Cathode Fall Potential Research Articles

Charged particles density distribution in the cathode fall region of the glow discharge in helium

In the present work, the mechanism of formation and propagation of the group of high energy electrons in the cathode regions of a glow discharge in helium is discussed. Using the method of the Monte Carlo collisions simulation, the beam electron energy distribution function in the cathode fall region of a glow discharge has been determined in the gas pressure range of 30−70 Pa. It is shown that the electron distribution function at the end of the cathode fall region contains a lot of electrons which have no any collisions and have energies close to the cathode fall potential. On the basis of the obtained results the distribution of the ion density was simulated using the Poisson equation. It is shown that the ion density distribution stays almost constant in the cathode fall region. The beam and ion density increased with the pressure growth.

Formation and energy relaxation of a fast electron beam in cathode regions of a glow discharge in helium

Results of a three-dimensional direct statistical simulation of formation and energy relaxation of a group of high-energy electrons in cathode regions of the low pressure (p < 1 Torr) glow discharge in helium are given. It is demonstrated that the electron distribution function at the exit from the cathode sheath contains a group (beam) of high-energy electrons which did not suffer inelastic collisions and had energy close to the cathode fall potential. The beam is shown to be a main source of charged particle production in the negative glow region. The calculated electron energy distribution function is compared with experimental data.

Characterization of suprathermal electron population in He dc glow discharges by optical emission and probe diagnostics

Evidence of the strong contribution of electrons with energies up to the cathode fall potential was found in low-pressure He dc glow discharge plasmas (3–8 mTorr), in agreement with expectations from the estimates of the mean free path of electron–neutral inelastic collisions. A simple gridded probe, of the retarding field analyzer type, was applied to the characterization of the full electron energy distribution function (EEDF) in He plasmas with significant contribution from suprathermal electrons (up to 3.5%). The inferred EEDFs were cross-checked with results from the He line ratio diagnostic and good agreement was found at several values of pressure and plasma current.

Influences of He Contents and Panel Working Gas Pressures in Ternary Gas Mixture on Discharge Characteristics in AC Plasma Display Panel

The discharge characteristics, particularly the address and sustain discharge characteristics, were examined relative to the He contents and panel working gas pressures under 11% Xe content in the 50-in. full HD AC-PDPs with a ternary gas mixture (Xe-He-Ne). The Xe content in this study was fixed at 11%. As the helium gas increases from 0 to 50%, the formative address delay becomes shortened by about 60 ns. In addition, the luminance are increased by about 15 cd/m2 because of enlarging the Xe2* excimer emission (823 nm) with an increase with the He gas. Also, the power consumption is reduced by about 30 W since the addition of He gas induces a reduction of cathode fall potential. The decrease in the gas pressure from 600 to 300 Torr causes a lower firing voltage, thereby resulting in reducing both the formative and statistical address delay times by about 71 ns and by about 65 ns, respectively. As a consequence, the pressure below 400 Torr and He content above 50% are the best panel factors suitable for high speed and low voltage driving of micro-discharge cells with the 50 in full HD cell size.

Emission of the third continuum of argon excited by a pulsed volume discharge

This paper presents the results of the observation of the third continuum band at 190 nm in a pulsed volume discharge at an argon pressure of 0.17–2 bar. The spatial-time kinetics of ultraviolet-visible photorecombination continuum and the third continuum of argon were measured and analyzed for the high- and low-current excitation regimes. Time-resolved imaging experiments with an intensified charge coupled device camera have shown that the second continuum of argon at 127 nm, Ar∗ lines and photorecombination continuum had a uniform distribution across the positive column of the discharge. However, the third continuum and Ar+∗ lines were emitted exclusively from the negative glow zone. This indicates to the existence of runaway electrons, accelerated in the electric field of the cathode layer and retarded in the negative glow zone. These electrons can achieve the energy of the cathode fall potential (130–250 eV). The radiative decay of the Ar22+ ions, created from Ar2+ precursors, is modeled. A good agreement has been achieved between the calculated and measured kinetics of the third continuum at different pressures, which supports the assignment of this continuum to the emission of Ar22+ ions. In contrast to the third continuum, the origin of the afterglow emission bands at 190 and 260 nm are connected with carbon-containing contaminants, accumulated inside the discharge chamber. These bands were disappeared during the gas circulation through the getter purifier.

Discharge characteristics of a plasma display panel cell: comparisons between binary and ternary gas mixtures

We have performed simulations on a coplanar structured alternating current plasma display panel cell sustained in the ternary He-Ne-Xe gas mixture and its discharge characteristics were compared with those of the conventional binary Ne-Xe mixture, by using the two-dimensional fluid model simulator. Since plasma display panels use micro-discharges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of discharge gas mixtures is one of the main factors that determine luminous efficacy and thus, intensive studies on discharge gas mixture are essential to optimize it. As the He concentration increases in the He-Ne-Xe mixture, luminance and luminous efficacy increase but power consumption decreases, which agrees well with the recent experimental findings. We have found that the enhanced ion mobilities in the gas mixture by adding He gas to the conventional Ne-Xe mixture play an important role in increasing luminous efficacy of a plasma display panel cell, by reducing the cathode fall potential. In addition, He atoms increase the number of Xe/sup */(/sup 3/P/sub 2/) in the excited state and thus, the dimer emission is increased while the resonant line is reduced with the He content. As a result, the total vacuum ultraviolet emission is increased and higher luminance and higher luminous efficacy can be obtained.

