Microsecond Discharge Research Articles

Near-Electrode Processes and the Modes of Stable Combustion of a Microsecond Discharge in Helium Under Ultraviolet Gas Preionization

Near-Electrode Processes and the Modes of Stable Combustion of a Microsecond Discharge in Helium Under Ultraviolet Gas Preionization

Microsecond Discharge Produced in Aqueous Solution for Pollutant Cr(VI) Reduction

This paper presents a detailed analysis of underwater electrical discharge parameters in the treatment of chromium (VI) used as a model pollutant to analyze the reduction process by plasma liquid interaction (PLI). Pin-to-pin microsecond discharges were performed in an aqueous Cr(VI) solution and the processes were characterized using electrical measurements, optical imaging and UV-Vis absorption measurements for [Cr(VI)] estimation. For the first time, the total reduction of Cr(VI) was successfully achieved by PLI process and a maximum energy yield of 4.7 × 10−4 g/kJ was obtained. Parametric studies on electrode geometry, applied voltage, electrodes gap and pulse duration are presented in detail. Finally, an analysis of the process is proposed by comparing our results of the energy yield calculation based on the injected energy with those of the literature and by providing an estimation of the global energy efficiency of the process.

Multiphysics analysis of thermal fluid in quasi-DC discharge in water

In the process of microsecond and millisecond pulsed discharge in water, a liquid low-density region will be formed by the effect of Joule heating. Then, thermal fluid is formed. Thermal fluid can influence the flow field and temperature distribution; and thus, it will affect the development of discharge. In this paper, the schlieren technology is used to observe the development of thermal fluid. The temperature field around the thermal fluid is calculated by the quantitative schlieren method. Finite element analysis is used to simulate the development of thermal fluid. Results show that the development of thermal fluid involves the coupling of electric fields, flow fields, and thermal fields. When there is an electric field, the movement of thermal fluid is mainly driven by the electric force, and it conforms to electrohydrodynamics. When the electric field disappears, the movement of thermal fluid is mainly driven by pressure. Due to Rayleigh–Taylor instability in the thermal fluid's head, the thermal fluid takes on a mushroom shape. The change in the thermal fluid's development direction on the side of the electrode leads to a short increase in the equivalent resistance of the gap. The study of thermal fluid is helpful to qualitatively understand quasi-DC discharge in water.

A parallel PIC-MCC simulation of microsecond discharge modeling in EDM

A parallel PIC-MCC simulation of microsecond discharge modeling in EDM

Experimental investigation on the evolution of plasma properties in the discharge channel of a pulsed plasma thruster

Pulsed plasma thrusters (PPTs) are an attractive form of micro-thrusters due to advantages such as their compactness and lightweight design compared to other electric propulsion systems. Experimental investigations on their plasma properties are beneficial in clarifying the complex process of plasma evolution during the micro-second pulse discharge of a PPT. In this work, the multi-dimensional evolutions of the light intensity of the PPT plasma with wavelength, time, and position were identified. The plasma pressure was obtained using an iterative process with composition calculations. The results show that significant ion recombination occurred in the discharge channel since the line intensities of CII, CIII, CIV, and FII decreased and those of CI and FI increased as the plasma moved downstream. At the center of the discharge channel, the electron temperature and electron density were in the order of 10 000 K and 1017 cm−3, respectively. These had maximum values of 13 750 K and 2.3 × 1017 cm−3 and the maximum temperature occurred during the first half-cycle while the maximum number density was measured during the second half-cycle. The estimated plasma pressure was in the order of 105 Pa and exhibited a maximum value of 2.69 × 105 Pa.

Effects of water states on the process of underwater electrical wire explosion under micro-second timescale pulsed discharge

This paper studied the influence of water parameters on the behaviour of an electrical wire explosion. In the experiments, a Cu wire of four sizes was exploded in water medium with different conductivity, hydrostatic pressure, and temperature. Under three typical discharge types, the electrical characteristics, shock wave, and optical emission phenomena were obtained and analysed. It has been found that the ambient medium changed the wire explosion process via adjusting the energy deposition or suppressing the later cavity expansion. Furthermore, wire explosion and its accompanied phenomena could be regulated based on the shunt effect. Finally, the mechanisms of the influence of water medium on a water gap breakdown and wire explosion were compared, and possible applications discussed.

