Product Of Gas Pressure Research Articles

The effect of micro-gap discharge paths on ionization coefficients and similarity theory

In order to investigate the impact of discharge paths at the micrometer scale on breakdown, two sets of different electrodes were arranged with electrode gaps ranging from 10 μm to 100 μm and gas pressures varying from 1 kPa to 100 kPa. The research has revealed that without an insulating layer at the edge of the electrode, when the product of gas pressure (p) and electrode gap (d) is less than 60Pa·cm, the number of positive ions cannot satisfy the conditions for self-sustaining discharge at the electrode gap (d). As a result, the discharge path varies along a longer path (s) to satisfy the conditions for self-sustained discharge, thereby maintaining the minimum breakdown voltage. This long-path discharge mechanism affects the ionization coefficient, resulting in an inconsistency between the ionization coefficient ratio at different distances and their respective scale factor (k) values. Therefore, on a micrometer scale, changes in the path make the application of similarity theory no longer applicable.

Measuring gas discharge in contact electrification

Contact electrification in a gas medium is usually followed by partial surface charge dissipation caused by dielectric breakdown of the gas triggered during separation of the surfaces. It is widely assumed that such discharge obeys the classical Paschen’s law, which describes the general dependence of the breakdown voltage on the product of gas pressure and gap distance. However, quantification of this relationship in contact electrification involving insulators is impeded by challenges in nondestructive in situ measurement of the gap voltage. The present work implements an electrode-free strategy for capturing discrete discharge events by monitoring the gap voltage via Coulomb force, providing experimental evidence of Paschen curves governing nitrogen breakdown in silicone-acrylic and copper-nylon contact electrification. It offers an alternative approach for characterizing either the ionization energies of gases or the secondary-electron-emission properties of surfaces without the requirement of a power supply, which can potentially benefit applications ranging from the design of insulative materials to the development of triboelectric sensors and generators.

More efficient charging of ferroelectrets via tuning of the Paschen breakdown

Charging by means of dielectric barrier discharges (DBDs) is a critical step in the preparation of ferroelectrets (also called piezoelectrets). Triggering of the DBD charging in ferroelectrets is governed by Paschen's law. The Paschen-breakdown voltage Vb of common gases exhibits a U-shaped dependence on the product of gas pressure p and electrode spacing d (internal-cavity height in the present ferroelectret context). This allows for a more efficient charging strategy for ferroelectrets whose pd value at atmospheric pressure is different from the (pd)min value of the Paschen-breakdown curve. For easier triggering of the DBD charging, the pd is adjusted toward (pd)min (corresponding to Vb, min of the Paschen curve) by controlling the gas pressure in the cavity. Subsequently, pd is restored to its value at ambient pressure under the charging voltage in order to obtain a high remanent polarization. The proposed charging scheme is easy to operate and can significantly improve the charging efficiency of ferroelectrets with a wide range of cavity geometries.

Experimental verification of modified Paschen’s law in DC glow discharge argon plasma

Breakdown voltage of a gas is the required voltage to start a discharge or electric arc through the gas. Paschen’s law describes the characteristics of gas breakdown voltage between two electrodes. This law states that the Gas breakdown voltage(VB) depends only on the product of gas pressure (p) and gap length(d) between electrodes (VB=f(pd)). In this paper, the effect of electrode separation length(d) and electrode radius (r) on gas breakdown voltage is studied experimentally. A gas discharge system with a large gap length compared to electrode radius is used for the study. Paschen curves are plotted for different electrode separation lengths and electrode radii. It is observed that gas breakdown voltages deviates from Paschen’s law and depend on the d/r ratio also in addition to the product of gap separation and pressure, i.e. VB=f(pd,d/r). This relation, already reported in the analyses of micro gap discharge and theoretical studies, is known as modified Paschen’s law. In order to experimentally verify the modified Paschen’s law in large discharge gaps, many experiments are conducted by varying both electrode separation and electrode radii but keeping the d/r ratio always same. It is observed that for different discharge system geometries, if d/r ratio is same, the break down voltages are same for same pd value. The Paschen’s curves are also plotted for different experiments and it is observed that the curves overlap if d/r ratio is set same for all experiments. Thus, the work presented in this paper experimentally verify the modified Paschen’s law.

