Dust particle charge screening in the dry-air plasma produced by an external ionization source
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Dust Particle Charge Screening in the DryAir Plasma Produced by an External Ionization Source I. N. Derbenev and A. V. Filippov* State Research Center of the Russian Federation Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow, 142190 Russia *email: [email protected] Received January 13, 2015
Abstract—The ionic composition of the plasma produced by an external ionization source in dry air at atmo spheric pressure and room temperature and the screening of the electric field of a dust particle in such a plasma have been investigated. The point sink model based on the diffusiondrift approximation has been used to solve the screening problem. We have established that the main species of ions in the plasma under + – – consideration are O 4 , O 2 , and O 4 and that the dust particle potential distribution is described by a super position of four exponentials with four different constants. We show that the first constant coincides with the inverse Debye length, the second is described by the inverse ambipolar diffusion length of the positive and negative plasma components in the characteristic time of their recombination, the third is determined by the conversion of negative ions, and the fourth is determined by the attachment and recombination of electrons and diatomic ions. DOI: 10.1134/S1063776115080178
1. INTRODUCTION Studying the dusty plasma produced by an external ionization source in electronegative gases is of great importance in the physics of atmospheric phenomena [1, 2], in designing an autonomous source of energy based on a dusty plasma [3–5] and inertgas halide lasers [6]. In the first case, the ionization occurs through cosmic rays and radioactive decay products of elements in the Earth’s crust and air and has a mean rate of 10–15 cm–3 s–1 above the dry land [7]. In the second case, the gas is ionized by the decay products of α or βactive dust at a rate of 1013–1015 cm–3 s–1 [3– 5]. In the third case, the rate of gas ionization by a beam of fast electrons reaches 1020 cm–3 s–1 or higher [6]. Note also [8], in which a dusty plasma in air with nanoparticles was used for the destruction of cancer cells. Knowledge of the screening pattern in such a plasma will allow the sizes of the region of quasineu trality breaking and mutual influence of charged mac roparticles on one another to be estimated. The problem of the screening of the electric field of a dust particle placed in the plasma of electropositive gases produced by an external ionization source was solved previously in [9–12]. The screening of a macro particle in inert gases was shown to be described by a superposition of two or more Debye exponentials, with the number of exponentials being determined by the number of equations that describe the charging under given conditions. The charging in a plasma with an external gas ionization source in the case of elec tronegative gases with one species of negative ions was
studied numerically in [13, 14] (in a streamer channel in [15]) and
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