This paper describes a usage of a low-current coaxial plasmatron for generation of nitrogen oxide molecules. Glow-type discharge in vortex air flow is sustained at an average current from 0.05 to 0.2 A that corresponds to an average discharge power from 65 to 160 W. The diameter of an exit nozzle of the plasmatron is of 0.5 cm, and the air flow is varied from 0.2 to 1.5 g/s. In such conditions, the discharge burns in nonsteady-state regime, when a sustainment of a plasma jet/plume and a plasma column in the plasmatron nozzle is accompanied by the spontaneous glow-tospark transitions. Due to the special design of the anode nozzle, an efficient interaction of the air flow with the plasma plume and plasma column is provided. Typical contents of nitric monoxide in the output gas are of about several grams per cubic meter, and the cost for formation of one molecule is from 50 to 35 eV.
This paper describes the results of investigation of the positive column in a glow discharge at atmospheric pressure. The total discharge current is varied from 0.02 A to 0.22 A that corresponds to the current density from 25 A/cm2 to 125 A/cm2. It is demonstrated that the effective gas pressure in the column lies in a range (60–90) Torr, and the reduced electric field is changed from 16 V/cm Torr at minimum current to 8 V/cm Torr when the current is increased to 0.22 A. The principal processes that are responsible for sustaining the plasma column have been defined. The main channel of the charged particle losses is the dissociative recombination of the ion NO+. The comparable contribution into the ionization gives the ionizing collisions of electrons with the oxygen molecules in the ground state, the ionization of NO molecules, and the associative ionisation when the metastable nitrogen molecules collide with each other.
Nonstationary processes in atmospheric-pressure glow discharge manifest themselves in spontaneous transitions from the normal glow discharge into a spark. In the experiments, both so-called completed transitions in which a highly conductive constricted channel arises and incomplete transitions accompanied by the formation of a diffuse channel are observed. A model of the positive column of a discharge in air is elaborated that allows one to interpret specific features of the discharge both in the stationary stage and during its transition into a spark and makes it possible to calculate the characteristic oscillatory current waveforms for completed transitions into a spark and aperiodic ones for incomplete transitions. The calculated parameters of the positive column in the glow discharge mode agree well with experiment. Data on the densities of the most abundant species generated in the discharge (such as atomic oxygen, metastable nitrogen molecules, ozone, nitrogen oxides, and negative oxygen ions) are presented.
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