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This paper presents a novel approach to test surface material charging under electron flux representative of space conditions below 400 keV. The experimental protocol used to test space material electrical properties consists in adapting the electron flux distribution to mimic worst case spectra met in space. Input environments are taken from Kp > 5 specifications at geosynchronous orbit (GEO) and from the analysis of both RBSP and LANL spacecraft data at middle Earth orbit (MEO) and GEO. Experimental results using GEO specifications show that the surface potential strongly depends on the energetic particle flux. Above a given > 100-keV electron flux, the radiation-induced conductivity tends to govern the charging dynamics. A numerical analysis based on the environments selected in this paper shows that charging levels could be larger at MEO than at GEO. [ABSTRACT FROM AUTHOR]

The interest in the use of atmospheric-pressure plasma jets (APPJs) is constantly growing. APPJs offer various ranges for applications, such as wound healing, cancer treatment, and dental care. The complex plasma chemistry plays an important role in each of these fields but is often poorly understood. In this paper, the production of atomic oxygen in a radio frequency helium–oxygen plasma is investigated by means of a numerical simulation. A 1-D discharge of an atmospheric-pressure plasma jet is created with the plasma module of COMSOL Multiphysics, using a set of 25 reactions. Many 1-D simulations usually cannot estimate the power deposition in a correct way because of suspected arising losses, such as radiation and inefficiencies of the external circuit. In order to match the experimental power deposition of 13 W, high voltages (855 V) are required in the model. Such high voltages cause changes in the plasma characteristics like a switch in the glow mode. The impact of the voltage on the plasma is investigated by the comparison of a low-voltage (325 V) simulation, which matches the experimental oxygen production, and a high-voltage (855 V) simulation, which matches the experimental power deposition. Outcomes of this paper further support the idea that the power deposition measured in experiments is higher than the actual power deposition coupled to the plasma. [ABSTRACT FROM AUTHOR]

The planned China fusion engineering test reactor (CFETR) needs one or more negative-ion-based neutral beam injectors (N-NBIs) with a beam energy of 500 or even 1000 keV. In order to prepare for CFETR, a prototype of CFETR N-NBI is being designed. The prototype needs an acceleration grid power supply (AGPS) rated at 200 kV/25 A with a maximum pulselength reaches to 3600 s. The AGPS adopted a single-stage inverter-type high-voltage power supply (HVPS). The output voltage ripple is an important specification of the AGPS, which can affect the efficiency and stability of N-NBI system by influencing the beam divergence. However, the conventional methods cannot be used to limit the output voltage ripple of the inverter-type HVPS used as AGPS of CFETR N-NBI prototype. This paper simplified the AGPS to an insulated three-phase three-level (TPTL) dc–dc converter connected with a dual dc link. The working process of the TPTL dc–dc converter with duty-cycle modulation has been analyzed, and two main continuous conduction modes are described. The influence of key parameters such as duty cycle of inverter, leakage inductance of transformer, and output current on output voltage ripple is analyzed. Based on the analysis results, a so-called combined control strategy was proposed to keep the output voltage ripple at a level. The proposed strategy is suitable for the cases where the object output voltage is below 175 kV. Some simulations were carried out by using MATLAB/Simulink. The results showed that the analysis in this paper is reliable and the proposed control strategy has a good performance. [ABSTRACT FROM AUTHOR]

We have studied the two-electron pseudodot (TEPD) system immersed in plasma environments under the influence of a monochromatic linearly polarized laser field. The four different sets, constituted by the potential parameters, of the more general exponential cosine screened Coulomb potential are used to characterize the Debye and quantum plasma environments. The time dependent in the Schrödinger equation arising from the laser field is interchanged to the potential energy term from the kinetic energy term through the dipole approximation and the Kramers–Henneberger transformation. Then, the laser-dressed potential that denotes the effects of the laser radiation field is constituted by using the Ehlotzky approximation. In that case, as the analytical solution is impossible just now due to the complicated form of the Schrödinger equation, the numerical solution is carried out via the asymptotic iteration method. In this paper, the pseudodot system is considered because the quantum dots are very similar to atomic systems, and the pseudoharmonic potential is successful in explaining the atomistic structures. However, it is an important motivation for us that, as well as the importance of the laser–plasma interactions, the laser field is a considerable exciter for radiating, which exhibits remarkable confinement effects. Since, as well as the screening effects exhibited by plasmas on atomic systems, and their significant results, the plasma is a significant experimental argument in manufacturing and modification of the quantum dots, the plasma effects are taken into consideration in this paper. Within these motivations, all parameters that operate on the energies of TEPD system with the laser effect in plasmas are analyzed in detail, and the corresponding results are discussed thoroughly. [ABSTRACT FROM AUTHOR]

