Discharge Configuration Research Articles

Investigation on the Behavior of Electrons in the Bullet as Well as Its Dependence on Applied Voltage and H2O Concentration in the Atmospheric-Pressure Ar/H2O Plasma Jets

This article presents a systematic investigation on the behavior of electrons in the bullet in the Ar/H2O plasma jet in increasing the applied voltage and water vapor concentration based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte Carlo method. The scattering angle of the electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The following results are obtained. The evolution characteristic of the angle spectrum of electrons in the bullet in increasing the applied voltage is the same as that in increasing water vapor concentration, namely, the electrons scattered toward the target get increasingly less. When increasing the applied voltage, the OH density, the electron density, and the average electron energy $E_{\mathrm {ave}}$ increase. However, the increase in water vapor concentration leads to an evidently increasing OH density and a decrease in both the electron density and $E_{\mathrm {ave}}$ . In the range of electron scattering angles below 90° in the bullet, the percentage of electrons with energy above 3.27 eV (the threshold of inducing dissociative electron attachment to water molecule) increases with increasing applied voltage but presents a slight decrease in increasing water vapor concentration. The majority of electrons to most probably interact with the target are of energies higher than 3.27 eV. Finally, a notable effect of H2O admixture is that it gives rise to the decrease in not only $E_{\mathrm {ave}}$ but also the electron density in the bullet, especially the latter decreases evidently.

Corona and Electric Field Distribution Analysis in 400 kV Line Insulators

The performance of insulator strings in transmission lines can be improved by corona rings owing to their electric field grading property. The insulation performance of the string depends on the corona ring parameter settings. In this study, the design of a corona ring for a 400 kV non-ceramic overhead line insulator is presented. Two parameters were altered during the investigation, ring measurement (R) and ring tube breadth (r) while maintaining a constant ring height (h). Based on electric field distribution, the proposed composite insulators were compared with glass insulators. Simulation studies were performed for the insulator strings, including corona rings with different design parameters. The corona discharge and optimal configuration results were analyzed, and it was found that the electric field was lower with composite insulators.

Piezoelectric Direct Discharge: Devices and Applications

The piezoelectric direct discharge (PDD) is a comparatively new type of atmospheric pressure gaseous discharge for production of cold plasma. The generation of such discharge is possible using the piezoelectric cold plasma generator (PCPG) which comprises the resonant piezoelectric transformer (RPT) with voltage transformation ratio of more than 1000, allowing for reaching the output voltage >10 kV at low input voltage, typically below 25 V. As ionization gas for the PDD, either air or various gas mixtures are used. Despite some similarities with corona discharge and dielectric barrier discharge, the ignition of micro-discharges directly at the ceramic surface makes PDD unique in its physics and application potential. The PDD is used directly, in open discharge structures, mainly for treatment of electrically nonconducting surfaces. It is also applied as a plasma bridge to bias different excitation electrodes, applicable for a broad range of substrate materials. In this review, the most important architectures of the PDD based discharges are presented. The operation principle, the main operational characteristics and the example applications, exploiting the specific properties of the discharge configurations, are discussed. Due to the moderate power achievable by PCPG, of typically less than 10 W, the focus of this review is on applications involving thermally sensitive materials, including food, organic tissues, and liquids.

Theoretical model and experimental investigation optically triggered hollow-cathode discharge formation

In order to investigate the process of optically triggered discharge formation, a model of ion space-charge formation based on classical plane electrodes and revised for a characteristic hollow-cathode discharge (HCD) configuration is proposed in this paper. The primary modified factor in our model is the penetrating electric-field parameter, which influences the ionization of trigger electrons and is calculated via particle simulation. Optical-trigger experiments are carried out using different voltages and under different seed-electron conditions, provided by two different photocathodes, Cu and Mg. The ion-accumulation rates calculated by our model are compared to the discharge-formation time, which is deduced from optical-trigger experiments. The results demonstrate that the process of positive space-charge formation is dominant in the HCD formation process or trigger delay, which is highly dependent on the seeding-electron density and applied voltage, and can therefore be quantitatively described by our model. Additionally, electron-beam generation is investigated by optically triggered HCD experiments on Mg- and Cu-photocathode-based devices. The results show that a more efficient trigger device is capable of generating an electron beam with higher amplitude and density.

