Abnormal Glow Discharge Research Articles

Rotational and vibrational temperatures of transient atmospheric glow plasma

Plasma ignition can significantly improve the efficiency and performance of combustion devices through the enhancement of combustibility limits. Investigating plasma development for fundamental experimental flame conditions (i.e. spherical flame experiments) can provide insight into how plasma thermalizes the combustible mixture and, therefore a better understanding of flame development in future experimental studies. This study observed an ignition system designed to produce spherical flames in quiescent gas inside a constant-volume combustion chamber. Rotational and vibrational temperature measurements of dry atmospheric air glow plasma are reported. Measurements were taken for a transient discharge with currents less than 0.5 A. The electrode wire geometry and discharge variation resulted in an ellipsoid-shaped kernel and plasma region with an abnormal glow discharge. The measured temperatures were compared to the conductive thermal kernel boundary observed with Schlieren imaging. Maximum rotational and vibrational temperatures of 3000 K and 10 000 K, respectively, were observed near the anode electrode for a 0.5 A current. The temperature decreased with the axial distance from the anode, while a constant temperature was observed in the radial direction. Lower currents resulted in a smaller temperature, with minimum measured rotational and vibrational temperatures of 1500 K and 5000 K, respectively. The results were compared with available experimental literature and the variation observed was a result of the transient nature, which resulted in hysteresis in temperature vs discharge current measurements.

Fluid modeling of CF3I/CO2 arc formation process

The environmentally friendly insulating gas CF3I is a promising replacement for SF6 due to its excellent insulation and arc extinguishing performance. In the arc chamber of high-voltage circuit breakers filled with CF3I/CO2, the near-electrode sheath dominates the current transfer process between contact and arc column during arc formation, which has a significant effect on the transition from glow to arc discharge. The 30%CF3I/70%CO2 was taken as the research object in this research, and a more perfect fluid model was established considering the influence of diffusion current. The arc formation process between the contacts at the preliminary stage of circuit breaker interruption was conducted. The results show that the arc formation process can be divided into three stages: glow discharge, abnormal glow discharge, and arc discharge. As the arc formation process proceeds, the thickness of the near-cathode sheath decreases gradually. When the arc reaches stability with the current density 8×106–1.6×107A·m−2, the thickness of the near-cathode sheath is 7 μm, the steep voltage fall near the cathode sheath is generated within 7 μm away from the cathode surface, and this voltage fall almost does not change with the current density. CF3I− is the dominant negative ion between the contacts, which indicates that CF3I has excellent electron adsorption performance and is beneficial to arc deionization. The computational results of this work were compared with the existing experimental ones, which shows that the model used in this work is accurate enough. Finally, suggestions for model optimization and future work are given.

Numerical simulation study on microdischarge via a unified fluid model

Numerical simulation has become an indispensable tool in the study of gas discharge. However, it is typically used to reveal microscopic properties in a discharge under specific conditions. In this work, a unified fluid model for discharge simulation is introduced in detail. The model includes the continuity equation, the energy conservation equation of the species (electrons and heavy particles), and Poisson’s equation. The model takes into account some processes such as cathode electron emission (secondary electron emission and thermionic emission), reaction enthalpy change, gas heating, and cathode heat conduction. The full current-voltage characteristic (CVC) curve covers a range of discharge regimes, such as the Geiger-Müller discharge regime, Townsend discharge regime, subnormal glow discharge regime, normal glow discharge regime, abnormal glow discharge regime, and arc discharge regime. The obtained CVC curve is consistent with the results in the literature, confirming the validity of the unified fluid model. On this basis, the CVC curves are obtained in a wide pressure range of 50–3000 Torr. Simulation studies are carried out focusing on the discharge characteristics for microgap of 400 µm at pressures of 50 Torr and 500 Torr, respectively. The distributions of typical discharge parameters under different pressure conditions are analyzed by comparison. The results indicate that the electric field in the discharge gap is uniform, and that the space charge effect can be ignored in Townsend discharge regime. The cathode fall region and the quasi-neutral region both appear in glow discharge regime, and the space charge effect is significant. In particular, the electric field reversal occurs in abnormal discharge regime due to the heightened particle density gradient. The electron density reaches about 10<sup>22</sup> m<sup>–3</sup> in arc discharge regime dominated by thermionic emission and thermal ionization, with the current density increasing. The gas temperature peak is 11850 K when the pressure is 500 Torr, and the cathode surface is heated to nearly 4000 K due to heat conduction. The present model can be used to simulate gas discharge across a wide range of condition parameters, promoting and expanding fluid model applications, and assisting in a more comprehensive investigation of discharge parameter properties.