This paper embodies the results of experimental studies of a dielectric barrier discharge low-temperature nonequilibrium plasma reactor that runs in air and nitrogen at atmospheric-pressure conceived for surface treatment applications. A homemade reactor, of typical plane-to-plane geometry with the dielectric covering the upper electrode which is stressed by a high voltage (40 kV, 3–20 kHz) is used. Electrical signals (current and voltage), optical emission spectroscopy records, and total light emission measured by photomultiplier have been analyzed and used to distinguish different plasma regimes which are studied for the treatment of a lignocellulosic material (sugarcane bagasse). In the filamentary discharge regime, the gas temperature of few tens of degree Celsius above the ambient one was determined, the electronic temperature of some electronvolts and electron density in the range of 1012–1013 cm−3 were estimated. Plasma treated pellets of sugarcane bagasse were analyzed by diffuse reflectance infrared Fourier transform spectrometry and the relative results obtained under filamentary discharge regime have shown significant degradation of the lignin macromolecule. It has been shown important modifications on the lignocellulosic material, namely, the plasma attacks drastically the lignin bonds. Strong modification of lignin was observed near wavenumber of 3400 cm−1, due to stretching vibrations of OH, and for the band 1114 cm−1 which is related to C=C and C=O stretching. Severe decrease of the band intensity 1596 cm−1, which due to C=C stretching and C=O, is also a result of the treatments done in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a new configuration of dielectric-barrier discharge (DBD) reactor with three electrodes was manufactured and used to produce ozone. Designed flatly, this reactor is capable of establishing three different discharge modes from type of the volume and surface discharges, without modifying its internal structure. The aim of presenting this paper is to experimentally analyze the three discharge modes and their combination using a second channel to produce ozone. The two reactor channels are identical in terms of dimensions, material, and manufacturing process. Two frequency-adjustable pulse generators of the same electrical characteristics and two high-voltage transformers were used in the course of the experiments. The applied sinusoidal voltage is from 0 to 12 kVp-p. The frequency range was determined and fixed for all three discharge modes for the highest ozone concentration at a fluctuation rate of 1 L/min. Effects of increasing the applied voltage on the obtained concentration from the three different discharge modes were experimentally analyzed. Using the provided inlets–outlets, the effect of flowing gas through the length and width of the discharge area on ozone concentration was investigated, and appropriate flow directions were determined for the flowing gas under either of the three discharge modes. Experimentally results have been done for this three discharge modes as well as hybrid modes. The maximum ozone production rate achieved up to 14.52 g/h in the series combination of two different volume discharge. At 96% oxygen purity, ozone production yield, in two modes volume discharge VaDBD and surface discharge SDBD, have been improved up to 529.87 g/kWh. However, the total input power of the entire system is 120.2 W. [ABSTRACT FROM AUTHOR]

The collision frequencies between electrons and air molecules are important parameters when analyzing electrical breakdown. Different values for the collision frequency in atmospheric air have been reported in academic literature; the current analysis method for breakdown in waveguides and filters considers an electric field-independent term. However, some authors have remarked the importance of an electric field dependence of the collision frequency. In this paper, the collision frequency of electrons, accelerated by the presence of an electric field, against air molecules is obtained. The collision frequency is calculated from experimental data, for breakdown voltages at dc in positive polarity in a wide atmospheric pressure range using a plane–plane plates configuration. As waveguide filters are currently designed with a 3-dB tolerance below the electrical breakdown thresholds, this paper analyses the current methods for these breakdown threshold calculations, and proposes a novel correction factor for the collision frequency in order to approximate the analytic calculations to experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the capacitances of the two-stage bushing that is installed in the 1-MV test bed for neutral beam injectors in the future fusion reactors are calculated by modeling the bushing in a 3-D electrostatic code. One of the modeling results is the stored energy in the bushing, which corresponds to 1/2 CV2. After evaluating the bushing capacitance, a MATLAB/Simulink model is presented to model the possible breakdown in the bushing and between the electrodes in the 1-MV test bed. When a breakdown occurs between anode and cathode, an overcurrent is drawing that can cause damage in the electrode surfaces while an overvoltage takes place when the breakdown happens between the bushing stages. Such damage has been observed experimentally in the past. This paper also presents some of the possible protection against the breakdown in the 1-MV test bed to dissipate the stored energy in order to protect the electrode surfaces and the bushing. The suggested protections presented in this paper are damping resistors, surge arrester individually, and both of them. Also, a coil can be added to the DR either in series or in parallel. [ABSTRACT FROM AUTHOR]

In this paper, a complete flux scheme (CFS) has been implemented in 1-D fluid model for simulating the pulsed dielectric barrier discharge (DBD) in pure argon at atmospheric pressure. The characteristic quantities of the pulsed DBD have been systematically calculated by using the CFS and presented in comparison with those by using the exponential difference scheme (EDS). This paper shows the following results. There is the two-pulse discharge mode in the present simulation. The two discharge currents obtained using the CFS and EDS converge to the same result in good agreement with the experiment as spatial step length decreases, but the CFS has a fast convergence performance compared to the EDS. With a small grid number, the numerical scheme has an evident effect on the characteristic quantities in the time region corresponding to the first discharge pulse. This paper suggests that in the pulsed DBD, the usage of the CFS with a properly small grid number can give more accurate result and also presents a high calculation efficiency. [ABSTRACT FROM AUTHOR]

