The effect of the configuration of a single electrode corona discharge on its acoustic characteristics

A new sparker system based on pulsed spark discharge with a single electrode has already been utilized for oceanic seismic exploration. However, the electro-acoustic energy efficiency of this system is lower than that of arc discharge based systems. A simple electrode structure was investigated in order to improve the electro-acoustic energy efficiency of the spark discharge.Experiments were carried out on an experimental setup with discharge in water driven by a pulsed power source. The voltage–current waveform, acoustic signal and bubble oscillation were recorded when the relative position of the electrode varied. The electro-acoustic energy efficiency was also calculated. The load voltage had a saltation for the invaginated electrode tip,namely an obvious voltage remnant. The more the electrode tip was invaginated, the larger the pressure peaks and first period became. The results show that electrode recessing into the insulating layer is a simple and effective way to improve the electro-acoustic energy efficiency from 2% to about 4%.     

Underwater pulsed spark discharge influenced by the relative position between the top of a pin electrode and an insulating tube

Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges. The position relationship between the needle tip and insulation layer significantly affects the discharge patterns. We carried out experiments on underwater pulsed discharge with the needle tip protruding from, recessing into, and flushing with the insulating tube. The results are as follows. First, underwater pulsed discharge has a strong randomness under the experimental conditions. Different discharge patterns appeared under the same experimental environment. Second, recession into the insulator surface led to a higher probability of occurrence but a lower strength of spark discharge than protrusion. Third, between the needle tip protruding from and recessing into the insulation material, the average speed of propagation of underwater pulsed spark discharge decreased by an order of magnitude. The study shows that the optimum length of needle tip protruding from the insulation layer is 1 mm to obtain a strong underwater pulsed spark discharge.     

Plasma Discharge Process in a Pulsed Diaphragm Discharge System

As one of the most important steps in wastewater treatment, limited study on plasma discharge process is a key challenge in the development of plasma applications. In this study, we focus on the plasma discharge process of a pulsed diaphragm discharge system. According to the analysis, the pulsed diaphragm discharge proceeds in seven stages： （1） Joule heating and heat exchange stage; （2） nucleated site formation; （3） plasma generation （initiation of the breakdown stage）; （4） avalanche growth and plasma expansion; （5） plasma contraction; （6） termination of the plasma discharge; and （7） heat exchange stage. From this analysis, a critical voltage criterion for breakdown is obtained. We anticipate this finding will provide guidance for a better application of plasma discharges, especially diaphragm plasma discharges.     

The Degradation of Organic Pollutants by Bubble Discharge in Water

Organic pollutants could be degraded by using bubble discharge in water with gas aeration in the discharge reactor and more plasma can be generated in the discharge process.When pulsed high voltage was applied between electrodes with gas aerated into the reactor,it showed that bubbles were broken,which meant that breakdown took place.It could also be observed that the removal rate of phenol increased with increasing discharge voltage or pulse frequency,and with reducing initial phenol concentration or solution electric conductivity.It could remove more amount of phenol by oxygen aeration.With increasing oxygen flow rate,the removal rate increased.There was little difference with air or nitrogen aeration for phenol removal.The solution temperature after discharge increased to a great extent.However,this part of energy consumption did not contribute to the reaction,which led to a reduction in the energy utilization efficiency.     

Investigation on discharge characteristics of a coaxial dielectric barrier discharge reactor driven by AC and ns power sources

A coaxial dielectric barrier discharge(DBD) reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond(ns)pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.     

Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge

Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity.     

A comparative study on the activity of TiO2 in pulsed plasma under different discharge conditions

In the present study,a combination of pulsed discharge plasma and TiO_2(plasma/TiO_2)has been developed in order to study the activity of TiO_2by varying the discharge conditions of pulsed voltage,discharge mode,air flow rate and solution conductivity.Phenol was used as the chemical probe to characterize the activity of TiO_2in a pulsed discharge system.The experimental results showed that the phenol removal efficiency could be improved by about 10%by increasing the applied voltage.The phenol removal efficiency for three discharge modes in the plasma-discharge-alone system was found to be highest in the spark mode,followed by the spark–streamer mode and finally the streamer mode.In the plasma/TiO_2system,the highest catalytic effect of TiO_2was observed in the spark–streamer discharge mode,which may be attributed to the favorable chemical and physical effects from the spark–streamer discharge mode,such as ultraviolet light,O_3,H_2O_2,pyrolysis,shockwaves and high-energy electrons.Meanwhile,the optimal flow rate and conductivity were 0.05 m~3l~(-1)and 10μS cm~(-1),respectively.The main phenolic intermediates were hydroquinone,catechol,and p-benzoquinone during the discharge treatment process.A different phenol degradation pathway was observed in the plasma/TiO_2system as compared to plasma alone.Analysis of the reaction intermediates demonstrated that p-benzoquinone reduction was selectively catalyzed on the TiO_2surface.The effective decomposition of phenol constant(D_e)increased from 74.11%to 79.16%when TiO_2was added,indicating that higher phenol mineralization was achieved in the plasma/TiO_2system.     

