Double layer in a cylindrical hollow-cathode discharge (original) (raw)
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Influence of Electron Injection on the Characteristics of a Hollow Cathode Glow Discharge
2, 2021
The article presents the results of experimental studies of a glow discharge with a hollow cathode in helium and argon gases using an auxiliary discharge as an electron emitter. The authors proposed to make the electrode common for both discharges in the form of a cylindrical metal mesh. The advantage of this design is explained as follows. The connection between the discharges is carried out through holes in the grid with a geometric transparency of 0.2, which makes it possible not only to smoothly control the glow discharge current, but also to enhance the discharge current. Plasma is known to be one of the most efficient electron emitters; however, its use as a cathode in devices with a glow discharge at low gas pressures is complicated by the fact that a grid with small holes is required to separate the electron flow from the plasma, and it is impractical to use such a system in view of low mechanical strength of the grid Since the hollow cathode works effectively at low gas pre...
Characterization of a dc atmospheric pressure normal glow discharge
Plasma Sources Science and Technology, 2005
Atmospheric pressure dc glow discharges were generated between a thin cylindrical anode and a flat cathode. Voltage-current characteristics, visualization of the discharge and estimations of the current density indicate that the discharge is operating in the normal glow regime. Emission spectroscopy and gas temperature measurements using the 2nd positive band of N 2 indicate that the discharge forms a non-equilibirum plasma. Rotational temperatures are 700 K and 1550 K and vibrational temperatures are 5000 K and 4500 K for a 0.4 mA and 10 mA discharge, respectively. The discharge was studied for inter-electrode gap spacing in the range of 20 µm-1.5 cm. It is possible to distinguish a negative glow, Faraday dark space and positive column regions of the discharge. The radius of the primary column is about 50 µm and is relatively constant with changes in electrode spacing and discharge current. Estimations show that this radial size is important in balancing heat generation and diffusion and in preventing thermal instabilities and the transition to an arc.
Hybrid model for a cylindrical hollow cathode glow discharge and comparison with experiments
Spectrochimica Acta Part B: Atomic Spectroscopy, 2002
Some of the fundamental characteristics of the hollow cathode glow discharge are presented for different discharge conditions, based on a hybrid Monte Carlo fluid model, and on electrical and spectroscopic measurements. The Monte Carlo model describes the movement of the fast electrons as particles, while in the fluid model, the slow electrons and positive ions are treated as a continuum. The transient continuity equations are solved together with the Poisson equation in order to obtain a self-consistent electric field. The source terms of the continuity equations and the electron multiplication coefficient (used for the determination of the secondary electron emission coefficient) are obtained from the Monte Carlo simulation. These two models are run iteratively until convergence is reached. Typical results are, among others, the charged particles densities, the fluxes, the electric field and potential distribution. It is found that the influence of the bottom of the cylindrical hollow cathode cannot be neglected. A very good agreement between calculations and experimental data was obtained.
Plasma Sources Science and Technology, 2021
A discharge plasma is created by simultaneously biasing two concentric spherical grids with axisymmetric orifices. In this geometry, space charge structures in the form of multiple quasi-spherical luminous plasma bodies appear simultaneously inside and around the cathodes. The plasma formations are highly interdependent supplying each other with the particle flow and current closure necessary for the maintenance of the discharge. To diagnose these structures, space-resolved cold Langmuir probe measurements and optical emission spectroscopy investigations were performed in the axial direction allowing for the mapping of the axial profiles of plasma potential, electron temperature and density, ion density and optical emission. The existence of an accelerating double layer in the vicinity of the holes has been confirmed here, and in previous research (Teodorescu-Soare C T et al 2016 Phys. Scr. 91 034002; Schrittwieser R W et al 2017 Phys. Scr. 92 044001; Teodorescu-Soare C T et al 2019...
Plasma properties of a DC hollow cathode discharge
2006
We have investigated the plasma properties of a Hollow Cathode Discharge (HCD) using different dimensions of hollow cathode aperture (1 to 8 mm) in argon operating medium. The diagnostic used to investigate the plasma properties is a tiny Langmuir probe. The diameter and length of the Langmuir probe was chosen such that it draws a measurable current from the plasma causing a minimal perturbation to the surrounding plasma and remains rigid within the plasma as well as the cylindrical probe theories are applicable while calculating the electron temperature and plasma density. The probe was placed perpendicular to the axis of the hollow cathode at a distance of 20 mm from the hollow cathode side. The HCD was operated in the voltage range of 600 to 1000 V and pressures range of 70 to 100 mtorr. We observed that electron temperature and density varies with the operational condition. The estimated electron temperature is less than 10 eV and the temperature is maximum in the range of 3 to 5 mm diameter of the hollow cathode and a pressure range of 75 to 85 mTorr. The calculated maximum density is of the order of 10 10 cm -3 .
