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In this work the Time Correlated Single Photon Counting method with digital post-processing was implemented to study the development of a surface barrier discharge powered by a sinusoidal alternating voltage. The resolution obtained with digital TCSPC was shown to be no worse than 300 ps with photodetectors function rise time 15 ns and oscilloscope sample rate 10 GHz. Selection of the pulses after at the postprocessing stage allowed to study the multipulse mode of the DBD, obtain the space–time diagrams of the discharge light emission and estimate the velocity of negative and positive microdischarges propagation. [ABSTRACT FROM AUTHOR]

Two-dimensional fully coupled electromagnetic (EM) wave-plasma simulations are used to study the formation, early transient and quasi-steady state of the argon plasma excited by a two-dimensional discontinuous microstrip line. The EM waves that normally propagate in the microstrip transmission line, radiate and scatter at the position of the gap and the electric field is enhanced primarily at the corner of the gap. The microdischarge is preferentially formed at this position of the EM field hotspot and in low frequencies propagates on the dielectric surface, much like a microwave surface streamer. In longer times, diffusion dominates and the whole gap is filled with plasma of maximum density in the order of 1020 m − 3 while it occupies a volume larger than the gap. Cycle-averaged mean electron temperatures range from 2.8 to 3.9 eV, while the plasma reaches a quasi-static regime in approximately 2 µs having reconfigured the transmission and radiation patterns of the slitted microstrip line. The tunability of the microstrip due to plasma formation provides means for sustaining the discharge in a stable regime. For the same input EM power, the electron temperature increases with increasing excitation frequency while electron densities found to decrease. For the same wave frequency, a decrease of the electron densities with increasing gap is also found in addition to a restriction of the discharge expansion. Finally, thicker dielectrics result to higher electron densities and electron temperatures as well as absorbed power from the plasma. These findings are attributed to the dependence of absorbed EM power and skin depth on the EM wave angular frequency, the critical for shielding electron density as well as the restructuring of the S-parameters due to the changes in operational parameters. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the effect of the applied potential and pressure on the DC microdischarge in a 90%He–10%Xe gas mixture at intermediate pressure. The range of pressure is about 50–110 Torr, and the applied potential is between 390 and 450 V. The model is based on the fluid description with multiple species. The parameters of particle transport and their rate coefficients strictly depend on the electron energy. In the framework, we have developed an empirical expression of the ion's mobility in the mixture as well as that of secondary electron emission coefficient. The results show that the particle densities and metastable atom state augment with augmentation of applied potential or pressure, and a strong electric field is presented at the cathode, it is equal to 14.3 kV/cm for (50 Torr and 390 V), and it is reached to 54.9 kV/cm for (110 Torr and 450 V). The validity test of our results is carried out from comparison with experimental results. [ABSTRACT FROM AUTHOR]

DC corona discharge has been widely used for the application of volatile organic compounds (VOCs) degradation. In this article, the microdischarge was found in an improved wire-plate corona discharge reactor, which could extremely promote the toluene degradation efficiency. Due to the porous insulating materials attached to the grounded electrode, microdischarge could be easily induced by the accumulated charge on the insulating layer during corona discharge. An influence of parameters of microdischarge was systematically investigated, such as volume resistivity of insulating materials, layer thickness ($d$), the number of pores ($n$), and pore size ($s$). It is found that a better toluene degradation could be obtained when a porous insulating layer with low volume resistivity and small pore was coated on the grounded electrode of the corona discharge reactor. With the polytetrafluoroethylene (PTFE) insulating layer of $d =5 0\,\,\mu \text{m}$ , n $= 50\,\,\mu \text{m}$ , and s $= 10\,\,\mu \text{m}$ , the degradation efficiency of toluene reached 54.2% when the discharge power was 24 W, while the efficiency is only 40.8% compared to the negative dc corona discharge alone. Besides, the concentration of CO2 and CO produced during the degradation of toluene was also increased by 189 and 293 ppm due to the induction of microdischarge. The investigations on the microdischarge-enhanced corona plasma reactor could not only offer an effective way for toluene degradation but also provide new insight on the improvement of plasma reactors for VOCs’ decomposition. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the process of growth of different carbon deposits in low-current electrical microdischarges in argon with an admixture of cyclohexane as the carbon feedstock. The method of synthesis of carbon structures is based on the decomposition of hydrocarbons in low-temperature plasma generated by an electrical discharge in gas at atmospheric pressure. The following various types of microdischarges generated at this pressure were tested for both polarities of supply voltage with regard to their applications to different carbon deposit synthesis: Townsend discharge, pre-breakdown streamers, breakdown streamers and glow discharge. In these investigations the discharge was generated between a stainless-steel needle and a plate made of a nickel alloy, by electrode distances varying between 1 and 15 mm. The effect of distance between the electrodes, discharge current and hydrocarbon concentration on the obtained carbon structures was investigated. Carbon nanowalls and carbon microfibers were obtained in these discharges. [ABSTRACT FROM AUTHOR]

