Showing papers on "Atmospheric pressure published in 2006"
TL;DR: In this article, a new cold plasma jet generator is developed for surface modification of materials at atmospheric pressure, which is composed of two concentric cylindrical all-metal tube electrodes, and the argon is fed into the inner grounded electrode, the outer electrode is connected to the highvoltage power supply and covered with a layer of dielectric, and then a stable cold plasminar jet is formed and blown out into air.
Abstract: A new cold plasma jet has been developed for surface modification of materials at atmospheric pressure. This new cold plasma jet generator is composed of two concentric cylindrical all-metal tube electrodes. The argon is fed into the inner-grounded electrode, the outer electrode is connected to the high-voltage power supply and covered with a layer of dielectric, and then a stable cold plasma jet is formed and blown out into air. The plasma gas temperature is only 25–30 °C. Preliminary results are presented on the modification of polypropylene (PP) and polyethylene terephthalate (PET) fibres by this cold plasma jet. The water contact angle of these materials is found to decrease after plasma treatment and it will recover a little in two months. The chemical changes on the surface of polymers are studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) is used to study the changes in surface feature of polymers due to plasma treatment. The hydrophilicity and surface structure of these materials after plasma treatment are discussed. The results show that such a plasma jet is effective.
241 citations
TL;DR: In this paper, a numerical simulation of a dc microplasma discharge in helium at atmospheric pressure was performed based on a one-dimensional fluid model and the microdischarge was found to resemble a macroscopic low pressure dc glow discharge in many respects.
Abstract: A numerical simulation of a dc microplasma discharge in helium at atmospheric pressure was performed based on a one-dimensional fluid model. The microdischarge was found to resemble a macroscopic low pressure dc glow discharge in many respects. The simulation predicted the existence of electric field reversals in the negative glow under operating conditions that favor a high electron diffusion flux emanating from the cathode sheath. The electric field adjusts to satisfy continuity of the total current. Also, the electric field in the anode layer is self adjusted to be positive or negative to satisfy the “global” particle balance in the plasma. Gas heating was found to play an important role in shaping the electric field profiles both in the negative glow and the anode layer. Basic plasma properties such as electron temperature, electron density, gas temperature, and electric field were studied. Simulation results were in good agreement with experimental observations.
188 citations
TL;DR: In this paper, in-depth modelling of electrolysers suggests that electrolysis at atmospheric pressure is electrically more energy efficient if parasitic energy consumption and gas losses are incorporated in both cases.
166 citations
Patent•
07 Jul 2006
TL;DR: In this article, a method of coating a surface of a workpiece with fluorocarbon to be hydrophobic or super-hydrophobic using atmospheric pressure glow plasma was proposed.
Abstract: The present invention relates to a method of coating fluorocarbon or hydrocarbon on the surface of a workpiece using atmospheric pressure plasma. More particularly, the present invention relates to a method of coating hydrocarbon or fluorocarbon on the surface of a workpiece using plasma generated under atmospheric pressure such that the workpiece can have a hydrophobic or super-hydrophobic surface. The method of coating a surface of a workpiece with fluorocarbon to be hydrophobic or super-hydrophobic according to the present invention comprises the steps of generating first atmospheric pressure glow plasma by supplying a reaction gas into a discharge space formed between a first electrode and a second electrode, the reaction gas containing hydrogen gas, fluorocarbon gas and inert gas, the first and second electrodes being connected to an RF power supply of an atmospheric pressure plasma generator; and approaching the workpiece to the first electrode downstream of a reaction gas flow passing through the discharge space, such that the plasma created in the discharge space is transferred into a space between the first electrode and the workpiece to generate a second atmospheric pressure glow plasma therein, whereby a fluorocarbon coating layer can be formed on the surface of the workpiece.
161 citations
TL;DR: In this paper, the rotational and vibrational temperatures of DC normal glow discharges were measured by comparing modelled optical emission spectra with spectroscopic measurements from the discharge.
