Abnormal Glow Discharge Research Articles

Large-Area Cold Atmospheric Pressure Discharges Realized by Mesh Covered Tube-Plate Electrodes in Open Air

A large-area atmospheric pressure plasma with low temperature and high electron density was realized using mesh covered tube-plate electrodes at an RF power as low as 4 W. The gas temperature is less than 351 K, while the electron temperature is about 5000 K. The estimated electron density is on the order of 1012 cm-3. Electrical measurements indicate that the discharges are capacitive and operated in an abnormal glow discharge mode. In addition, a self-bias observed at the powered tube electrode increases with increasing power and is positive at high powers.

Unusual behaviour of current–voltage relations in an unbalanced grid-assisted magnetron sputtering system

Current–voltage relations were measured in an unbalanced grid-assisted magnetron sputtering system at different inter-electrode distances and magnetic field configurations. The intensity and configuration of the magnetic field were adjusted through an electromagnetic coil placed at the magnetron centre. This scheme allows observation of the current–voltage relations under conditions of weak and strong plasma confinement. Surprisingly, for some inter-electrode distances, a decreasing discharge current with increased magnetic field was observed. This unusual behaviour in grid-assisted magnetron discharges can be useful for a better understanding of abnormal glow discharges assisted by a magnetic field.

Effects of experimental conditions on the growth of vertically aligned carbon nitride nanocone arrays

Vertically aligned carbon nitride nanocone (CNNC) arrays were prepared on Ni-covered (100) silicon wafers by an abnormal glow discharge plasma assisted chemical vapor deposition method. In order to control the growth of the CNNC arrays, the distance of the anode tip to the substrate surface was adjusted for it affected the contents and activities of the species in the plasmas leading to the CNNC growth. Based on the characterization of the as-grown thin films and the analysis of the growth environments, the effects of the experimental conditions on the growth of the CNNC arrays were studied and their growth mechanism was discussed. The tip−substrate distance strongly affects the CNNC growth. Under appropriate experimental conditions, the vertically-aligned and intact CNNC arrays with the β-C3N4 microstructure and the minimum tip curvature diameter of only 3–4nm could be fabricated. This kind of CNNC arrays have many potential applications, such as tips for microscopes, electron-emitting units in field emission displays, electron-capture electrodes of solar cells etc.

Pressure and Discharge-Voltage Dependence of Self-Sustaining Pulses in Air-Glow Discharge

The details of formation of micro discharges in air-glow discharge plasma are experimentally studied. The number of micro discharges formed per second is strongly related to both pressure and discharge voltage. This number tends to show reflections of the Patchen curve as far as its pressure dependence is concerned. The discharge-voltage dependence indicates that the transition from normal to abnormal glow discharge is not a sudden one, but has its roots during the normal glow stage and is initiated by the micro discharges which can be regarded as the early stage of abnormal glow.

Electric field distribution in the cathode-fall region of an abnormal glow discharge in hydrogen: experiment and theory

We present the results of an experimental and theoretical study of the electric field distribution in the cathode-fall (CF) region of an obstructed abnormal glow discharge in hydrogen. The distribution of electric field strength was measured using an improved Stark polarization spectroscopy technique of the hydrogen Balmer beta line profile. The developed technique extends field measurements to the low-field region while remaining in good agreement at larger field strengths with the well established Stark polarization peak separation electric field measurement technique. The experimental electric field distribution is modeled by a simple analytical formula, adopted after consideration of elementary processes relevant in the CF. It fits the experimental distribution within error bars and consequently enables determination of the CF parameters such as its thickness and the mean free path for electrons in the CF region.

An Approach of the Sintering YBa2Cu3O7−δ System

The abnormal glow discharge applied to the sintering process is a recent technique used for processing both metallic and ceramic materials. In this paper, we use the abnormal glow discharge as an alternative method for the sintering step of the YBa2Cu3O7−δ superconductor material. The physical properties of the sintered samples by glow discharge were compared with the properties of sintered samples in resistive furnace, which is commonly used for production of high temperature superconductor ceramics. The structural analysis of the YBa2Cu3O7−δ samples was carried out by the X-ray diffraction technique, microstructural analysis by Scanning Electron Microscopy and electrical resistivity by the four probes method (resistance measurements as a function of temperature). The experimental results permitted to establish the similar structure and morphology for all samples: produced by plasma and resistive furnace sintering. The superconducting behavior was corroborated for both sintering processes.