Direct conversion of mechanical energy into direct current (DC) by triboelectric nanogenerators (TENGs) is one of the desired features in terms of energy conversion efficiency. Although promising applications have been reported using the triboelectric effect, effective DC generating TENGs must be developed for practical purposes. Here, it is reported that continuous DC generation within a TENG itself, without any circuitry, can be achieved by triggering air breakdown via triboelectrification. It is demonstrated that DC generation occurs in combination with i) charge accumulation to generate air breakdown, ii) incident discharge (microdischarge), and iii) conveyance of charges to make the device sustainable. 10.5 mA m−2 of output current and 10.6 W m−2 of output power at 33 MΩ load resistance are achieved. Compared to the best DC generating TENGs ever reported, the TENG in this present study generates about 20 times larger root‐mean square current density. [ABSTRACT FROM AUTHOR]

This article by employing a zero-dimensional model investigates vacuum ultraviolet (VUV) emission from a xenon–neon microdischarge. The effects of the pressure, the input voltage, and the neon fraction are carefully studied. For specific input voltages, the microdischarge operates in an oscillatory regime which is called the self-pulsing regime. The self-pulsing frequency is mainly affected by the input voltage as well as the pressure. Increasing the input voltage enhances the average densities but has no effects on the peak densities. However, the pressure has significant effects on both densities. The main peaks of the VUV emission spectrum are seen at $\lambda =173$ nm and $\lambda =147$ nm which are attributed to xenon triplet-excited dimers and resonance-level excited atoms, respectively. Adding the neon gas enhances the emission at 147 nm through reducing the power loss in elastic collisions, but attenuates the emission at 173 nm. The results also show that steady-state densities of the major VUV emitters in the stationary regime are higher than the time average densities in the self-pulsing regime. Although, the lower power consumption of the self-pulsing regime has a more decisive effect such that the VUV emission efficiency in the self-pulsing regime is greater than that of the stationary regime. [ABSTRACT FROM AUTHOR]

In a dielectric barrier discharge, countless pulsed microdischarges with a diameter of about $100~\mu \text{m}$ appear and disappear. Since such microdischarges will affect ozone generation, it is important to understand their characteristics. In the case of a short discharge gap, which has been adopted recently, the transferred charge of a microdischarge is treated as a sphere on the dielectric to simplify the modeling. In this article, we discuss how various parameters affect ozone generation by comparing simulation and experimental results. We also discuss the influence of the thickness and dielectric constant of the dielectric barrier on the characteristics of ozone generation. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the process of growth of different carbon deposits in low-current electrical microdischarges in argon with an admixture of cyclohexane as the carbon feedstock. The method of synthesis of carbon structures is based on the decomposition of hydrocarbons in low-temperature plasma generated by an electrical discharge in gas at atmospheric pressure. The following various types of microdischarges generated at this pressure were tested for both polarities of supply voltage with regard to their applications to different carbon deposit synthesis: Townsend discharge, pre-breakdown streamers, breakdown streamers and glow discharge. In these investigations the discharge was generated between a stainless-steel needle and a plate made of a nickel alloy, by electrode distances varying between 1 and 15 mm. The effect of distance between the electrodes, discharge current and hydrocarbon concentration on the obtained carbon structures was investigated. Carbon nanowalls and carbon microfibers were obtained in these discharges.

In this article, we are interested in giving a detailed study of the nonlocal ionization theory (NIT) and their secondary electron emission coefficient (SEEC). As for expelling, we present the spatial distributions of both Coulomb logarithm of electron–electron and electron-ion collisions, ionization and excitation frequency ratios, and source term of particle charged, as well as ion temperature in helium and neon dc microdischarge at high pressure. The pressure range is from 40 to 70 torr, and the applied potential is from 200 to 230 V. In the framework, we have developed an empirical expression of the secondary electron emission corresponding to the helium and neon discharge. The current–voltage results are in good agreement with the experimental data. We have computed the real ion temperature using the generalized Einstein’s relation, and in my knowledge, this is for the first time in the literature. As a result, the helium ion temperature reached 34 times the gas temperature at the cathode and reached 56 times the gas temperature in neon. [ABSTRACT FROM AUTHOR]