Minimum breakdown parameters through H2, He, N2 and Ar gases

The gas discharge plasma has attracted the attention of scientists and technologists because it is a source of electrons and ions beams which are needed and used in several applications and modern instruments. Minimum breakdown voltage of the cylindrical coaxial virtual cathode oscillator is investigated on Nitrogen (N2), Argon (Ar), Helium (He) and Hydrogen (H2) through different anode transparencies. The study includes the effect of secondary electron emission on the minimum breakdown voltage (Vb)min and the product of gas pressure P and inter-electrode distance d, Pdmin. The changes in the minimum breakdown voltage with the gas pressure are studied where pressure is the main factor of electric discharge. Paschen curve is studied through electric discharge for Ar and H2 by using different anode transparencies. This study aims to understand the parameters that can affect the minimum voltage (Vb)min at which the gas transfers from a non-conducting state to a conducting state. The study is carried out on a cylindrical coaxial vircator for different gases and different anode transparencies.

Investigation on the effect of nonlinear processes on similarity law in high-pressure argon discharges

In this paper, the effect of nonlinear processes (such as three-body collisions and stepwise ionizations) on the similarity law in high-pressure argon discharges has been studied by the use of the Kinetic Global Model framework. In the discharge model, the ground state argon atoms (Ar), electrons (e), atom ions (Ar+), molecular ions (Ar2+), and fourteen argon excited levels Ar*(4s and 4p) are considered. The steady-state electron and ion densities are obtained with nonlinear processes included and excluded in the designed models, respectively. It is found that in similar gas gaps, keeping the product of gas pressure and linear dimension unchanged, with the nonlinear processes included, the normalized density relations deviate from the similarity relations gradually as the scale-up factor decreases. Without the nonlinear processes, the parameter relations are in good agreement with the similarity law predictions. Furthermore, the pressure and the dimension effects are also investigated separately with and without the nonlinear processes. It is shown that the gas pressure effect on the results is less obvious than the dimension effect. Without the nonlinear processes, the pressure and the dimension effects could be estimated from one to the other based on the similarity relations.

Experimental study on breakdown voltage of high pressure and high temperature helium gas between parallel electrodes

The DC and 50Hz AC breakdown voltage of helium between two parallel copper electrodes were measured to obtain the base data for insulation design of the electrical equipment working in the high pressure and high temperature helium gas in High Temperature Reactor (HTR). The measurements were performed in the distance of 0.25–0.53mm, the temperature of 15–180°C, and the pressure of 0.05–7MPa. It has been proved that, for both DC and 50Hz AC, the breakdown voltage increases with the increasing of the pressure, with the increasing of the distance, and with the decreasing of the temperature. The DC breakdown voltage is about 1.4 times of the value of 50Hz AC or, in other words, is similar to the peak value of 50Hz AC. The Paschen law, describing the relationship between the breakdown voltage of helium (Ub) and the product of gas density and electrode distance (ρd), was presented for DC and 50Hz AC respectively, based on the experimental data at high pressure and high temperature. Good linearity is shown in the data. Furthermore, the linear fitting equation was also presented. The slope of Paschen curve about Ub-ρd at the range of large ρd is influenced by the collision cross section and the ionization energy of helium atom, and not influenced by the temperature, for DC. Both for DC and 50Hz AC, the slope of Paschen curve about Ub-ρd is about 6×105 times of the slope of Paschen curve about Ub-Pd, where Pd is the product of gas pressure and electrode distance. Both for DC and 50Hz AC, the breakdown voltage of helium is less than one fifth of the value of air, at 0.1MPa and room temperature. However, the breakdown voltage of helium at 180°C and 7MPa is larger than the value of air at 0.1MPa and room temperature.

Effect of distribution of electric field on low-pressure gas breakdown

A low-pressure gas breakdown in a gap of the non-uniform electric field between two plane-parallel electrodes was studied. The experiments were specially designed to neatly separate the effect of a centered dielectric tube in between the electrodes on the breakdown from the effect of the electric field distribution determined by the electrode geometry on the breakdown. For a given electrode radius and an interelectrode distance, when the diameter of the centered dielectric tube in between the electrodes is smaller, the breakdown voltage is lower, which is most possibly as a result of the flashover more easily happening along the surface of the smaller tube on which the more charged particles are accumulated. When the dielectric tube in between the electrodes is removed, the breakdown voltage depends not only on the product of gas pressure and gap length but also on the aspect ratio of the gas gap, i.e., Ub = f(pd, d/r). Furthermore, Ub = f(pd, d/r) was proved to automatically fulfill two necessary conditions for the similar discharges in the non-uniform electric field, which implies that Ub = f(pd, d/r) is an expression of the similarity theorem in the breakdown of a gap between two plane-parallel electrodes and confirms Townsend's prediction that the general similarity theorem can be applied equally to the breakdowns in non-uniform fields.

