Earthed Electrode Research Articles

Time- and space-resolved LIF measurement of the concentration of OH radicals generated by surface barrier discharge emerging from liquid water

The concentration of OH radicals has been mapped in three-dimensions by scanning planar laser-induced fluorescence (LIF) in the vicinity of surface barrier discharge emerging from liquid water and propagating along a fused silica dielectric tube in argon. The concentration peaked in the region of active discharges near the water level at the value of 1.5 × 1021 m−3 and decreased with the distance on a characteristic length of ∼0.4 mm, which suggests that the OH transport is dominated by diffusion. The OH production increases with power input (P) until it saturates for P > 0.75 W. It has been observed that the repetitive discharge appearance at preferred locations can be changed to stochastic (i.e. macroscopically homogeneous) by increasing the thickness of deionized water covering the earthed electrode.

Mechanism of pH Variation and H2O2 Generation in Water Exposed to Pulsed Discharge Plasma

Positive and negative pulsed discharge plasma is generated above test liquid containing NaCl in Ar atmosphere, and the spatiotemporal variation of pH value in the liquid is visualized by a colorimetric method using bromothymol blue. Furthermore, polarity effects on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> generation are examined by electrochemical calculation and a colorimetric method using titanium sulfate. When the positive pulsed discharge plasma is generated, the pH value of the liquid is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the dissociation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , formed by the charge exchange reaction between Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, while the pH value of the vicinity of an earthed electrode is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation through the electrolysis of water. When the negative pulsed discharge plasma is generated, the pH value of the liquid is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> reduction, respectively, through the reaction of hydrated electrons with H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , while the pH value in the vicinity of the earthed electrode is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the electrolysis of water. The generation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is found to be promoted when the positive pulsed discharge plasma is generated, and this increase rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is in approximate agreement with the calculated generation rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which is produced from OH generated by electrolysis.

Effect of Interfacial Condition between Film and Earthed Electrode on Space Charge Measurement

Effect of Interfacial Condition between Film and Earthed Electrode on Space Charge Measurement

Electrical excitation of the local earth for resonant, wireless energy transfer

Here we demonstrate wireless energy transfer that exploits the conductivity and permittivity of soil to create a potential gradient on the surface around an earthed electrode, distributing electrical energy over the area. This generated surface potential can be amplified using a special standing-wave receiver for harnessing the distributed energy. We have experimentally mapped the surface potential around the electrode and plotted the received energy covering an area of 1200 m2. Key operating parameters are determined with a discussion on optimizing the system efficiency. This technique could address the challenge of distributing electrical energy to many low power devices over large outdoor areas without the use of wires.

Experimental investigation of cooling of a plate by ionic wind from a corona-forming wire electrode

We report on the results of experimental investigations of the kinematic structure of ionic wind from a wire electrode placed near a heated plate, which plays the role of the earthed electrode. Experiments are carried out in a wide range of voltages for different polarities of the wire for several values of the electrode gap. We compare the structures of the flows emerging as a result of natural convection in open air for different positions of the plate and in the presence of a fast ionic wind jet that considerably intensifies heat transfer in the boundary layer at the heated planar electrode. Local temperature distributions over the plate surface are obtained, as well as the integral dependences of the effective heat removal on the electric parameters of the corona discharge. The velocity of air flows with ionic wind reaches 4 m/s, and the heat power removed from the plate for fixed overheating increases ninefold compared to the situation with natural convection.

Ion current density profiles in negative corona gaps versus EHD confinements

This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode.

The Effect of the Earthed Electrode Size on the Ignition Voltage of Low-Pressure RF Capacitive Discharge in Argon

The effect of the grounded electrode diameter on the ignition voltage using 13.56 MHz in argon gas is studied experimentally. The results indicate a systematic decrease of the breakdown voltage with increasing electrode area for the same pd value. No multi-valued breakdown voltages are observed. The Paschen minimum is not affected by the electrode diameter as long as the parallel plane approximation is valid. A modified Paschen equation which takes into account indirect discharge via the chamber walls at high pd values gives reasonable fits to the experimental data.