This paper summarizes our recent studies on a gas breakdown in microgaps with a surface protrusion on the electrode with more detailed information. The breakdown voltages are quantified when the discharge enters into the subnormal glow region with negative differential resistance, using a 2-D fluid model. The breakdown characteristics are evaluated with the effects of the protrusion geometries, such as protrusion size and aspect ratio, as well as the discharge polarity. It is found that in an atmospheric-pressure microgap, the protrusion size has a more profound effect on the breakdown voltage than its aspect ratio, which is due to the competition between the current density enhancement and the effective cathode emission area. As gas pressure varies, the surface protrusion on the electrode results in a combined Paschen’s curve, which transits from long-gap behavior at low pressure to short-gap behavior at high pressure. The key parameters on the breakdown characteristics with the surface protrusion are elucidated. [ABSTRACT FROM AUTHOR]

The development of microdischarges and the inception dynamics of subsequent microdischarges in an electrode arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode, operated in air with a small toluene admixture, is studied. The discharge is operated with sinusoidal high voltage. A gated ICCD camera and a current probe enable the recording of images and current pulses of the single microdischarges, respectively, while the spatio-temporally resolved development is measured with a multi-dimensional time-correlated single photon counting technique. The overall discharge dynamics changes significantly if a concentration of 35 ppm toluene is added to dry air. A lower high voltage amplitude than in dry air is needed for stable discharge operation. This can be explained by the lower ionization energy of toluene compared to molecular oxygen and nitrogen. The microdischarge development is the same with or without admixture, i.e. a positive (cathode directed) streamer mechanism is observed. Lower mean power is dissipated into the discharge when toluene is admixed. The main effect caused by toluene admixture is the suppression of high-energy microdischarges in case of the cathodic pin half-cycle of the sinusoidal high voltage. The influence on the inception voltage by additional ionization mechanisms and volume memory effects, the consumption of energetic electrons for toluene decomposition reactions, and the modification of the surface by plasma treatment are discussed as possible reasons. [ABSTRACT FROM AUTHOR]

Abstract Soft sparking can be utilized to dismiss the intrinsic porosity problem of plasma electrolytic oxidation (PEO) coatings on aluminum alloy, since this type of surface treatment generates a dense inner layer. Researchers usually recognize soft sparking through the anodic voltage drop, along with the decline in light and acoustic emissions. Analysis of V - I transients in the anodic pulse of bipolar DC current reveals the decline in RC time constant is a forerunner, which reflects the transition in micro arc state prior to the conventional definition. In studying the negative current dependence and the current frequency dependence of soft sparking, the results suggest the time constant may serve as an auxiliary indicator, monitoring growth activity variations and further assuring the dense inner layer. The role of time constant is exemplified in the soft sparking experiments at 500 Hz and duty 40%. Microstructure analysis reveals three relatively dense stacks separated by two layers of pores and loose grains. The porous layer is attributed to the micro arc state of less intense microdischarges, marked as a substantial drop in the R 2 C 2 value. Matching between stratified layers and R 2 C 2 rises-and-falls is verified in two electrolytic solutions with and without chromia inclusions. Thus, we suggest time constant as a probing tool of microdischarges softening to help analyze the events prior to voltage drop. Graphical abstract Unlabelled Image Highlights • Detection of soft sparking phenomena in PEO through pulse transients • The slow time constant of fluctuations reveals stratification of the PEO coating. • A flat profile of slow time constant and voltage drop suggests a dense inner layer. • Time constant of slow response can be an auxiliary indicator of microdischarges. [ABSTRACT FROM AUTHOR]

A packed bed dielectric barrier discharge (DBD) is widely used for plasma catalysis applications, but the exact plasma characteristics in between the packing beads are far from understood. Therefore, we study here these plasma characteristics by means of fluid modelling and experimental observations using ICCD imaging, for packing materials with different dielectric constants. Our study reveals that a packed bed DBD reactor in dry air at atmospheric pressure may show three types of discharges, i.e. positive restrikes, filamentary microdischarges, which can also be localized between two packing beads, and surface discharges (so-called surface ionization waves). Restrikes between the dielectric surfaces result in the formation of filamentary microdischarges, while surface charging creates electric field components parallel to the dielectric surfaces, leading to the formation of surface discharges. A transition in discharge mode occurs from surface discharges to local filamentary discharges between the packing beads when the dielectric constant of the packing rises from 5 to 1000. This may have implications for the efficiency of plasma catalytic gas treatment, because the catalyst activation may be limited by constraining the discharge to the contact points of the beads. The production of reactive species occurs most in the positive restrikes, the surface discharges and the local microdischarges in between the beads, and is less significant in the longer filamentary microdischarges. The faster streamer propagation and discharge development with higher dielectric constant of the packing beads leads to a faster production of reactive species. This study is of great interest for plasma catalysis, where packing beads with different dielectric constants are often used as supports for the catalytic materials. It allows us to better understand how different packing materials can influence the performance of packed bed plasma reactors for environmental applications. [ABSTRACT FROM AUTHOR]

