Study of the Dark Phase in the Initial Stage of the Positive Column Formation in an Argon Glow Discharge (original) (raw)
Related papers
Journal of Physics D: Applied Physics, 2008
The constriction of the positive column of a glow discharge in argon was studied both experimentally and theoretically. In experiments the direct current discharge was maintained in a cylindrical glass tube of 3 cm internal diameter and 75 cm length. The voltage-current U(I ) characteristics of the discharge were measured at a gas pressure P from 1 to 120 Torr in a wide range of discharge currents. At P > 20 Torr the measured U(I ) characteristics display the classical hysteresis effect: the transition from the diffuse to the contracted discharge form (with increasing current) occurs at a current higher than that for reverse transition (with decreasing current). It was also found that in some cases the so-called partially contracted form of the discharge is realized, when the diffuse and contracted forms coexist in the discharge tube.
Spectroscopic Investigation of Argon DC Glow Discharge in Plasma Medium
Journal of Naval Sciences and Engineering
In this study, UV-VIS-NIR (Ultraviolet Visible Near-Infrared) spectra emitted from Argon Glow discharge plasma in a low vacuum were recorded with a high-resolution Czerny-Turner type spectrometer. Argon plasma was produced at a pressure of 5mTorr and with a voltage of 584 V. Argon plasma was produced between two parallel stainless steel plates anode and cathode with a diameter of 15 cm, a thickness of 0.8 cm, and a distance of 13 cm between them. The radiative and collisional processes of the Argon plasma medium were modeled by the PrismSPECT atomic physics software (Software). The distributions of ion densities were calculated using the Saha-Boltzmann equation. The intensity of the excited energy levels of Ar(I) and Ar (II) ions were calculated in the electron temperature range of (0.4-3.5eV) and the mass density of (10-4-10-1gr/cm3). The UV-Visible-NIR spectra were simulated and compared with experimental spectra. The ratios of the intensities of the ArII/ArI (1s22s22p63s23p44f1/1...
Journal of Physics D-applied Physics, 2003
We report studies on argon glow discharges established between flat disc electrodes, at pressure × electrode separation (pd) values between 45 and 150 Pa cm, with special attention to heavy-particle processes including heavy-particle excitation induced light emission. The discharges are investigated experimentally and also through self-consistent hybrid modelling. The comparison of the experimental and computed light intensity distributions verifies the correctness of the model, which gives a detailed insight into the discharge operation. The efficiency of heavy-particle excitation shows a universal dependence on the reduced electric field. At the higher pd values the scaling of electrical characteristics and light emission intensity with electrode separation is verified, however, additional processes (radial losses of charged particles and reduction of the active cathode area) result in the violation of scaling at the lowest pd value when the discharge tube diameter is kept constant.
Study of a contracted glow in low-frequency plasma-jet discharges operating with argon
Physics of Plasmas, 2015
In this work, we present an experimental and theoretical study of a low frequency, atmospheric plasma-jet discharge in argon. The discharge has the characteristics of a contracted glow with a current channel of submillimeter diameter and a relatively high voltage cathode layer. In order to interpret the measurements, we consider the separate modeling of each region of the discharge: main channel and cathode layer, which must then be properly matched together. The main current channel was modeled, extending a previous work, as similar to an arc in which joule heating is balanced by lateral heat conduction, without thermal equilibrium between electrons and heavy species. The cathode layer model, on the other hand, includes the emission of secondary electrons by ion impact and by additional mechanisms, of which we considered emission due to collision of atoms excited at metastable levels, and field-enhanced thermionic emission (Schottky effect). The comparison of model and experiment indicates that the discharge can be effectively sustained in its contracted form by the secondary electrons emitted by collision of excited argon atoms, whereas thermionic emission is by far insufficient to provide the necessary electrons. V
Emission of the third continuum of argon excited by a pulsed volume discharge
Physics of Plasmas, 2009
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 ء lines and photorecombination continuum had a uniform distribution across the positive column of the discharge. However, the third continuum and Ar ء+ 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 eV͒. The radiative decay of the Ar 2 2+ ions, created from Ar 2+ 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 Ar 2 2+ 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.