Ozone Production Characteristics in a Dielectric Barrier Discharge Type Ozonizer Driven by Pulsed Power

Ozone has many applications in various fields with an advantage of low environmental load, i.e., water treatment, sterilization, deodorization, bleaching, etc. While the dielectric barrier discharge (DBD) is mainly used for practical ozone generator, the various discharge methods have been studied to achieve higher yield and higher concentration of ozone generation in recent years. This study is carried out to compose ozone using a Blumlein type pulse forming network (B-PFN) as a discharge power source combined with the ordinary DBD type ozone generator. The ozone generator is equipped a pair of coaxial cylinder electrodes. The inner electrode is stainless steel cylinder and is applied pulsed voltage. The outer electrode is covered by glass lining of inner surface of electrode and is act as earthed electrode. This generator gives maximum ozone concentration of about 57g/Nm3 by negative polarity and maximum ozone yield of about 900g/kWh by positive polarity. These results are compared with other results using pulsed power discharges. We also investigated temporal variation of ozone concentration, related to “Ozone zero phenomena”.

Partial inerting – A possible means of eliminating the brush-discharge-ignition hazard with explosive gases and vapours?

It was found that the brush discharge ignition hazard with IIA gases/vapours (propane) can be eliminated by reducing the oxygen/nitrogen volume ratio in the atmosphere to the order of 15/85. The condition is that the diameter of the earthed electrode ≤ 40 mm. Published information on whether an oxygen/nitrogen ratio of 15/85 is acceptable as regards the oxygen deficiency hazards is contradictory. With IIB gases/vapours (ethylene) the oxygen/nitrogen ratio must be reduced to at least 10/90 to eliminate the brush-discharge-ignition hazard. Lowering the oxygen/nitrogen ratio to this level will undoubtedly present a substantial oxygen deficiency hazard to humans. ► Brush discharge ignition of IIA gases can be eliminated if the O 2 /N 2 volume ratio is reduced to ≤15/85. ► The condition is that radii of curvature of earthed electrodes ≤20 mm. ► Whether or not this is acceptable in terms of oxygen deficiency hazards to humans is unclear. ► With IIB gases an O 2 /N 2 ratio << 15/85 is required for eliminating the brush discharge ignition hazard. ► When assessing the brush discharge ignition hazard all MIEs must be determined by identical methods.

Hydrogenated amorphous carbon and carbon nitride films deposited at low pressure by plasma enhanced chemical vapor deposition

Hydrogenated amorphous carbon (a-C:H) films were deposited by plasma enhanced chemical vapor deposition from methane, argon diluted methane, and nitrogen diluted methane at 26.7 Pa with a 13.56 MHz RF power supply. In this pressure regime, multiple-scattering of carbon species within the plasma phase is expected during the transport to the substrates placed on both the driven and the earthed electrodes. These films were analyzed using UV–VIS optical transmittance, monochromatic ellipsometry, Raman spectroscopy and current–voltage measurements. From these results, the effect of the plasma conditions and the effective flux of the carbon species controlled by the input power through the negative self bias are found to be important in the deposition process. The growth conditions at the higher pressure regime are important to synthesize a-C:H films from low energetic carbon species, since it reduces the defect density and improves the quality of the films. Furthermore, the effect of nitrogen on the growth conditions of a-C:H:N films is observed.

Gas analogue of the Ganna effect under conditions of two-electrode discharge of continuous current

The existence of a mode of periodic movement of a volumetric charge of negative sign from an electrode with a negative potential (600–4500 V) in the direction of the other earthed electrode was discovered. The experiments were carried out with the discharge of a constant current in the presence of the pressure of air (10−3–10 Torr) in tubes with various internal diameters (3.8, 6.6, 15.5, 20.1, and 25.8 mm) but with the same (510 mm) distance between the electrodes. The opportunity for the appearance of the mode of periodic discharge was provided by the connection to the potential output of a source of several condensers of large capacity (300 μF). It is supposed that the discovered periodic mode of the gas discharge is similar to the Gann effect—the movement of a volumetric charge of negative sign in the volume of a semiconductor.