O2 and CO2 Dielectric Barrier Discharges (DBD) were studied at elevated (i.e., above atmospheric) pressure regimes (1-3.5 bar). It was demonstrated that these operational conditions significantly influence both the discharge dynamics and the process efficiencies of O2 and CO2 discharges. For the case of the O2 DBD, the pressure rise results in the amplification of the discharge current, the appearance of emission lines of the metal electrode material (Fe, Cr, Ni) in the optical emission spectrum and the formation of a granular film of the erosion products (10-300 nm iron oxide nanoparticles) on the reactor walls. Somewhat similar behavior was observed also for the CO­2 DBD. The discharge current, the relative intensity of the CO Angstrom band measured by Optical Emission Spectroscopy (OES) and the CO2 conversion rates could be stimulated to some extent by the rise in pressure. The optimal conditions for the O2 DBD ( P = 2 bar) and the CO2 DBD ( P = 1.5 bar) are demonstrated. It can be argued that the dynamics of the microdischarges (MD) define the underlying process of this behavior. It could be demonstrated that the pressure increase stimulates the formation of more intensive but fewer MDs. In this way, the operating pressure can represent an additional tool to manipulate the properties of the MDs in a DBD, and as a result also the discharge performance. [ABSTRACT FROM AUTHOR]

An atmospheric pressure glow microdischarge (μAPGD) operated between a gaseous microjet and a flowing liquid cathode and sustained in various atmospheres (Ar, He, CO 2 ) and in different discharge-systems (fully open-to-air, semi-closed) was investigated by optical emission spectrometry (OES). The morphology of the emission spectra of all the discharges was discussed. The effect of the microjet-supporting gas flow rate on the intensity of the interfering molecular bands, emission from analyte atomic lines and spectroscopic parameters was thoroughly studied. It was noticed that the appearance, the electron number density, optical temperatures and behavior of the CO 2 -μAPGD system completely differed from those assessed for the noble gas-μAPGD system. Regardless of the applied microjet-supporting gas, cutting off the air supply caused a reduction of the NO and N 2 molecular bands intensity, however, an apparent decrease in emission from analytical atomic lines was simultaneously noticed. Nevertheless, for μAPGD operated in a semi-closed system, detectability of several metals (Cd, Co, Hg, Zn) evaluated with OES was improved twice. The obtained Limits of Detection (LODs) covered the range from hundreds μg L − 1 (for metals characterized by low emission, i.e. Cr, Pb), through tens (Ca, Co, Cu, Hg, Mn, Sr, Zn) and several μg L − 1 (Ag, Cd, Cs, In, Mg, Tl), to < 1 μg L − 1 for alkali metals (K, Li, Na, Rb). The measurement repeatability of μAPGD-OES operated in the open-to-air system was below 1% and it was noticeably better than this received for the semi-closed system. The accuracy of μAPGD-OES was confirmed by analysis of ground water samples (ERM-CA615 and ERM-CA616). [ABSTRACT FROM AUTHOR]

A novel device for ozone production in an air microplasma at atmospheric pressure has been developed. A power supply for exciting and sustaining the microdischarge, whose working frequency is set in relation to the kinetics of the chemical reactions taking place in the microdischarge at voltages above the first ionization potential of the gas, has been designed and fabricated. Emphasis is made both in the design of the microplasma reactor and in its electro-optical characterisation, with the purpose of determining the operating conditions of the discharge. An equivalent electronic model of the discharge has been implemented. This model allows us to study energy transfer processes from the power supply to the plasma. Emission spectroscopy techniques have been used to obtain the emission spectra of the microplasma, with which macroscopic plasma parameters such as the electronic temperature and heavy species temperatures can be inferred and the state of equilibrium assessed. The prototype developed is useful not only for the synthesis of ozone but also for the synthesis of hydrogen and other chemical species. [ABSTRACT FROM AUTHOR]

