experimental results on electron beam generation. Index Terms--Magnetic switch, pulsed compression, pulsed high-voltage, pulsed power.

Solid-state Marx generator circuits have been widely studied in recent years. Most of them are based on capacitive energy storage (CES), with the basic principle of charging in parallel and discharging in series. In this article, we propose a solid-state Marx circuit using inductive energy storage, where inductors play the role of principal energy storage element. When combined with an opening switch, the inductor can generate an output voltage of $L$ dI/dt, where $I$ is the inductor current. Multiple circuits can be stacked to obtain output voltage adding, as in Marx circuit using CES. In the demonstration experiments, the test on a four-stage inductive Marx circuit has been carried out. With the charging voltage of −200 V, the output peak voltage of ~9.2 kV was generated on an 800- $\Omega $ load with a rise time of ~46 ns. [ABSTRACT FROM AUTHOR]

A compact step-down dc-dc converter has been developed for applications to solid-state Marx generator. The purpose is to allow Marx switches to be able to operate without direct power supply from the ground level circuits. The main voltage across the switch is used as the power source which is converted to a dc voltage that can be used to power the drivers of the solid-state switches. Experiments have been carried out to demonstrate the ability and the performance of the dc-dc converter, as well as its effectiveness in a four-stage Marx generator. [ABSTRACT FROM AUTHOR]

A solid-state pulsed power generator has been developed. It is based on Blumlein pulse forming network (PFN) combined with saturable pulse transformer (SPT). The primary circuit is switched by a switching unit consisting of three MOS-gated thyristors connected in parallel. The SPT functions both as a transformer to increase the voltage and as a closing switch for the secondary circuit. The PFN on the secondary side is charged by the transformer and switched by the SPT so that a pulsed output is generated on a matched load. In the demonstration experiment using one module, an output with peak voltage of ~10.4 kV and pulsewidth of ~160 ns was obtained on a resistive load of $52~\Omega $. Furthermore, three identical modules, sharing a common primary circuit, have been connected in series to demonstrate voltage adding, where a peak output voltage of ~30 kV was obtained on a load of $156~\Omega $ with energy efficiency of ~54 %. This pulsed power generator has been tested at repetition rate of 20 kHz in burst mode. [ABSTRACT FROM AUTHOR]

We have modified a solid-state Marx generator by inserting inductors into the circuit so that the inductive energy can boost the output voltage to a level several times as high as $n \times V_{0}$ , where $n$ is the number of Marx stages and $V_{0}$ is the charging voltage of each stage. Switches in the Marx generator are properly controlled allowing certain energy transfer from the capacitors to the inductors before the output begins. As a result, when all capacitors and inductors are connected in series, the voltage generated on the load is from both capacitive energy storage and inductive energy storage. In the demonstration experiment, we have used a 4-stage Marx circuit to generate an output voltage with a peak value of ~ 9 kV on a 400- $\Omega $ load, with a charging voltage of 800 V. [ABSTRACT FROM AUTHOR]

Pulsed power generation using solid-state linear transformer driver (LTD) with inductive energy storage has been experimentally studied. This is a feasibility study in order to explore this new approach by proving its operation principle and demonstrating its typical performance. Magnetic cores in LTD modules are used as intermediate energy storage from which the electrical energy is extracted when the switches are turned off. Voltage adding has been confirmed by using a three-module stack and, with an input charging voltage 41.5 V, a peak output voltage of ~2.6 kV was obtained on a 120- $\Omega $ resistive load, with pulsed length of ~51 ns and rise time of ~24 ns. [ABSTRACT FROM AUTHOR]

Linear transformer driver (LTD) is a relatively new circuit method for pulsed power generation. Solid-state LTD-based generators are being developed for industrial applications. A key issue on LTD performance is its efficiency. An LTD module using silicon carbide (SiC) MOSFETs has been developed, aiming at reducing the circuit loss and improving the overall efficiency. This article reports the experimental results on comparison between the LTD modules using silicon MOSFETs and SiC MOSFETs. The intent is to quantitatively confirm the advantage of using SiC power devices on LTD, before we decide to build a multimodule LTD system. [ABSTRACT FROM AUTHOR]

