Hollow needle-to-plate electrical discharge at atmospheric pressure

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Ecological applications dealing with the cleaning of flue gases, the decomposition of volatile hydrocarbons and the destruction of toxic pollutants require, in order to reach high efficiency, the use of non-thermal plasma sources. Typical sources of such non-equilibrium plasmas are barrier discharge, direct current (DC) or alternating current (AC) gliding arc, pulsed or DC corona and DC atmospheric pressure discharge stabilized by a fast gas flow (APD-GFS). In case of APD-GFS the gas flows in a rectangular channel, the top wall of which serves as the anode and the multi-needle cathode is built into the bottom wall of the channel. In order to prevent the transition to a spark and to stabilize this type of discharge the velocity of the gas should be about 100-200 m s-1 or the discharge current must be limited. To avoid the problem connected with the acceleration of the primary (polluted) gas at such a velocity, the external flow of the primary gas around the needle electrodes can be superimposed by a flow of a secondary gas through the needles. Thus the primary gas need not be accelerated to high velocity and in order to stabilize the discharge a relatively small amount of a secondary gas supplied through the needle is required. This work is therefore focused on the study of the DC APD-GFS in hollow needle-to-plane geometry. The basic electrical characteristics, magnetic noise and integral emission spectra of this type discharge with the flow of nitrogen or air through the needle are given.