Abstract: DC normal glow (NG) discharges were created in atmospheric pressure air for a pin to plate type geometry. The rotational and vibrational temperatures of the discharge were measured by comparing modelled optical emission spectra with spectroscopic measurements from the discharge. The temperatures were measured as a function of discharge current, ranging from 50 µA to 30 mA, and discharge length, ranging from 50 µm to 1 mm. Rotational temperatures from 400 to 2000 K were measured over this range. Vibrational temperatures vary from 2000 K to as high as 5000 K indicating a non-equilibrium plasma discharge. Spectroscopic measurements were compared using several different vibrational bands of the 2nd positive system of N2, the 1st negative system of and the UV transitions of NO. NO and transitions were also used to determine the electronic temperature and density. The discharge temperature appears to be controlled by two cooling mechanisms: (1) radial conductive cooling which results in an increase in temperature with increasing discharge current and (2) axial cooling to the electrodes which results in a temperature saturation with increase in discharge current. The measured discharge temperature initially increases rapidly with discharge current then becomes nearly constant at a higher discharge current. Thus, radial cooling appears to dominate at lower discharge currents and the axial cooling at higher discharge currents. The vibrational temperature decreases with increasing rotational temperature due to increased vibrational to translation relaxation but the discharge remains non-thermal and stable over the range studied. The discharge appears to have a maximum vibrational temperature at the low current limit of the NG regime.
161 citations
TL;DR: In this article, four kinds of additive gases (helium, argon, nitrogen, and CO2) were used to investigate their effects on methane conversion, as well as product selectivity, and discharged power.
159 citations
TL;DR: Analysis of fish oils by APPI shows significantly enhanced target analyte intensities in comparison with APCI and ESI, which demonstrate the benefits of using LC/APPI-MS for lipid analysis.
Abstract: In this work, we compare the quantitative accuracy and sensitivity of analyzing lipids by atmospheric pressure photoionization (APPI), atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI) LC/MS. The target analytes include free fatty acids and their esters, monoglyceride, diglyceride, and triglyceride. The results demonstrate the benefits of using LC/APPI-MS for lipid analysis. Analyses were performed on a Waters ZQ LC/MS. Normal-phase solvent systems were used due to low solubility of these compounds in aqueous reversed-phase solvent systems. By comparison, APPI offers lower detection limits, generally highest signal intensities, and the highest S/N ratio. APPI is 2−4 times more sensitive than APCI and much more sensitive than ESI without mobile-phase modifiers. APPI and APCI offer comparable linear range (i.e., 4−5 decades). ESI sensitivity is dramatically enhanced by use of mobile phase modifiers (i.e., ammonium formate or sodium acetate); however, these ESI adduct signals...
155 citations
TL;DR: In this article, a nitrogen microplasma jet operated at atmospheric pressure was developed for treating thermally sensitive materials, without any risk of arcing or electrical shock, and it exhibited a long plasma jet of about 6.5 cm with temperature near 300K, not causing any harm to human skin.
Abstract: A nitrogen microplasma jet operated at atmospheric pressure was developed for treating thermally sensitive materials. For example, the plasma sources in treatment of vulnerable biological materials must operate near the room temperature at the atmospheric pressure, without any risk of arcing or electrical shock. The microplasma jet device operated by an electrical power less than 10W exhibited a long plasma jet of about 6.5cm with temperature near 300K, not causing any harm to human skin. Optical emission measured at the wide range of 280–800nm indicated various reactive species produced by the plasma jet.
145 citations
TL;DR: In this article, an atmospheric pressure capacitive discharge source was developed that operates at power densities over 100 W cm−3, and the ground state nitrogen atom concentration was measured at the exit of the source by titration with NO, and it was found to reach a maximum of 3.0 ± 0.2 eV.
Abstract: An atmospheric pressure capacitive discharge source has been developed that operates at power densities over 100 W cm−3. The ground state nitrogen atom concentration was measured at the exit of the source by titration with NO, and it was found to reach a maximum of 3.0 ± 0.8 × 1017 cm−3 at 6.0 vol% N2 in argon, 250 °C and 150 W cm−3. This is equivalent to 2.3 vol% of N atoms in the afterglow. At these conditions, the electron density and temperature are estimated to be 3.1 × 1012 cm−3 and 1.2 eV. A plug-flow model of the plasma and afterglow was developed, and it was determined that the maximum N atom concentration achievable is limited by three body recombination.
141 citations
TL;DR: In this article, a nonlinear time-dependent two-temperature collisional-radiative model for air plasma has been developed for pressures between 1kPa and atmospheric pressure to be applied to the flow conditions of space vehicle re-entry into the Earth's atmosphere.