A 1-D model for the simulation of transition from glow microdischarge to arc discharge with a thermionic cathode was built using COMSOL Multiphysics. The extended fluid model was coupled with the gas heating equation for the self-consistent simulation of discharge at atmospheric pressure in a wide range of currents. Both the secondary electron emission and the thermionic emission were taken into account simultaneously to allow for the transition. In order to properly account for thermionic emission, cathode heating was considered—heat flux equation was solved in a 1-D solid domain with heat fluxes on the cathode surface from the discharge domain used as boundary conditions. A thorough set of plasma-chemical reactions with account of molecular ions of argon was used. Using the external circuit allowed for obtaining stable solutions in a wide range of currents. By changing ballast resistance, the classical current–voltage characteristic of direct current discharge with transition from glow to arc was obtained. The distributions of such discharge parameters as charged and excited particle densities and fluxes, electron mean energies and temperatures, gas temperature, and electric potential were obtained for microdischarge, arc discharge, and transitional state. Time-dependent simulations allowed for obtaining the dynamics of discharge formation. It is shown that after the breakdown, the cathode is heated by the discharge current for a time of tens of milliseconds, and then, transition to stable arc discharge with thermionic cathode takes place. [ABSTRACT FROM AUTHOR]

Most commercial communications and broadcast satellites operating at microwave radio frequencies use traveling wave tube amplifiers (TWTAs) as high power transmitters. Since TWTAs work at high voltages, it is not uncommon to experience micro-discharges, especially early in life. This observation led to the introduction of an autonomous restart function in the companion high voltage power supply (the electronic power conditioner or EPC) of the TWTA as a safety feature. A microdischarge with enough energy above a threshold would lead to a momentary removal of high voltages, followed by an automatic restart, which is usually sufficient to allow the microdischarge event to clear with minimal loss of RF transmission. In most cases the energy involved in the microdischarge is low enough that the removal of high voltages is not required and the event may go undetected. However, an unusual signature was first noted in early 1997 on a Ku-band satellite transmitter, where the characteristics of the microdischarge event were such that the control anode voltage dropped below nominal and typically recovered over a 20 min period. Such microdischarge events became known as the “20 min Effect” which has since been observed over subsequent years on other Ku-band TWTAs, as well as on Ka-band and S-band satellite TWTA transmitters in numerous satellites. This paper summarizes the in-orbit data on such microdischarges as well as the believed cause. In addition, the paper includes results from three S-band TWTAs which have operated on life test for many years. Due to ease of their monitoring instrumentation as contrast to monitoring microdischarges on orbiting operational satellites via telemetry, new data have been accumulated on this effect. The data substantiate the previous findings that microdischarges do not significantly affect satellite operation or their transmissions nor diminish the TWTAs performance, including long lifetime. [ABSTRACT FROM AUTHOR]

We investigate microdischarge formation inside catalyst pores by a two-dimensional fluid model for various pore sizes in the μm-range and for various applied voltages. Indeed, this is a poorly understood phenomenon in plasma catalysis. The calculations are performed for a dielectric barrier discharge in helium, at atmospheric pressure. The electron and ion densities, electron temperature, electric field and potential, as well as the electron impact ionization and excitation rate and the densities of excited plasma species, are examined for a better understanding of the characteristics of the plasma inside a pore. The results indicate that the pore size and the applied voltage are critical parameters for the formation of a microdischarge inside a pore. At an applied voltage of 20 kV, our calculations reveal that the ionization mainly takes place inside the pore, and the electron density shows a significant increase near and in the pore for pore sizes larger than 200 μm, whereas the effect of the pore on the total ion density is evident even for 10 μm pores. When the pore size is fixed at 30 μm, the presence of the pore has no significant influence on the plasma properties at an applied voltage of 2 kV. Upon increasing the voltage, the ionization process is enhanced due to the strong electric field and high electron temperature, and the ion density shows a remarkable increase near and in the pore for voltages above 10 kV. These results indicate that the plasma species can be formed inside pores of structured catalysts (in the μm range), and they may interact with the catalyst surface, and affect the plasma catalytic process. [ABSTRACT FROM AUTHOR]

The parameters for microdischarges of plasma medicine in air and argon vortex flows at atmospheric pressure for different shapes of electrodes (outlet nozzle and axis electrode diameters ratio set) have been investigated. The current-voltage characteristics of the designed systems have been analyzed, the parameters of the generated jets plasma have been investigated by means of the optical emission spectroscopy, and the form of plasma jets has been studied by using video camera.