Low temperature plasma carburizing of martensitic stainless steel

Abstract The present work reports results of successful low temperature plasma carburizing of martensitic stainless steel carried out in dc abnormal glow discharge. Very promising results are presented, which are confirmed by microstructural analysis, XRD and microhardness profiles of the treated samples.

Gliding Glow Discharge in Tornado

The gliding-arc-in-tornado discharge is an example of a “warm plasma” source and is an attractive tool for fuel conversion processes. This paper demonstrates that, at relatively low currents below 530 mA, this discharge is an atmospheric-pressure normal or abnormal glow discharge. This implies applicability of the glow discharge theory and experimental data for evaluation of plasma parameters in technological systems.

Influence of cathode material on generation of energetic hydrogen atoms in a glow discharge

In this paper influence of cathode material on formation of fast hydrogen atoms in an abnormal glow discharge is investigated using Balmer alpha emission spectroscopy. Energetic H atoms are generated in charge exchange reactions of hydrogen ions that are accelerated in the electric field, and also formed in the backscattering process at the cathode surface. Copper and graphite cathodes were used. Investigation was performed in two orthogonal directions of observation in pure hydrogen and argon-hydrogen mixture. The shapes of the profiles are examined together with the space intensity distribution of Balmer alpha line. Reduced atom reflection from graphite was manifested in the spectroscopic result, in accordance to the field acceleration model. The effect was evident only at high ion energies. This is explained by energy dependence of reflection coefficient for H atoms.

Characterization of the discharge in array needle cathodes and applications

In this paper, a new direct current (DC) plasma source for surface alloying using array-needle-cathode has been designed and manufactured. The array-needle-cathode is used to produce a stable abnormal glow discharge plasma in a rectangular chamber. During the surface alloying process, it is noticed that the discharge modes severely influenced the plasma parameters including electron density (Ne) and electron temperature (Te). The Te obtained by optical emission spectrometry (OES) through the comparison of the relative intensity of N in 3919Å and 3995Å is between 1.44eV and 5.40eV. The distribution and fluctuation of Te in the two-dimensional planar are revealed by analysis of digital camera images. It is concluded that the discharge by the array- needle-cathode is a kind of new plasma source which can generate stable plasma with a high electron temperature applicable for surface alloying. Lastly, with this array-needle-cathode plasma source (ANCPS), W-Mo-N alloyed layer on Ti alloy is explored in this paper.

Organic chemistry of NH3and HCN induced by an atmospheric abnormal glow discharge in N2-CH4mixtures

The formation of the chemical products produced in an atmospheric glow discharge fed by a N2-CH4 gas mixture has been studied using Fourier Transform InfraRed (FTIR) and Optical Emission Spectrometry (OES). The measurements were carried out in a flowing regime at ambient temperature and pressure with CH4 concentrations ranging from 0.5% to 2%. In the recorded emission spectra the lines of the second positive system CN system and the first negative system of N2 were found to be the most intensive but atomic H, H, and C (247 nm) lines were also observed. FTIR-measurements revealed HCN and NH3 to be the major products of the plasma with traces of C2H2. These same molecules have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the chemical and physical mechanisms prevalent in Titan's atmosphere with these smaller species believed to be the precursors of heavier organic species in Titan's atmosphere and on its surface.

Decolorization of Aqueous Acid Red B Solution During the Cathode Process in Abnormal Glow Discharge

This paper investigated some chemical and physical factors which probably affect the decolorization of aqueous acid red B solution by atmospheric abnormal glow discharge. When the aqueous solution served as the cathode, effective decolorization occurred in the inert gas discharges as well as in the active gas discharges. The hydroxyl radicals were mainly responsible for the decolorization in the solution phase. The gas ionization potential may influence the decolorization effect.