Similarity of gas discharge in low‐pressure argon gaps between two plane‐parallel electrodes

The similarity of gas discharge in low-pressure argon gaps between two plane-parallel electrodes was investigated by experiments, numerical simulations and theoretical analysis. It was found by the experiments that the breakdown voltages depend not only on the product of gas pressure and gap length, but also on the aspect ratio of the gap, i.e. U b = f ( pd , d/r ). It was theoretically proved that U b = f ( pd , d/r ) is also a special case, the non-uniform electric field between plane-parallel electrodes, of similarity theorem of gas discharge. It was found by the experiments that there exist similar glow discharges only in two gaps with a limited scaled-down factor k . By theoretical analysis, it was explained that the forbidden processes such as the stepwise ionisation and the inelastic collision of the second kind violate the similarity of discharge as k increases, which was verified by the numerical simulations of the discharges with or without these two forbidden processes taken into account.

Experimental study on the transition of the discharge modes in air dielectric barrier discharge

Dielectric barrier discharge (DBD) usually manifests as a filamentary streamer discharge in atmospheric air, which limits its industrial application prospect, and the homogeneous DBD with homogeneity and stability has a wider application prospect in the field of material surface treatment, thin film deposition and plasma sterilization than the filamentary one. In order to study the generation condition for the homogeneous DBD in atmospheric air, the characteristics of DBD in the pressure range from 10 Pa to atmospheric pressure are experimentally studied by measuring their electrical discharge parameters and observing their light emission phenomena. The transition of the discharge mode with a change in pressure is observed, and a critical pressure value for generating the homogeneous DBD is obtained, with the influence of barrier materials, their thickness and surface roughness and the air gap distance on the critical pressure values being investigated experimentally. The experimental results show that three characteristic types of discharge modes, including the homogeneous mode, the mixed mode and the filamentary mode, are observed with an increase in pressure. The dielectric barrier plays an important role in the generation of the homogeneous DBD, and the critical pressure values will be larger if the barrier thickness is smaller and the air gap distance is smaller. The critical pd values (the product of gas pressure p and gas gap width d) are almost constant with the change in the air gap distance, which can be improved by reducing the thickness of the dielectric barrier and by selecting appropriate barrier materials, as is validated by the experimental results.

Experimental Study of Similarity Laws in Gas Breakdown with Repetitive Nanosecond Pulses

It has been known that breakdown voltage has a functional dependence on the product of gas pressure and gap distance. Furthermore, the product of gas pressure and breakdown time lag is related to electric field divided by gas pressure. In this paper, both these similarity laws were investigated in repetitive nanosecond-pulse breakdown of dry air and nitrogen. The experimental results indicated that breakdown voltage was close to DC value when repetition rate was up to 1 kHz, and the product of gas pressure and breakdown time lag is unambiguously associated with E-field strength divided by gas pressure under repetitive nanosecond-pulse conditions.

Observation on CNT-FED under various vacuum levels and calculation on number of electron–gas collisions

Based on experimental observation and theoretical analysis, it explicates that light emission of a carbon nanotube-field emission display (CNT-FED) is mainly caused by electron bombardment on the phosphour if the level of vacuum ranges from 10 −4 to 5 Pa. In this case, light emission of the phosphour excited by ultraviolet (UV) light derived from gas discharge cannot be observed. If vacuum level is greater than 5 Pa, no emitted light is observed, since a large amount of gas ionisation reduces the electric potential difference between the cathode and the anode. To analyze collision between electron and gas under field emission conditions, a mathematical and physical model was built. Based on this model the number of electron–gas collisions is calculated. Calculations results indicate that the product of gas pressure and distance between the electrodes ( pd) is a better parameter to characterize the effect of vacuum level for FED than gas pressure only. Calculations results also show that if the distance between the cathode and the anode is increased, it should be to improve the vacuum level to obtain the same effect.