Abstract: A nonlinear time-dependent two-temperature collisional-radiative model for air plasma has been developed for pressures between 1kPa and atmospheric pressure to be applied to the flow conditions of space vehicle re-entry into the Earth’s atmosphere. The model consists of 13 species: N2, O2, N, O, NO, N2+, O2+, N+, O+, NO+, O2−, O− in their ground state and major electronic excited states and of electrons. Many elementary processes are considered given the temperatures involved (up to 10 000K). Time scales to reach the final nonequilibrium or equilibrium steady states are derived. Then we apply our model to two typical re-entry situations and show that O2− and O− play an important role during the ionization phase. Finally, a comparison with existing reduced kinetic mechanisms puts forward significant discrepancies for high velocity flows when the flow is in chemical nonequilibrium and smaller discrepancies when the flow is close to chemical equilibrium. This comparison illustrates the interest of using a ti...
128 citations
TL;DR: In this article, an atmospheric pressure microplasma jet is developed for depositing homogeneous thin films from C2H2, and the adjustment of the gas flow through the microplasmas jet assures optimal flow conditions as well as minimizes deposition inside the jet.
Abstract: An atmospheric pressure microplasma jet is developed for depositing homogeneous thin films from C2H2. The adjustment of the gas flow through the microplasma jet assures optimal flow conditions as well as minimizes deposition inside the jet. In addition, the formation of an argon boundary layer surrounding the emerging plasma beam separates the ambient atmosphere from the flow of growth precursor. Thereby the incorporation of nitrogen and oxygen from the ambient atmosphere into the deposited film is suppressed. Soft polymerlike hydrogenated amorphous carbon (a-C:H) films are deposited at the rate of a few nm/s on the area of a few square millimeters.
15 Mar 2006
TL;DR: AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.
Abstract: In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.
TL;DR: In this paper, the degradation of aqueous solutions of various dyes (e.g., Orange I, Crystal Violet, and Eriochrome Black T) used for the textile industry was performed by means of a special nonthermal quenched plasma technique (i.e., the gliding arc technique, which results from an electric discharge at atmospheric pressure and ambient temperature).
Abstract: The degradation of aqueous solutions of various dyes (e.g., Orange I, Crystal Violet, and Eriochrome Black T) used for the textile industry was performed by means of a special nonthermal quenched plasma technique (i.e., the gliding arc technique, which results from an electric discharge at atmospheric pressure and ambient temperature). The gaseous species formed in the discharge, and especially the OH radicals, induce strong oxidizing effects in the target solution, so that bleaching of the solution and degradation of the solute result, as evidenced by absorbance and chemical oxygen demand (COD) measurements. The two processes were considered as matching reactions, and overall kinetic data were derived when possible. A tentative mechanism based on literature data is also presented.
TL;DR: A novel hydride atomizer based on atmospheric pressure dielectric barrier discharge (DBD) plasma that offers the advantages of low operation temperature and low power consumption in comparison with the currently used electrothermal quartz atomization operated at 900 degrees C with a power supply of several hundred watts is described.
Abstract: This paper describes a novel hydride atomizer based on atmospheric pressure dielectric barrier discharge (DBD) plasma. The plasma was generated with a 3700-V, 20.3-kHz, and 5-W electrical power sup...
TL;DR: In this paper, a quadrupole mass spectrometer is used to measure axial species and temperature profiles within catalytic partial oxidation foam monoliths at atmospheric pressure with 0.3mm spatial resolution.
Abstract: Methods are presented to measure axial species and temperature profiles within catalytic partial oxidation foam monoliths at atmospheric pressure with 0.3 mm spatial resolution using a capillary sampling technique with a quadrupole mass spectrometer. The system allows sampling within the catalyst with negligible interference in flow or temperature by using a 0.6 mm quartz capillary containing a thermocouple and possessing a 0.3 mm side orifice. The capillary tightly fills a concentric channel drilled within the 10 mm long ceramic foam minimizing gas bypass. This technique has been used to measure axial catalyst species profiles at temperatures up to 1300 °C for catalytic partial oxidation of methane and ethane to synthesis gas and ethylene, respectively. CH4 and O2 conversion are approximately twice as fast on Rh than on Pt. For C2H6 the reaction products at the catalyst entrance are H2, H2O, CO, and CO2. Ethylene production begins only after ~4 mm into the catalyst after most of the O2 has reacted. Transient operation where the feed composition is varied stepwise between different C/O ratios has also been used to characterize these systems. The capillary sampler has a time resolution of ~0.05 s, and C/O step changes within 0.5 s have been achieved using mass flow controllers. For switches from C/O = 0.6 to 1.4, sharp overshoots are observed for syngas (H2 and CO) and similar undershoots for combustion products (H2O and CO2). By placing the sampling orifice at different positions and stepping the C/O ratio, spatio-temporal profiles can be obtained. Spatio-temporal profiles are extremely important in validating detailed reaction mechanisms because their information content is much higher compared to integral steady state measurements at the reactor outlet. The spatial profiles show where and how quickly different species are formed or consumed along the catalyst axis. Transient profiles provide additional diagnostics of mechanisms and surface coverages because they show how temperature and species concentrations follow a perturbation from steady state.
