Homogeneous atmospheric pressure discharge using a dielectric barrier discharge in air at 50 Hz was investigated. Porous alumina ceramic sheets were used as a dielectric barrier. In this paper we compare the filamentary discharge initiated by using glass sheets as a dielectric and the glow discharge obtained by the porous alumina sheets as a dielectric.Generally, the discharge in a dielectric barrier arrangement consists of a large number of filaments. Using porous alumina sheets Al 2 O 3 , an atmospheric pressure glow discharge (APGD) plasma has been obtained. This APGD discharge is characterized by a homogeneous profile of long lifetime (∼5 ms) and the current is one pulse per half cycle of the power supply. The electrical measurements and the emission spectrum confirm that the discharge has been formed in the glow mode.

A silent discharge ozonizer has been constructed with a design that enables the study of ozone concentration behaviour as a function of different parameters when oxygen used as a working gas. The behaviour of ozone concentration as a function of discharge current density has four characteristic regions. The concentration is enhanced by more than threefold whenever gas pressure is reduced by a factor of two. The flow rate of the working gas is a more effective parameter on ozone concentration than the gas pressure. When the flow rate is kept constant, and the pressure is decreased by 100%, the ozone concentration increases by only 10%. On the other hand, when the flow rate is decreased by 13%, the ozone concentration increases by 200%, whenever the gas pressure is kept constant. The concentration is nearly doubled when the gap space is increased by four times under the same conditions. The length of the discharge region, the thickness and the dielectric constant of the insulating materials are found to have a considerable effect on the generated ozone concentration. Also, the ozone concentration is ten times less when air is used instead of oxygen as a working gas. A maximum efficiency of 185 g/kWh, is obtained for the present system.

The dependences of the breakdown voltage (V b ), the normal glow potential (V n ), and the cathode fall potential (V cn ) 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. V cn was found, also, to decrease with the gas pressure.

Abstract-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.

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