Microdischarge-induced reaction processes working at atmospheric pressure create fractal-like network structure of metal nano-particles which shows variable electric and optical properties. Due to their smallness, microdischarges or microplasmas can be installed in a gas-tubing system, and they enable us to create a compact chemical reduction reactor which includes decomposers of molecules, gas flows, and aqueous solutions with metallic ions at atmospheric pressure. Ammonia (NH) gas is successfully decomposed in this reactor, and its products which include mainly hydrazine (NH) and flow in the downstream induce reduction reactions for AgNO solution. Various parameters in the reactor trigger formation of functional patterns of silver nano-particles like partially transparent layers whose conductivity is variable. Optical properties of this equivalent films show some absorption spectra coming from structure resonances, which can be an optical metamaterials in this self-assembly process. [ABSTRACT FROM AUTHOR]

Plasma technology has been widely applied in the ozone production, material modification, gas/water cleaning, etc. Various nanomaterials were produced by thermal plasma technology. However, the high temperature process and low uniformity products limit their application for the high value added chemicals synthesis, for example the functional materials or the temperature sensitive materials. Microplasma has attracted significant attentions from various fields owing to its unique characteristics, like the high-pressure operation, non-equilibrium chemistry, continuous-flow, microscale geometry and self-organization phenomenon. Its application on the functional nanomaterial synthesis was elaborately discussed in this review paper. Firstly, the main physical parameters were reviewed, which include the electron temperature, electron energy distribution function, electron density and the gas temperature. Then four representative microplasma configurations were categorized, and the proper selection of configuration was summarized in light of different conditions. Finally the synthesis, mechanism and application of some typical nanomaterials were introduced. [ABSTRACT FROM AUTHOR]

A dynamic model of microdischarge with a mobile liquid cathode was presented. The possibility of electron autoemission was substantiated. It was suggested that the liquid cathode rate be calculated by the Navier-Stokes equation. A scheme that shows the development of a plasma formation depending on the thickness of the coating was given. The objects found on the coating surface and in the sludge were shown to correspond to the model. [ABSTRACT FROM AUTHOR]

The parameters for microdischarges of plasma medicine in air and argon vortex flows at atmospheric pressure for different shapes of electrodes (outlet nozzle and axis electrode diameters ratio set) have been investigated. The current-voltage characteristics of the designed systems have been analyzed, the parameters of the generated jets plasma have been investigated by means of the optical emission spectroscopy, and the form of plasma jets has been studied by using video camera. [ABSTRACT FROM AUTHOR]

Diffuse Coplanar Surface Barrier Discharge (DCSBD) is a novel type of atmospheric-pressure plasma source developed for high-speed large-area surface plasma treatments. The statistical behavior of microdischarges of DCSBD generated in artificial air atmosphere was studied using time-correlated optical and electrical measurements. Changes in behavior of microdischarges are shown for various electrode gap widths and input voltage amplitudes. They are discussed in the light of correlation of the number of microdischarges and the number of unique microdischarges' paths per discharge event. The 'memory effect' was observed in the behavior of microdischarges and it manifests itself in a significant number of microdischarges reusing the path of microdischarges from previous half-period. Surprisingly this phenomenon was observed even for microdischarges of the same half-period of the discharge, where mechanisms other than charge deposition have to be involved. The phenomenon of discharge paths reuse is most pronounced for wide electrode [ABSTRACT FROM AUTHOR]

An original method of decomposition of heavy hydrocarbons into light fractions in the plasma of a microarc discharge initiated between electrodes submerged in a liquid is proposed. The characteristics of the microarc discharges between electrodes submerged in different liquids were investigated. A chromatographic analysis of the gases formed in this case has been performed. [ABSTRACT FROM AUTHOR]

This paper presents a monolithic pulsed high-voltage (HV) generator utilizing a single piezoelectric element (PZT51 disk, 5 mm in diameter and 740 \mum thick) with electrodes series-connected via a flexible polyimide cable. The design, fabrication, assembly, and testing of the HV generator are described. In response to transient mechanical load, the HV generator is evaluated within the stress range from 1 to 5 MPa, and the corresponding peak output voltages vary from 100 to 900 V. Performance comparison between single-electrode pair HV generator and three-electrode pair device indicates series-connected electrodes on a monolithic PZT element greatly boost the output voltage under the same mechanical load conditions. In further tests, the generated high-voltage pulses exceed 1.35 kV and are successfully used to initiate microdischarges on monolithically patterned electrodes across a 75 \mum air gap. The measured capacitance of the test HV generator is 25 pF and the calculated charge delivered to the terminal electrodes in each discharge is 34 nC. The nonlinear piezoelectric property of the PZT51 in transient mode is studied. We experimentally obtain a linear increase of the effective piezoelectric coefficient as the applied pressure increases within the range from 1 to 5 MPa. [2012-0356] [ABSTRACT FROM PUBLISHER]