A Comparative Investigation on the Behaviors of Electrons in the Plasma Bullets in Atmospheric-Pressure Argon and Helium Plasma Jets

This article presents a comparative investigation on behaviors of electrons in the Ar and He plasma jets by means of the numerical simulation based on a typical needle-plate discharge configuration with positive applied pulsed voltage and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. Emphasis is placed on the electrons in the bullet in the jets. In Ar, the bullet velocity is low and the electron density in the bullet is high, compared to He. In He, the energy spectrum of electrons (ESEs) in the bullet is of a low peak and a wide distribution, and the corresponding average electron energy is evidently high, contrary to Ar. The reason for this evident difference is mainly due to their different excitation energies and ionization energies as well as their different cross sections. In Ar and He, two electron densities N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Next in the bullet have been calculated. The former is the electron density in the bullet and the latter refers to a density of electrons in the bullet with energy above the lowest excitation threshold inducing the dissociative electron attachment (DEA) to water molecules. Consequently, not only N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> but also N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ext</sub> in Ar is higher than in He, meaning more generation of reactive species in aqueous solution via DEA mechanism. The ESEs in the bullet in Ar are more sensitive to the applied voltage amplitude than in He, thus in Ar, the increase in the applied voltage amplitude induces more evident increase in the average electron energy in the bullet than in He.

A Numerical Investigation on the Behavior of Electrons in the Bullet in the Atmospheric- Pressure Argon Plasma Jet

Electrons are generated abundantly in the plasma jet and play an active role in the mass transfer of reactive species in the aqueous solution in plasma medicine. Such an importance requires knowledge of the behavior of electrons in the plasma jet. The objective of this work is to understand the electron behaviors in the bullet in the plasma jet, including the angle spectrum of electrons (ASEs) and the related energy spectrum, so as to have an insight into those electrons which most probably interact with the target. The numerical modeling based on a needle–plate discharge configuration in conjunction with a 1-D Particle-in-Cell Monte-Carlo Collision (PIC-MCC) simulation method was used to achieve this task. The scattering angle of electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The ASE in the bullet is close to a sinusoidal distribution. As the bullet propagates, the temporal evolution of ASE indicates that relatively more electrons in the bullet are scattered into the angle range below 90°, but at any moment when the propagating bullet is close to the target, ASE in the bullet generally remains unchanged. In addition, relatively less electrons in the bullet are scattered into the angle range below 90° due to the increase of the applied voltage amplitude. For the considered voltage amplitudes below 7 kV, the number of electrons in the angle range below 90° is within 47% of electrons in the bullet and, in these electrons, the proportion of non-subionization electrons reaches about 12%. These results may be taken into consideration in investigating the mass transfer of reactive species in plasma medicine.

Tungsten particles fabrication by a microjet discharge

As a consequence of interaction of a microjet discharge with the tungsten electrodes, tungsten material is released to plasma, and tungsten particles, of submicron size, are formed. The obtained particles were analyzed to establish a correlation of their morphology, size distribution and chemical composition with the discharge configuration and distance to collector. Experimental conditions were identified leading to spherical tungsten particles.

Development of a small-scale helical surface dielectric barrier discharge for characterizing plasma–surface interfaces

Understanding plasma–surface interactions is important in a variety of emerging research areas, including sustainable energy, environmental remediation, medicine, and high-value manufacturing. Plasma-based technologies in these applications utilize surface chemistry driven by species created in the plasma or at a plasma–surface interface. Here, we develop a helical dielectric barrier discharge (DBD) configuration to produce a small-scale plasma that can be implemented in a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell and integrated with a commercial Fourier transform infrared (FTIR) spectrometer instrument to study plasma interactions with inert or catalytic solid media. The design utilizes the entire surface of a cylinder as its dielectric, enhancing the plasma contact area with a packed bed. In this study, we characterize the electrical and visual properties of the helical DBD design in an empty reaction cell and with added potassium bromide (KBr) powder packing material in both air and argon gas environments at ambient conditions. The new surface DBD configuration was integrated into a DRIFTS cell and the time evolution of water desorbing from the KBr packed bed was investigated. Measurements show that this configuration can be operated in filamentary or glow-like mode depending on the gas composition and the water content absorbed on KBr solid media. These results not only set the basis for the study of plasma–surface interactions using a commercial FTIR, but also show that controlling the gas environment and water content in a packed bed might be useful for studying different plasma regimes that are typically not possible at atmospheric pressure.