Plasma decoloration of dye using dielectric barrier discharges with earthed spraying water electrodes

The plasma decoloration process of indigo carmine aqueous solution is investigated in this paper using a dielectric barrier discharge with earthed spraying water electrodes (spraying DBD). The influence of high voltage and air gaps on decoloration and the power consumption in the process are discussed. The indigo carmine aqueous solution was employed as a grounded spraying water electrode. The plate electrode was covered by a layer of glass dielectric on its inter-electrode surface and supplied with AC 50 Hz high voltage. The spraying DBD non-thermal plasma was formed in the air gap between the water electrodes and the glass dielectric plate. The experimental results have shown that the decoloration rate increases with rising high voltages and decreasing air gaps. When the air gaps were 30 mm and the voltage was 30 kV, the decoloration rate went up to 95% in 18 min. Using a lesser amount of power the higher decoloration rate could be reached when the air gaps were 30 mm and the voltage was 25 kV.

Electric field-controlled mesoscale burners

The use of field-induced drag exercised on corona-generated ions is optimised for inducting the air needed for stoichiometric combustion in compact, simple, lightweight, robust and self-contained burners with no moving parts. These burners operate with a wide variety fuels without sooting, at intensities sufficient to release power in the region of several kW. Gaseous and liquid fuels are injected and the flame stabilized immediately above an earthed ring electrode using various designs of capillary feeds to wicks of ceramic wool which also act as porous plug burners and bluff body flame stabilizers. The several regimes of flame stabilization at various flow velocities are discussed. Blowers involving multi-staging and the addition of field-induced swirl are explored but the favored ion blower design is the simplest, smallest and most economical. At about 7 ml in volume, it can deliver some 1.2 L/s of air, corresponding to a thermal output of 4–5 kW for stoichiometric hydrocarbon mixtures. The fraction of a Watt needed for the ion-driven air induction is so negligible a proportion of the thermal output that, if necessary, it could be generated thermoelectrically at the burner mouth. Short, premixed, highly turbulent flames are stabilized for C n H 2 n+2 with n = 1 , 3, 6, 10 and with meths (denatured ethanol), for the smallest blower dimensions, operating at an electrical input of about 0.4 W. The largest thermal power outputs for a given wick area are achieved with those fuels that are least prone to sooting. The burner is designed to operate also in the absence of natural convection; i.e., in microgravity environments.

Inducing gas flow and swirl in tubes using ionic wind from corona discharges

Air induction and rotation about the axis of a vertical tube is generated by an assembly of corona discharges between pinpoints and earthed electrodes, which induces a swirling ionic wind. The mechanism is elucidated and the geometrical configuration of the electric field lines of force is optimised by studying the deposition of charged particles on the earth electrodes, by numerical modelling of a simplified geometry and ultimately by maximising the measured tangential velocities. Upward convective flows of up to a litre per second are provided by an additional ionic wind pump at the base of the tube. With assemblies of up to three layers of six points each, tangential velocities of up to 3.3 m/s (≈900 rpm) are attained at the periphery, as recorded by small Pitot tubes. The concept, developed particularly for microgravity environments, appears suitable for adding a substantial centrifugal contribution to the operation of electrostatic precipitators and as a basis for further progress on electrical field-controlled burners.

Maximizing ion-driven gas flows

Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, we investigate methodologies for increasing their flow velocities, both theoretically and by experiments. The parameters evaluated include divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. We find that the behavior of ionic wind generators is analogous to that of fans and our modifications have more than doubled the maximum previously reported ion-driven wind velocities.

Particle-in-cell simulation of an electron shock wave in a rapid rise time plasma immersion ion implantation process

A one-dimensional Monte Carlo collision‐particle-in-cell plasma computer code was used to simulate plasma immersion ion implantation by applying a negative voltage pulse to the substrate while the reactor wall is grounded. The results presented here show the effect of short rise time pulses: for rise times shorter than the electron plasma period stypically 5 ns/ kVd, an electron shock wave is observed where a rapidly expanding sheath heats the electrons up to high energies. Many of these fast electrons are expelled from the plasma leading to a high plasma potential and thus to a high surface electric field on the earthed electrode which could give rise to non-negligible electron field emission. © 2005 American Institute of Physics . fDOI: 10.1063/1.1872894g