Photoelectric characteristics are an important reference for high-voltage discharges and are closely related to the excited mode of the high-voltage source. In this paper, we built a large-scale volume dielectric barrier discharge (DBD) system, which is composed of multilayer parallel-plate DBD electrodes and is excited by a high-voltage source in the power density modulation (PDM) mode. Subsequently, we analyzed the applied energy equation and evaluated the DBD systems photoelectric characteristics. The results show that the energy values of different applied voltage cycles during a PDM period exhibit significant differences. However, the average energy in a PDM period is approximately constant. Moreover, the equivalent capacitance of the DBD cell is a function of both the applied voltage and energy density. For the DBD cell, with the increase in both the applied voltage and energy loaded on the DBD cell, the total equivalent capacitance ($C$) is approximately constant, the dielectric capacitance ($C_{\mathrm{ d}}$) increases exponentially and decreases linearly, while the discharge gap capacitance ($C_{\mathrm{ g}}$) decreases and increases in the same cases. In addition, the relative intensities of the discharge emission increase and the energy efficiency ratios of the relative photoquantum yield of active species decline with the increase in both the applied voltage and energy density loaded on the DBD cell. The experimental results have been analyzed by evaluating the influence of the electrical parameters, and the underlying physical principles have been discussed. This paper clearly demonstrates that the photoelectric characteristics of the DBD reactor are significantly influenced by both the applied voltage and energy density, thus providing helpful insights into the energy evaluation and application of high-voltage discharges. [ABSTRACT FROM AUTHOR]

The past measurements of the plasma density and potential profiles near the exit of the keeper electrode in a hollow cathode device suggested that turbulent ion acoustic fluctuations and ionization instability in the cathode plume significantly increased the energy of the ions that flow from this region. The lifetime of keeper electrode is limited by sputtering or ion bombardment of the Molybdenum surface exposed to the discharge plasma. Increases in the cathode gas flow reduce the amplitude of the fluctuations and the number and energy of the energetic ions, which decreases the erosion rate of the keeper electrodes. However, as the cathode gas flow is raised for a given discharge current, the performance of a 5-kW Annular-Geometry Ion Engine (AGI-Engine) declines. There is a strong relationship between the performance and the lifetime of the ion thruster. To validate whether the 20-A hollow cathode satisfied China’s communication satellite platform’s application requirement for North-South station keeping, this paper analyzed the effect of the cathode gas flow on the performance and the lifetime of the AGI-Engine. Different from the previous methods, this paper first tracked the movement of energetic ions generated in the plume of the hollow cathode, predicted erosion rates, found where they hit the keeper electrode, and then determined the amount of material that they sputtered. A review of past experimental results was presented first. Next, based on the existing experimental data, theoretical analysis and numerical calculations were performed to determine the optimum gas flow range and the performance curve of the 20-A hollow cathode. The results showed that the primary erosion mechanism of the keeper electrode was caused by impact from Charge Exchange Xenon (CEX) ions, which caused the cathode orifice to be widened and attenuated over time. However, heavy double xenon ($\text{X}_{\text{e}}^{++}$) ions, which struck the keeper electrode more severely than CEX ions, were the most crucial factor that limited the lifetime of the 20-A hollow cathode due to their high energy and large mass. [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 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]

This paper discusses the control of a modular multilevel converter (MMC) used as a grid interface for the klystron modulators in the compact linear collider (CLIC). The converter has a DC side load which takes short-duration power pulses, causing high DC side power fluctuations that are not tolerable if seen by the AC grid. The DC–AC power decoupling capability of the MMC enables mitigation of the power ripple on the AC side, guaranteeing compliance with power quality requirements. However, the pulse repetition rate of the CLIC modulators is synchronized the 50-Hz AC grid and this induces permanent power imbalance in the arms of the MMC, causing voltage deviation and overmodulation unless appropriate balancing strategies are implemented. Unlike existing arm balancing methods that control 50-Hz circulating currents to balance the arm powers, the method proposed in this paper introduces an augmented modulation strategy where modulation signals are redistributed among arms based on the demand from a balancing controller. The resulting controller has lower complexity and its simple structure enables an easier design of the balancing loop, which guarantees predictable dynamics in operation. The effectiveness of the method has been demonstrated in simulation for the full-scale CLIC converter ratings and experimentally on a 7-kW MMC prototype operating with a 3.3-kA pulsed DC load. [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]

Melamine formaldehyde microspheres are widely used in dusty plasma experiments for their monodispersity, sphericity, low mass density, and well defined sizes. This paper summarizes problems that were encountered in numerous applications of these grains in different laboratory simulations. and the already published results are discussed in view of new experiments. The main results of this paper are connected with changes of the grain mass due to the decreased pressure and/or increased temperature and variations of the grain dimensions, its shape, and mass density under electron or ion bombardments. By contrast to the work function estimated from field emission properties, we have found the photoelectric work function (4.5 eV) being close to that expected. A sputtering of the grains using a 30-keV ion beam revealed their unexpected heterogeneity. [ABSTRACT FROM AUTHOR]

One of the most important features of atmospheric-pressure nonequilibrium plasmas (APNPs) is its capability of generating high concentration of reactive species while keeping low gas temperature. To generate such plasma, alternative current (ac) voltage and pulsed dc voltage have been used separately. In this paper, the combination of ac voltage and pulsed dc voltage is used to generate APNPs for the first time. The plasma characteristics, including the power deposited to the plasma, the gas temperature, the emission spectra, and the O atom concentration of the plasma for different phase shifts of the two power supplies, are investigated. It is found that when the pulsed dc voltage is added on the negative ac half period at the phase shift of about 90°, the average power deposited to the plasma, the gas temperature, and the optical emission spectrum of O atom all reach their maxima. On the other hand, the ground state O atom concentration has two peaks; one of the peaks also appears when the phase shift is about 90°. When the pulsed dc voltage is applied on the positive half period at the phase shift of 270°, the O concentration reaches another peak and the peak value is higher than that when the ac or the pulsed dc power supply works alone. Furthermore, at the phase shift of 270°, the gas temperature of the plasma and the total power deposited to the plasma are all lower than the case when the ac or the pulsed dc power supply works independently. Thus, it is more energy efficient to adjust the phase shift to 270° for applications such as plasma medicine where the gas temperature of the plasma at or close to room temperature is strictly required. [ABSTRACT FROM AUTHOR]

