Plasma decay in the afterglow of a high-voltage nanosecond discharge in air

Abstract

International audienceThe decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 1–10 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 10¹2 cm–3. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electron–ion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three- body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination

Comparative Study of Nonequilibrium Plasma Generation and Plasma-Assisted Ignition for Different C2 Hydrocarbons

“…In these gases, the rate of cluster ion formation was high and the dominant mechanism of electron loss in the discharge afterglow was dissociative electron recombination with cluster ions formed during the plasma decay. Under the same conditions, the role of cluster ions in the plasma decay in O 2 , air and some other O 2 -containing mixtures was observed to be minimal and the composition of positive ions in the discharge afterglow was dominated by O 2 + ions [9][10][11]. Here, measurements did not agree with calculations using the available rates for dissociative electron-ion recombination.…”

“…Equation (3) neglects the heating of electrons in superelastic collisions with electronically and vibrationally excited particles (see [9,10]). This assumption is justified by a small energy input in the discharge under the conditions studied.…”

“…The procedure of this calculation was described previously [9,10] and allows for the consideration of all electron collisional processes with molecules that are usually used to calculate the non-equilibrium electron energy distribution, electron transport and excitation rate coefficients in discharge plasmas. In our case, it was important to consider all inelastic electron processes including the excitation and quenching of the rotationally excited states of molecules, the processes that are important at moderate values of T e .…”

“…American Institute of Aeronautics and Astronautics The observations were analyzed in the zero-dimensional approximation under the assumption that the discharge plasma is uniform. In reality, the discharge developing in the dielectric tube generates a radially non-uniform plasma (see, for instance, [3,9,10]). To estimate the effect of plasma non-uniformity on the measured data, we took still photographs of the discharge and extracted the corresponding radial distribution of the emission intensity using the inverse Abel transform.…”

“…The ion composition and lifetime of plasmas in this case can differ greatly from the ion composition and plasma lifetime in quasi-stationary discharges. Plasma decay after a high-voltage nanosecond discharge has been studied in N 2 , CO 2 , H 2 O [8], O 2 , air [9,10] and Ar:O 2 and СО 2 :О 2 mixtures [11] where the temporal evolution of electron density was experimentally and numerically studied at room gas temperature and moderate (1-10 Torr) pressures.…”