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The results of an experimental study of the generation of runaway electrons (REs) during the formation of a negative streamer in an 8.5-mm-long point-to-plane gap filled with air are presented. Negative nanosecond voltage pulses (18 kV, $\tau _{0.5}\approx 10$ ns, and $\tau _{0.2-0.9} \approx 4$ ns) were applied across the gap. In this paper, we attempted to determine when REs are generated relative to the appearance of the streamer. In our previous studies of a positive streamer, we have shown that the formation of the streamer is accompanied by a dynamic displacement current (DDC) caused by the redistribution of electric field strength in the gap. This current can be easily measured with a collector placed behind a grounded grid electrode. The collector is typically used to measure the current of REs at negative polarity. In this paper, we were able to measure together and separately the DDC caused by a negative streamer and the RE beam current. This allowed us to accurately determine the moment of generation of REs. [ABSTRACT FROM AUTHOR]

To enhance the heat dissipation of high-power light-emitting diodes (LEDs), corona wind based on corona discharge was promoted. In this paper, we aimed at reinforcing the intensity of corona wind by modifying the needle electrode with graphene solution. To explore the differences in the graphene-coated electrode and the original bare electrode on the electrical characteristics, the intensity of corona wind, and LED heat dissipation, a corona wind cooling system and a thermal test system were built for the experimental study. The results showed that the graphene-coated electrode system could produce corona wind at a lower voltage. In addition, the discharge current of the graphene-coated electrode system is higher than that of the bare electrode system under the same discharge voltage. The graphene-coated electrode system can induce a faster corona wind and the highest speed is about 3.4 m/s, showing that it is more efficient than the bare electrode system in corona wind production. Moreover, the temperature drop of LEDs for the graphene-coated system is greater, which means that the corona wind cooling system can reduce the junction temperature of the LED chips effectively. Ultimately, as the discharge power increases, the average convective heat transfer coefficient increases. Indeed, the result of this paper can be used for the wide variety of the graphene-coated corona wind generator application as a promising technology for the LED heat management. [ABSTRACT FROM AUTHOR]

This paper consists of two parts. In the first part, the emission was generated in air, and the waveform recording the spectral line at 337 nm (= prominent N2 laser line) was noted. The pulse forming network (PFN) Marx generator having a large ($50~\Omega$) internal impedance was used. The pulses of the nitrogen emission at 337.1 nm of long ($< 3~\mu \text{s}$) duration and of short (≈10 ns) duration were obtained. The photodiode registered both the spontaneous emission and the stimulated (laser) emission in the 337 ± 5 nm spectral range. The data show that the laser emission predominates in the pulses of long duration. In the second part of this paper, it is suggested that the ultraviolet (UV) radiations emitted by the sun, together with the electric fields present at high altitudes, are capable of exciting the N2 molecules to the upper excited $\text{C}^{3}\Pi _{u} $ level to yield the laser emission of long duration. On the basis of the laser energy content dissipated into the plasma, the size of the transient luminous events (TLEs) known as the elves and the sprites was evaluated. The dynamics of initially small size, highly compressed, and very hot plasma formed inside the sprite was presented. It is proposed that the TLEs named “crepuscular twilight in the sky of New York” observed on December 28, 2018; “mysterious bright flash” occurred in Russia on January 9, 2018; and maybe the Tunguska event happened in Siberia on the morning of June 30, 1908 should be included in the list of the TLEs. [ABSTRACT FROM AUTHOR]

A novel brushless self-excited air-core compensated pulsed alternator (BSACPA) is presented in this paper. It consists of two submachines in cascade, among which one serves as an exciter and the other works as a generator. The rotor windings of the two submachines are connected by a reverse phase sequence to realize reversal of the magnetic field. The stator windings are connected by a rectifier to realize the brushless self-excited structure. As an air-core compensated pulsed alternator (CPA) of new topology, it is necessary to derive its mathematical model and carry out a comparative design. Thus, this paper focuses on the detailed design and analysis of a BSACPA prototype, which includes dimensional design and equivalent circuit establishment. In addition, the critical speed is also acquired. Accordingly, the numbers of winding coil turns are designed to increase the discharge current and power based on the theoretical analysis. Finally, the analysis and design are verified by finite-element analysis (FEA). [ABSTRACT FROM AUTHOR]

This paper discusses a novel methodology to increase the voltage droop compensation range in generalized solid-state bipolar high-voltage Marx modulators with one resonant stage. To maintain the modularity characteristic of bipolar Marx modulators, the imbedding of additional resonant stages is not straightforward. Nevertheless, this paper proposes to add a second resonant stage to the already existing resonant-type voltage droop compensation stage. This second stage increases the voltage droop compensation percentage of a generalized solid-state bipolar Marx generator. The compensation of the bipolar pulse voltage droop is now achieved by adding two auxiliary synchronous compensation resonant voltages, to the output capacitive decaying voltage. Simulation and experimental results are presented for six Marx plus two resonant stages, 16% voltage droop, with 3-kV pulse amplitude, 100- $\mu \text{s}$ pulsewidth, 40-ms relaxation time, and 10-Hz pulse repetition rate. [ABSTRACT FROM AUTHOR]