High power pseudospark switches (PSSs) can control pulsed high voltage, high peak current discharges. In this paper, a PSS in series with a saturable inductor at the anode is investigated. The commutation process is analyzed with a time-resolved method. And the effects of the number of magnetic cores and anode voltages on discharge characteristics are studied experimentally. At the beginning of commutation process, when the anode voltage is 10.4 kV with four magnetic cores, the inductor is unsaturated, and there is a flat plateau of the forward voltage drop after the anode voltage drops rapidly to about 200 V, at the same time the current rise rate is 2.8 kA/ $\mu \text{s}$. When the inductor is saturated, there is a voltage spike that occurs at the end of the flat plateau, and the current simultaneously rises rapidly at the rate of 6.4 kA/ $\mu \text{s}$. The current sharp rise lags behind the voltage drop of the pseudospark gap, and the electrode erosion and energy dissipation reduce significantly. When the anode voltage is 15.6 kV, the commutation losses reduce by about 30% with seven cores in series at the anode. As a result, it is evident that the discharge process will speed up if the anode voltage is higher. And the trigger delay decreases by up to 8% when the anode voltage varies from 5.2 to 15.6 kV. Finally, in order to obtain a reproducible pseudospark discharge by the use of a saturable inductor, the number of magnetic cores has to be optimized for different anode voltages. [ABSTRACT FROM AUTHOR]

Amorphous magnetic core has been widely used in pulsed power technology with applications including plasma science research, high-power microwave generation, and material surface treatment. For different applications, dynamic properties of the magnetic core will vary with stimulated magnetic field which determines by magnetization time and waveform of the driving voltage. In this paper, toroidal amorphous magnetic core ($\Phi ~540$ – $740\times25$ mm) was investigated theoretically, numerically, and experimentally. Specifically, the circuit is analyzed. A high-voltage test stand, which can generate different driving voltages with same components, was designed and developed in our laboratory. Dynamic properties, including magnetic induction change, coercive force and losses, were studied under three different typical waveforms with the same magnetic flux. Driving voltages of the pulses were 12, 12, and 6 kV and the magnetization rates were 0.6, 1.2, and 0.6 T/ $\mu \text{s}$ , respectively. Experimental results show reasonable agreement with the numerical analysis. [ABSTRACT FROM AUTHOR]

Studies have been taken into the breakdown voltage jitter of corona-stabilized switch at high repetition rate up to several kHz. It is thought that the gas recovery affect the jitter of breakdown voltage directly at high repetition rate, because the gas switch will breakdown at a low voltage if the gas cannot fully recover. The breakdown voltage jitter is called voltage jitter in the following paper. However, based on the experimental results, the voltage jitter still exists at low repetition rate, even at single-shot mode. This is not explained by the previous studies. In this paper, voltage jitter below 100 Hz of a corona-stabilized switch is investigated experimentally. A corona-stabilized switch is introduced, using a cylindrical electrode as the cathode and a plane electrode as the anode. The gas used between the electrodes is SF6. A negative pulse with a maximum width of 30~\mu \texts is used to charge this switch. The tested factors include gas pressure, gap space, repetition rate, and switch geometry. Experimental results show that voltage jitter is mainly affected by the gas pressure and switch geometry. It is seen that voltage jitter decreases as gas pressure increases and a suitable cathode geometry presents a low voltage jitter. Critical volume is a region close to the highly stressed electrode, where the presence of an electron will lead to an electron avalanche which attains a critical size and hence leads to a stabilizing corona. Critical volume is introduced to explain the experimental results. It is found that less voltage jitter can be achieved with a smaller and more concentrated critical volume, as well as efficient corona stabilization. The results indicate that voltage jitter may be reduced by optimize the critical volume at low repetition rate. [ABSTRACT FROM PUBLISHER]

Because it possesses higher current turn-off capability, the inverse current commutation with semiconductor devices (ICCOS) is a better option for the opening switch of an inductive pulsed power supply than the integrated gate commutated thyristor. This paper investigates the counter-current capacitor, which is the key component that determines the turn-off result and the volume of the counter-current branch. The major contributions of this paper include the following: 1) deriving an analytical expression for the minimum precharged capacitor voltage that can reliably turn off the main switch; 2) verifying this expression through a series of experiments within a current range of 0 to 4000 A and an energy range of 0 to 50 kJ; 3) giving an approximate expression for the optimal capacitance that minimizes the precharged energy; and 4) investigating the variation trends of the optimal capacitance and the corresponding optimal precharged energy with varying inductor current. [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]