Analytical model of the breakdown mechanism in a two-phase mixture

A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration. It is of interest in many different areas, such as in macroparticle-contaminated insulated systems, gas–liquid discharges, dusty plasmas and processing plasmas. Based on Townsend's theory, a physical model in analytical form for the breakdown mechanism in TPM is presented. In this model, two factors that influence the electron avalanche propagation are considered: macroparticles distorting the electric field and capture of the electrons. According to this breakdown mechanism and the dipole-enhanced model for calculating the maximum local field strength in TPM, the modified Paschen' law for TPM is presented to calculate the breakdown voltage. When the number of series of macroparticles (m) between two plate electrodes is very small, such as when m = 1, the breakdown voltage of the TPM is always lower than that of gas. With an increase in m or a decrease in the radius of macroparticles, the breakdown voltage tends to increase gradually for the same volume fraction of macroparticles. When m ≫ 1, the breakdown voltage of TPM may be lower or higher than that of gas, depending on the ratio of the number of saturation electrons captured by a macroparticle to the cell primary electrons generated at the cathode. Some other relevant factors, such as the volume fraction of macroparticles, the dielectric mismatch, the charging rate and the product of gas pressure and the gas length, are also discussed.

Low pressure argon plasma created by a microwave surface wave

Low pressure (0.01-10Torr) argon discharges created by surface waves, at 2-45 GHz and 100-500 W, are characterized. The radial and axial profiles of the electron temperature and density are determined by single and double probes. An increase in the electron density is related to the absorption of the wave power and to the higher ionization efficiency at high pressures. The developed theories are used to explain the axial distribution of the electron density. The probe measurements confirm the presence of maxwellian electron energy distributions in the ranges of gas pressure and wave power. The discharge parameters, e.g. total power needed to maintain the discharge, the mean power required for maintaining the electron, θ, the average maintaining electric field and the effective electric field ⟨E eff⟩ are computed as a function of the gas pressure (P). Similarity laws for θ/P and E eff/N n are developed as a function of the product of gas pressure and plasma radius.

Back-diffusion of electrons in argon in the presence of an electric field

Measurements of electron back-diffusion to plane cold cathodes in a uniform electric field in Ar do not agree satisfactorily with theories derived from first principles. The process has been re-analysed in terms of one-dimensional diffusion and drift with allowance made for the Ramsauer-Townsend effect, which causes the electron's energy and mean free path to vary from its initial value at the cathode to its equilibrium value in the applied field. The analytically obtained expression for the ratio of collected to emitted current densities j/j0, which follows similarity rules, depends on pl, the product of gas pressure and electrode separation, and on the reduced field, E/p. It is found that for values of (E/p)34/(pl)>or approximately=10, j/j0 becomes independent of pl.

The electron temperature in a medium-pressure radio-frequency flowing positive column plasma

An expression for the electron temperature in a medium-pressure radio-frequency flowing positive column plasma has been derived for a cylindrical discharge tube. The effect of flow on electron temperature increases as the product of gas pressure and tube radius decreases.

New method for determining the electron swarm parameters in attaching gases

This method requires the generation of electrons from a point source at a cathode and the measurement of both the amplification and radial distribution of the electrons arriving at an anode, after drifting and diffusing through the gas in a uniform electric field. At each value of E/p0 (ratio of electric field to gas pressure) the experimental results are summarised on two curves expressed as a function of p0d (product of gas pressure and gap separation). The first curve represents the mean-square radial displacement, from an axis drawn through the point source perpendicular to the cathode, and the second represents the current amplification. These curves are easily analysed to give simultaneously the values of the ratio of the radial diffusion coefficient to mobility, Dr/μ, and attachment coefficient η, and the primary ionisation coefficient α. The method has been used to evaluate Dr/μ, η/p0 and α/p0 in CF4, and measurements have been made for 375 ≤ E/p0 ≤ 52.5 Vm−1 Pa−1 at 0°C.

The Pressure Dependence of the Second Ionization Coefficient in Hydrogen at Low Pressures

Experiments on sparking potentials in hydrogen at low pressures (10-100 mmHg) have shown that the sparking potential is not just a function of the product of gas pressure and sparking distance (Paschen's law), but decreases as the gas pressure is decreased. Values of the generalized secondary coefficient deduced from these results therefore show a pressure dependence which is approximately linear. The loss of excited molecules by collisions of the second kind proposed by Davies, Dutton and Llewellyn Jones seems inadequate to account quantitatively for these results. The loss of excited molecules by collision with the anode is suggested as an additional mechanism.