TL;DR: In this article, a direct current glow discharge sustained in helium at atmospheric pressure was developed, which operated within a voltage range of 300-900 volts (in the current-controlled mode) and at currents ranging over tens to hundreds of milliamps.
Abstract: A novel direct current glow discharge sustained in helium at atmospheric pressure has been developed. Current–voltage behavior and spectroscopic characteristics strongly suggest that the system operates in the glow regime, in spite of the high pressure. The diffuse and extremely stable discharge is typically operated within a voltage range of 300–900 volts (in the current-controlled mode) and at currents ranging over tens to hundreds of milliamps. Spatially resolved spectroscopic measurements of some selected species are presented. Rotational temperature profiles were calculated using the OH emission spectrum, yielding values in the positive column ranging from 1300 to 1600 K.
TL;DR: In this article, a hybrid model was used to simulate dc argon micro glow-discharge at atmospheric pressure for a pin-plate electrode configuration with inter-electrode gap spacing of 200m together with an external circuit.
Abstract: A hybrid model was used to simulate a dc argon micro glow-discharge at atmospheric pressure The simulations were carried out for a pin-plate electrode configuration with inter-electrode gap spacing of 200??m together with an external circuit The predicted voltage?current characteristics and current density profiles identify the discharge to be a normal glow-discharge The neutral gas temperature predictions indicate that the discharge forms a non-thermal, non-equilibrium plasma Experimental studies were conducted to validate the numerical model Predictions from the numerical model compare favourably with the experimental measurements
TL;DR: The duration of the gas emission phase emerged as most significant variable for the distribution of landfill gas components within the biofilter, thus being of high relevance for biofilter operation.
01 Jun 2006
TL;DR: The electrical conductivity is predicted successfully as a function of Bruggeman's model for concentrated emulsions at elevated pressure versus air/W or C/W foams at atmospheric pressure.
Abstract: A nonionic-methylated branched hydrocarbon surfactant, octa(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether ( 5b -C 12 E 8 ) emulsifies up to 90% CO 2 in water with polyhedral cells smaller than 10 μm, as characterized by optical microscopy The stability of these concentrated CO 2 /water (C/W) emulsions increases with pressure and in some cases exceeds 24 h An increase in pressure weakens the attractive van der Waals interactions between the CO 2 cells across water and raises the disjoining pressure It also enhances the solution of the surfactant tail and drives the surfactant from water towards the water–CO 2 interface, as characterized by the change in emulsion phase behavior and the decrease in interfacial tension ( γ ) to 21 mN/m As the surfactant adsorption increases, the greater tendency for ion adsorption is likely to increase the electrostatic repulsion in the thin lamellae and raise the disjoining pressure As pressure increases, the increase in disjoining pressure and decrease in the capillary pressure (due to the decrease in γ ) each favor greater stability of the lamellae against rupture The electrical conductivity is predicted successfully as a function of Bruggeman's model for concentrated emulsions Significant differences in the stability are observed for concentrated C/W emulsions at elevated pressure versus air/W or C/W foams at atmospheric pressure
TL;DR: It is concluded that water is the non-wetting phase in this coal-water-CO2 system, and the exceptional behavior at atmospheric pressure is possibly related to the stability of water patches on the coal surface.
TL;DR: In this paper, an experimental study of the penetration of a liquid jet in a gaseous crossflow was conducted in an atmospheric pressure facility at air velocities up to 110 m/s and air temperatures up to 300°C using distilled water, acetone, and 4-heptanone as test liquids.