Plasma Physics Reports, 2001
The mechanism for the formation of the inverse electron distribution function is proposed and realized experimentally in a nitrogen plasma of a hollow-cathode glow discharge. It is shown theoretically and experimentally that, for a broad range of the parameters of an N 2 discharge, it is possible to form a significant dip in the profile of the electron distribution function in the energy range ε = 2-4 eV and, accordingly, to produce the inverse distribution with df ( ε )/ d ε > 0. The formation of a dip is associated with both the vibrational excitation of N 2 molecules and the characteristic features of a hollow-cathode glow discharge. In such a discharge, the applied voltage drops preferentially across a narrow cathode sheath. In the main discharge region, the electric field E is weak ( E < 0.1 V/cm at a pressure of about p ~ 0.1 torr) and does not heat the discharge plasma. The gas is ionized and the ionization-produced electrons are heated by a beam of fast electrons (with an energy of about 400 eV) emitted from the cathode. A high-energy electron beam plays an important role in the formation of a dip in the profile of the electron distribution function in the energy range in which the cross section for the vibrational excitation of nitrogen molecules is maximum. A plasma with an inverted electron distribution function can be used to create a population inversion in which more impurity molecules and atoms will exist in electronically excited states. © 2001 MAIK "Nauka/Interperiodica".
Hybrid model of a plane-parallel hollow-cathode discharge
Journal of Physics D: Applied Physics, 2000
The development of the hollow-cathode effect in a plane-parallel hollow cathode dc argon glow discharge was investigated experimentally and by means of a two-dimensional self-consistent hybrid model, combining the fluid description of positive ions and slow electrons with a particle simulation of fast electrons. In the experiments the discharge was formed between two flat disc copper electrodes (of 3.14 cm diameter and separated by a L = 2 cm gap) serving as cathodes and a metal tube surrounding these electrodes which served as the anode. The electrical characteristics of the discharge and the spatial intensity distribution of selected spectral lines (Ar I 750.3 nm, 811.5 nm and Ar II 476.5 nm) were recorded at current densities 0.1 mA cm −2 j 0.5 mA cm −2 and for gas pressures 0.2 mbar p 1 mbar. While at pressures of ∼1 mbar the cathode regions are developed separately for both cathodes, the light intensity distribution measurements demonstrated the gradual merging of the negative glows with decreasing pressure. At pL 0.8 mbar cm, a common negative glow is formed in the discharge. Complementing the experimental observations, the simulations made it possible to determine various discharge characteristics (e.g. spatial distribution of electric potential, ionization source, and ion density). At low pL values the simulations also indicated the existence of oscillating electrons. The spatial distribution of light intensity calculated for different pressures shows good qualitative agreement with the experimentally observed distributions.
Plasma Properties of a Low-Pressure Hollow Cathode DC Discharge
Iraqi Journal of Science
The current study involves an experimental investigation of plasma main parameters of a DC discharge with a hollow cathode (HCD) geometry in air using apertures of different diameters from the hollow cathode (1, 1.5, 2, and 2.5 cm). A tiny Langmuir probe is used to investigate the plasma properties. The HCD was operated at constant power of 12.4 W and gas pressures ranging between 0.1 to 0.8 torr. It was observed that the operational conditions strongly affect the electron temperature and density, while the hollow cathode diameter has not much influence. The main important observation was that at relatively high air pressure (>0.4 torr) two electron temperatures were obtained, while at relatively low pressure (<0.4 torr), a single electron temperature was found. The results showed that the measured electron temperature decreased nearly linearly with increasing gas pressure.
Characterization of the large area plane-symmetric low-pressure DC glow discharge
Spectrochimica Acta Part B: Atomic Spectroscopy, 2016
Electron density and temperature as well as nitrogen dissociation degree in the low-pressure (10-50 mTorr) large area plane-symmetric DC glow discharge in Ar-N 2 mixtures are studied by probes and spectral methods. Electron density measured by a hairpin probe is in good agreement with that derived from the intensity ratio of the N 2 2nd positive system bands I C ,1− 3 /I C ,0− 2 and from the intensity ratio of argon ions and atom lines I ArII /I ArI , while Langmuir probe data provides slightly higher values of electron density. Electron density in the low-pressure DC glow discharge varies with the discharge conditions in the limits of~10 8-10 10 cm −3. The concept of electron temperature can be used in low-pressure glow discharges with reservations. The intensity ratio of (0-0) vibrational bands of N 2 1st negative and 2nd positive systems I 391.4 /I 337.1 exhibits the electron temperature of 1.5-2.5 eV when argon fraction in the mixture is higher than nitrogen fraction and this ratio quickly increases with nitrogen fraction up to 10 eV in pure nitrogen. The electron temperature calculated from Langmuir probe I-V characteristics assuming a Maxwellian EEDF, gives T e~0 .3-0.4 eV. In-depth analysis of the EEDF using the second derivative of Langmuir probe I-V characteristics shows that in a low-pressure glow discharge the EEDF is non-Maxwellian. The EEDF has two populations of electrons: the main background non-Maxwellian population of "cold" electrons with the mean electron energy of~0.3-0.4 eV and the small Maxwellian population of "hot" electrons with the mean electron energy of~1.0-2.5 eV. Estimations show that with electron temperature lower than 1 eV the rate of the direct electron impact ionization of N 2 is low and the main mechanism of N 2 ionization becomes most likely Penning and associative ionization. In this case, assumptions of the intensity ratio I N 2 + ,391 /I N 2 ,337 method are violated. In the glow discharge, N 2 dissociation degree reaches about 7% with the argon fraction in the Ar-N 2 mixture b 10% and decreases afterwards approaching to~1-2% when the argon percentage becomes 90% and higher. The atomic nitrogen species is produced by electron-impact processes such as, collisions between electrons and nitrogen molecules or between electrons and N 2 + ions. At small Ar fraction in Ar-N 2 mixtures, the atomic nitrogen species is most likely produced by the collisions between electrons and N 2 + ions.