Investigation of plasma parameters, distributions, and optical emission for the anti-microbial performance of non-woven fabric under direct current glow discharge

The distribution of electron temperature Te and density Ne for direct current glow plasma discharge was investigated, using a single Langmuir probe, inserted inside the plasma cell. The radial temperature distribution has the same values, except with a small increment variation at the cathode edge, and an axial decrement for the temperature Te distribution profiles from the cathode fall region, passing the abnormal glow region, up to the faraway axial region.The radial distribution of the electron density Ne has its highest value at the cathode, with very intense plasma at the cathode fall region, and more Ne decrement in the abnormal glow region, passing the abnormal glow region up to the faraway axial region. In the axial Ne distribution, an increase in Ne from the cathode fall region reaches maximum values in the abnormal glow region and decreases in the faraway axial region.The optimal plasma surface treatment of non-woven silk fabric (n-WSF) can be achieved by utilizing a high plasma density and low energy of electrons to inactivate viable cells attached to (n-WSF) at very short application times, leading to complete inactivation, where the bacterial inactivation rate increases in the abnormal glow region. Based on analyses of the experimental data of initial and final densities of viable cells using survival curves in the abnormal glow discharge region, a dramatic inhibitory effect of plasma discharge on the residual survival microbe ratio was observed.

DETERMINATION OF SEVERAL IMPORTANT PARAMETERS OF HOLLOW ELECTRODES ABNORMAL GLOW DISCHARGE PLASMA UNDER THE INFLUENCE OF MAGNETIC FIELD AT DIFFERENT GAS PRESSURES

This paper investigates the impact of an axial magnetic field on several plasma parameters of hollow electrode argon abnormal glow discharge. The discharge is generated by applying a DC voltage ranging from 0-6KV. By varying the pressure and magnetic field strength (0-25mT), the plasma potential, frequency, and degree of ionization were measured. The plasma potential, frequency, and degree of ionization were evaluated using spectroscopic measurements of the electron temperature and density. The results of the experiment show that the plasma potential decreases as the magnetic field strength increases, while the plasma frequency increases for lower pressure but reaches a constant value for higher pressure due to the increasing number of excitation collisions among the plasma-charged particles. The degree of ionization, determined using the ideal gas law, shows a near-linear relationship with the axial magnetic field at both low and high pressure.

Electrical Discharge in a Cavitating Liquid under an Ultrasound Field.

A theoretical model for an electrical discharge in a cavitating liquid is developed and compared with experiments for the optimization of the water treatment device. The calculations based on solution of the Noltingk─Neppiras equation support the hypothesis that the electric field promotes the formation of vapor microchannels inside a liquid gap between the electrodes, where at a low gas pressure Paschen's conditions of rupture and abnormal glow discharge maintenance in those microchannels are fulfilled. Theoretical analysis of the cavitation processes and the discharge formation processes is in qualitative agreement with the experimental data obtained in this work in a water treatment device using a hydrodynamic emitter. The following graphic illustrates the experimental setup: (1) feeding tank, (2) hydrodynamic emitter, (3) zone of cavitation inside the plasma reactor, (4) high-frequency generator of electric impulses, and (5) outlet.

Formación de películas de poliacetileno sobre sustrato de cobre mediante descarga luminiscente anormal

The formation of polymeric films by plasma has become an alternative for the coating of metallic materials that require varying their surface characteristics and improving their resistance to corrosion; because by this method it is possible, in principle, to polymerize any gaseous hydrocarbon. In this work, the study of the formation of acetylene polymer films on a copper substrate, previously treated in an abnormal luminescent discharge regime in argon-hydrogen atmosphere, is presented. The polymeric formation was carried out in a continuum current abnormal glow discharge in an atmosphere of 60% Ar, 35% H2 and 5% C2H2 at a pressure of 2 Torr, at a temperature of 600 °C and with deposition times between 5 and 120 s. The structural and morphological analysis of the polymeric film deposited at different temperatures was performed by Infrared Spectroscopy and Scanning Electron Microscopy. Additionally, a characterization of the materials was carried out using corrosion resistance analysis.

Assessing apparent secondary electron yield from current–voltage characteristics of abnormal DC glow discharges

The problem of assessing apparent secondary emission coefficient based on electrical properties of direct-current (DC) glow discharges using numerical modeling is revisited. An analysis of potential sources of uncertainties resulting from errors in experimental data as well as from model assumptions and approximations is presented. An estimation method based on a previously developed analytical model of a DC glow discharge is suggested. Application of the method is demonstrated in the example available in the literature of current–voltage characteristics of DC glow discharges in argon with copper electrodes. Values obtained for the considered data fall into two distinguishable groups, closely corresponding to those for clean and dirty copper cathode surfaces. The obtained preliminary results suggest the feasibility of estimating apparent secondary emission coefficients in DC discharges using numerical modeling.