This paper presents the results of the experiment with an overmassed wire-array $Z$ -pinch load that is powered by a current pulse (amplitude ~4.3 MA and rise time $\sim 0.9~\mu \text{s}$) from a multidisk magnetocumulative generator. Interesting feature of the experimentally recorded soft X-ray (SXR) pulse is short (~10 ns) duration at a microsecond current rise time with total energy of several hundreds of kilojoules. Obtained results are the evidence of high-quality implosion of the current-carrying plasma. The 2-D magnetohydrodynamic code FLUX-rz was used for the numerical simulation and analysis of the obtained results. The calculations indicated that only ~30% of the initial load mass took part in the SXR generation. The main peculiarities of the overmassed $Z$ -pinch implosion are discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents the design and construction of a sample of Marx pulsed generator based on boost converter (BC) pulse-forming networks (BCPFNs). BCPFN is used instead of the conventional Marx floors for constructing this pulsed generator. BCPFN is carried out by connecting inductors and capacitors in series and parallel modes, respectively, by using solid-state switches, and during this procedure the pulsed generator converts to BC temporarily and increases the voltage of capacitors uniformly to a considerable value. This technique causes an increase in the discharging voltage level to the load that is many times more than its dc voltage source by charging the capacitors to a greater level. In order to take advantage of the benefits of Marx generator and PFN, this paper suggests a new circuit with the minimum number of switches. It means, to compose BCPFN and Marx, we have tried to design the circuit with fewer switches and instead of it we have achieved our desired performance with changing the operating mode in the states of BC, PFN, BCPFN, and BCPFN Marx. The results are simulated with MATLAB software. At the end, the experimental results of the construction of the above-mentioned system at low-power levels are presented, and the topology’s accuracy is proved by comparing them to the results of simulation. [ABSTRACT FROM AUTHOR]

A new modular pulsed-power source with fast rise time and step-wise arbitrary output waveform generation is currently under development to drive the Gepulste Elektronenstrahlanlage device investigated at the Institute for Pulsed Power and Microwave Technology (IHM). Acknowledging the complex design procedures necessary to set up a modular pulsed-power source for voltages of up to 120 kV, this paper focuses on the circuit design for a single stage and its validation prior to the generator assembly. Using a semiconductor-based Marx generator topology, the stages are designed to have an output voltage of 1 kV with a pulse current of up to 600 A. When connected to an ohmic load, the measured current rise times are in the order of 46 ns resulting in the current rise rates of up to 10 kA/ $\mu \text{s}$ using the commercial devices. The step-wise arbitrary output waveform is created by generating the switching commands on the stage using a microprocessor and a fast optical synchronization unit. Effective stage shielding is verified by operating the stage in a 100-kV, 2.5-kA electromagnetic interference test bed. This paper presents the design considerations and the corresponding measurements. [ABSTRACT FROM AUTHOR]

The linear induction launcher consists of two parts: the barrel section and the projectile section. The barrel contains of a long coaxial sectionalized group of coils that are energized by a capacitor bank or generator sets. This paper deals with the design, implementation, and experimental test of a coreless axial-flux permanent magnet (AFPM) pulsed alternator with a flywheel system as an energy source for linear induction coil launchers. The proposed coreless AFPM generator has a low internal inductance and resistance of stator windings without compensation windings when compared with the conventional iron core machines. This paper describes the coreless AFPM generator configuration and shows the simulation findings. [ABSTRACT FROM AUTHOR]

A novel high-voltage direct current (HVdc) power supply which has no transformer or voltage multiplier circuit is presented and analyzed in this paper. This is made possible upon the diodes storage delay phenomenon. This proposed power supply is compact, lightweight, and low cost. Its basic structure includes a diode with a proper reverse recovery specification that plays the role of a step-up transformer in the conventional HVdc supplies and a high-voltage capacitor which stabilizes the output voltage. This structure has remarkable advantages over the conventional transformer-based HVdc supplies, such as compactness, a low ripple output, and a low-cost power supply. Performance of the proposed method and its accuracy are investigated in this paper. The results are verified by implementation of a 1.2-kV prototype supply. [ABSTRACT FROM AUTHOR]

Chronic wounds are a major complication for diabetes mellitus (DM) patients, which cause discomfort and an increase in medical costs. The purpose of this study is to investigate the medical application and possible mechanisms of a cold atmospheric plasma jet in healing DM chronic wounds. In this paper, the genetic diabetic BKS.DB mice are used as the diabetic wound healing animal model, which have a stable glucose level and can avoid the effects or complications induced by surgical and chemical interventions. The helium atmospheric-pressure dielectric-barrier-discharge (AP-DBD) plasma jet is employed to treat the diabetic mice wounds with the fixed treatment time and distance of 15 s and 20.0 mm, respectively. The wound healing, histological, immunohistochemical, and cytokine analyses are conducted to evaluate the efficacy of the helium AP-DBD plasma jet on the chronic wound healing of the genetic diabetic mice. The experimental results show that the helium AP-DBD plasma jet treatment of wounds of genetic diabetic mice can regulate the secretion of transforming growth factor- $\beta $ (TGF- $\beta$) and fibroblast growth factors (FGFs), limit the inflammatory response and excessive cell proliferation, accelerate the process of re-epithelialization, and consequently, promote the chronic wound healing process. [ABSTRACT FROM AUTHOR]

Marx generator using all-solid-state devices has been studied for many years. Higher parameters are always the demand for new applications. Traditional all-solid-state Marx generator can output high voltage due to its series topology, but the current is always limited by the switch. In this paper, a stage-stage paralleled topology of Marx generator for high current has been proposed. Topology structure and driving mode comparison for current balance have been analyzed. The paralleled driving mode for the current balance and the shaping waveform has been proposed. For experiment, a four-stage-four-paralleled Marx generator with metal–oxide–semiconductor field-effect transistors (MOSFETs) has been constructed with output pulses 2.2 kV, 730 A (depending on the load), rise time of 31 ns, fall time of 56 ns, and adjustable pulsewidth from 400 to 800 ns. [ABSTRACT FROM AUTHOR]

Ferrite spiral delay lines intended for synchronization of high-voltage generators. The results of output pulses’ time stability are presented. All testes were carried out in both single- and two-channel systems. Adjustable precise synchronization of two nanosecond high-voltage generators (−150-kV, 5-ns full-width at half-maximum) are analyzed in this paper. The trigger high-voltage pulse was split into two channels to switch on identical double forming lines of each generator through controlled high-pressure spark gaps (nitrogen 60 atm). Designed coaxial ferrite spiral lines with an external bias field were installed in both synchronized channels. Adjustment of the bias field not only sharpens the trigger pulse but also varies its front delay and, respectively, the start of the driven generators. The maximum delay of one channel relative to the other was 1.5 ns. The minimum standard time deviation (relative jitter) of two nanosecond high-voltage generators was determined at the level of 55 ps. [ABSTRACT FROM AUTHOR]