This paper proposes an active resonance circuit based on multiple series gaps (MSG) with voltage-dividing network and self-charging trigger device. The working principle of active resonance circuit, MSG, and triggering device is described in detail. To determine the optimal parameter setting of MSG, the effects of the voltage frequency, equalizing resistance, and voltage-dividing capacitance on the voltage distribution of MSG are analyzed by simulation. To realize the interrupting process of short fault current and determine the operation requirements of the main devices of precharge direct current (dc) circuit breaker, a simulation model of interrupting short fault current is performed. Furthermore, an experiment of four-series gaps is presented to verify the turn-on characteristic of the MSG and an experiment of artificial current zero is set up to testify the feasibility of the active resonance circuit. The simulation and experimental results show that the active resonance circuit proposed in this paper can generate an artificial zero current and is suitable for precharge dc circuit breaker. [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]

The effective control of magnetohydrodynamic instabilities in fusion experiments by means of actively controlled coils calls for challenging dynamic requirements to the relevant power supply (PS) systems. The first part of this paper gives an overview on typical requirements and technological solutions adopted in some present fusion experiments. Then, the advantages of SiC devices with respect to the Si ones are described in this paper, including lower switching losses, higher switching speed, higher operating junction temperature, and higher voltage capability. As an application example, this paper reports on the case of the PS system for resistive wall mode control in the JT-60SA satellite tokamak, where analyses showed the difficulty of satisfying the demanding requirements in terms of high current bandwidth (3 kHz) and short latency ( <50~\mu \texts ) with a simple H-bridge topology adopting standard IGBT. On the contrary, the use of Si–SiC IGBT with the same topology can allow meeting the specifications, as demonstrated by the development and test of such a power amplifier, rated for $300~A_{{\mathrm{pk}}}$ and 240 V. [ABSTRACT FROM AUTHOR]

Linear and nonlinear properties of obliquely propagating waves are studied in a degenerate dense cold magnetoplasma, comprising of Thomas–Fermi distributed electrons and ions as well as non-degenerate negatively charged dust particulates. By using the plane wave approximation, a linear dispersion relation for the dust-cyclotron (DC) and dust-acoustic (DA) waves is derived and analyzed numerically. For fully nonlinear waves, a Sagdeev pseudopotential theory is employed to derive an energy-balance equation and the soliton existence domain depending upon the dust concentration $(h)$ , obliqueness $(L_{z})$ , and Mach number $(M)$. Numerical analysis reveals that the parameter $h$ enhances the domain for allowed Mach numbers, i.e., $M_{1} < M < M_{2}$ and therefore favoring the solitary excitations, where $M_{1}$ and $M_{2}$ are the lower and upper Mach numbers, respectively. In addition, the dust concentration significantly reduces the amplitude and the profile sharpness of the solitary pulses. Similarly, variations in the obliqueness parameter and the Mach numbers modify the wave characteristics. This paper is important for understanding the nonlinear properties of electrostatic excitations in degenerate dusty magnetoplasma, relevant to white dwarfs (WDs), namely $GD56,\,\,GD29-38,\,\,GD362$ , and $WD2115-560$ , being termed as the DUSTY DAZ WDs. [ABSTRACT FROM AUTHOR]

The front plates and embedded particle sensor shells that are part of the electric field instrument (EFI) on the Swarm satellites have recently been used as planar Langmuir probes, as an additional diagnostic tool to infer environment parameters. The interpretation of measured currents in terms of the plasma density or incoming flow speed, however, requires a knowledge of the front plate effective cross section $A_{\textrm {eff}}$. Measurements made under various space plasma conditions have led to the conclusion that this cross section is generally larger than the known geometrical cross section $A_{\textrm {geo}}$. Interpretations of measurements have thus been made using fixed relative enhancements of $A_{\textrm {geo}}$ ranging from 8% to 17%. In this paper, results from kinetic simulations are presented, from which the effective cross section can be determined over a range of plasma parameters. These are used to shed light on the physical mechanisms responsible for this enhancement and construct an empirical fit to the relative enhancement $\delta $ , where $A_{\textrm {eff}} = A_{\textrm {geo}}(1 + \delta)$ , and, in turn, enable improvements in the accuracy of inferred plasma parameters. [ABSTRACT FROM AUTHOR]

Measuring the charge on a nearby space object during close proximity, servicing, and rendezvous and docking operations without requiring physical touch remains challenging despite decades worth of data on spacecraft charging and its risks. This paper proposes the means to identify the charge on a closely neighboring space object and its elemental composition by examining the X-ray spectrum generated by energetic electrons impacting the target. In particular, deconvolution of the bremsstrahlung X-ray continuum provides an estimate of the landing energy of the electrons. Knowing the initial electron energy, the potential difference between the source and the target is determined. Additionally, characteristic X-rays emitted during the process of energetic electron–matter impact allows the relative abundance of elements in the target to be determined. Spatial separations in the order of tens of meters are required between an electron gun and the corresponding detector to maximize the collection of the bremsstrahlung spectrum. This could be achieved with either the single-craft and deployable booms or through the use of two spacecraft. Electron beam energies of 40 kV are found to generate sufficient levels of X-rays for potential determination at over 10 m from the target and to determine the landing energy of the beam to within 0.14% using commercial X-ray detectors. [ABSTRACT FROM AUTHOR]