As a new method to enhance nanosecond pulsed power, aiming improvement of cold plasma applications, a type of circuit that is amplified by synchronization of double simple inductive energy storage (IES) circuits with a semiconductor opening switch (SOS) diode was designed and evaluated. The secondary parts of double simple IES circuits which consist of capacitors, a pulse transformer, MOS-gated thyristors, and an SOS were connected in parallel and in series, and power amplification was attempted by synchronization of reverse currents of the SOS diodes in two circuits. As a result, when the load was also connected in parallel and in series according to circuit connection way, two times higher pulsed voltage and current were obtained at the load in cases of serial and parallel connections, respectively. When the load was a wire to a cylinder coaxial electrode, power of one pulsed discharge increased by the synchronization of the connected two circuits. The ratio of the power increase is expected by simple circuit calculations to be affected by the stray capacitance at the pulse transformer. This fact proves that the synchronization of the IES circuits is an available method for achievement of high power. [ABSTRACT FROM AUTHOR]

Nonequilibrium plasma is an effective and one of versatile advanced oxidation process due to the formation of reactive species such as hydroxyl radicals, oxygen atom, and hydroperoxyl radicals. In pulsed discharge, free electrons gain energy from an imposed electric field and lose this energy through collisions with neutral gas/liquid molecules. The transfer of energy to the molecules leads to the formation of a variety of new species including atoms, free radicals, and ions. These products are all active chemically, and in our case, we measure the amount of hydroxyl radicals generated in the reactor and also the amount of escaped ozone generated in the reactor and decolorized indigo reagent in a graduated cylinder (GC). In this paper, we used oxygen and argon gases in various flow rate and mixed ratios to feed a gaseous phase in a water spraying droplet reactor. The experimental results indicated that the oxygen and O2/Ar mixture flow rates in spraying reactor have an effect on both hydroxyl radical generation and decolorization of indigo reagent solution. Argon gas discharge has less effect on hydroxyl radical production compared to the oxygen gas discharge with the same flow rates and no effect on the decolorization of indigo reagent solution in GC. We obtained remarkable results on both hydroxyl radical generation rate and decolorization efficiency of indigo reagent solution when we discharged with the mixture of O2/Ar “especially when the ratio has more oxygen than argon gas.” Hence, the presence of oxygen in the water spray plasma discharge is very important as it influence the generation of reactive species such as O atoms and ozone in the gas and liquid phase, which can react directly with organic contaminants and also contribute to more production of hydroxyl radicals in the aqueous phase. [ABSTRACT FROM AUTHOR]

We have studied a water treatment by pulsed discharge plasma. To produce the plasma, pulsed high voltage is applied to an electrode. At previous studies, effects of peak, width, rise rate, and repetition rate of pulsed voltage have been confirmed. According to the studies, there is more loss at a latter part of a pulse. To reduce the loss, we investigated an effect of lowering the latter part of the pulse. In addition, an effect of periods between pulses was also investigated for optimization of pulse application timing. Those are new investigations, which were able to be carried out by various pulse forming technologies using a solid-state linear transformer driver. As the result, energy efficiency for organic compounds decomposition increased with a decrease of the latter part of pulses and with an increase of periods between pulses. A possible reason of that is the decrease of disappearance reactions of radicals owing to the decrease of those concentrations. Hence, short pulse and long periods realizes water purification of high-energy efficiency. [ABSTRACT FROM AUTHOR]

In the field of pulsed power, gas switches have been widely used due to their high operating voltages and currents. One example of these gas switches is the thyratron, which is in use for some particle accelerators even today. At the Extreme Energy-Density Research Institute, the Nagaoka University of Technology, Nagaoka, Japan, such devices are in use. In recent times, semiconductor switches have been considered as possible replacements due to their ease of maintenance and control. In general, it is difficult to achieve the same ratings for maximum switching current and voltage of a gas switch with a single semiconductor device, so connecting many in series, parallel, or a different scheme is often applied. We propose a study to evaluate a Marx topology using MOS-gated thyristors capable of high current output. The attractive factors of these semiconductors are the low gate current required for turning ON, a low resistance during the ON-state, a four-stage prototype was built, and it achieved a peak output of 1 kV and 1 kA with a $2~\mu \text{s}$ pulsewidth. To improve the output voltage and current, a ferrite core was implemented as a magnetic switch on every stage; this method has been used before to improve the efficiency of thyristors, however, not combined with circuit topologies like a Marx generator. Adding these magnetic switches increased the efficiency to 89% (from 70%) and allowed an output of 2.2 kV and 2.2 kA without changing the shape of the pulse or the rise time. [ABSTRACT FROM AUTHOR]

A new scheme of pulsed voltage adding using inductively charged Blumlein lines has been proposed and experimentally demonstrated. The circuit principle is explained based on the analogy with capacitively charged Blumlein lines. In the experiments, striplines have been used for inductive energy storage, and SiC power devices have been used as the opening switches. The experimental results have proved both the circuit behavior and the voltage adding by using multimodule stack. This circuit method is expected to become a new approach to compact and repetitive pulsed-power generation. [ABSTRACT FROM AUTHOR]