Iterative kinetic model application in diagnostics of argon abnormal DC glow discharges

Iterative kinetic model application in diagnostics of argon abnormal DC glow discharges

Breakdown mode and parameter space of micro-discharge sustained by thermionic emission

Gas breakdown driven by thermionic emission in a microgap to produce low-temperature plasma is studied using a 1D implicit particle-in-cell/Monte Carlo collision model. The influence of background gas pressure, external driving voltage, cathode temperature and discharge gap on argon glow micro-discharge in the parallel plate was simulated. Different parameters and conditions have different effects on the gas breakdown at small size. The discharge gap of hundreds of µm has little influence on the gas breakdown and only changes the plasma distribution. As the applied voltage increases, the gas changes from a non-breakdown mode to a breakdown mode, and the gas breakdown is more sensitive to the applied voltage than the gas pressure at low voltages. In all breakdown modes, the gas pressure hardly changes the plasma evolution characteristics. At appropriate cathode temperatures, the density of electrons and ions increases rapidly, forming a stable sheath, and the equivalent resistance of the discharge gap becomes smaller as the temperature rises and the plasma is in abnormal glow discharge.

Spectral Characteristics of DC Short Glow Discharge Plasma With Grid Electrodes

The characteristics of post-cathode plasma maintained by a self-made DC short glow-discharge plasma generator with grid electrodes were measured by optical emission spectroscopy. The discharge existed in an abnormal glow discharge mode at a voltage of 250–400 V and a helium pressure of 3–15 Torr and a discharge gap of 3 mm. The results indicate that the intensity distribution of helium atom spectral lines in the post-cathode space differs from that in the post-anode space. The temperature of electron excitation in the post-cathode plasma reaches its peak of 1500–3000K at 5–6 mm from the grid cathode. The difference in the intensity distributions of helium atom spectral lines in the post-cathode and post-anode spaces is associated with electron generation mechanism in these cases.

Synthesis of Ti21.5V40Cr38.5 alloy by abnormal glow discharge plasma

The paper describes the structural-phase state and sorption characteristics of the Ti21.5V40Cr38.5 alloy synthesized by melting in abnormal glow discharge plasma and arc melting. X-ray diffraction patterns showed the presence of the main TiVCr phase with a body-centered cubic (bcc) lattice and Ti2O phase with a hexagonal close packed (hcp) lattice. The maximum hydrogen capacity of the samples obtained by melting in abnormal glow discharge plasma after 3 cycles was 3 wt%.

Investigation on plasma enhanced decomposition of ammonium dinitramide (ADN) based propellant with optical diagnosis

Plasma-enhanced decomposition is a promising method to achieve reliable ignition and better thruster performance with an ADN-based propellant. High-speed imaging and optical emission spectroscopy are used to characterize the discharge plasma produced from ADN-based propellant vapor and argon carrier gas within parallel planes. Discharge regimes are independently controlled by varying working parameters. The transition from abnormal glow discharge (AGD) to filamentary discharge (FD) is identified from voltage-current characteristics and sudden changes in excitation electron temperature (Te-exc) and electron density (Ne) under a pressure of 0.2–10 kPa. Instabilities develop because there are more freedom degrees and higher collision probabilities after ADN-based propellant vapor is added. The product of Te-exc and Ne shows a higher energy transfer efficiency from input power to vapor in the FD regime. Water molecules increase the net dissociative attachment rate and effectively quench Ne. Although preheated vapor (as the discharge medium) has a much lower Ne, more radicals appear such as OH, NH, CH, CN, N2, N2+, and C2, which promote chemical interactions in an electric field and increase the probability of successful ignition. This can be attributed to thermalization due to an increase in the translational kinetic energy and rotational excitation, which has an important impact on chemical reaction kinetics. Therefore, preheating is verified as critical for improving the ignition and performance of a plasma-assisted ADN-based thruster.

Comparative Analysis of the Parameters of the Normal and Abnormal DC Glow Discharges

A comparative numerical study of the parameters of normal and abnormal direct current glow discharges between two flat disk electrodes with a radius of 3 cm in a 1-cm-high electric discharge gap is performed. A two-dimensional axisymmetric drift-diffusion model of the glow discharge is used for the numerical simulation, including equations for the transfer of electrons and molecular nitrogen ions, and the Poisson equation for finding the electric potential in the discharge gap taking into account the regions of the space charge and the positive column. Abnormal discharges are obtained when the radius of the cathode decreases. A numerical procedure is proposed for smoothing local maxima of the electric field strength near the boundaries of the abnormal glow discharge cathode, which ensures the stability of the solution and the weak effect on the calculated data. The numerical simulation results of the electrodynamic structure of normal and abnormal glow discharges are presented.