Low-density polyethylene (LDPE) is a nonpolar polymer commonly used as an insulating material. Although its applications in the spacecraft industry are limited, LDPE is widely utilized as a model system to study electron transport through disordered insulating materials under simulated space weather conditions. The charge transport models developed using this system may then be extended to more commonly used spacecraft materials such as polyimides. Several proposed charge transport models share high complexity and many free fitting parameters. For better estimation of initial values of these free parameters, the correlation between charge transport and its chemical origins should be made. Whenever possible, experimental measurements should be used as initial values for each of the free fitting parameters to improve model accuracy. In this paper, we studied alterations of the chemical properties of LDPE after irradiation by high-energy (100 keV) electrons using Fourier transform infrared spectroscopy (FTIR) and bulk conductivity measurements. Moreover, we utilized a quadrupole mass spectrometer (QMS) to identify the ablated species released from the solid during irradiation. These measurements offer insight into the structural and chemical damages of the material. Results of the performed analysis are correlated with the underlying chemical changes that occur in LDPE during irradiation. [ABSTRACT FROM AUTHOR]

Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current–voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge. [ABSTRACT FROM AUTHOR]

Modeling the dynamics of charged dust particles, confined in a glass box placed on the lower electrode of a Gaseous Electronics Conference cell, requires that the interactions between the charged dust, plasma, and boundaries need to be accounted for in a self-consistent manner. The charged lower electrode affects the plasma conditions throughout the glass box, altering the electron and ion densities and temperatures within the plasma sheath. These plasma characteristics determine the charge collected on the walls of the surrounding glass box, the electric potential within the glass box, the dust charge, and ultimately the dynamics of the dust. This paper describes the steps taken to build a simple model of the relationship between the plasma conditions and the potential within the box as well as the expected dust charge near the center of the box. The calculated potential and dust charge are used to construct acceleration maps for the dust, which are compared to experimentally measured acceleration of the dust within the box. [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]

The multigap gas switch has been widely used in liner transformer drivers (LTDs), but there is still room for improvement on its self-breakdown and triggering characteristics. In this paper, based on the circuit model of the six-gap gas switch, the gap voltage distribution during the charging and triggering process is analyzed, and the optimization on self-breakdown and triggering characteristics by mounting resistors and capacitors in parallel with switch gaps are theoretically and experimentally investigated. The results indicate that compared with the original switch, when the self-breakdown voltage is about ±90 kV, the standard deviation is reduced from 7.5 to less than 3 kV; for a charging voltage of ±80 kV and by operating at 60% working coefficient, when the negative trigger voltage is 75 kV, the jitter of the switch is reduced from 6.1 to 1.4 ns. [ABSTRACT FROM AUTHOR]

The uniform gas discharge has long been pursued for realizing or improving some practical applications but is difficult to achieve due to the fact that nonuniform discharges are much easier to be generated in most cases. Usually, achieving uniform gas discharge requires sophisticated devices, and the operation is complicated and time-consuming. In this paper, we introduce simple and flexible multimethods for realizing uniform discharge from patterned structures under dielectric-barrier discharge (DBD) systems by varying experimental controlling parameters, and these methods can be employed in combination. The effects of driving frequency, voltage, duty ratio, and magnetic/electric field on glow DBD structure are investigated. It is found that a uniform glow DBD is obtained when frequency, voltage, and duty ratio are either very high or very low and also by the introduction of strong magnetic/electric field. The underlying physics of these methods is consistent as the elimination of a focusing effect of space electrons. It is concluded that the key of achieving uniform discharge is to uniformize the distribution of space charges. [ABSTRACT FROM AUTHOR]

Measuring the solid armature’s in-bore motion state using B-dot probes is significant for studying the electromagnetic emission. The common method uses B-dot probes to acquire the discrete time points when the armature passes by them. These points can be interpolated into a curve of the armature’s displacement. However, considering the rapid current changes, the points contain an error. What is worse, it is difficult to recover the armature’s whole process motion by limited discrete points. In this paper, by deeply digging out the information contained in induced electromotive force curve of B-dot probes, a novel measurement method is proposed, which we can recover solid armature’s in-bore whole process motion without any interpolation. At the beginning, considering the current skin and velocity skin effects, a precise 3-D model is built. By analyzing the effect of the current changing rate, the discrete precise time points when the armature passes by them are getting. Then, through the mathematical transformation and applying Newton’s second law, a novel method to acquire velocity curve, displacement curve, and acceleration curve of armature’s in-bore motion in the whole launch process is put forward. Finally, the simulation model of 9-m rail gun with 18 B-dot probes is built. Simulation shows that the proposed method can obtain precise armature’s in-bore motion state in the whole electromagnetic emission process and can deduce in-bore force curve of the armature, which is significant for fault diagnosis of launcher. [ABSTRACT FROM AUTHOR]

The fluid equations of plasma, including the ion isothermal flow, are examined over the wide range of ion temperature. The aim of this paper is to study the ion temperature effect on both the plasma and sheath asymptotic structures as well as the plasma–sheath structure. The fluidal equations of plasma are solved in the plasma and sheath asymptotic limits and it is demonstrated that the ion temperature does really have significant effect on the particles density and electric potential distributions. Also, in the eigenvalue problem of plasma, the plasma equations are numerically solved in the whole region from the plasma center to the floating point and it is found that the ion temperature affects on the floating variables significantly. The full solution of the warm plasma equations needs to cross a singular point and how to cross this point will be described. [ABSTRACT FROM AUTHOR]