Pulsed atmospheric discharge has been studied by using a pulsed high-voltage generator based on linear transformer driver (LTD) scheme. Taking advantage of the output flexibility of the LTD, we have studied gas discharge behavior by applying two consecutive pulses to a coaxial discharge load consisting of a wire and a pipe. The experimental results have shown that the discharge current of the second pulse is always lower than that of the first pulse for the same voltage amplitude, when the two pulses are too close to each other (<100 \mu s ). An explanation for this phenomenon has been explored by using a model that considers the effect of residual charge left by the first pulse. The findings obtained by this paper will help us understand the fundamental characteristics of pulsed atmospheric discharge. [ABSTRACT FROM PUBLISHER]

Pulsed-power generator based on linear transformer driver (LTD) technology has been used to demonstrate waveform control for pulsed atmospheric discharge. This kind of discharge load is known for its time-varying impedance where constant voltage usually does not result in constant current. In this paper, an LTD system has been combined with a field-programmable gate array in order to generate a flexible voltage waveform which, in turn, dictates the discharge current. The experimental results have proved that the current of a discharge load can be arbitrarily controlled, to a certain extent, by properly adjusting the applied voltage. This kind of current waveform control should have significant implications for various applications of discharge-generated plasmas. [ABSTRACT FROM PUBLISHER]

We have studied the water treatment by spraying into a pulsed discharge space in air, to decompose refractory organic compounds included in industrial waste water. In practical application, a large quantity of water must be treated. Hence, we made a reactor with seven electrodes and a pulsed power generator of higher power. To verify the effect of the enlargement of water treatment system, the treatment of indigo carmine solution was carried out using seven-electrode reactor, and was compared with the treatment by a previous one-electrode reactor. When discharge energy and flow rate, which is seven times higher than that at one-electrode reactor, were given to seven-electrode reactor, time of the treatment by seven-electrode reactor was seven times shorter than that by one-electrode reactor. On the other hand, when the discharge energy and flow rate of both reactors were similar, the treatment time for seven-electrode reactor was shorter than that of the one-electrode reactor most likely due to a decrease of the disappeared ozone and OH radical. From these results, we conclude that it is possible to shorten the treatment time without decreasing the energy efficiency, by increasing both the number of the electrode and the discharge power. [ABSTRACT FROM AUTHOR]

For a water treatment method that sprays waste water droplets into a pulsed discharge space, the effect of the flow rate and size of water droplets was investigated by experiments to investigate the optimum spraying method. Indigo carmine solution was decomposed at the flow rate of water from 3 to 12 L/min and the decomposition amount for energy consumed in a reactor was measured. When the flow rate was 3 L/min, the energy yield was lower because the amount of water passing through the ozone space was little. When the flow rate was from 6 to 12 L/min, the energy yield was similar because the ozone dissolved in water was saturated. Furthermore, the water treatment was performed by water droplets of different sizes. Size of the water droplets was varied by varying the diameter of holes of a nozzle. Two nozzles that have holes of 0.3 or 1.8 mm in diameter were used for the experiment. When the flow rate was same, the variation of size of the water droplets does not affect the energy efficiency. From this result, it is considered that the concentration of ozone and hydroperoxyl radicals in water does not depend on the diameter of water droplets. Above results show that the flow rate needs to be increased until the saturation of ozone for the treatment of high energy yield. [ABSTRACT FROM PUBLISHER]

Forward pumping current is required for current interruption operation of a semiconductor opening switch (SOS). In this study, the influence of the forward pumping current on current interruption of the reverse current has been investigated experimentally. The duration and the peak value of the forward current were varied and the reverse current obtained under different conditions has been compared. As a result, it has been found that a short forward current can lead to high peak value of the reverse current. It is considered from the results that the density of the minority carriers is increased by the forward current of shorter duration because recombination consumes fewer carriers. Furthermore, when the duration of the forward current shortens with a lower peak value and depletion the peak value of the reverse current increases, the interruption of reverse current quickens. This can be explained by the fact that the time during which minority carriers are turned around by the reverse current is shorter in case of less accumulation and faster removal of minority carriers. With these investigations, it has been understood that relatively short and low forward current and high reverse current is needed for high efficiency inductive energy storage circuit using the SOS. [ABSTRACT FROM PUBLISHER]