Diagnostic method based on spontaneous emission to evaluate the detonation cycle

A study on a hydrogen-fuelled single-cycle pulse detonation device, through pressure and spontaneous emission measurements, was carried out. Detonation initiation was effectively achieved by applying a 65 J microsecond discharge associated with the Shchelkin spiral with very small errors in the diagnostic method. OH* and H2O* temporal emission measurements were applied at the nozzle exit to establish correlations to specific impulses, determined from pressure curves. OH* emission images were also captured to verify detonation propagation at the exhaust. Both the OH* and H2O* emitters correlated well with the specific impulses, and the integrated areas under emission peak maxima resulted in improved correlations. It was found that the OH* amount per kilogram of fuel grows exponentially with the specific impulse based on fuel, while the H2O* emission area per kilogram of mixture decays exponentially with the specific impulse, based on the mixture. The OH* images demonstrate stable detonation propagations and validate the established correlations. Furthermore, a new optical method was developed for detonation cycle diagnostics.

Highly efficient conversion of methane using microsecond and nanosecond pulsed spark discharges

Plasma-assisted methane (CH4) activation is a promising way for a hydrogen (H2) production. In this paper, we describe our studies of microsecond and nanosecond pulsed spark discharge plasmas use in a CH4 pyrolysis for a H2 production. The dependence of CH4 conversion and gas discharge product composition on discharge power, discharge gap length and gas flow rate are studied. The electrical and optical characteristics of the discharges are also studied to reveal discharge plasma parameters and chemical reactions leading to CH4 pyrolysis. Experimental results show that H2 and acetylene (C2H2) are the major gas discharge products accompanied by trace gas discharge products, such as ethane (C2H6), ethylene (C2H4) and carbon. The highest CH4 conversion and H2 yield, 91.2% and 38.4%, respectively, are achieved with an energy conversion efficiency of 44.3% using the microsecond pulsed spark discharge at a gap length 6 mm and a gas flow rate 50 mL/min. The carbon balance under the studied operating parameters varies from 66.7% to 92.8%. The morphology of carbon deposition is presented by two crystal forms identified by SEM and Raman spectral analyses. Finally, comparatively low electron temperature and high vibrational molecular temperature are observed in our experiments, which suggests that V-V transition for CH4 excitation process and V-T transition for CH4 heating process play important roles in CH4 pyrolysis sustained by the pulsed spark discharge.

High energy-storage density of lead-free BiFeO3 doped Na0.5Bi0.5TiO3-BaTiO3 thin film capacitor with good temperature stability

In this work, the lead-free and BiFeO3 doping Na0.5Bi0.5TiO3-BaTiO3 thin films [(0.94-x)Na0.5Bi0.5TiO3-0.06BaTiO3-xBiFeO3 (NBT-6BT-xBFO), x = 0.00, 0.01, 0.03, 0.05 and 0.07] were deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method. The enhanced ferroelectric properties and high energy-storage density have been achieved at 5% BiFeO3 substitution. Moreover, the 5% BiFeO3 doping Na0.5Bi0.5TiO3-BaTiO3 (0.89NBT-0.06BT-0.05BFO) thin-films exhibited a high dischargeable energy density (Wrecovered) of 42.9 J/cm3 with a corresponding energy-storage efficiency (η) of 65.7% under an electric field of 1720 kV/cm, and the high temperature stabilities with regard to their energy-storage properties over temperatures ranging from room temperature to 260 °C were demonstrated, and the charging and discharging characteristics demonstrate the faster microsecond discharge and large dielectric strength of the thin film capacitor. The results indicated that the 0.89NBT-0.06BT-0.05BFO thin-films might be promising environmentally friendly lead-free materials for energy-storage capacitor application.