Induction synchrotron (IS) has become the focus of improving the intensity of high energy ion beams in recent years. But because of the pulse voltage of the induction accelerating cell cannot adjust quickly, causing the mismatch of the magnetic deflection field and accelerate electric field, there is a serious beam loss problem in IS. The simulation of beams longitude dynamics proves that increasing the number of accelerating cells can effectively reduce the loss. In this paper, a novel compact induction accelerator module is introduced. Compared with the existing induction accelerator module of KEK, the new design can increase the number of accelerating cells to more than five times in the same installation space and improves the voltage top drop of the acceleration pulse significantly. [ABSTRACT FROM AUTHOR]

The multipactor (MP) phenomenon can generate exponentially increasing electron populations in RF vacuum systems, leading to components becoming damaged. This paper uses numerical methods to analyze an RF vacuum window in a coaxial line under various standing wave conditions. Our methods are first benchmarked against the analytic and experimental results for the traveling wave and the numerical results for standing waves that were found in previous work. Second, the effect of standing waves on electron motion in the axial direction is discussed and related to electron trajectories in the presence of an RF window. It is found that standing waves with the magnetic maximum located behind the RF window lead to window collisions that can affect MP depending on the power, frequency, and conductor radii. For a low number of window collisions, MP was highly predictable by earlier work, but as the percentage of collisions occurring on the window surpassed approximately 50%, a novel mode of MP emerged to dominate the phenomenon. [ABSTRACT FROM AUTHOR]

The vacuum transverse magnetic field (TMF) contacts have the advantages of simple structure, short current path, and low cost. Arcing process and arc characteristics between the TMF contacts directly determine the temperature distribution and ablation of the contact surface, which are closely related to the breaking ability of the contacts. The axial magnetic field (AMF) component generated by the TMF contact structure also affects the arcing process. In this paper, five kinds of contacts with different starting positions of spiral slots were experimentally investigated in a demountable vacuum chamber. The arc appearance and the arc characteristics during different arcing stages and the surface utilization of the contacts were analyzed. The magnetic characteristics of arc in different stages were simulated. It was found that the arc with small AMF component has a large diameter and small range of motion. The arc with large AMF component might jet toward the outside of the interelectrode. [ABSTRACT FROM AUTHOR]

This paper presents the numerical simulation results of characteristics and efficiency of separation of uranium ion fluxes and its fission products in the process of the plasma separation. The movement of beams of heavy (238 u) and light (160 u) single-charged ions in vacuum and in helium buffer plasma has been investigated at a pressure of 10 mtorr, magnetic fields 0.8–1.2 kG and electrical potentials up to 1 kV. The interaction between the ion beams and their interaction with the buffer plasma has been taken into account. The numerical simulation of plasma has been conducted in a drift–diffusion approximation. It has been shown that the presence of buffer plasma in the area of ion fluxes and occurring compensation of their space charge can greatly improve the separation efficiency compared to the separation of ion fluxes in vacuum. [ABSTRACT FROM AUTHOR]

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. This current melt erosion (CME) has been experimentally studied in the current range of 10–20 kA/mm with a 20-mm caliber lab-scale rail launcher, and payload separated method was used to keep the recovered armatures intact. Thus, the onset behavior and erosion patterns of CME can be successfully observed in such relatively low current densities. In this paper, we will further our study to analyze the patterns of CME with the increasing current densities under the effect of different initial mechanical contact force. Results show that CME all start at the side edge, and then spreading longitudinally and transversely with the increase of current. It is found that the starting position of CME appears near the trailing edge at small mechanical contact force and moves to the leading edge with larger mechanical contact force. At the same current magnitude, erosion amounts are much more under small mechanical contact force. Stationary mechanical contact pressures and current distribution of armature surface are simulated to investigate the effect of initial mechanical contact force on starting position of CME. Current distributes at the edges of actual contact zone and the maximum of current density appears at the side edges of armature. As the initial mechanical contact force increases, actual contact zone and current density move toward to the leading edge from trailing edge. It can be confirmed that the erosion starting position is at the side edge along actual contact zone and will move toward to the leading edge from trailing edge with the increase of initial mechanical contact force. Smaller initial mechanical contact force will cause more erosion at the same current magnitude because of larger current density. Furthermore, an average friction coefficient calculation method is proposed to evaluate the melt lubrication effect of CME. The result shows that the lubrication effect becomes better with larger current densities. [ABSTRACT FROM AUTHOR]

Paschen’s law gives the inception voltage for an electrical discharge as a function of the product of gas pressure and the gap distance between the two infinite planar electrodes. It is known that the deviations from Paschen’s law occur when the temperature is increased. Historically, two theoretical corrections, the Peek and Dumbar corrections, are proposed to predict the deviation from Paschen’s law by increasing the temperature. To carry out an experimental investigation on the deviation from Paschen’s law by increasing the temperature, a customized system was designed, which can operate at temperatures up to 400 °C and at pressure up to 1 MPa, calculated at room temperature, with an interelectrode distance between $100~\mu \text{m}$ and 6.6 mm and an error on the interelectrode distance measurement of $20~\mu \text{m}$. In this paper, first, the results from the experimental investigation on the deviation from Paschen’s law at temperature up to 400 °C are presented. The results are then compared with theoretical corrections, and finally, a theory to explain the results is proposed and discussed. [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]