Compulsators are ac generators which are used for electromagnetic launch applications over the past few decades. This paper presents the work carried out by the authors to design a compulsator for a railgun which has been built and tested with a capacitor bank of 20 kJ as the pulsed-power source in the author’s laboratory. The generator topology selected for the compulsator is a single phase, two-pole machine with iron core and passive compensation. The design is based on the criterion of achieving maximum projectile exit velocity with the additional condition that natural current zero is synchronized with the instant of the projectile’s exit. The effect of varying the different parameters of the compulsator on the performance of the system has also been studied and discussed in this paper. By means of performance analysis, the necessary background for the design of the actual compulsator has also been achieved. [ABSTRACT FROM PUBLISHER]

Repetitive high pulsed electric field (PEF) is an effective method to kill microorganisms and bacteria in water treatment applications. The PEF can be generated by applying high-power electromagnetic pulse across the sample to be treated. There are two main types of high-voltage pulse generators, namely, unipolar and bipolar. In this paper, a full-bridge submodule-based modular high-voltage pulse generator, having the ability to generate unipolar and bipolar high-voltage pulses with different shapes from a relatively low-voltage input dc supply, is proposed. In the proposed configuration, relatively low-voltage insulated gate bipolar transistors (IGBTs) are required to generate the high-voltage bipolar pulses. A thyristor rated at the level of the pulsed output voltage is required in the proposed configuration to bypass the load during the charging process of capacitors. In the proposed approach, a thyristor is used instead of the self-commutated high-voltage switch (e.g., series-connected IGBTs), as thyristors are available with high-voltage ratings and possess inherent reverse voltage blocking capability. A detailed illustration of the proposed configuration and its operational concept are introduced in this paper. Simulation and experimental results are presented to validate the proposed approach. [ABSTRACT FROM AUTHOR]

Atmospheric-pressure plasma jets (APPJs) are widely used in biomedical treatment, surface modification, and sterilization, among others because of their advantages of simple structure, strong chemical activities, nonthermal effects, and convenient handling. In this paper, a nanosecond-pulse power generator based on Marx circuit is proposed. The apparatus consists of a nanosecond-pulse generator with crowbar switch and a needle-ring structure electrode. The nanosecond-pulse generator is modularly designed with ten stages; MOSFETs are used as the main switch and crowbar switch on each stage. A field-programmable gate array is used to generate two-channel trigger pulse signals to control the turn-on or turn-off of switches. The generator can produce repetitive pulses with output voltages of up to 8 kV, pulsewidth of 100–1000 ns, rise time of less than 30 ns, and pulse repetition frequencies of 1 Hz to 1 kHz. The designed nanosecond-pulse generator and the needle-ring structure electrode are used to produce argon plasma jets into open air, and the experiments show that the nanosecond-pulse generator can sustain stable APPJs. This paper lays a foundation for the further exploration of the biomedical effects of APPJs. [ABSTRACT FROM PUBLISHER]

In recent years, all solid-state Marx generators have been found more and more extensive applications in industrial, environmental, and biological fields. All solid-state Marx generators have many requirements for their drive circuits, such as good synchrony for driving signals at different stages, fine isolation between control signals and the main circuits, adjustable pulsewidths and frequencies, and good driving abilities. This paper proposes a high-performance drive circuit for a 24-stage Marx generator based on IGBTs. A half-bridge circuit using IR2110 outputs a high-current turning-on drive signal (positive) and a turning-off drive signal (negative) with adjustable dead time. The control drivers are input to the common primary side of 24 nanocrystalline magnetic transformers, which isolate the control circuit and the main circuit. Through gate circuits at the second sides of the magnetic cores, the turning-on drive signal charges 24 gate–emitter capacitors to required voltages and consequently all IGBTs move into on state until the turning-off signal arrives. Similarly, the negative turning-off drive signal charges all gate–emitter capacitors to a negative voltage which ensures all IGBTs stay in the off state. Therefore, the pulsewidth is determined by the phase difference between the turning-on and turning-off drive signals. Equipped with this drive circuit, the 24-stage Marx generator is able to produce stable high voltage pulse with a peak value of −9.6 kV, PRF $0.05\sim 5$ kHz, and different pulsewidths. In this paper, the design details and experimental confirmation of the proposed drive circuit are illustrated. [ABSTRACT FROM AUTHOR]

Bipolar junction transistors (BJTs) have been widely studied and used in nanosecond high-voltage pulse generators due to the advantages of fast switching speed and high repetitive frequency. Usually the Marx-type circuit is used to raise the peak value of output pulses. In this paper, a traditional BJT-Marx circuit using charging resistors is analyzed theoretically and experimentally. Based on the results, the structure of a circuit is changed to decrease the isolation voltage across the resistors, and diodes are used to replace charging resistors to block capacitors discharging to resistors. Experimental results showed that the three Marx generators proposed in this paper output pulses with higher voltage amplitude, and the last improved circuit outputs pulses with faster fall times at a higher efficiency. [ABSTRACT FROM AUTHOR]

This paper shows how to use modular Marx multilevel converter diode ( \textM^3 CD) modules to apply unipolar or bipolar high-voltage pulses for pulsed power applications. The \textM^3 CD cells allow the assembly of a multilevel converter without needing complex algorithms and parameter measurement to balance the capacitor voltages. This paper also explains how to supply all the modular cells in order to ensure galvanic isolation between control circuits and power circuits. The experimental results for a generator with seven levels, and unipolar and bipolar pulses into resistive, inductive, and capacitive loads are presented. [ABSTRACT FROM AUTHOR]