Abstract: Results are presented from an experimental study of the penetration of a liquid jet in a gaseous crossflow. The experiments were conducted in an atmospheric pressure facility at air velocities up to 110 m/s and air temperatures up to 300°C using distilled water, acetone, and 4-heptanone as test liquids. Penetration was determined from two-dimensional Mie scattering images of the spray. In addition to the wellestablished effect of momentum flux ratio, the results indicate that Weber number and liquid viscosity, through their effect on drop size and the trajectory of the liquid column, also affect the spray’s penetration. A correlation was developed based on these results which accurately predicts the effect of momentum flux ratio, Weber number, and liquid viscosity on spray penetration over the range of conditions studied.
TL;DR: In this paper, the potential of surface modifications realized with FDBD and APGD in different atmospheres (N2+ H2 and N2+ NH3 mixtures) on poly(tetrafluoroethylene) to determine the relative influence of both the discharge regime and the gas nature on the surface transformations.
Abstract: Plasma polymer surface modification is widely used in the biomedical field to tailor the surface properties of materials to improve their biocompatibility. Most of these treatments are performed using low pressure plasma systems but recently, filamentary dielectric barrier discharge (FDBD) and atmospheric pressure glow discharge (APGD) have appeared as interesting alternatives. The aim of this paper is to evaluate the potential of surface modifications realized with FDBD and APGD in different atmospheres (N2+ H2 and N2+ NH3 mixtures) on poly(tetrafluoroethylene) to determine the relative influence of both the discharge regime and the gas nature on the surface transformations. From XPS analysis, it is shown that the discharge regime can have a significant effect on the surface transformation; FDBDs operating in H2/N2 lead to a high concentration of amino-groups with high specificity but also important damaging on the surface. Glow discharges in both H2/N2 and NH3/N2 lead to lower concentrations of amino-groups with lower specificity but lower surface damaging. Therefore, this simple surface treatment seems to be an effective, low cost method for the production of uniform surface modification with amino-groups that can subsequently be used to graft various chemical functionalities used for biomaterial compatibility.
TL;DR: A capacitively coupled, atmospheric pressure plasma has been developed that produces a high concentration of reactive species at a gas temperature below 300°C as discussed by the authors, and the concentration of ground-state oxygen atoms produced by the discharge was measured by NO titration, and found to equal 1.2±0.2vol%, or 1.4×1017cm−3, using 6.0vol% O2 in argon at 150W∕cm3.
Abstract: A capacitively coupled, atmospheric pressure plasma has been developed that produces a high concentration of reactive species at a gas temperature below 300°C. The concentration of ground-state oxygen atoms produced by the discharge was measured by NO titration, and found to equal 1.2vol%, or 1.2±0.4×1017cm−3, using 6.0vol% O2 in argon at 150W∕cm3. The ozone concentration determined at the same conditions was 4.3±0.5×1014cm−3. A model of the gas phase reactions was developed and yielded O atom and O3 concentrations in agreement with experiment. This plasma source etched Kapton® at 5.0μm∕s at 280°C and an electrode-to-sample spacing of 1.5cm. This fast etch rate is attributed to the high O atom flux generated by the plasma source.
Patent•
23 Oct 2006TL;DR: In this paper, the authors present a system and method for cooling a combustion gas charge prior. But this method requires the prior to be compressed intake air, exhaust gas, or a mixture thereof.
Abstract: The present invention relates to a system and method for cooling a combustion gas charge prior. The combustion gas charge may include compressed intake air, exhaust gas, or a mixture thereof. An evaporator is provided that may then receive a relatively high temperature combustion gas charge and discharge at a relatively lower temperature. The evaporator may be configured to operate with refrigeration cycle components and/or to receive a fluid below atmospheric pressure as the phase-change cooling medium.
TL;DR: DAPCI is demonstrated to be a useful ambient detection method for nitroaromatic explosives absorbed on surfaces because their different chemistry facilitates analyte identification.
Abstract: Acetonitrile vapor and air are useful reagents for the selective detection of nitroaromatic compounds using atmospheric pressure ion/molecule reactions. Reagent ions CH2CN- and CN- generated from acetonitrile, and O-*, OH- and OOH- produced from the oxygen in air, react with vapor-phase and condensed-phase nitroaromatics in the course of atmospheric pressure chemical ionization (APCI) and desorption atmospheric pressure chemical ionization (DAPCI), respectively. The homogeneous and the heterogeneous phase reactions both lead to the formation of the same anionic adducts. These adducts have characteristic fragmentation patterns upon collisional activation, which makes these two reagents valuable for the selective detection of particular nitroaromatics, including explosives present as components of complex mixtures. Complementary information is available from the two reagents because their different chemistry facilitates analyte identification. DAPCI is demonstrated to be a useful ambient detection method for nitroaromatic explosives absorbed on surfaces.
