Plasma decay in air and O₂ after a high-voltage nanosecond discharge

Abstract

This paper presents the results of experimental and theoretical studies of an afterglow in room temperature air and O2 excited by a high-voltage nanosecond discharge for pressures between 1 and 10 Torr. We measured time-resolved electron density by a microwave interferometer for initial electron densities in the range (2–3) × 1012 cm−3. Discharge uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body electron recombination with ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when the rate of three-body recombination was increased by an order of magnitude and when the dependence of the recombination rate on electron temperature was changed. This could testify that the well-understood mechanism of three-body electron recombination with atomic ions could be noticeably modified in the case of molecular ions.

Gasdynamic Flow Control by Ultrafast Local Heating in a Strongly Nonequilibrium Pulsed Plasma

“…The fulfillment of this condition greatly simplifies the theoretical analysis of experimental data. It is these conditions that were realized, e.g., in experiments [96,97], where the dynamics of changes in the electron density during plasma decay in air (1-10 Torr) after a highvoltage nanosecond discharge with a specific energy deposition of 0.002-0.02 eV/mol was studied using microwave interferometry. Numerical simulation [96,97] showed that plasma decay under these conditions can be described on the basis of a fairly simple kinetic scheme, in which the main channel for the loss of charged particles is electron-ion recombination with positive ions, including cluster ions formed in the discharge afterglow.…”

“…This process has been well studied for atomic ions [114,115] and has hardly been studied for molecular ions. At the same time, it was suggested that the rate of three-body recombination for molecular ions (in particular, for ions [96,97,116]) can be much higher than for atomic ions and that, in these cases, there are different dependences of the recombination rate coefficients on Т е .…”

“…15 and 16 show the results of numerical zero-dimensional modeling of the evolution of the effective electron temperature and the charged particle densities in the afterglow of a discharge in dry and humid air at atmospheric pressure. The kinetic scheme of collisional processes describing plasma decay in this case is taken from [96,97,109]. In this case, the above-described specificities in collisional processes were taken into account.…”

“…In this case, the above-described specificities in collisional processes were taken into account. As in [96,97,109], it was assumed that the plasma is homogeneous and that the energy deposition in the discharge is so small that the influence of excited particles on the kinetics of plasma decay can be neglected. It was assumed that the electric field in the end of the discharge disappears at times much shorter than the relaxation time of Т е and the plasma density.…”

“…The relaxation of Т е during plasma decay was simulated based on the numerical solution of the equation [95][96][97] (1) together with the balance equations for electrons and ions in the zero-dimensional approximation. Here, ν ε is the relaxation frequency of the electron energy in collisions with molecules, n i is the ion density, k 3 is the coefficient of three-body electron-ion recombination, k 2 is the coefficient of binary dissociative recombination of electrons with ions, and I is the energy acquired by free electrons upon three-body electronion recombination.…”