The de-excitation of nitrogen excited states after spark gap discharge was investigated with time-resolved optical emission spectroscopy method. Recombination of ionized particles was experimentally proved less than several tens microseconds. After the recombination process, it was shown that atomic nitrogen in ground state [N(4S)] and molecular nitrogen in first excited state [N2($\text{A}^{3} {\Sigma }_{u}^{+}$)] was long-lived particles (metastable state) after gas discharge. Characteristics of decay for N(4S) and [N2($\text{A}^{3} {\Sigma }_{u}^{+}$)] were studied, and their lifetime and decay of density were estimated in this paper. Peculiar unexponential decay of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) showed there was reproduction process of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) after gas discharge. N(4S) could be the source for reproduction process under their mechanism of three-body recombination. Low ionization energy and high ionization collision cross section of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) make it a possible factor limiting the switch recovery. The de-excitation of metastable states opens novel perspectives for understanding the recovery of gas switch. [ABSTRACT FROM AUTHOR]

Intermediate-frequency power technology is widely used in aircraft power-supply systems. This paper studies the appearance and motion of vacuum plasmas in an axial magnetic field (AMF) and butt contacts at 360–800 Hz. Under the influence of an AMF, electrons travel in a cylindrical spiral, which is advantageous for maintaining arc diffusion. The experimental results show that when the contact separation was 3 mm, the vacuum arcs were uniformly distributed and diffused in the AMF contacts. We found that the maximum magnetic pinch pressure in the arc column was approximately $10^{4}$ Pa. However, in butt contacts, the arc was intense and was clearly constricted. The order of magnitudes of the magnetic pinch pressure in the center reached $10^{5}$ Pa at the minimum radius of the arc column around the current peak, which formed a higher pressure gradient that caused the plasma and metal vapor to flow to the lower pressure region and form a plasma jet. [ABSTRACT FROM AUTHOR]

This paper outlines the requirements for a source of buffer plasma, which is necessary for elaboration of plasma separation method of substances and following foundations development of plasma reprocessing technology of spent nuclear fuel and radioactive waste. Such source is implemented on the basis of a helicon discharge, allowing plasma generation in a cylindrical volume with characteristic dimensions on the order of 1 m and bounded by metal walls. At plasma-forming gas (argon) pressure of 1 mTorr, radial profiles of density $n_{e}$ and temperature $T_{e}$ of electrons were obtained for various magnetic field magnitudes (0–200 G) and RF power (up to 6 kW) using double probe and optical methods. The typical value of $T_{e}$ amounted to eV units and $n_{e}$ was about 1012 cm−3. [ABSTRACT FROM AUTHOR]

Discharge behaviors of high-power impulse magnetron sputtering with different targets have been investigated. Distinct current–voltage curves and target current waveforms are observed. Breakdown voltage and the maximum target current show a periodic drop with the increase of atomic number in subgroups and periods. The target current density is found to be mainly affected by the secondary electron emission yield. Thus, its magnitude is unable to directly evaluate the ionization degree of sputtered atoms in high-power impulse magnetron sputtering (HiPIMS) process. In this paper, the interactive influence of secondary electron emission, sputter yield, and ionization energy on the ionization degree of sputtered atoms is discussed based on the analysis of the voltage and current characteristics. As a result, targets can be categorized into three sorts according to the ionization degree: 1) low ionization degree targets, such as Ag and C less than 10%; 2) intermediate ionization degree targets like Cr and Cu with 55% and 35%; 3) Ti, Zr, and Mo targets with the second ionization processes. These results provide institutive operation ranges for the state-of-the-art HiPIMS applications. [ABSTRACT FROM AUTHOR]

The influence of the electric parameters, applied voltage, and pulse repetition rate on the energy efficiency for hydroxyl radical production from pulsed discharge inside of a bubble is investigated in this paper, as a possible application for waste water treatment. To evaluate the energy efficiency, indigo carmine, a common dye, is used as a chemical probe of hydroxyl radicals. Argon is injected into water through a vertically positioned glass tube, into which high-voltage wire electrode is placed to generate plasmas at low applied voltage. The energy efficiency increases with the decreasing pulse repetition rate and output voltage with the same indigo carmine concentration. The results show that the energy efficiency for the hydroxyl radical production increases with the decreasing amount of energy input into the solution per unit time because of the decrease in the recombination reaction of the hydroxyl radicals in the solution. The impedance between the electrodes decreases with the increasing output voltage, which increases the ohmic losses in the solution but does not contribute to the production of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

High thrust density per thruster area is the most desired achievement in current ion thruster designs. Dual-stage ion thruster concept is introduced to improve the ion beam focusing capability of single-stage thrusters in order to maximize the achievable thrust density for a fixed thruster area. In this paper, a two-grid ion thruster is converted to a dual-stage one by adding an extractor grid. Then, improvement of ion beam divergence characteristic is numerically investigated through the parametric study of extractor grid’s geometrical and operational variables by a hybrid-particle-in-cell method. The sensitivity analysis shows that the beam divergence angle is very sensitive to acceleration-to-extraction voltage difference ratio. The effect of acceleration-to-extraction grid gap ratio is also significant. The initial dual-stage model is modified based on this result. The minimum divergence angle for the modified model is about 3.38° resulting in 70% and 60% improvement against the minimum divergence angle of the two-grid single-stage and the initial dual-stage numerical models, respectively. [ABSTRACT FROM AUTHOR]