Effect of Suction and Discharge Conditions on the Unsteady Flow Phenomena of Axial-Flow Reactor Coolant Pump

In order to study the effects of the suction and discharge conditions on the hydraulic performance and unsteady flow phenomena of an axial-flow reactor coolant pump (RCP), three RCP models with different suction and discharge configurations are analyzed by computational fluid dynamics (CFD) method. The CFD results are validated by experimental data. The hydraulic performance of the three RCP models shows little difference. However, the unsteady flow phenomena of RCP are significantly affected by the variation of suction and discharge conditions. Compared with that of Model E-S (baseline, elbow-single nozzle), the pressure pulsation in rotating frame of Model S-S (straight pipe-single nozzle) and Model E-D (elbow-double nozzles) is weakened in different degrees and forms, due to the more uniform flow fields upstream and downstream of the impeller, respectively. It indicates that the generalized rotor-stator interaction (RSI) actually exists between the rotating impeller and all stationary components causing the circumferentially non-uniform flow. Furthermore, improving the circumferential uniformity of the flow upstream and downstream of impeller (suction and discharge flow) also contributes to reducing the radial dynamic fluid force acting on the impeller. Compared with those of Model E-S, the dynamic FX and FY of Model S-S are severely weakened, and those of Model E-D also gain a minor amplitude decrease at fBPF. In contrast, the general pressure pulsation in fixed frame is mainly related to the rotating impeller and barely affected by the suction and discharge conditions.

Synergistic effect of charges and electric field: water droplet condensation and coalescence in a sub-saturated cloud chamber

In nature, the condensation, coalescence and growth of water droplets have a crucial positive effect on the process of cloud formation, which is hard to occur under a sub-saturated environment. In this paper, the growth of water droplets is detected in a 0.24 m3 sub-saturated cloud chamber with unipolar corona discharge and needle electrode configuration. The results show that the diameter of water droplets can grow up from submicron to 32 μm under −39 kV at relative humidity ∼85% and ambient temperature ∼10 °C. The growth mechanism in the evolution process is further discussed, focusing on the effect of charge on charged droplet condensation, and the synergistic effect of charges and electric field. The former is verified by the comparison of experimental average net charges of some typical diameter droplets and minimal charges needed to maintain self-growing. The latter is demonstrated by the analysis of charged droplet motion and the ionic wind recorded by a camera. The analysis is in good consistency with the experimental results, which suggests its promising and potential applications in the utilization of atmospheric water resources.

Numerical Investigation of Pressure Recovery for an Induced Draught Fan Arrangement

This study investigates the potential gain in operating volume flow rate and static efficiency for an induced draught fan arrangement by reducing the outlet kinetic energy loss. The reduction is achieved through pressure recovery, which is the conversion of dynamic pressure into static pressure. Downstream diffusers, stator blade rows, or a combination of these can recover pressure. Six different discharge configurations are tested for a fan. An annular diffuser with equiangular walls at an angle of 22° from the axial direction and a length equal to the fan diameter recovers the most pressure over a range of volume flow rates. The diffuser causes the operating volume flow rate and static efficiency to increase by 6.3 % (relative) and 20 % (absolute), respectively, compared to the initial design point of the particular fan.

Investigation on Application of Closed Cavity Inductively Coupled Plasma in Inlet Stealth

The design of inlet into S-shaped is a stealth method with limited effect. The ICP generated in closed quartz chamber is an effective solution to improve the stealth effect. In this paper, an inductively coupled plasma (ICP) generator with the size of 30cm×30cm×2cm which could be conformal with S-shaped inlet was designed, the discharge experiment was carried out to study the discharge configuration of air ICP and the distribution of the electron density in the core area of ICP under 100Pa and different discharge power was diagnosed with microwave interference method. On this basis, the three-dimensional electromagnetic model of inlet and the plasma generator were established and the finite-difference time-domain method was used to calculate the broad-band scattering parameter of the inlet with and without the ICP generator. The variation of radar cross section area (RCS) with the azimuth angle, electromagnetic wave frequency and discharge power of ICP was studied. The result indicated that the ICP generator could effectively improve the stealth effect of S-shaped inlet in the head direction.

Polarization Stark spectroscopy for spatially resolved measurements of electric fields in the sheaths of ICRF antenna.