Improved treatment of home-made glow discharge ion source

For a better treatment, a new class of DC ion source (DCIS) was developed and adapted to provide low-power, highly-density plasma and ion-current applications. Such an ion source operates under the mode of abnormal glow discharge being of the self-extraction category, with specific features such as simple operation, stable discharge, and the ability to use for a variety of plasma, ion, and electron beam applications. A teflon disc with different diameters has been installed in between the two electrodes. This disc covered the cathode area, reducing the discharge area on the cathode surface for discharge confinement, and thus allowing for a higher output ion beam current. Pressures of 10−4 mbar, a 3 mm gap between the electrodes, and a 5 mm teflon diameter were observed to be the optimal operating conditions. At this ideal distance, hydrogen, nitrogen, and argon gases were used to investigate internal and external operational parameters. Finally, the Paschen curves were determined for hydrogen, air, as well as nitrogen gases.

Numerical Simulation of Axisymmetric Abnormal Glow Discharge between Two Flat Disc Shaped Electrodes

Numerical Simulation of Axisymmetric Abnormal Glow Discharge between Two Flat Disc Shaped Electrodes

Study of UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 370.962 nm, Ne II 371.308 nm, and.Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal DC glow discharge in pure neon. Two sets of experimental profiles and electric field distributions, one for discharge with tungsten and the other with titanium cathode, were obtained by means of the optical emission spectroscopy (OES) and theoretically studied by the iterative CS kinetic model. It is shown that our theoretical model enables the determination of the most important CS parameters (e.g. the thickness of the CS region, and the theoretical distributions of electric field and gas temperature) and thereupon based accurate theoretical predictions of the experimentally observed profiles of the studied lines.

Development of plasma beam irradiation facility using applied-field MPD thruster to study plasma-surface interactions

A plasma beam irradiation facility was developed based on the applied-field magnetoplasmadynamic (AF-MPD) thruster concept for studying plasma-surface interactions. The AF-MPD thruster was chosen because it can produce a plasma beam with high plasma density in continuous-wave mode. Two types of AF-MPD thruster were developed and used in this study: a type I source with a wide thruster channel was used for a heat flux test with Ar or Xe gas, while a type II source with a narrow thruster channel was used for an ion flux test with H2 or He gas. The plasma initially showed the characteristics of abnormal glow discharges and then a transition to arc occurred when the plasma current exceeded a threshold value. It was found that a cathode made of thoriated tungsten significantly lowered the threshold current for the transition from abnormal glow to arc. The maximum heat flux provided by our facility was measured to be 7 MW m−2 using a custom-made heat flux sensor, while the maximum hydrogen ion flux was measured to be 1 × 1023 m−2 s−1 using a Langmuir probe. The electron temperature ranged between (4–5) eV, while the electron density at the plasma plume (downstream) ranged between (1–4) × 1018 m−3.

High-rate growth of single crystal diamond in AC glow discharge plasma

The detailed experimental behavior of an AC abnormal glow discharge plasma assisted chemical vapor deposition reactor for single crystal diamond (SCD) synthesis operating within the wide-range (20–250 Torr) pressure regime was presented. Within the discharge operating window absorbed power densities of 250–9000 W/cm3 were achieved and high quality SCD synthesis with growth rate up to 80 μm/h was demonstrated. At the power densities over 2500 W/cm3 the diamond substrates were located directly on water-cooled substrate holder without any intermediate molybdenum holder. The influence of several input experimental variables including pressure, N2 and Ar concentration, CH4 percentage, and discharge current on SCD deposition was explored. The quality of synthesized crystals approved competitive purity level of glow discharge CVD process.

Variation of Plasma Properties in Cylindrical Inertial Electrostatic Confinement Device by Changing the Anode Transparency

Inertial electrostatic confinement (IEC) is investigated in terms of direct-current discharge in a cylindrical configuration using nitrogen gas in the pressure range between 0.028 and 0.09 Torr. Discharge characteristics are determined for different anode transparencies of 84%, 92%, and 96% corresponding to 24, 12, and 6 anode rods, respectively. I-V characteristic curves indicate that the electric discharge is in the abnormal glow discharge region. The discharge voltage has the highest values for the low anode transparency for the same value of the discharge current. A double electric probe has been used to measure electron temperature and ion density. The low anode transparency (24 anode rods) enhances field uniformity and aligns the motion of electrons into a chord so that better electrostatic confinement is achieved. This will raise the ion density and lead to thermalization of the plasma, which reduces the electron temperature. The behavior of the electron temperature and the ion density was studied as a function of the gas pressure at the center and near the edge. The variation of the density and temperature in both positions can confirm the plasma confinement. In the low-pressure regime, the confinement process is reinforced. Because of the longer mean free path, electrons cause ionization at the center, which raises the ion density to about 1.44 × 1015 m−3 and the electron temperature to about 2.9 eV.