Transition of Discharge Mode of a Local Hollow Cathode Discharge

The discharge characteristics of hollow cathode discharge in argon in a cylindrical cavity are investigated experimentally. The voltage-current (V – I) characteristics and the light emission are measured. It is found that the discharge plasma is localized inside the hollow cavity, with an extensive Faraday dark space between the cathode and the anode. The discharge develops from predischarge to abnormal glow discharge, the hollow cathode effect (HCE) and a hybrid mode as the discharge current increases. The onset of the HCE is found for the first time by the transition from abnormal glow discharge together with a significant decrease in the slope of the V – I curve which shows a positive differential resistivity. The voltage increases proportionally with the current when the HCE is reached.

Plasma assisted parts' manufacturing: sintering and surface texturing - part II - influence of inter-cathode distance and gas pressure

The acquirements and potentiality universe of cleaning, heating and/or sputtering effects caused by plasma species bombardment phenomenon on the surface characteristics and finishing of manufactured parts treated in DC abnormal glow discharge opens a new research and development field, called here of Plasma Assisted Parts' Manufacturing (PAP'M). The adequate control of the sputtering mechanism allows the obtainment of different kinds of surface. Therefore, the design of rough or smooth surface, presenting a modified distribution of surface porosity and texturing could be idealized, in accordance with the desired surface characteristics, as the parts are simultaneously sintered and treated. This is the second part (out of two) of the work performed in hollow cathode discharge (HCD) and it presents the first results of the surface morphology's changes in the pressed iron samples and in the internal surface of the external cathode as a function of the inter-cathode distance and gas pressure. Potential applications include small diameters' cylindrical parts and components like axles, pins, pivots, and tubes and pipes presenting small internal diameters. Sputtering effects were quantified by means of mass loss, and Ra and Rz roughness measurements and qualified by means of SEM. Results indicate the sputtering mechanism is highly dependent of the hollow cathode effect, in HCD sintering and surface texturing treatments, comprising an important contribution to the development of green technologies for surface texturing, surface engineering, and part's manufacturing.

Plasma assisted parts' manufacturing: sintering and surface texturing - part I - influence of sintering time and temperature

The acquirements and potentiality universe of cleaning, heating and/or sputtering effects caused by plasma species bombardment phenomenon on the surface characteristics and finishing of manufactured parts treated in DC abnormal glow discharge opens a new research and development field, called here of Plasma Assisted Parts' Manufacturing (PAP'M). The adequate control of the sputtering mechanism allows the production of different kinds of surface. Therefore, the design of rough or smooth surface, presenting a modified distribution of surface porosity and texturing could be idealized, in accordance with the desired surface characteristics, as the parts are simultaneously sintered and treated. The first part (out of two) of this work performed in hollow cathode discharge (HCD) presents the results of the surface morphology's changes in the pressed iron samples and in the internal surfaces of the external cathodes as a function of the sintering time and temperature. Potential applications include small diameters' cylindrical parts and components like axles, pins, pivots, and tubes and pipes presenting small internal diameters. Sputtering effects were quantified by means of mass loss and Ra and Rz roughness measurements and qualified by means of SEM. The overall work comprises the study of different parameters, including sintering time and temperature (Part I), and inter-cathode distance and pressure (Part II). Results indicate the sputtering mechanism in HCD sintering and surface texturing treatments could be adequately controlled as a function of the plasma parameters, comprising an important contribution to the development of green technologies for surface texturing, surface engineering, and part's manufacturing.

High-pressure runaway-electron-preionized diffuse discharges in a nonuniform electric field

High-pressure nanosecond diffuse (volume) discharges in a nonuniform electric field are studied experimentally using a recording system with a ?100-ps time resolution. As the voltage pulse shrinks to a width of ≈100 ps, the initiation of a diffuse discharge without a source of additional ionization is facilitated; specifically, a runaway-electron-preionized diffuse discharge is ignited in atmospheric-pressure air in the case of short interelectrode gaps. It is found that a major energy deposit into the plasma of this discharge is from an abnormal glow discharge following a maximum of the gap voltage.