Recent studies have shown that rectangular high-voltage pulses have a high-performance in dielectric barrier discharges (DBDs). To generate the rectangular pulses used in the Marx generators, the most common way is driving two sets of switches synchronously with a different sequence. Because of the fast-changing current and voltage, the electromagnetic interference (EMI) will affect the circuit. Therefore, if two groups of switches were triggered mistakenly at the same time, it would cause the partial short-circuit phenomenon. In this paper, a new driving circuit with overcurrent protection for the Marx generators is proposed. It used only one synchronous signal to control two sets of switches. Experimental results showed that the short current could be limited within 100 A. The proposed driving circuit was applied to a seven-stage Marx generator, and 5-kV rectangular pulses can be obtained steadily at 1 kHz, which can greatly improve the stability of the system. [ABSTRACT FROM AUTHOR]

This paper describes the operation of a solid-state generator proposed to produce high-frequency bipolar high-voltage pulse bursts on resistive-type loads, intended for medical applications. The generator design is based on two independent solid-state unipolar positive Marx generators positioned back to back, where the load is placed between the outputs of the two generators. SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) are used in order to allow high-frequency operation. A generator with two five-stage Marx generators is experimentally tested in order to deliver up to 5000-V/50-A bipolar pulses, with 500-ns–10- $\mu \text{s}$ pulse widths and 200-ns–10- $\mu \text{s}$ relaxation time between positive and negative pulses. The generator operates in the burst mode from 1 to 200 pulses, in excess of 500 kHz within the burst, which can have a repetition frequency up to 1 kHz limited by the input 1000-V/200-W power supply, with forced air cooling. Results, with resistive-type loads, for several single pulse and burst mode operations are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we discuss and demonstrate the potential of normally-on GaN high-electron-mobility transistors (HEMTs) as opening switches in miniaturized pulsed-power circuits. The high-breakdown electric field of GaN (~3 MV/cm) makes it possible to fabricate high-voltage devices in small dimensions, resulting in smaller parasitics and faster switching times. GaN HEMTs as opening switches are compatible with inductive topologies, which offer more than one order of magnitude higher energy density than capacitive topologies, allowing further miniaturization of pulsed-power systems. In this work, we demonstrate the application of fabricated 1.5-kV normally-on GaN HEMTs on an inductive switching topology, resulting in 300-fold voltage step-up, which makes it possible to generate high-voltage pulses with a low-voltage dc source in miniaturized circuits. [ABSTRACT FROM AUTHOR]

In this paper, we studied the process of vacuum surface flashover of several polymeric materials initiated by 80-kV, 15-ns pulses with peak discharge current 3 kA. We measured breakdown propagation speed, energy input to the discharge, full ion charge and directional pattern of the plasma flow, the full energy of the particle flow, propellant mass loss, and thrust for polytetrafluorethylene (PTFE), polyethylene (PE), and polymethyl metacrylate (PMMA). In the case of PTFE, we obtained the maximum absolute values of thrust ($4.7~\mu \text{N}\cdot \text{s}$) and the full energy (66 mJ). The values of average mass velocity for all materials lie in the range of 3–7 km/s; values of the average velocity of ions lie in the range of 60–85 km/s. Directional patterns of charge and mass are similar and have distinct symmetry in equatorial and meridional planes. We estimated the temperature of the dielectric surface within a model of energy transfer from the discharge channel to the surface due to thermal conductivity. We showed that at this power level ($\sim 10^{7}$ W) and short duration of high-current stage of the discharge ($\sim 10^{-8}$ s), the propellant is consumed mainly during the stage of plasma channel formation. [ABSTRACT FROM AUTHOR]

A single-phase tubular permanent magnet linear generator (TPMLG) with a novel structure for Stirling engines is presented in this paper. TPMLG can directly convert mechanical energy into electrical energy and it is the main energy conversion device in Stirling power generation system. Its 3-D geometry and initial dimensions are given in detail. Due to the structural characteristic, the finite element (FE) method (FEM) is used to analyze the electromagnetic field. An FE model is established from the magnetic field perspective. Isolines of magnetic vector potential can be obtained, as TPMLG locates at −0.015, 0, and 0.015 m. The dynamic performances of TPMLG under different reciprocating frequencies are compared and analyzed. Compared with three different kinds of machines, it can be concluded that the proposed TPMLG can produce electricity with less weight and materials. [ABSTRACT FROM AUTHOR]

In this paper, a modular topology is presented for generating high-voltage pulsed power. The proposed structure consists of Marx-type modules, which are based on the switched-capacitor (SC) concept. This module receives an input voltage and, depending on the requirement of the user, produces an output voltage either equal to the input or twice as much as the input voltage, which shows the flexibility of our model. The capability of the module to produce a doubled output makes it appropriate for applications with low input voltage sources. Also, the topology has the capability of generating combined wide and narrow pulses. The topology was simulated in MATLAB Simulink and a laboratory setup was built to test its operation. The results validate the theoretical basis of the structure. [ABSTRACT FROM AUTHOR]

The plasma produced by a pulsed generator is an efficient tool for an airflow control. In this paper, a nanosecond pulsed generator constructed with a fast solid-state switch is designed for triggering synchronous discharges in plasma synthetic jet (PSJ) actuators connected in series. The generator delivers high-voltage pulses with a peak voltage varying from 0 to 20 kV, a rise time of 20 ns, a full-width at half-maximum of 200 ns, and a wide range of pulse-repetition rate varying from 0 to 5.5 kHz. It is proved that this generator is able to trigger synchronous discharges in three PSJ actuators in atmospheric air with a peak discharge current more than 90 A and a deposited energy per pulse of 39 mJ. A schlieren system is used to observe the airflow dynamics, which shows the high synchronization among the three PSJ actuators with a time triggering delay of about 20 ns. The synchronous operation of three PSJ actuators produces a plasma jet with a maximum velocity of 60 m/s and a precursor wave with a velocity of 350 m/s. [ABSTRACT FROM AUTHOR]