Ternary PVDF-based terpolymer nanocomposites with enhanced energy density and high power density

The development of advanced dielectric materials with high electric energy densities is of crucial importance in modern electronics and electric power systems. Herein, a kind of ternary poly(vinylidene fluoride)-based ferroelectric terpolymer nanocomposites are prepared using a facile solution cast method. The ternary nanocomposite that is composed of barium strontium titanate (BST) and boron nitride nanosheets (BNNS) can achieve increased dielectric constant and breakdown strength simultaneously. At the optimized filler contents, the ternary nanocomposite discharges an energy density of 24.4 J/cm3, which is 295% that of pristine terpolymer. Moreover, microsecond discharge speed of 2.81 μs along with a power density that is over 13 times that of the current commercial available biaxially oriented polypropylene (BOPP) have been achieved under an electric field of 200 MV/m. The incorporation of uniformly dispersed multicomponents into polymer matrix paves a way to significantly improve energy storage capability for dielectric polymer nanocomposites film capacitors.

High breakdown strength and low loss binary polymer blends of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) and poly(methyl methacrylate)

Dielectric materials with high breakdown strength and low loss are of crucial importance in capacitive energy storage electronics. Herein, a kind of polymer blend composed of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) ferroelectric terpolymer and linear dielectric poly(methyl methacrylate) (PMMA) is presented. The polymer blend shows a breakdown strength of 733 MV/m and a charge‐discharge efficiency over 90% at 200 MV/m with optimized PMMA content, which are 101% and 28% higher than that of neat terpolymer. Moreover, microsecond discharge time of 2.26 μs, along with a power density that is 3.6 times that of the current commercially available biaxially oriented polypropylene, as well as great cyclic performance, has been achieved under an electric field of 200 MV/m. The findings of this research demonstrate that the incorporation of linear dielectric PMMA into poly(vinylidene fluoride)‐based ferroelectric polymer provides a new strategy in designing high breakdown strength low loss dielectric materials for reliable compact flexible film capacitors.

On the physical nature of apokampic discharge

Experimental and theoretical investigations of a diffuse jet (streamer) of apokampic discharge are carried out for various values of air pressure. It is established experimentally that this regime of pulse-periodic discharge is formed stage by stage. At the first stage, in a microsecond discharge of a voltage pulse of positive polarity, a potential spark channel formed during the first pulses between two needle electrodes is transformed into a diffuse channel. At the second stage, a weakly glowing halo is formed near the discharge channel, and a bright offshoot arises near the bending point. Finally, at the third stage of discharge in the steadystate mode, for frequencies of a few to tens of kilohertz in each pulse, the offshoot becomes a source of plasma bullets (streamers) moving with a velocity of up to 200 km/s. As a result of simulation of a streamer in atmospheric pressure air under conditions corresponding to the experimental data, a propagation velocity of up to 400 km/s is obtained for the streamer. It is shown that the formation of a jet significantly depends on the air temperature.

Subsonic streamers in water: initiation, propagation and morphology

In this paper, we focus on the development and morphology of underwater subsonic streamers in a pin–plane electrode configuration. The processes of initiation, propagation and branching of underwater subsonic streamers are studied in detail, and the effects of applied voltage amplitude and polarity are discussed. The results show a similar initiation process for both polarities including the formation of a low-density shadowed region, an initial bubble and streamers. Joule heating is thought to be the dominant intrinsic dynamic in the initiation process. There is a distinct difference in the propagation mode and the morphology between positive and negative subsonic streamers. Positive subsonic streamers develop in the form of a bubble cluster with a constant low speed of 20–80 m s−1, but the development mode transition from bubble cluster to secondary streamer occurs at the final stage of streamer propagation. On the other hand, negative subsonic streamers develop in the form of tree-like structures with a thinner root and propagate faster at a speed of 100–370 m s−1, and the propagation velocity increases significantly near the final breakdowns. A specific phenomenon has been observed in which the breakdown voltage of positive polarity can be higher than that of negative polarity in micro-second underwater discharge. The above results indicate that the polarity effect of subsonic streamers is quite different from that of the supersonic streamers.