Calculation of Ion Mobilities and their Effects on Gas Discharge of AC Plasma Display Cells

We have found that ion mobilities in a gas mixture greatly affect discharge characteristics of a plasma display cell. Therefore, correct ion mobilities are required to obtain meaningful simulation results on plasma display cells. Since plasma display panels use microdischarges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of the discharge gas mixtures is one of the main factors that determine luminous efficacy. Thus, intensive studies on the discharge gas mixture are essential to optimize it and the accurate determination of ion mobilities in it is necessary. We have discussed how to determine necessary values of ion mobilities in various discharge gas mixtures including the three-species He–Ne–Xe mixture. Calculated ion mobilities and their effect on the discharge of an AC plasma display cell have also been presented and discussed. We have revealed that the enhanced ion mobilities in the gas mixture resulting from adding He gas to the conventional Ne–Xe mixture play an important role in increasing the luminous efficacy of a plasma display cell sustained in the He–Ne–Xe mixture by decreasing the cathode fall potential.

Electrical characteristics of a DC glow discharge

The dependences of the breakdown voltage (Vb), the normal glow potential (Vn), and the cathode fall potential (Vcn) on the argon gas pressure (P) and the distance (d) between two copper electrodes were studied. The normal glow potential was found to decrease as the gas pressure increases and to increase as the distance between the two electrodes increases. Vcn was found, also, to decrease with the gas pressure.

Monte Carlo simulation of electron motion in the cathode region of a magnetron glow discharge in argon

The motion of electrons in the cathode region of a magnetron glow discharge in low-pressure argon has been studied by Monte Carlo simulation. The influences of the transverse magnetic field on energy distribution of electron flux and ionization have been investigated for normal and abnormal discharges. It has been shown that the magnetic field increases collisions, and consequently decreases the mean electron energy. In normal discharges, under the magnetic field, fewer electrons enter the negative glow region with high energy, while ionization is remarkably enhanced in the cathode region. In abnormal discharges, it is found that the magnetic field required to influence the discharge has to be stronger than that in normal discharges. Under such a magnetic field, for example 0.3 T, though there are still a great number of electrons entering the negative glow region with energy corresponding to the cathode fall potential, the mean electron energy is decreased, and the electrons entering the negative glow region are less beam-like. Analyses for the simulation results and consideration of the practical use of the magnetic field have been given.

Electron Energy Distribution and Optical Characteristics of a Hollow Cathode Discharge

AbstractA model is proposed for the formation of the electron energy distribution in a hollow cathode discharge. On the basis of this model, an integral equation has been derived to calculate the electron distribution function over the entire cathode cavity volume. The equation holds true for both the isotropic distribution, and the case when the local distribution function is anisotropic. Solutions of the kinetic equation obtained are presented, for electron energies over 2–3 eV and up to the cathode fall potential. It is shown that the electron energy distribution function in this interval determines the optical characteristics of the hollow cathode discharge. A comparison is given of the calculated and measured radiation powers for the cases of the hollow cathode discharge in xenon and carbon dioxide. The discrepancy between the theoretical and experimental data does not exceed 20%.

Multi Electron-Temperature Models for a Hollow Cathode Glow Discharge

A numerical simulation is made of a cylindrical hollow cathode glow discharge in helium gas. Electrons are assumed to consist of two or three groups of different temperatures. Calculations are made for the following conditions: gas pressure of 0.24 kPa, cathode fall potential of 260 V and discharge current of 33 mA. Numerical results present number densities of electrons, ions and excited atoms of 64 excited levels as a function of the radial distance r. Experimentally determined population densities of excited atoms are also presented as a function of r. Agreement of calculation with experiment is good for densities at the center of the cathode. Calculated densities, however, have a larger peak near the edge of the negative glow than measured densities.

A simulation of electron motion in the cathode sheath region of a glow discharge in argon

Electron motion in the cathode sheath region of a glow discharge in argon has been simulated for a linearly decreasing electric field using a one-dimensional computer model. Distribution functions for the electron flux crossing the sheath have been calculated for 12 values of the cathode fall between 180 and 1400 V encompassing the normal and abnormal regimes. Macroscopic variables including the Townsend ionisation coefficient, the electron multiplication factor and the mean electron energy have been determined for cathode fall values between 180 and 1000 V. It is shown that the proportion of electron flux crossing the sheath without collisions increases as the cathode fall is raised. When the cathode fall is in the range 300-900 V, the electron flux at the sheath/negative-glow boundary is found to be highly directional with distinct beam-like characteristics. Beyond 900 V, the largest component in the distribution of electron flux to reach the boundary region is the collision-free group. These electrons enter the negative glow with energies corresponding to the cathode fall potential and are nearly mono-energetic. In this case, the entire cathode sheath/negative-glow region can be referred to as an 'electron-beam' glow discharge.