Following the pioneering research studies by individual inventors and teams from the 1840s to the 1960s on various aspects of electromagnetic launch using railguns, coilguns, and linear motors, there has been an explosion of interest since the 1970s. Much of this growth has been discussed at the International Electro-Magnetic Launcher Symposia that have taken place approximately every two years from 1980 to 2018. A brief description and a summary of the early work of pioneers in this field as well as the symposia is provided here. Selected papers from the symposia have been archived in the IEEE Transactions on Magnetics and the IEEE Transactions on Plasma Science. [ABSTRACT FROM AUTHOR]

Air-core compensated pulsed alternator (ACPA) has been applied to the field of pulsed power technology, especially electromagnetic launch. The high-field current and the rotating speed of the ACPA bring the benefits of high power and energy density, but also make it suffer from low reliability and poor performance due to the serious heat and wear in the slip rings and brushes. To solve this problem, a novel brushless self-excited ACPA (BSACPA) is presented in this paper. It consists of two submachines in cascade, namely, an exciter and a generator, for which the air-gap flux rotation directions are opposite. The rotor windings are specially arranged and adopt the principle of negative sequence alternate current excitation, thus eliminating brushes and slip rings, and no rotary rectifier diode is needed. First, the structure and the operation principle of the BSACPA are described. Second, the magnetic field distribution and the coupling between the two submachines are analyzed. Third, the mathematical model of BSACPA is established. Finally, the validity of its operation principle is verified by finite-element and circuit analyses. In conclusion, BSACPA achieves the brushless structure and provides a new solution to improve the performance and the reliability of a conventional ACPA. [ABSTRACT FROM AUTHOR]

Low-temperature plasma ion mobility spectrometry (LTP-IMS) is the method to identify some materials by measuring concentration of gas phase ions. IMS used in a wide range of laboratory-based biomedical research studies. A nanosecond pulse generator is necessary for LTP-IMS apparatus to enable direct analysis of various chemical compounds without having to evaporate the analyte or seek a solvent or any reagent. In this paper, a dual Marx pulsed generator for LTP-IMS Ionization power supply is proposed based on a new combination of some solid-state switches including insulated gate bipolar transistor (IGBT) and avalanche bipolar junction transistors (BJTs). The compact dual Marx generator is composed of a series of avalanche BJTs and an IGBT as the trigger switch, where its rise time is reduced from 100 to 5 ns by using an avalanche BJT in its command circuit. In this way, a controllable high-voltage pulse generator has designed, built, and tested. The proposed circuit can be used to generate the repetitive high-voltage pulses necessary for low temperature ionization in advanced IMS apparatus. The output voltage has an amplitude of up to 6 kV with pulse widths in the range of 40–1000 ns and pulse repetition rates up to 2 kHz, having rise time and fall time less than 10 ns independent of the load specifications. [ABSTRACT FROM AUTHOR]

This paper focuses the tunability of a reflex triode virtual cathode oscillator (vircator). The vircator cathode is a bimodal carbon fiber (CF) material, while the anode is polished pyrolytic graphite. These materials have ideal operating characteristics for use within a vircator. These materials have high operating temperatures greater than 1000 K which support large current densities of ~200 A/cm2. A 12-stage, 158-J pulse-forming network (PFN)-based modular Marx generator is used to drive the vircator at 350 kV, 4 kA with ~100-ns pulsewidth at a pulse repetition frequency up to 100 Hz. The 12 stages of the Marx are constructed from a PFN using five, 2.1 nF, high-voltage ceramic capacitors in parallel. The Marx is broken into six modules each containing two stages. The Marx modules are machined from acetyl copolymer commonly called Delrin to provide rigidity and strength. Each Marx module includes air supply lines machined directly into each block, allowing external airlines to connect to each module chamber, rather than every spark gap. After the Marx erects, the energy is used to drive the virtual cathode oscillator (vircator) where subsequent frequency generation is manipulated through a new rectangular waveguide used as the resonant cavity. The new design has three parts of the cavity that can be changed; the bottom plate, back wall, and anode–cathode gap (A–K) distance. Each of these parts moves via linear actuators, two on the bottom plate, one on the A–K gap, and linear bellows for the back wall. The square waveguide cavity is welded into a circular stainless steel sleeve and is housed within a 10-in circular vacuum chamber. The anode is stationary in the vacuum chamber and connects to the Marx generator through a nickel shaft that feeds through the back wall, circular sleeve, and the rectangular waveguide. The anode is pyrolytic graphite, while the cathode is CF. The waveguide bottom plate, back wall, and cathode move around the stationary anode. This allows the height of the resonant cavity and the back wall distance from A–K gap to be independently changed of each other. [ABSTRACT FROM AUTHOR]

The vessel’s pulse load can intermittently produce pretty high power in a very short time. Considering their periodical charge-and-discharge process, the system variables of integrated power system (IPS) are characterized by a periodic alternating process rather than a single-equilibrium point. It is not suitable to evaluate the operational performance according to the equilibrium point. In this paper, a periodic orbit model of the IPS and its algorithm is proposed according to sensitivity analysis of end value of system variables to their initial value. The algorithm can be used for distributed compute of system variables, which adjust system variables according to the sensitivity to make the end value equal to the initial value. And, the calculation speed of the algorithm can be increased greatly. The model and the algorithm lay the foundation for assessing the operational performance of the IPS with pulse load. The proposed method has been verified by the simulation test. [ABSTRACT FROM AUTHOR]

This paper puts forward a novel high-voltage pulse generator, which can output a near square waveform across the load. The generator is composed of a conventional Marx generator, an $LC$ filter and a metal–oxide varistor (MOV) in parallel with the load. The Marx generator and the filter form a two-section type-A Guillemin pulse forming network (PFN). The PFN outputs a near square waveform and the MOV further stabilizes the voltage because of the MOV’s nonlinear resistivity. Circuit simulation verifies the working principle. Design parameters for the conventional PFN are derived. Considering the stray inductance of the filter, a more realistic PFN circuit is proposed and its parameters are derived. Preliminary experiments are conducted and verify the concept. Typical output waveforms have 20–30-ns rise time, 1000–1100-ns pulsewidth, and ~7-kV peak voltage. The pulse generator based on this concept is suitable to be used as a compact, long-pulse high power microwave modulator as it has a simple design, a well-defined flat top and it can output near constant voltage even if the load’s impedance varies. [ABSTRACT FROM AUTHOR]