Experimental verification of the vaporization's contribution to the shock waves generated by underwater electrical wire explosion under micro-second timescale pulsed discharge

This paper studies pressure waves generated by exploding a copper wire in a water medium, demonstrating the significant contribution of the vaporization process to the formation of shock waves. A test platform including a pulsed current source, wire load, chamber, and diagnostic system was developed to study the shock wave and optical emission characteristics during the explosion process. In the experiment, a total of 500 J was discharged through a copper wire load 0.2 mm in diameter and 4 cm in length. A water gap was installed adjacent to the load so that the current was diverted away from the load after breakdown occurred across the water gap. This allows the electrical energy injection into the load to be interrupted at different times and at different stages of the wire explosion process. Experimental results indicate that when the load was bypassed before the beginning of the vaporization phase, the measured peak pressure was less than 2.5 MPa. By contrast, the peak pressure increased significantly to over 6.5 MPa when the water gap broke down after the beginning of the vaporization phase. It was also found that when bypassing the load after the voltage peak, similar shock waves were produced to those from a non-bypassed load. However, the total optical emission of these bypassed loads was at least an order of magnitude smaller. These results clearly demonstrate that the vaporization process is vital to the formation of shock waves and the energy deposited after the voltage collapse may only have a limited effect.

Defects and Charge-Trapping Mechanisms of Double-Active-Layer In-Zn-O and Al-Sn-Zn-In-O Thin-Film Transistors.

Active matrix organic light-emitting diodes (AMOLEDs) are considered to be a core component of next-generation display technology, which can be used for wearable and flexible devices. Reliable thin-film transistors (TFTs) with high mobility are required to drive AMOLEDs. Recently, amorphous oxide TFTs, due to their high mobility, have been considered as excellent substitutes for driving AMOLEDs. However, the device instabilities of high-mobility oxide TFTs have remained a key issue to be used in production. In this paper, we present the charge-trapping and device instability mechanisms of high-mobility oxide TFTs with double active layers, using In-Zn-O (IZO) and Al-doped Sn-Zn-In-O (ATZIO) with various interfacial IZO thicknesses (0-6 nm). To this end, we employed microsecond fast current-voltage (I-V), single-pulsed I-V, transient current, and discharge current analysis. These alternating-current device characterization methodologies enable the extraction of various trap parameters and defect densities as well as the understanding of dynamic charge transport in double-active-layer TFTs. The results show that the number of defect sites decreases with an increase in the interfacial IZO thickness. From these results, we conclude that the interfacial IZO layer plays a crucial role in minimizing charge trapping in ATZIO TFTs.

Fabrication of Wound Capacitors Using Flexible Alkali-Free Glass

Alkali-free glasses, which exhibit high energy storage densities ( $\sim 35$ J/cc), present a unique opportunity to couple high temperature stability with high breakdown strength, and thus provide an avenue for capacitor applications with stringent temperature and power requirements. Realizing the potential of these materials in kilovolt class capacitors with >1 J/cc recoverable energy density requires novel packaging strategies that incorporate these extremely fragile dielectrics. In this paper, we demonstrate the feasibility of fabricating wound capacitors using 50- $\mu \text{m}$ -thick glass. Two capacitors were fabricated from 2.8-m-long ribbons of thin (50 $\mu \text{m}$ ) glass wound into 125–140-mm-diameter spools. The capacitors exhibit a capacitance of 70–75 nF with loss tangents below 1%. The wound capacitors can operate up to 1 kV and show excellent temperature stability to 150 °C. By improving the end terminations, the self-resonance can be shifted to above 1 MHz, indicating that these materials may be useful for pulsed power applications with microsecond discharge times.