A multichannel spectroscopic diagnostic based on the Stark effect on helium lines was developed and implemented in IShTAR (Ion Cyclotron Sheath Test ARrangement) to measure the spatial distribution of electric fields across the radio frequency sheaths of the ion cyclotron antenna. Direct measurements of the DC electric fields in the antenna sheaths are an important missing component in understanding the antenna-plasma edge interactions in magnetically confined fusion plasmas since they will be used to benchmark theoretical models against real antenna operation. Along with the high-resolution Czerny-Turner monochromator and a detector with an intensifier, the hardware relies on the 2 chained set of linear-to-linear fiber bundles that provide seven optical channels capable of resolving an 8.4 mm region in the vicinity of the antenna's box. The diagnostic is supported with local helium gas puff, enabling it to operate in nonhelium plasmas. Spatially resolved electric field was measured for two discharge configurations, one with and one without the ICRF antenna. The results show a clear difference in the shape of the DC electric field's spatial profile for the two cases studied, with the elevated values when the ICRF antenna was operating. This demonstrates the ability of the diagnostic to measure even small relative changes in the intensity of the electric field.

A new type of non-thermal atmospheric pressure plasma source

The unique applications of Non-Thermal Atmospheric pressure Plasmas (NTAP) are associated with its enormous potential for providing technological capabilities for new products and technologies. In such plasmas, most of the electrical energy is deposited in the electron component of the plasma, while plasma ions and neutral components remain at or near room temperature. This paper presents the NTAP source that combines the characteristics of a dielectric barrier discharge (DBD) by discharge configuration and a non-thermal plasma jet (NTPJ) by plasma jet formation.

Surface modification of activated carbon using an atmospheric pressure dielectric barrier discharge (DBD) plasma jet

We successfully modified an activated carbon layer using an atmospheric pressure plasma jet. The plasma was generated in dielectric barrier discharge (DBD) configuration using Cu wire and Cu tape separated by dielectric glass with an inner diameter of ∼1 mm. An alternating current of 1.5 kV was supplied to the electrodes to generate the plasma using a mixture of Ar gas and ammonia vapor at varied flow speeds of 1 to 7 L/min for one-minute treatment. The changes to the wettability of the carbon surface were estimated from the contact angle of a water drop. After plasma treatment, a significant improvement in the surface hydrophilicity was observed. The contact angle decreased to ∼6° from its initial contact angle of 74°. This hydrophilic property was likely due to the successful attachment of an amino group supplied by the NH3 plasma. An amino-functional group was covalently bound to the carbon, which happened after etching by Ar plasma during the plasma jet processing. In addition, Fourier transform infrared (FTIR) profiles were taken to provide definitive proof of the suggested amino surface modification. Overall, the plasma treatment described in the present study may become a tool in surface treatment modification applications conducted in atmospheric conditions for carbon-based materials.

Numerical modeling of a DBD in glow mode at atmospheric pressure

In this work, a fluid model of helium glow discharge at atmospheric pressure in a dielectric barrier discharge configuration has been developed and the discharge was numerically simulated. The transport equations for charged and excited species are self-consistent coupled to the Poisson equation for the electrical field calculation. A finite difference method technique is adopted; a detailed numerical procedure modeling is given. The addition of some nitrogen impurities to the helium successfully reproduced the discharge evolution during the breakdown. The numerical results showed that the discharge has a structure similar to DC low-pressure glow discharges and confirms the establishment of the glow regime at atmospheric pressure under very adequate conditions. The profiles of physical and electrical discharge parameters knowing that, particle densities, electric field, drift velocity, voltages and discharge current are presented and analyzed. A detailed study was made of the effect of nitrogen impurities on the stability of the glow mode of the discharge, and on the evolution of its parameters.

Integrated Coagulation-Membrane Processes with Zero Liquid Discharge (ZLD) Configuration for the Treatment of Oil Sands Produced Water

This study explores the feasibility of implementing five hybrid coagulation-membrane processes for the treatment of the boiler blow-down (BBD) water from an oil sands steam assisted gravity drainage (SAGD) operation. The processes involved (1) direct nanofiltration (NF) of the BBD water, (2) pre-treatment of the NF retentate using ion exchanger regeneration wastewater (IERW) as a chemical coagulant followed by NF, (3) pre-treatment of BBD water using IERW followed by NF, (4) dual pre-treatment of BBD water using IERW and soda ash (sodium carbonate, Na2CO3) followed by NF, and (5) forward osmosis (FO) treatment of the BBD water using IERW as a draw solution followed by NF treatment of diluted draw solution. These scenarios were compared based on total flux decline ratio (DRt), flux recovery ratio (FRR), and total dissolved solids (TDS) removal over the final NF treatment to suggest an efficient treatment technique to avoid an undesired increase in the capital and operating expenses. It was found that process-1 provided the highest selectivity toward dissolved solids (80%) with a flux decline and recovery ration of 89.6% and 97.4%, respectively. Considering the permeation flux, process-4 exhibited the lowest flux decline (86.1%) and highest recovery ratio (97.5%) compared to other processes, proving the successful role of soda ash softening, as a chemical pretreatment method, in improving the performance of membrane filtration. Process-2 presented a mediocre performance with DRt, FRR, and TDS rejection of 93.3%, 97.3%, and 74%, respectively. Finally, process-3 and process-5 showed the lowest performance among all the scenarios with low flux recovery and low permeability, respectively. In addition, process-3 was expected to be cost-efficient since it only uses an on-site generated waste as a coagulant for the chemical pretreatment of the membrane filtration unit. The optimum scenario was proposed to be the two-stage membrane process, with direct NF of BBD followed by the post-treatment of the retentate via a hybrid chemical conditioning using IERW and soda ash softening, followed by a second NF. Overall, this integrated process offered a highly efficient mean with a zero liquid discharge (ZLD) system for the treatment of high pH wastewaters into an uncontaminated stream for the boilers.