In this paper, a high-voltage unipolar pulse power generator is introduced for electroporation applications. Operating principle of the proposed structure is based on the buck–boost (BB) converter. The generator is comprised of parallel modules connected to the converter through an SCR and is supplied by a low-voltage dc source. Each module consists of an insulated gate bipolar transistor (IGBT), two diodes, and a capacitor. In fact, the proposed topology is a combination of the Marx generator and BB (MG-BB) converter. In comparison with other modular MG-BB structures, the proposed topology achieves interesting advantages including simpler structure, reduction of IGBTs voltage rating, and reducing number of components (inductors and switches). In order to clarify the features of the proposed structure, it has been compared with other unipolar MGs considering different aspects including the number of circuit components, number of required input supplies, amplitude of the output pulse, and the maximum voltage across switches and diodes. To validate the effectiveness of the structure, simulation and experimental results are presented. The results confirm that the proposed topology is capable of generating unipolar pulses with desirable amplitude and repetition frequency using a low-voltage dc supply. [ABSTRACT FROM AUTHOR]

The challenging demands of pulsed electron beam devices (such as the GESA device) with respect to their pulsed power supply have led to the development of a new semiconductor-based Marx generator. At a maximum output voltage of 120 kV and 600-A pulse current for a duration of up to 100 $\mu \text{S}$ , stepwise arbitrary output waveforms are desired. A fast rise time of the generator is achieved by using fast switching circuitry, low inductance capacitors, and a low inductance stage arrangement. For low jitter triggering of all stages and efficient signal transmission, the generator uses an optical bus system for communication. Due to the inherent dynamic load characteristics of the GESA device, the generator features a fast overcurrent protection scheme. This paper presents selected design aspects of the generator and their validation in a small-scale assembly able of delivering up to 8 kV at 600-A load current. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of effect of high-power UV-radiation plasma, generated by electric discharges, on germination rate of Altaic flax seeds (Linum altaicum). It was found that UV-radiation scarifies flax seeds by means of cracks formation in the seeds’ coat. The cracks shorten moisture penetration time to a seed bud thus twice increasing the germination rate. It is found that the germination rate function has the three-stage character; the velocity-growth function has the view of three pulses, which separates the seeds into three subgroups. Division of the group into subgroups is stipulated by the probabilistic nature of the cracks formation. The number of subgroups is equal to the number of layers +1. We calculated average times of natural moisture penetration through the flax seed coat layers: $T_{s} =11.8$ h through the spermoderm and $T_{e} =17.7$ h through the endosperm. It is possible that scarification of the flax seed coats can shorten the germination time for these times. We also noted that some seeds could die due to the effect of high-power UV radiation. So, it is necessary to find more sparing regimes of the seeds UV irradiation. [ABSTRACT FROM AUTHOR]

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon. [ABSTRACT FROM AUTHOR]

In this paper, the experimental results of the behavior of an X-pinch plasma conducted in a small capacitive generator of low impedance and inductance are reported. The generator produces currents of the order of 120 kA in times about 500 ns, when a charging voltage of 24 kV, and wires as load are used. W, Al, and Cu X-pinches of different diameters were tested. The experimental observations show a similar global dynamic to those observed in experiments of higher current and shorter quarter period, with an intense emission of energetics X-rays (>5 keV) generated by plasma dynamics in the cross point of wires. The fast plasma dynamic is evidenced from the strong change of frequency in the current-derivative signal, which is correlated with the X-ray signals observed from the radiation detectors. From the time-integrated pinhole images and time-integrated aperture images, filtered with different aluminum foils of different thicknesses, an estimated X-ray source size of $70~\pm ~20~\mu \text{m}$ with energies above 7 keV is obtained. [ABSTRACT FROM AUTHOR]

This paper presents the results of predictive calculations of the parameters of pulses of soft X-ray radiation (SXR) on a four-module electrophysical facility GAMMA-4 (the current pulse amplitude is ~3 MA with rise time of ~60 ns) that has been constructed in Russia. Scaling numerical simulation of implosion of a cylindrical single and nested multiwire array in 0-D, 2-D, and 3-D radiation magnetohydrodynamic– approximations is performed, taking into account, the updated double-loop equivalent electrical circuit of the GAMMA-4. The main purpose of the conducted studies was the numerical optimization of the multiwire array parameters to obtain the best characteristics of the SXR pulse generated as a result of Z-pinch implosion on the axis of the system. [ABSTRACT FROM AUTHOR]

This paper demonstrates the improved simulation of a Z-pinch experiment with 2-D magnetohydrodynamic code FLUX-rz developed in RFNC-VNIIEF. A Z-pinch load was nested wire array powered by a helical magnetocumulative generator with the current pulse $I_{\max } \approx 4.2$ MA and effective rise time $\tau \approx 400$ ns. Validation of X-ray spectral measurements carried out with scintillation detector filters pointed out a necessity to take into consideration both the scintillator “dead” layer and oxide films on the aluminum filter surface. [ABSTRACT FROM AUTHOR]