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated(PM) radio-frequency(RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 10~(17) m~(-3) within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.     

Research on Nanosecond Pulse Corona Discharge Attenuation

A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control. Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted. The results show that the wave front decreases sharply during the corona discharge along the corona wire. The higher the amplitude of the applied pulse is, the more the amplitude of the wave front decreased. The wave attenuation responds in a lower corona discharge inversely. To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design.     

Experimental study on nanosecond pulsed pin-to-plate discharge in supersonic air flow

Development of magnetohydrodynamic acceleration technology is expected to improve wind tunnel simulation capability and testing capability. The underlying premise is to produce uniform and stable plasma in supersonic air flow, and gas discharge is an effective way to achieve this. A nanosecond pulsed discharge experimental system under supersonic conditions was established, and a pin-to-plate nanosecond pulsed discharge experiment in Mach 2 air flow was performed to verify that the proposed method produced uniform and stable plasma under supersonic conditions. The results show that the discharge under supersonic conditions was stable overall, but uniformity was not as good as that under static conditions. Increasing the number of pins improved discharge uniformity, but reduced discharge intensity and hence plasma density. Under multi-pin conditions at 1000 Hz, the discharge was almost completely corona discharge, with the main current component being the displacement current, which was smaller than that under static conditions.     

Electrical Characteristics of Pulsed Corona Discharge Plasmas in Chitosan Solution

Pulsed discharge plasma has exhibited active potential to prepare low molecular weight chitosan. In the present study, the viscosity of ehitosan solution was decreased noticeably after treated with pulsed corona discharge plasma. An experimental investigation on electrical characteristics of pulsed corona discharge plasma in chitosan solution was conducted with a view toward getting insight into discharge process. Factors affecting I-V curve, single pulse injec- tion energy and pulse width were studied. Experimental results showed positive effect of pulsed peak voltage on discharge plasma in chitosan solution. Pulse-forming capacitor greatly influenced the discharge form, and 4 nF was observed as a suitable value for efficiently generating stable discharge plasmas. As the electrode distance was larger than 10 ram, it had slight impact on dis- charge plasma due to the excellent conductive-property of chitosan solution. The injection energy significantly increased with air flow rate, while the pulse width hardly changed as the air flow rate increased from 0.5 m^3/h to 1.0 m^3/h. This study is expected to provide reference for promoting the application of pulsed corona discharge plasma to ehitosan solution treatment.     

Influence of electrical parameters on H2O2 generation in DBD non-thermal reactor with water mist

A dielectric barrier discharge (DBD) reactor is introduced to generate H2O2 by non-thermal plasma with a mixture of oxygen and water mist produced by an ultrasonic atomizer.The results of our experiment show that the energy yield and concentration of the generated H2O2 in the pulsed discharge are much higher than that in AC discharge,due to its high energy efficiency and low heating effect.Micron-sized liquid droplets produced by an ultrasonic atomizer in water mist have large specific surface area,which greatly reduces mass transfer resistance between hydroxyl radicals and water liquids,leading to higher energy yield and H2O2 concentration than in our previous research.The influence of applied voltage,discharge frequency,and environmental temperature on the generated H2O2 is discussed in detail from the viewpoint of the DBD mechanism.The H2O2 concentration of 30 mg 1-1,with the energy yield of 2 g kW-1h 1 is obtained by pulsed discharge in our research.     

脉冲强磁体专用设计软件开发

在设计脉冲强磁体时,需综合考虑材料的电性能、热性能和机械性能,优化磁体结构,使其达到最佳。本工作开发的脉冲强磁体专用设计软件,不仅能准确计算放电过程、温度和应力分布,还能使用优化技术,寻找最佳磁体结构,提高磁体设计水平和效率。实验结果表明,软件分析结果与实验结果吻合。     

Three modes of a direct-current plasma jet operated underwater to degrade methylene blue

A direct-current air plasma jet operated underwater presents three stable modes including an intermittently-pulsed discharge, a periodically-pulsed discharge and a continuous discharge with increasing the power voltage. The three discharge modes have different appearances for the plasma plumes. Moreover, gap voltage-current characteristics indicate that the continuous discharge is in a normal glow regime. Spectral lines from reactive species(OH, N_2, N_2~+, H_α,and O) have been revealed in the emission spectrum of the plasma jet operated underwater.Spectral intensities emitted from OH radical and oxygen atom increase with increasing the power voltage or the gas flow rate, indicating that reactive species are abundant. These reactive species cause the degradation of the methylene blue dye in solution. Effects of the experimental parameters such as the power voltage, the gas flow rate and the treatment time are investigated on the degradation efficiency. Results indicate that the degradation efficiency increases with increasing the power voltage, the gas flow rate or the treatment time. Compared with degradation in the intermittently-pulsed mode or the periodically-pulsed one, it is more efficient in the continuous mode, reaching 98% after 21 min treatment.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