TL;DR: In this paper, a two-dimensional (axially symmetric) computational model of the microdischarge formation in a barrier discharge for short (1-2 mm) gaps in air at atmospheric pressure is proposed.
Abstract: A two-dimensional (axially symmetric) computational model of the microdischarge formation in a barrier discharge for short (1–2 mm) gaps in air at atmospheric pressure is proposed. A non-homogeneous electric field, caused by a residual non-uniform charging of the dielectric barriers, is considered as an important reason for the filament formation by a Townsend mechanism. The ion–electron emission from the dielectric covering the cathode is treated as the principal secondary process; the secondary emission coefficient in the model is selected to be consistent with the Paschen voltage. For an applied sinusoidal voltage, this follows the microdischarge development on a microsecond scale. It is shown that even a slight inhomogeneity of the initial electric field leads to the formation of a narrow microdischarge channel.The two-dimensional dynamics of the radiation from a microdischarge for the case of the second positive and the first negative systems of nitrogen is simulated and compared with recent experimental data. The effects of the secondary emission coefficient and of a distribution of residual surface charges are investigated. It is shown that the level of inhomogeneity of the residual surface charge distribution does not affect the radius of the microdischarge channel, but affects its two-dimensional structure.The proposed model explains satisfactorily the experimental results for the velocity of the cathode-directed ionizing wave and the emission of the N2 second positive system from a microdischarge.
TL;DR: In this article, the authors present clear evidence of two different discharge modes of the atmospheric pressure RF-excited plasma needle and the transition mechanism by the finite element method, and demonstrate that the plasma needle operates as a corona discharge at low power and that the discharge mode transitions to a glow discharge at a critical power.
Abstract: We present clear evidence of two different discharge modes of the atmospheric pressure RF-excited plasma needle and the transition mechanism by the finite element method. The gas used is helium with 0.1% nitrogen addition. The needle has a point-to-plane geometry with a radius of 30 µm at the tip, 150 µm at the base and an inter-electrode gap of 1 mm. We employ the one-moment fluid model with the local field approximation. Our simulation results indicate that the plasma needle operates as a corona discharge at low power and that the discharge mode transitions to a glow discharge at a critical power. The discharge power increases but the discharge voltage drops abruptly by a factor of about 2 in the corona-glow transition. The plasma density and ionization is confined near the needle tip in corona-mode while it spreads back along the needle surface in glow-mode. The corona-glow transition is also characterized by a dramatic decrease in sheath thickness and an order of magnitude increase in plasma density and volume-averaged ionization. The transition is observed whether or not secondary electron emission is included in the model, and therefore we suggest that this is not an α –γ transition.
Proceedings Article•
04 Jun 2006
TL;DR: In this article, the authors compared atmospheric and near-atmospheric pressure glow discharges generated in both pure helium and helium-air mixtures using a plasma chemistry code originally developed for simulations of electron-beam-produced air plasmas.
Abstract: Atmospheric and near-atmospheric pressure glow discharges generated in both pure helium and helium-air mixtures have been studied using a plasma chemistry code originally developed for simulations of electron-beam-produced air plasmas. Comparisons are made with experimental data obtained from high-pressure glow discharges in helium-air mixtures developed by applying sinusoidal voltage wave forms between two parallel planar metallic electrodes covered by glass plates, with frequencies ranging from 10to50kHz and electric field strengths up to 5kV∕cm. The code simulates the plasma chemistry following periodic pulsations of ionization in prescribed E∕N environments. Many of the rate constants depend on gas temperature, electron temperature, and E∕N. In helium plasmas with small amounts (∼850ppm) of air added, rapid conversion of atomic helium ions to molecular helium ions dominate the positive ion kinetics and these species are strongly modulated while the radical species are not. The charged and neutral species concentrations at atmospheric pressure with air impurity levels up to 10000ppm are predicted. The negative ion densities are very small but increase as the air impurity level is raised, which indicates that in helium-based systems operated in open air the concentration of negative ions would be significant. If water vapor at typical humidity levels is present as one of the impurities, hydrated cluster ions eventually comprise a significant fraction of the charged species.