The Marx circuit structure based on fast high-power semiconductor devices is the classical way of generating picosecond pulses. However, most reported studies suggest that as the number of stages in the Marx circuit increases, the output pulse amplitude tends to saturate. This has of late made high-voltage picosecond-pulse generation a challenge. In this paper, as the number of stages increases, the internal resistance of the avalanche transistor tends to decrease with increasing current flowing through the avalanche transistor. A step-by-step wiring and debugging of the avalanche transistor-based Marx circuit demonstrates this experimentally. That is, for a certain range in the number of stages, saturation of the output pulse amplitude for the Marx circuit of avalanche transistors is not apparent. Introducing a parallel structure for the transistors not only increases the current level of the entire circuit but also further reduces the equivalent resistance of the avalanche transistors, thereby improving the output efficiency. Drawing on microstrip transmission theory, and combining the Marx circuit and avalanche transistor parallel structure, component parameters and circuit topology of the picosecond-pulse generator were redesigned, and a 30-level Marx circuit with a parallel structure of two avalanche transistors was developed. The picosecond-pulse generator outputs a pulse with adjustable voltage amplitude of 0.9–3.1 kV, a 350-ps full-width at half-maximum, a 150-ps rise time, and an adjustable high-stability repetition rate of up to 10 kHz. The number of pulses is precisely controlled. The generator is an all-solid-state compact device with high frequency suitable for research needs. [ABSTRACT FROM AUTHOR]

This paper puts forward a repetitive high-voltage pulse modulator, consisting of a step-up pulse transformer to decrease the number of needed semiconductor switches, and a bipolar Marx generator to reduce the turns ratio of PT, leakage inductance, and distributed capacitance, and also to improve the pulse shape. An equivalent circuit of the proposed modulator considering parasitic elements is established. Based on the equivalent circuit, circuit operation is analyzed in detail. In order to verify the theory analysis and circuit operation, simulations are conducted. In addition, a laboratory prototype is implemented. The simulations and experimental results of resistive load and dielectric-barrier discharges load turn out matched quite well with the theory analysis, demonstrating that the prototype can operate with a voltage amplitude in the range of 0–25 kV, a repetition rate of 0.1–5-kHz stably. [ABSTRACT FROM AUTHOR]

Repetitive high-voltage square pulses are of great importance for producing long-pulse electron beams and high-power microwaves. One of possible technologies for the generation of such pulses is a Marx generator using pulse forming network (PFN) stages, often combined with a pulse sharpening technique to reduce the rise time to a few nanoseconds (peaking stage). This paper presents an innovative design, named the “zigzag design,” for the optimization of the compactness and of the rise time of 400-kV–85-ns PFN-Marx. Thanks to this design, the 16 stages of this generator, which delivers an open circuit output voltage of 720 kV, fit in a 650-mm length. For a slightly overmatched load ($Z_{\mathrm {load}} = 100 ~\Omega$), the output voltage reaches 400 kV with a rise time as less as 5 ns. The inductance reduction associated with the innovative zigzag design, which allows this sharp rise time with no need for a peaking stage, is described. The 85-ns plateau duration of the pulse is given by the PFN construction of each stage, which is based on six ceramic capacitors (2.1 nF–45 kV) connected within a strip line. The 16 PFN stages are housed in a 360-mm diameter gas pressurized vessel. Burst mode operation for a duration of 10 s at a pulse repetition frequency of 100 Hz is reported, for a resistive load and for the electron beam diode of a X-band relativistic backward-wave oscillator (BWO). To reach further compactness, the BWO system is integrated on side of the generator vessel and a U-shaped gas pressurized line connects both systems through a compact conical vacuum insulator. [ABSTRACT FROM AUTHOR]

At Wuhan National High Magnetic Field Center, a 100-MVA/100-MJ pulsed generator and two 67.5-MW converter modules have been installed as power supply for pulsed magnets. Long-pulsed magnetic field with 50-T/100-ms flat-top has been produced and 100-T pulse magnetic field is under commissioning by utilizing this pulsed generator converter. In this high-power occasion, the three-phase voltages undergo serious harmonics, large notches, amplitude variation, rapid frequency fluctuation, and phase jump simultaneously. Synchronization method with fast dynamics, excellent harmonics rejection, and smooth time-domain response is expected, which is difficult for the conventional synchronous reference frame phase-locked loop (SRF-PLL). Therefore, this paper presents a new synchronization method based on compensation of phase deviation. In this method, the phase of three-phase voltages, which is achieved by summing filtered phase deviation and phase of a given $d$ - $q$ rotating reference frame, is open-loop computed directly. The main attributes of the method are the fact that its dynamics is independent of the input vector amplitude, better harmonics rejection/dynamics tradeoff, and smooth time-domain response. Comparative experiments are performed between the proposed synchronization method and SRF-PLL. [ABSTRACT FROM AUTHOR]

This paper describes the design strategy for a new Marx generator, based on SiC metal–oxide–semiconductor field-effect transistors (MOSFETs), proposed for Kicker magnet applications. As a starting point, the possible replacement of a thyratron tube associated with an existing kicker system, at CERN, is considered. The specifications of the output pulse are: 40-kV, 3.2-kA, 3- $\mu \text{s}$ flat top duration, 30-ns rise- and fall-time, and 1-Hz repetition rate. A theoretical study for a Marx generator topology, using 50 stages, each 800-V stage comprising 24 SiC MOSFETs in parallel, each MOSFET conducting approximately 140-A pulses is considered. In addition, a four-stage prototype has been evaluated, with almost full current and 3 kV, based on the proposed design, in order to assess the technological advantages of such a system and limitations for the scale up. First tests using parallel SiC MOSFETs are described and results discussed in light of the proposed topology and the physical structure of the assembly. [ABSTRACT FROM AUTHOR]

Explosive-driven magnetic flux generator is one of the most efficient techniques for producing ultrahigh magnetic fields in a relatively large volume. To create a more reliable system suitable for extreme magnetic fields applications, a compact explosive-driven magnetic flux compression system with a small amount of explosive for generating multimegagauss fields was developed. In this paper, the design for reproducibly generating megagauss fields, and the experimental results of this generator are presented in detail. The experimental results show that peak fields in the range of 580–710 T can be reliably generated by the generator with about 3-kg Comp-B explosive. [ABSTRACT FROM AUTHOR]