Effects of Plasma Aerodynamic Actuation on Corner Separation in a Highly Loaded Compressor Cascade

This paper reports experimental results on the effects of plasma aerodynamic actuation (PAA) on corner separation control in a highly loaded, low speed, linear compressor cascade. Total pressure loss coefficient distribution was adopted to evaluate the corner separation control effect in wind tunnel experiments. Results of pressure measurements and particle image velocimetry (PIV) show that the control effect of pitch-wise PAA on the endwall is much better than that of stream-wise PAA on the suction surface. When both the pitch-wise PAA on the endwall and stream-wise PAA on the suction surface are turned on simultaneously, the control effect is the best among all three PAA types. The mechanisms of nanosecond discharge and microsecond discharge PAA are different in corner separation control. The control effect of microsecond discharge PAA turns out better with the increase of discharge voltage and duty cycle. Compared with microsecond discharge PAA, nanosecond discharge PAA is more effective in preventing corner separation when the freestream velocity increases. Frequency is one of the most important parameters in plasma flow control. The optimum excitation frequency of microsecond discharge PAA is 500 Hz, which is different from the frequency corresponding to the case with a Strouhal number of unity.

Ultra High Energy Density Nanocomposite Capacitors with Fast Discharge Using Ba0.2Sr0.8TiO3 Nanowires

Nanocomposites combining a high breakdown strength polymer and high dielectric permittivity ceramic filler have shown great potential for pulsed power applications. However, while current nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Here, we develop a new synthesis method for the growth of barium strontium titanate nanowires and demonstrate their use in ultra high energy density nanocomposites. This new synthesis process provides a facile approach to the growth of high aspect ratio nanowires with high yield and control over the stoichiometry of the solid solution. The nanowires are grown in the cubic phase with a Ba0.2Sr0.8TiO3 composition and have not been demonstrated prior to this report. The poly(vinylidene fluoride) nanocomposites resulting from this approach have high breakdown strength and high dielectric permittivity which results from the use of high aspect ratio fillers rather than equiaxial particles. The nanocomposites are shown to have an ultra high energy density of 14.86 J/cc at 450 MV/m and provide microsecond discharge time quicker than commercial biaxial oriented polypropylene capacitors. The energy density of our nanocomposites exceeds those reported in the literature for ceramic/polymer composites and is 1138% greater than the reported commercial capacitor with energy density of 1.2 J/cc at 640 MV/m for the current state of the art biaxial oriented polypropylene.

Influence of excitation voltage waveform on dielectric barrier discharge plasma aerodynamic actuation characteristics

Plasma flow control, based on the plasma aerodynamic actuati on generated by air discharge, is an active field in aerodynamics due to its potential application in performance improvement of future aircraft. In order to better understand the underlying physical mechanism of plasma flow control, it is i mportant to investigate the relationship between the operating parameters and the plasma aerodynamic actuation characteristics. This paper reports the electrical, optical and mech anical characteristics of surface dielectric barrier discharge p lasma aerodynamic actuation excited by microsecond and nanosecond high voltage waveforms. The nanosecond discharge is more diffuser than the microsecond discharge and the discharge current is much larger at the same applied voltage amplitude. The optical emission intensity of the nanosecond discharge plasma is stronger than that of the microsecond discharge plasma, while the rotational and vibrational temperatures of N2 in the nanosecond discharge plasma are less. In addition, the relative intensity of the first negative system of N + 2 (B 2 � + u ! X 2 � + g ) and the second positive system of N2(C 3 �u ! B 3 �g) is much less in the nanosecond discharge plasma. The velocity measurements indicate that the air flow induced by the nanose cond discharge plasma aerodynamic actuation is vertical to the dielectric surface, while that induced by the microsecond discharge actuation is parallel to the dielectric surface.

Measurement of Acoustic Emission Wave by Using Optical Fiber Sensor during Microsecond Discharge

In this study, we investigate the effect of discharge current on the occurrence of burst AE wave caused by microsecond discharge. Electrical discharge duration was changed from about 1µs to 8µs by using condenser circuit. Effect of current behavior was estimated by comparing with experimental signal and simulation one. AE wave was detected by optical fiber vibration sensor. The optical fiber vibration sensor is located on an aluminum work-piece (cathode) plate. Simulation was carried out with MSC. Marc. As the results, it was found that AE wave was occurred by a force depending on electrical current behavior. The force direction was machining direction. The force has been occurred during microsecond discharge.