Pulsed high-current discharge in water: adiabatic model of expanding plasma channel and acoustic wave

This paper presents the results of a theoretical and experimental study of the use of a pulsed discharge in water to obtain a strong acoustic wave in a liquid medium. A discharge with a current amplitude of 10 kA, a duration of 400 ns, and an amplitude pulsed power of 280 MW in water at atmospheric pressure created an expanding acoustic wave with an amplitude of more than 100 MPa. To describe the formation of the discharge channel, an isothermal plasma model has been developed, which made it possible to calculate both the expansion dynamics of a high-current channel and the strong acoustic wave generated by it. Our calculations show that the number density of plasma in the channel reaches 10²⁰ cm^–3, while the degree of water vapor ionization is about 10%, and the channel wall extends with a velocity of 500 m s−1. The calculations for the acoustic wave are in good agreement with measurements.     

Spectroscopic diagnosis of plasma in atmospheric pressure negative pulsed gasliquid discharge with nozzle-cylinder electrode

The plasma characteristics of a gas-liquid phase discharge reactor were investigated by optical and electrical methods.The nozzle-cylinder electrode in the discharge reactor was supplied witha negative nanosecond pulsed generator.The optical emission spectrum diagnosis revealed that OH(A~2∑~+?→?X~2Π,306–309 nm),N~3_2(CΠ→B~3Π_g,337 nm),O(3p~5p→3s~5s~0,777.2 nm)and O(3p~3p→3s~3s~0,844.6 nm)were produced in the discharge plasma channels.The electron temperature(T_e)was calculated from the emission relative intensity ratio between the atomic O 777.2 nm and 844.6 nm,and it increased with the applied voltage and the pulsed frequency and fell within the range of 0.5–0.8 e V.The gas temperature(T_g)that was measured by Lifbase was in a range from 400 K to 600 K.     

Direct impact characteristics of magnesite fragmentation by pulsed discharge in water

To clarify direct impact characteristics (pressure and position) of middle-grade magnesite fragmentation by pulsed discharge in water, this work uses pressure film to accomplish passive measurement through pulsed discharge experiment and obtain the pressure. The impact position is determined by image analysis of fragmentation product morphology, crack edge and discharge channel. Then, pressure load on magnesite surface is numerically analyzed based on the measured pressure obtained from the film. Results indicate that, at 10 mm discharge gap, the impact pressure increases with the discharge voltage, and the discharge voltage to disintegrate magnesite is −40 kV. The impact position is normally in the boundary among different mineral components. Simulation analysis indicates that, the pressure load applied directly on magnesite surface is approximately 142.5 MPa at −40 kV and greater than the compressive strength of magnesite, thus leading to the fragmentation.     

Evolution of Striation in Pulsed Glow Discharges

In this work,striations in pulsed glow discharges are studied by experiments and Particle-In-Cell/Monte Carlo Collision (PIC/MCC) simulation.The spatio-temporal evolution of the potential and the electron energy during the discharge are analyzed.The processes of striation formation in pulsed glow discharges and dielectric barrier discharges (DBD) are compared.The results show that the mechanisms of striation in pulsed DC discharge and DBD are similar to each other.The evolution of electron energy distribution function before and after the striation formation indicates that the striation results from the potential well of the space charge.During a pulsed breakdown,the striations are formed one by one towards the anode in a weak field channel.This indicates that the formation of striations in a pulsed discharge depends on the flow of modulated electrons.     

Effect of Airflows on Repetitive Nanosecond Volume Discharges

Atmospheric pressure discharges excited by repetitive nanosecond pulses have attracted significant attention for various applications.In this paper,a plate-plate discharge with airflows is excited by a repetitive nanosecond pulse generator.Under different experiment conditions,the applied voltages,discharge currents,and discharge images are recorded.The plasma images presented here indicate that the volume discharge modes vary with airflow speeds,and a diffuse and homogeneous volume discharge occurs at the speed of more than 35 m/s.The role of airflows provides different effects on the 2-stage pulse discharges.The 1st pulse currents nearly maintain consistency for different airflow speeds.However,the 2nd pulse current has a change trend of first decreasing and then rapidly increasing,and the value difference for 2nd pulse currents is about 20 A under different airflows.In addition,the experimental results are discussed according to the electrical parameters and discharge images.