Application of the Direct Radon Transform for Processing of a Spatiotemporal Dependence of Spontaneous Emission from a Nanosecond Discharge in Long Tubes

In the present work, the application of the direct Radon transform for precision velocity measurements in physical experiments is considered. As a concrete example, we consider an experimental spatiotemporal dependence of spontaneous emission from a nanosecond discharge in the region of forming ionizing waves of the potential gradient (IWPG) [1]. As is well known, nanosecond gas breakdowns in long gas-discharge tubes are accompanied by the formation of IWPG propagating from the high-voltage electrode to the earthed electrode with positive and negative polarity of the applied voltage [2]. The velocity of these ionization waves depends on a number of factors, in particular, on the gas pressure and the applied voltage amplitude, and is typically in the range 10–10 cm/s. The main peculiarity of the wave breakdown mechanism is that virtually all electric field applied to the gap is concentrated at the IWPG front. These discharges are efficient active media for lasers on self-limiting transitions and plasma Penning lasers on mixtures of inert gases with easily ionized compounds [2, 3]. Figure 1 shows the experimental spatiotemporal distribution of the spontaneous emission intensity, in relative units, in the form of a two-dimensional black-and-white image with black color corresponding to the intensity minimum and white color corresponding to the intensity maximum. Figure 2 shows the direct Radon transform [3]

An EPR study at X- and W-band of defects in a-C:H films in the temperature range 5–300 K

Electron paramagnetic resonance (EPR) measurements have been made at X-band (≈9.5 GHz) and W-band (≈95 GHz) of a-C:H films on (1 0 0) silicon substrates; the sample temperature was varied in the range 5–300 K. Two types of film were examined. The first type are amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapour deposition (PECVD) with negative self bias voltages in the approximate range 100–500 V. The second type were initially highly polymeric-like a-C:H films grown on Si placed on the earthed electrode of a PECVD system but were subsequently implanted with either 6×10 15 cm −2 B + or 2×10 16 cm −2 B + ions. At both X- and W-band and throughout the temperature range 5–300 K the EPR signal of the carbon unpaired electrons consists of a single symmetric line with g=2.0026±0.0002. As the temperature is lowered, several samples develop a dependence on sample orientation of the external field required for resonance. This anisotropy is explained in terms of the demagnetising fields more usually encountered in ferromagnetic resonance.

Ignition tests with brush discharge between a spherical electrode and a PVC plate in hydrogen–air mixture

In this work, we report the ignition potential between an earthed spherical metal electrode and a charged insulating plate in hydrogen–air mixture. The test results indicate that it is very difficult to generate brush discharge when the surface potential of the plate center is less than −10 kV. And it is very difficult to ignite the hydrogen–air mixture when the surface potential of the plate center is less than −20 kV. The ignition can be generated when the range of the hydrogen concentration is 20–25%.

Dynamic analysis of motion of spherical metallic particles in non-uniform electric field

This paper presents a theoretical analysis of the dynamics of motion of spherical metallic particles under non-uniform fields for direct-current gas-insulated switchgear (dc GIS) and for electrostatic separators/sizers (ESS). The particle equations of motion between a pair of diverging conducting plates are numerically solved in three dimensions using a computational algorithm. The upper plate is energized by HV dc or HV ac of variable frequency, while the lower one is grounded. In the case of ESS, the lower electrode is also mounted horizontally on a vibratory conveyor. The results reveal that the particle exhibits several phenomena during motion depending on its initial position, radius and density, angle between the diverging plates, tilt angle of the electrode system, and frequency and amplitude of the applied voltage. The influence of vibratory-conveyor variables on the separation/sizing process is studied in the light of the particle trajectory in the third dimension. Moreover, the results are interpreted using dimensional analysis. The use of HV ac causes the separation/sizing process to be imprecise; the higher the applied-voltage frequency and the larger the particle radius, the higher is the risk of breakdown. Depending on the tilt angle and orientation of the earthed electrode relative to the divergent angle between the electrodes, particle trapping can be helped or hindered. Therefore, several factors should be taken into consideration in the design and installation of the particle drivers and traps in GIS. Finally, the effects of dielectric coating on the electrode and of gas pressure on the particle trajectory are also studied.