Degradation of crystal violet in water solution using post discharge DBD plasma treatment: Factorial design experiment and modeling

In this study, highly oxidative ozone species, generated through dielectric barrier discharge (DBD) plasma, were used to decolorize crystal violet (CV) in aqueous solutions. The solution was exposed to a post-discharge plasma with a mixture of oxygen and argon as carrier gas. The exhaust plasma gas was brought into contact with the solution to be treated in a bubbler by the post discharge configuration. The degradation of the contaminants would be improved by the enhancement of the reactive species diffusion in the solution in the post discharge configuration. The effects of different parameters including oxygen percentage in the carrier gas, discharge power, and total flow rate were investigated on the efficiency of CV removal. Further, the concentrations of ozone in the gas and liquid phases were measured via iodine and indigo methods, respectively. Under optimal conditions, the entire dissolved CV was degraded after 60 s of plasma treatment. Kinetic study revealed that the reaction between ozone and CV follows the behavior of a first-order reaction. After plasma treatment, the aromatic fragment and its intermediates completely disappeared. Analysis of variance with an excellent coefficient of determination of 0.988 ensured a satisfactory fit between second-order regression model and the experimental data. The high CV removal rate constant of 4.88 min−1 obtained at a low discharge power of 5 W was of paramount importance in comparison with previous studies.

Experimental Investigation on a Multicathode Dielectric-Barrier Discharge: Effects of Airflows

The dielectric-barrier discharges (DBDs) under airflow have been widely used in the fields of airflow control, plasma-assisted combustion, and surface modification. Our previous work demonstrates that the discharge intensity under airflows could be adjusted by a discharge configuration with upstream and downstream electrodes. In this paper, a further investigation of discharges under airflows is processed with a multicathode DBD configuration. With the injection of airflows to the discharge region, the first upstream region produces a decrement of discharge intensity, while the following downstream region always provides greater discharge intensity than that of the adjacent upstream discharge region. An optimal discharge configuration is found by appropriately selecting the distances between the cathodes, wherein the last downstream region can produce maximum discharge intensity. The mechanisms are analyzed by considering the transport effect of airflows and the lifetime of charged and metastable particles. The charged and metastable particles are transported to the downstream region, and these particles always act as the responsible seeds to enhance the downstream discharges. In addition, due to the limited lifetime of charged and metastable particles, the enhancement effect may be weakened under long transport distances. Finally, potential applications for multicathode DBDs are also provided.

Material Characterization of Plasma-Treated Aluminum Particles via Different Gases

ABSTRACTThis work describes exploration of mitigating the parasitic amorphous alumina (Al2O3) shell of aluminum nanoparticles (n-Al) and modifying the surface using different plasmas, leading to n-Al with thinner shell and different coatings including carbons and oxidizing salt called aluminum iodate hexahydrate (AIH), respectively. The approach exploits a prototype atmospheric non-thermal plasma reactor with dielectric barrier discharge (DBD) configuration for nanoparticle surface modifications using n-Al of 80 nm average diameter as an example. Preliminary results indicate that the amorphous Al2O3 shell surrounding the active aluminum core can be mitigated with inert plasmas by as much as 40% using either helium (He) or argon (Ar). The particle surface becomes carbon-rich with carbon monoxide (CO) / He plasmas. By immersing the plasma-treated n-Al in an iodic acid (HIO3) solution, AIH crystals can be formed on the n-Al surface. Transmission electron microscopy (TEM) is used as a major tool to study the details of the modified surface morphologies, diffraction patterns, and chemical composition of the modified n-Al. The results demonstrate effective surface passivation of n-Al via atmospheric plasma techniques.