Distributions of Electron Density and Electron Temperature in Magnetized DC Discharge (original) (raw)
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Comparison of electron temperature in DC glow discharge and AC glow discharge plasma
Journal of Physics: Conference Series, 2019
Knowing electron temperature and electron density is important for any plasma related applications. In this research, the electron temperature and electron density of argon plasma generated by low frequency AC power supply and a high voltage DC power supply were investigated. The measurements were compared, both experimentally and theoretically. For the experiment, a long glass cylindrical tube was used as a chamber where the electrodes were placed at 37.5 cm apart. A high voltage function generator power supply was operated at various frequencies and it was also used for DC operation. The electron temperatures were measured by Optical Emission Spectroscopy (OES) technique for different operating pressures of 0.1 mbar, 0.6 mbar and 1.1 mbar. For the simulation, both plasma theory and finite element method were used to simulate dynamics of the plasma in the cylindrical setup. From the experiment, the range of breakdown voltage was found to be between 0.80 to 2.3 kV. The length of DC ...
Study the Effect of the Magnetic Field on the Electrical Characteristics of the Glow Discharge
Low-density plasma is generated in a cylindrical DC magnetron discharge tube. The radial and axial distributions of the magnetic field strengths are drawn. The discharge current and voltage (I a-V a) characteristic curves of the glow discharge have been measured for Ar and He gases pressures. The effect of the applied magnetic field on the (I a-V a) characteristic curves and on the cathode fall thickness is discussed. The breakdown potentials (V B) of the discharge are lower when the magnetic field is applied.
Plasma Sources Science & Technology, 1998
We compare to the probe method a spectroscopic method for determining in plasmas the electron distribution function (EDF) over a wide energy range. For a test of the radiative-collisional model we use to describe the plasma radiation, the measured vibrational distributions of 0963-0252/7/3/008/img12(C-B) and 0963-0252/7/3/008/img13(B-X) were compared with calculated ones using our model and EDFs measured by Langmuir probes. From this comparison we obtain a value for the rate constant for vibrational relaxation at the walls. In a second step we invert the system of model equations for obtaining the EDF from measured line intensities. From the vibrational structure of the emission spectra of the nitrogen molecule the EDF is obtained in the energy range of 1.5-4.5 eV. From the relative intensities of the emission of nitrogen molecules and helium atoms the EDF for electron energies above 11 eV is derived. In the region between these ranges the EDF is interpolated. The results agree within the limits of the experimental errors with the EDF measured directly by the probe.
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.
On the accuracy and limitations of fluid models of the cathode region of dc glow discharges
Journal of Physics D: Applied Physics, 2009
This paper compares the performance and limitations of different models of the cathode region of cold-cathode low-pressure dc glow discharges: (i) we review known modelling approaches, (ii) develop our own simulation codes based on these approaches, (iii) perform calculations using these codes for reference sets of discharge conditions, which allows a critical comparison of the models and (iv) for a further check of the simulation results we carry out Langmuir probe measurements of electron densities in abnormal Ar glow discharges. The theoretical approaches include fluid models both neglecting and including the electron energy balance equation, as well as hybrid models, which combine the fluid treatment of slow plasma species with the kinetic simulation of fast electrons. We also test the effect of the choice of the ionization source term in fluid models. We find that the electron densities calculated from the fluid models are far (several orders of magnitude) below the experimental values even if the electron energy equation is considered in the calculations. This weakness of fluid models clearly points out the importance of an accurate calculation of the ionization source term, which can only be accomplished by a kinetic approach under the conditions of highly nonlocal electron transport in the cathode region of glow discharges. In hybrid models Monte Carlo simulation is used for this purpose, and indeed, this approach gives electron densities comparable to our experimental data.
Double layer in a cylindrical hollow-cathode discharge
Plasma Physics Reports, 2010
A dc cylindrical coaxial glow discharge with an inner grid anode has been studied. The region between the two electrodes is seen dark, while a brightly glowing region forms inside the grid anode up to the center. The current voltage characteristic of a dc cylindrical glow discharge in nitrogen is similar to that of a normal glow discharge, while the normal glow discharge voltage decreases with increasing pressure. The min imum plasma potentials are observed in the hollow cathode region due to the accumulation of electrons at the back of the grid anode. At the center, some of the passed electrons are converged, so their potential is decreased. These electrons have a sufficient time to be redistributed to form one group with a Maxwellian electron energy distribution function. The electron temperature measured by electric probes varies from 1.6 to 3.6 eV, while the plasma density varies from 3.9 × 10 16 to 7 × 10 13 m-3 , depending on the discharge current and probe position. The plasma density increases as the electrons move radially from the grid toward the cen tral region, while their temperature decreases.
Langmuir double probe is a very useful diagnostics for studying the plasma parameters at low pressure discharge and this paper reports the measurement of electron temperature (), ion saturation current () and electron density () in a low pressure DC glow discharge in air using I-V characteristics of double probe and the objective of the study is to investigate the effect of pressure and applied voltage on the plasma parameters in the discharge. In addition, Debye length (), plasma frequency (), floating potential () have also been calculated and their dependance on the applied voltage and working pressure have been studied. Measurements show that (), () and () gradually decrease on increasing the applied voltage or working pressure, but (), (), and () increases on increasing the applied voltage and working pressure. The maximum values of these parameters are obtained at 0.5 mbar pressure.
Plasma Sources Science and Technology, 2013
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.
The Edge Effect on the EEDF Measurements of Magnetized DC Plasma
The localized plasma parameters at the edge of the discharge electrodes cell have been investigated for axial distribution, such as the electric field distribution, the electron energy distribution functions (EEDF), the electron temperature (T e) and the electron density (N e), all have been determined with and without the applications of external magnetic field using Langmuir single probe in the three regions of the discharge. The EEDF was investigated using two different methods e.g. the graphical method and the electron current second derivative method. The electron energy distribution functions are maxwellian only in the positive column region (P.C.) and non-maxwellian in the cathode fall (C.F) and the negative glow (N.G.) regions, where two groups of electrons were observed. The diffusion coefficients and the electron temperatures are lower in the presence of the magnetic field, where T e decreased from 6.5 to 3 eV for C.F, from 5.18 to 2.6