Spectroscopic Study of Argon DC Glow Discharge
IEEE Transactions on Plasma Science, 2007
In this paper, emission spectra of both positive column (PC) and negative glow (NG) regions of the dc glow discharge have been measured at different pressures and currents. The intensity of the lines in the NG is in the order of five times of that corresponding lines' intensity in the PC region. It is found that the line intensity increases linearly with the discharge current, while it increases as P α with the gas pressure. The electron temperature T e has been estimated using the line-to-lineintensity-ratio technique. It is found that T e derived by this technique generally decreases with the pressure. Also, T e in NG region is about 3/2 of that in the PC.
Physical Review E, 2001
The accuracy of secondary-electron emission coefficients, that are used as input data of discharge models, seriously influences the calculated discharge characteristics. As it is very difficult to consider all possible electron emission processes of a cold cathode separately, in most of the recent models an apparent secondary coefficient ␥ is applied, which is often assumed to be constant, even for a wide range of discharge conditions. In contrast with this common assumption, the present calculations-based on a heavy-particle hybrid modelshow that in abnormal glow discharges ␥ varies considerably with changing discharge conditions: a factor of 3 change of ␥ has been found in the range of reduced current densities (0.04 mA cm Ϫ2 Torr Ϫ2 р j/p 2 р4 mA cm Ϫ2 Torr Ϫ2 ) covered in this study. The present simulations also confirm that ionization by heavy particles plays a significant role in the ion production at the abnormal cathode fall. Moreover, it is shown, that the fast heavy particles reflected from the cathode surface play the dominant role in the gas heating.
Axial emission profiles and apparent secondary electron yield in abnormal glow discharges in argon
European Physical Journal D, 2002
This paper reports investigations of argon glow discharges established between flat disk electrodes, at pressure × electrode separation values between 45 Pa cm and 150 Pa cm. Parallel to the experimental studies the discharge is also described by a self-consistent hybrid model. The model uses as input data the measured electrical characteristics, this way making it possible to determine the apparent secondary electron emission coefficient. The model is verified through comparison of the measured and calculated spatial profiles of light emission, which are in good agreement for a wide range of conditions in the abnormal glow mode. Additionally, we investigate the dependence of the field reversal position on the discharge conditions and test the usual assumption that the position of the peak of emission closely coincides with the cathode fall - negative glow boundary.
Measurements of Some Argon Plasma Parameters Glow Discharge Under Axial Magnetic Field
2019
This paper investigates the characteristics some of argon plasma parameters of glow discharge under axial magnetic field. The DC power supply of range (0-6000) V is used as a breakdown voltage to obtain the discharge of argon gas. The discharge voltagecurrent (V-I) characteristic curves and Paschen’s curves as well as the electrical conductivity were studied with the presents of magnetic field confinement at different gas pressures. The magnetic field up to 25 mT was obtained using four coils of radius 6 cm and 320 turn by passing A.C current up to 5 Amperes. Spectroscopic measurements are employed for purpose of estimating two main plasma parameters electron temperature (Te) and electron density (ne). Emission spectra from positive column (PC) zone of the discharge have been studies at different values of magnetic field and pressures at constant discharge currents of 1.5 mA. Electron temperature (Te) and its density are calculated from the ratio of the intensity of two emission lin...
Spatial variations of non–uniform argon glow discharge
The spatial variation of a non-uniform glow discharge due to the different diameters of the same discharge tube on the plasma parameters is attracting a considerable attention. For this reason the fundamental spatial plasma parameters of an argon glow discharge have been measured by using fast three couple of Langmuir double probe (TCDP) technique. The orbital motion limited (OML) theory has been used, since the probe radius is smaller than Debye length ξ < 1. The axial and radial variation of the electron temperature and density have been investigated. The results can be summarized as follow: due to the rise in the space-charge confinement with decreasing the tube radius and discharge current, the space-charge density increases, the electron temperature decreases.