Pacific Northwest National Laboratory (PNNL) has developed an ultra-low-background proportional counter (ULBPC) made of high purity copper. These detectors are part of an ultra-low-background counting system (ULBCS) in the newly constructed shallow underground laboratory at PNNL (at a depth of ~30 m water-equivalent). To control backgrounds, the current preamplifier electronics are located outside the ULBCS shielding. Thus the signal from the detector travels through ~1 m of cable and is potentially susceptible to high voltage microdischarge and other sources of electronic noise. Based on initial successful tests, commercial cables and connectors were used for this critical signal path. Subsequent testing across different batches of commercial cables and connectors, however, showed unwanted (but still low) rates of microdischarge noise. To control this noise source, two approaches were pursued: first, to carefully validate cables, connectors, and other commercial components in this critical signal path, making modifications where necessary; second, to develop a custom low-noise, low-background preamplifier that can be integrated with the ULBPC and thus remove most commercial components from the critical signal path. This integrated preamplifier approach is based on the Amptek A250 low-noise charge-integrating preamplifier module. The initial microdischarge signals observed are presented and characterized according to the suspected source. Each of the approaches for mitigation is described, and the results from both are compared with each other and with the original performance seen with commercial cables and connectors. [ABSTRACT FROM AUTHOR]

A novel method for the removal of soot from a diesel particulate filter using pulsed electric discharges is presented. High voltage pulses of between 18 and 25 kV of nano to microsecond duration and with pulse energies of typically 100-200 mJ were applied to the filter via a series spark gap. Initial slow erosion of the soot layer proceeds via the formation of microdischarges. Subsequent spark discharges removed the accumulated soot more effectively from a larger filter volume. Average soot removal rates of ∼0.1-0.2 g/min were achieved at 50 Hz breakdown frequency by optimizing both electrode geometry and breakdown voltage. On-engine long term testing of the technology showed soot removal by pulsed discharge to be reliable, efficient and uniform; a total of 100 g of soot was deposited and removed over 18 filter regeneration cycles. [ABSTRACT FROM AUTHOR]

Abstract: The principle of dielectric-barrier discharge (DBD) producing 146nm vacuum ultraviolet (VUV) light is introduced in this article. MgF2 and Kr are used as the output window and the discharge gas, respectively, in the VUV light source. Fairly wide, narrow-bandwidth UV light could be generated with peak wavelength of 146nm and a full width at half maxima of 12nm. In addition, the impact of air pressure, voltage amplitude and frequency to the light source is also analyzed. [Copyright &y& Elsevier]

Abstract: A novel maskless microplasma etching method based on parallel scanning probe microscopy is presented in this paper. The advantages of proposed etching system are high etching rate, high fidelity, simple-structure, and flexible to fabricate various material. The SiO2 cantilever probe with microplasma reactor and nano-aperture at the hollow tip is designed and successfully fabricated with good quality. Experiment results show that the devices can discharge stably in SF6 gas. The voltages–current (V–I) curves exhibit negative differential resistance of about 0.5MΩ in a classical hollow cathode discharge mode. The pd scaling values (p and d are the SF6 gas pressure and characteristic dimension of the microdischarge devices, respectively) for minimum ignition voltage are observed about 0.3–0.4Pam. Active F atom lines can be obviously found from the optical emission spectroscopy of microdischarge devices in SF6 gas. A two-dimensional fluid model is used to simulate the dispersion distance and etching rate of silicon when the microplasmas are ejected through the nano-aperture. The experiment and simulation results verify the feasibility of the ongoing experiments of silicon maskless etching. [Copyright &y& Elsevier]

A combined experimental and computational simulation study of direct-current plasma discharge phenomena in small-length-scale geometries (< 10\ \mu\m) is described. The primary goal is to study discharge breakdown characteristics in small-length-scale geometries as quantified by a modified Paschen breakdown curve and the quench characteristics in these discharges. A modified mesoscale friction tester apparatus is used for the experiments. A self-consistent nonequilibrium plasma model is used for the simulation studies. The model includes field-emission effects, which is a key process in determining small-length-scale breakdown behavior. The breakdown and quench curves obtained from the experiments and simulations showed the same general trends. Quantification of the heat fluxes from the simulations shows higher erosion at the cathode and a highly nonlinear heating behavior with applied overvoltages above the breakdown threshold. [ABSTRACT FROM AUTHOR]