Self-Assembled Fabrication and Characterization of Vertically Aligned Binary CN Nanocone Arrays

Vertically aligned binary CN nanocone (CNNC) arrays were prepared by a direct-current abnormal glow discharge plasma-assisted reaction deposition method. CNNCs were grown on silicon wafers covered by Ni intermediate layers. The experiments were carried out in environments of methane and nitrogen mixtures, with a total pressure of 5 Torr and CH 4 /N 2 pressure ratios of 1/50 to 1/10. As-grown short CNNCs can have tip diameter of curvature of only 2 nm to 3 nm and are mainly crystalline β-C 3 N 4 , while long CNNCs are mainly amorphous with inclusions of β-C 3 N 4 -coated Ni crystals. Based on characterization and analysis of the as-grown binary CN nanostructures, their growth mechanism is proposed and discussed.

Synthesis of Crystalline Carbon Nitride Nanocone Arrays by Direct‐Current Discharge Plasma‐Assisted CVD

AbstractCrystalline carbon nitride nanocone (CNNC) arrays are prepared by a rather simple and facile direct current, abnormal glow discharge plasma‐assisted (PA) CVD method. The CNNCs are grown on the surfaces of (100) silicon wafers covered by Co/Ni intermediate layers. The experiments are carried out in an atmosphere of mixtures of methane and nitrogen, under a total pressure of 4000 Pa, and CH4/N2 pressure ratios in the range 1:50–1:5. The as‐grown CNNCs are vertically aligned in arrays with rather perfect crystallinity, and smallest tip diameters of 2–3 nm. Based on the optical emission spectra from the abnormal glow discharge plasma, the growth mechanism of the as‐grown CNNCs is discussed.

On the accuracy and limitations of fluid models of the cathode region of dc glow discharges

This paper compares the performance and limitations of different models of the cathode region of cold-cathode low-pressure dc glow discharges: (i) we review known modelling approaches, (ii) develop our own simulation codes based on these approaches, (iii) perform calculations using these codes for reference sets of discharge conditions, which allows a critical comparison of the models and (iv) for a further check of the simulation results we carry out Langmuir probe measurements of electron densities in abnormal Ar glow discharges. The theoretical approaches include fluid models both neglecting and including the electron energy balance equation, as well as hybrid models, which combine the fluid treatment of slow plasma species with the kinetic simulation of fast electrons. We also test the effect of the choice of the ionization source term in fluid models. We find that the electron densities calculated from the fluid models are far (several orders of magnitude) below the experimental values even if the electron energy equation is considered in the calculations. This weakness of fluid models clearly points out the importance of an accurate calculation of the ionization source term, which can only be accomplished by a kinetic approach under the conditions of highly nonlocal electron transport in the cathode region of glow discharges. In hybrid models Monte Carlo simulation is used for this purpose, and indeed, this approach gives electron densities comparable to our experimental data.

Computational simulation of coupled nonequilibrium discharge and compressible flow phenomena in a microplasma thruster

The microplasma thruster (MPT) concept is a simple extension of a cold gas micronozzle propulsion device, where a direct-current microdischarge is used to preheat the gas stream to improve the specific impulse of the device. Here we study a prototypical MPT device using a detailed, self-consistently coupled plasma and flow computational model. The model describes the microdischarge power deposition, plasma dynamics, gas-phase chemical kinetics, coupling of the plasma phenomena with high-speed flow, and overall propulsion system performance. Compared to a cold gas micronozzle, a significant increase in specific impulse is obtained from the power deposition in the diverging section of the MPT nozzle. For a discharge voltage of 750 V, a power input of 650 mW, and an argon mass flow rate of 5 SCCM (SCCM denotes cubic centimeter per minute at STP), the specific impulse of the device is increased by a factor of ∼1.5 to about 74 s. The microdischarge remains mostly confined inside the micronozzle and operates in an abnormal glow discharge regime. Gas heating, primarily due to ion Joule heating, is found to have a strong influence on the overall discharge behavior. The study provides a validation of the MPT concept as a simple and effective approach to improve the performance of micronozzle cold gas propulsion devices.