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Study of Positive Column in Glow Discharge under Medium Pressures Using Computational Experiment
Laca, Marek ; Hrachová, Věra (advisor) ; Novák, Stanislav (referee) ; Roučka, Štěpán (referee)
The positive column of the oxygen and argon-oxygen direct current glow discharge was investigated using a fluid plasma model at pressures around hundreds of pascals and discharge currents from ten to forty miliampers. The model describes the infinitely long positive column in cylindrical discharge tube. It is based on the continuity equation for particle concentration with the collisional right hand side. The model utilises the drift-diffusion approximation of particle flux and the mean-electron-energy approximation for the description of the electron interaction. The radial profile of particle concentration and interaction with the glass wall of the discharge tube is taken into account. The model predicts the electric field and the particle concentration in the positive column. The simulation results were compared with the measured intensity of electric field strength in the oxygen and argon-oxygen mixture. The impact of discharge conditions, like the pressure and gas composition, on the properties of the positive column was investigated. The model confirmed that the strength of longitudinal electric field at medium pressures is about 40 V/cm in oxygen, molecular gas, and it is about 3 V/cm in argon, noble gas.
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Study of Positive Column in Glow Discharge under Medium Pressures Using Computational Experiment
Laca, Marek ; Hrachová, Věra (advisor) ; Novák, Stanislav (referee) ; Roučka, Štěpán (referee)
The positive column of the oxygen and argon-oxygen direct current glow discharge was investigated using a fluid plasma model at pressures around hundreds of pascals and discharge currents from ten to forty miliampers. The model describes the infinitely long positive column in cylindrical discharge tube. It is based on the continuity equation for particle concentration with the collisional right hand side. The model utilises the drift-diffusion approximation of particle flux and the mean-electron-energy approximation for the description of the electron interaction. The radial profile of particle concentration and interaction with the glass wall of the discharge tube is taken into account. The model predicts the electric field and the particle concentration in the positive column. The simulation results were compared with the measured intensity of electric field strength in the oxygen and argon-oxygen mixture. The impact of discharge conditions, like the pressure and gas composition, on the properties of the positive column was investigated. The model confirmed that the strength of longitudinal electric field at medium pressures is about 40 V/cm in oxygen, molecular gas, and it is about 3 V/cm in argon, noble gas.
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Modelling of glow discharge positive column of oxygen in the middle pressures region
Laca, Marek ; Hrachová, Věra (advisor) ; Plašil, Radek (referee)
The aim of the presented work was to create model of the glos discharge positive column of the oxygen in the middle pressures (in range 100-1000 Pa) with the methods of the computer physics, specifically with the method of the chemical kinetics. I have focused on the existence of two forms of the discharge positive column in the oxygen, low and high gradient form with axial electrical field about 100 V/m and 1 kV/m. I developed continuous model of the low temperature plasma as the steady state solution of the continuity equation with the neglected divergent member. The model involves twelve different kinds of the particles and reactions among them: electrons, ground and excited states of the atomic and molecular oxygen, of course negative and positive ions. I had numerically solved time evolution of the particle concentration at constant pressure, until the system reached equilibrium state. My numerical results were compared with experimental measurements of the electron density, which had been done in the Department of Surface and Plasma Science. To get a consistency between my results and experimental ones for electron density, I had to variate reaction coefficients of the reactions in which charged particles are produced.
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