To control an input energy for a load, an impedance control with a gap distance of an electron beam diode was studied using an intense pulsed-power generator. The output current of the pulsed-power generator as a function of the gap distance of electron beam diode was measured. It indicated that the behaviors of the experimentally obtained peak current and the theoretically obtained space-charge limited current were found to decrease with an increase in the gap distance. The input energy for the load was estimated from the output current, which decreased with an increase in the gap distance. It also revealed the space-charge limited current suppresses the input energy for the load with a decade. [ABSTRACT FROM PUBLISHER]

A solid-state linear transformer driver stack has been developed to demonstrate pulsed power generation and output pulse shaping. It consists of 30 modules each using 24 power metal–oxide–semiconductor field-effect transistors as switches. The output voltage of the stack is the superposition of the voltage pulse of each module no matter if the modules are switched synchronously or not. In synchronous operation, the output voltages of all modules are added up to reach an output voltage up to \(\sim 29\) kV with a maximum output current of \(\sim 240\) A. The pulsewidth is variable in the range of 50–170 ns. On the other hand, by carrying out separate switching of different modules, the output waveform can be varied by performing pulse shaping. The control signals for pulse shaping experiment are generated using an field-programmable gate array board that allows potentially automatic waveform optimization. [ABSTRACT FROM PUBLISHER]

In this paper, we investigated a water treatment method that sprays waste water droplets into a pulsed discharge space. To increase energy efficiency of this method, a pulsed power generator should output a pulsed power of a high peak and a short pulse width and be low circuit loss, high repetition rate, high power, and high stability. An inductive energy storage circuit using a semiconductor opening switch was studied to satisfy the above-mentioned requirement. Initially, effect of turn ratio of a pulse transformer (PT) in the circuit was investigated. Energy transfer efficiency and the pulsewidth of the output voltage increased with the PT turn ratio, resulting in an increase of the efficiency of the water treatment system. Then, the effect of the load impedance was investigated. The result showed that an optimum resistance to maximize the efficiency exists. From these results and a previous experimental report, we concluded that the optimization conditions are summarized below. The turn ratio and the inductance in the secondary circuit should be as high as possible under the condition, which does not output the very long pulse. The impedance of the discharge at an electrode for the water treatment should be a value that maximizes the energy transfer efficiency. Capacitance of capacitors in the circuit should be adjusted to obtain optimal peak voltage for the generation of active species. [ABSTRACT FROM PUBLISHER]

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

Using a modified loop antenna, RF plasmas are formed under high vacuum without collisions between neutral atoms and a test piece or a target (Si) that is mounted in the plasma. By applying a negative high voltage to the target, carbon ions are implanted into the target by the three-dimensional ion implantation method. Films thus formed have been identified as DLC (diamond-like carbon) by Raman spectra, X-ray diffractometry, and Rutherford back scattering. In the case of a target of WC with 10% Co, it has been found that the sticking force of the film is 60 N and the friction coefficient 0.13. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 1–11, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20444 [ABSTRACT FROM AUTHOR]

Power semiconductor devices, such as insulated-gate bipolar transistors, metal-oxide-semiconductor field-effect transistors, and static-induction thyristors, are used in different kinds of pulsed power generators developed for different applications. In addition, the semiconductor opening switch is found to have very effective applications in pulsed power generation by inductive energy storage. Semiconductor switches have greatly extended the scales of pulsed power parameters, especially in repetition rate and lifetime. They have also enabled new areas of pulsed power applications, such as accelerators, flue-gas treatment, and gas lasers. [ABSTRACT FROM AUTHOR]

Abstract: The feed-forward control of the amplitude and phase of a high-power RF pulse based on the overdrive technique is applied to an L-band electron linac to ensure that the energy of the electron beam is uniform and constant enough for the recommissioning of a terahertz (THz) free-electron laser (FEL) at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The quality of the electron beam is evaluated using the time-resolved measurement of its energy spectrum; the energy is constant within 0.1% during the electron macropulse for 15MeV energy except for the transient period in the leading edge. A high-power, stable FEL operation that reaches saturation is obtained using beam conditioning. The characteristics and performance of the FEL for THz radiation are measured at the end of an evacuated transport line. The frequency ranges from 2 to 12THz, from 25 to 150μm in wavelength, and the maximum energy in the FEL macropulse with a ~3μs duration is 3.7mJ at 67μm; using these values, the peak power in the macropulse is calculated to be 1.2kW, while that in the micropulse with a 20ps duration is calculated to be 0.5MW. These values are comparable to those in the THz range of other FELs that are based on normal conducting RF linacs. [Copyright &y& Elsevier]