Prebreakdown Air Ionization in the Atmosphere

Abstract

This chapter is devoted to the analysis of electron-ionization and -elimination processes at early stages of electric-discharge development in air at altitudes of mainly 0–90 km. In this chapter, ionization processes in an external electric field, as well as background ionization by fast particles and electron attachment and detachment with participation of atomic and molecular oxygen, are considered. Temperature and concentration dependences of rate constants are described. Analysis of ionization models allowing simplified approaches to detailed computation models is undertaken. It is shown that the electric breakdown process in air, under the influence of an external electric field, comprises several stages that are different with respect to different altitudes over the Earth. Numerical modeling on the basis of a detailed plasma chemical model, taking into account the heating of gas by the discharge, has shown that the relaxation processes leading to gas V. Bychkov et al. (eds.), The Atmosphere and Ionosphere: Elementary Processes, Monitoring, and Ball Lightning, Physics of Earth and Space Environments, DOI 10.1007/978-3-319-05239-7_2, © Springer International Publishing Switzerland 2014 69 heating also lead to the appearance of a nonlinear stage of electric breakdown. The considered phenomena can be convenient in the consideration of a high-altitude origination of natural discharges in fields of thunderstorm clouds. Keywords Ionization • Attachment • Detachment • Breakdown • Gas discharge • Elementary processes • Models of the ionization • Chemical kinetics model • Atmosphere • Mesosphere 2.1 Introduction Practical problems of electric-discharge devices applied in air at different altitudes requires knowledge of ionization thresholds because ionization is a source of charged particles in plasma and thus determines the efficiency of the applied devices (Raizer 1991; Aleksandrov et al. 2008). Therefore, the solution to ionization-threshold determination in electric-discharge devices at a given altitude actually comes connected to a set of applications and stimulates investigations devoted to these questions. From data available in the literature, it is known that the development of discharge in air has been well described with respect to processes of origination and elimination of electrons in direct ionization, attachment, detachment, and other processes (Akishev et al. 1994). Determination of effective ionization thresholds requires the rate constants of corresponding processes to be determined with sufficiently high accuracy in the vicinity of the ionization threshold. This condition requires clarification (on the basis of experimental measurements or calculations on the basis of solution of the Boltzmann equation to determine an Electron-Distribution Function over Energies (EDFE), and the subsequent inte-gration of electron-molecule process cross sections with EDFE) the rate-constant values of the basic processes. Nevertheless, there exist many questions about the initial stage of ionization in air under real conditions. According to the work of (Aleksandrov et al. 2011), which was devoted to the research of ionization processes in the troposphere at altitudes of 4–12 km, it was shown that the measured breakdown of air electric field strength is approximately 3 V/cm, which is considerably lower than the breakdown of electric field strength near the surface of the Earth. In the work of (Bychkov et al. 2004), which discusses questions of ionization in the longitudinal discharge in a stream of air, there are breakdown fields considerably smaller than those near the Earth. Research results of ionization processes at higher altitudes where ionization processes can take place, leading to electric discharge phenomena, such as sprites, jets, etc. (Khodataev 2013; Raizer et al. 1998) are of great interest. The purpose of this chapter is the consideration of a prebreakdown stage of discharge development in air; determination of the dependence of ionization in 70 N.V. Ardelyan et al.