High-voltage, nanosecond, high-repetitive-frequency, and portable pulse generators are always required in many fields. Avalanche transistor-based Marx circuits have been widely studied to generate pulses satisfying the above requirements. However, the basic topology of an avalanche transistor-based circuit, configuration of circuit parameters, and optimal working performance (including output impedance matching) were still scarcely discussed. In this paper, the detailed process of analyzing and designing a compact Marx generator using avalanche transistors was described. Based on the conventional principles of avalanche transistors and Marx circuit, a list of useful and interesting conclusions was discovered by experiment. An example with specific parameter requirements was utilized for the clearness of illustration. The 12~cm\times 4 cm Marx circuit could finally generate pulses with a 2.5-kV amplitude, 6.0-ns width, 10-kHz repetitive frequency, lower than a 100-ps jitter and $\sim 125$ -kW maximum peak output power on a matched 50- $\Omega $ resistive load. The pulse amplitude could be adjusted from 1.5 to 2.5 kV and the pulse width could also be broadened. This paper may help to provide a reference to similar methods of producing high-voltage, nanosecond, and high-repetitive-frequency pulses. [ABSTRACT FROM PUBLISHER]

As the energy level in the projectile increases, it becomes necessary to use multiple pulsed alternators discharging in parallel into the electromagnetic launcher. Another reason for having more than one machine is that one needs to compensate for the torque and gyroscopic effects of the pulsed alternator. This requires that machines be built in counter-rotating pairs. These machines are identical in all respects except for their direction of rotation. A study was conducted to determine how the machines can be motored so that they stay in lock step in speed and phase as they are motored to full speed. The methods of connecting these multiple machines are discussed. The aim of the connection scheme is to allow the machines to naturally stay locked in speed and phase throughout its operating range. Sensitivity of the performance of these machines to small variations in the machine parameters, which is to be expected in the machines, is discussed. Sensitivity of the discharge performance to small phase angle mismatches due to tolerances is also discussed. To verify the conclusions of the paper, an experiment was performed on two identical 50-kVA machines discharging into a low impedance load. The motoring system that is discussed in this paper was implemented in this experiment, which kept the machines in lock step. This motoring system is described. Thereafter, discharges were made at various speeds and field current levels. Phase angle mismatches were introduced between the two machines to see how it affected current sharing. The results and conclusions of these tests are presented in this paper. [ABSTRACT FROM PUBLISHER]

Matching devices in the form of electro-exploded current opening switches (EEOSs) or explosive current opening switches (EOSs) are used for transforming current pulses of magnetocumulative generators (MCGs) into voltage pulses of hundreds of kilovolts at high-impedance loads. Current pulse sharpening is accompanied by significant losses of the stored energy. Using EOSs are more preferable to EEOSs from the point of view of the energy losses since it does not lead to efficiency decrease in the MCG operation. This paper considers magnetocumulative multimodule systems consisting of several synchronously operating and serially connected small helical MCGs. Each generator is equipped with an explosive current opening switch. The voltages generated at each opening switch are summarized into the load. Fast operation of MCGs allows using very thin foils in the opening switches and obtaining the short voltage pulse front. Results of the works on creating high-voltage devices based on helical MCGs of a 60-mm diameter and disk EOSs of a 200-mm diameter are presented in this paper. In the experiment, the device consisting of two modules provides a voltage pulse of 370 kV with a rise time of $\sim 170$ ns into a load of 29 $\Omega $ and an inductance of 0.5 $\mu $ H. Maximum power in the load is $\sim 4.3$ GW, and the emitted energy is $\sim 1.1$ kJ. The four-module device forms the pulse with the characteristic current rise time of $\sim 100$ ns in the similar load at twice smaller current. [ABSTRACT FROM PUBLISHER]

Nowadays, disk magnetocumulative generators (DMCGs) are the most powerful and power-consuming magneto-cumulative generators (MCGs). The problem of necessary initial energy supply to the generator circuit is very urgent at creating high-performance disk generators. Preliminary energy amplification in experiments with DMCG is provided with helical MCGs. Along with preset energy supply, the preamplifier should have small characteristic current rise time. It is necessary for decreasing thermal and mechanical supply current effect on elements of the disk generator. This means increasing the output power of the preamplifier and associated with obtaining maximum possible initial energy in the DMCG. Initial inductance and resistance of the DMCG circuit became higher with an increase of the DMCG sizes and the number of its elements. This required increasing the power of earlier used preamplifiers. This paper presents experimental results of the MCG-240 characteristics improvement at the expense of turns distribution change and application of more powerful explosive. Other possibilities of the preamplifier power increase are considered in this paper. [ABSTRACT FROM PUBLISHER]

This paper develops a novel symmetric dielectric barrier discharge (DBD) plasma as an ion source for environmental mass spectrometry (MS) applications. The conventional linear-type DBD plasma generator suffers the drawback of floating voltage at the plasma outlet. This paper develops an innovative symmetric T-shaped DBD plasma generator to produce atmospheric plasma with zero-floating potential for high-sensitivity MS analysis. By changing the geometric configuration and the drive phase of the symmetric T-shaped DBD plasma generator, the resulting symmetric structural design can fully cancel the floating potential and noise signal. Therefore, the main objective of this paper is to compare the differences between traditional linear-type DBD and the symmetric T-shaped DBD designs using MS, spectroscopy, and some basic electrical measurements. The most suitable parameters are determined by changing the electrode design, voltage, temperature, gas flow rate, diameter, and other parameters of the plasma tube. The symmetric T-shaped design generator produces the zero-potential plasma that generates fewer ambient gas molecules to form ozone, NOx, water clusters, and other strong oxidizing molecules such that less damage to the MS samples occurs. This in turn results in a less fragmented ion signal and higher sensing performance for rapid MS applications. In addition, the proposed system can directly ionize gas, liquid, and solid samples at more than 10^7 -cm ^-3 ion concentration. Results show that more information-rich spectra can be obtained with the developed symmetric T-shaped DBD plasma generator compared with the typical linear-type DBD generator. [ABSTRACT FROM PUBLISHER]