A microplasma thruster has been developed of electrothermal type using azimuthally symmetric microwave-excited microplasmas. The microplasma source was ~2 mm in diameter and ~10 mm long, being operated at around atmospheric pressures; the micronozzle was a converging-diverging type, having a throat ~0.2 mm in diameter and ~1 mm long. Numerical and experimental results with Ar as a working gas demonstrated that this miniature electrothermal thruster gives a thrust of >1 mN, a specific impulse of ~100 s, and a thrust efficiency of ~10% at a microwave power of <10 W, making it applicable to attitudecontrol and station-keeping maneuver for a microspacecraft of <10 kg. [ABSTRACT FROM AUTHOR]

This paper reports on dc pulse-powered microdischarges in air at atmospheric pressure and their potential utility in chemical sensing. For electrode gaps of 50-100 µm, microdischarges take the form of a glow discharge, an arc discharge, or a hybrid of the two. Arc microdischarges have high optical intensity but suffer from high background emission. Glow microdischarges have low background emission, but the prominent emission is confined in the UV-blue region of the spectrum. The arc-glow hybrid has characteristics that are intermediate between the two and can be tuned by circuitry to suit the chemical sensing application. A handheld system for chemical analysis using synchronized emission spectroscopy of these pulsed microdischarges is demonstrated. The system employs an exchangeable sensor chip (different for gas and liquid samples), a control circuit, and a commercially available portable spectrum analyzer coupled to a handheld computer. A pump and inert carrier gases are not utilized. The system can generate one or a series of single-shot microdischarges per chemical analysis. The gas discharge microchip, which utilizes electroplated copper electrodes on a glass substrate, has an electrode separation of 75 µm and an active area of 300 × 300 µm². The handheld system has been used to detect 17 ppm of acetone vapor in air. The liquid discharge microchip also has an electrode gap of 75 µm and an active area of 1 × 1 mm². It uses a porous cathode fabricated by micromolding and sintering glass frit slurry in a microchannel. When a microdischarge is initiated between the metal anode and the wet cathode, the liquid is sputtered into the microdischarge and emits characteristic line spectra. In this configuration, the system can detect 2 ppm of aqueous Cr without preconcentration. [ABSTRACT FROM AUTHOR]

Abstract: A magnetized microdischarge plasma is generated at low pressure with planar electrodes and a non-uniform magnetic field configuration causing closed E × B electron drift. Stable generation with a 1 mm electrode gap has been achieved in 0.5–55 Torr of argon. The breakdown voltage curve is found to have two local minima, the lower of which is believed to be caused by strong electron magnetization, as supported by simple Monte Carlo simulations. The current–voltage curves show strong variations between operation at 10 Torr and lower pressures. The plasma confinement, as inferred from the luminous emission of the annular-shape discharge, appears to be stronger at low pressures. Optical emission is used to infer electron excitation temperatures, which are estimated to be about 1 eV. [Copyright &y& Elsevier]

Atmospheric dielectric barrier discharges (DBDs) are typically used for activation and modification of surfaces, sterilization, bioactivation and deposition of coating barriers. Atmospheric DBDs have the advantage that, at a relatively high pressure, a cold but chemically active plasma is created. Spectra from the ozone synthesis system, using oxygen gas, have been detected in the range 300-400 nm. The dependences of the spectral intensity on the discharge voltage and the oxygen pressure has been studied. The half-width of the detected lines has been found to be within 20 Å approximately. The electron temperature within a microdischarge has been estimated by using the relative intensity of the line-to-line ratio technique of the identified spectral lines. An average mean electrons temperature of 3.6 eV has been obtained and found to be insensitive to gas pressure variation. [ABSTRACT FROM AUTHOR]

An atmospheric micro plasma is generated in micro gap electrodes with a dielectric barrier. Discharge voltage is only around 1 kV, although the electrode gap is less than 100 µm. Ozone is generated through the micro plasma electrode, which removes indoor air pollutants such as formaldehyde and nitric oxides. By making the micro gap between dielectric barrier electrodes smaller, a higher ozone concentration could be obtained. [ABSTRACT FROM AUTHOR]

The present paper studied the appearance evolution of microdischarges, the phase composition and the morphology transition of the coating formed by plasma electrolytic oxidation on AZ91D magnesium alloy. The appearance of microdischarges population experienced apparent changes in size, spatial density and colour, which related with the changes of the type and quantity of the disintegrated gas bubbles generated in the interface between the electrolyte and substrate. Correspondingly, the diameter of micropores together with netlike fine microcracks increased when the higher voltage was employed. The coating composed of MgO, MgAl2O4 and there existed a fluoride enriched zone of about 1–2 m m at the film/substrate interface, which may be closely related with the decomposition of the hexafluorinealuminate ion and the initiation, damping of the microdischarges. [ABSTRACT FROM AUTHOR]