冷陰極蛍光ランプの陰極降下電圧に関する考察

冷陰極蛍光ランプの陰極降下電圧に関する考察

小電流熱陰極蛍光ランプの陰極降下電圧に関する検討

小電流熱陰極蛍光ランプの陰極降下電圧に関する検討

The Monte Carlo Calculations for the Distribution Function of Energetic Electrons in a Plane-Parallel Hollow Cathode

The energy distribution of high-energy electrons was calculated from the plane-parallel hollow-cathode glow discharge of helium gas. Calculations showed an energy distribution function similar to that of a cylindrical cathode whose function had already been obtained by the authors. However, few electrons whose energy equalled the cathode fall potential existed in the central region, contrary to the many electrons in that region in the cylindrical cathode.

DC Gas-Discharge Display Panel with LaB6 Thin-Film Cathode

A dc gas-discharge display panel with LaB6 thin-film cathodes is proposed for data information systems. A thin-film, having a crystallographic orientation of [100], was formed on a Ni thick-film using the electron-beam evaporation technique. The low work function of the crystallographic orientation provided a low operating voltage. The normal cathode fall potential for the thin-film cathode in a Ne+Ar (0.4%) gas discharge was approximately 80 V, about 1/2 that of the commonly used Ni thick-film cathode. The display panel consisted of two glass plates: cathodes were formed on one plate (substrate) and anodes on the other. The cathodes and anodes were perpendicular to each other, and were separated by barriers formed in parallel between the anodes. Low voltage, high luminance, high luminous efficiency and stable operation were attained without the use of Hg.

A simulation of electron motion in the cathode sheath region of a glow discharge in helium

Electron motion in the cathode sheath region of a glow discharge in helium has been simulated using a one-dimensional computer model. Distribution functions for the electron flux across the cathode sheath have been calculated for fourteen values of the cathode fall between 150 and 1700 V. Macroscopic variables including the Townsend ionisation coefficient, multiplication coefficient and mean electron energy have been determined for the cathode fall range 150-1000 V. It is shown that the proportion of electron flux crossing the cathode sheath without collisions increases as the cathode fall is raised. For a cathode fall between 400 and 1400 V, the electron flux at the cathode sheath/negative glow boundary possesses beam-like characteristics. Beyond 1400 V, the largest component, in the electron flux distribution, to reach the sheath boundary is the collision-free group. These electrons enter the negative glow with energies corresponding to the cathode fall potential, and are practically mono-energetic. The authors propose that this is a suitable criterion to refer to the entire cathode sheath/negative glow region as an 'electron-beam' glow discharge.

Helium singlet and triplet metastable number densities in hollow-cathode/metal-vapour lasers

Number densities of helium singlet and triplet metastable states in the hollow cathode discharge appropriate to metal vapour lasers have been measured; in particular their dependence on discharge current and pressure, cathode fall potential and cadmium partial pressure has been explored. Singlet and triplet densities behave differently with discharge parameters; whereas the former saturate with both current and pressure, the latter increase linearly with discharge current and follow the distinctive behaviour exhibited by the cathode fall potential as a function of pressure. Radial profiles of the metastable densities are also reported.

Laser heterodyne measurement of electron densities in a hollow cathode discharge

A laser heterodyne system has been developed to measure electron densities in a hollow-cathode discharge as used in metal vapour lasers. The beat frequency between two helium-neon lasers, one of which contains the discharge under investigation within its cavity, is monitored in real time as the discharge is rapidly switched off. The beat frequency changes because of refractive index changes in the plasma. By comparing the beat frequency changes at two wavelengths (0.6328 and 1.15 mu m), electron density and gas density changes have been determined. Electron densities have been measured in a cylindrical hollow cathode discharge (6 mm diameter, 10 cm long) in helium gas over a range of filling pressures (1-15 Torr) and discharge currents (10-150 mA). Electron density is found to behave linearly with discharge current, and to follow the cathode fall potential with pressure.

Electron energy distributions in the negative glow and their relevance to hollow cathode lasers

Electron energy distributions have been measured in and near the negative glow of an abnormal glow discharge in helium at pressures in the range 3-25 Torr. The experimental technique involved the use of a differentially pumped retarding-field analyser. The measured distributions are distinctly non-Maxwellian. In particular, the distribution in the negative glow close to the cathode dark space shows a prominent 'tail' of high-energy electrons and a 'beam' component at the cathode fall potential ( approximately 300 V). The significance of these results for hollow cathode helium/metal-vapour lasers is discussed.