Anode Plasma Formation at the Initial Stage of a Nanosecond Air Discharge
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Anode Plasma Formation at the Initial Stage of a Nanosecond Air Discharge E. V. Parkevicha,b,*, A. I. Khirianovab, A. V. Agavonova, S. I. Tkachenkob,c, A. R. Mingaleeva, T. A. Shelkovenkoa, A. V. Oginova, and S. A. Pikuza a
b
Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia Moscow Institute of Physics and Technology, Institutskii per. 9, Dolgoprudnyi, Moscow oblast, 141700 Russia c National Research Center “Kurchatov Institute,” pl. Akademika Kurchatova 1, Moscow, 123182 Russia *e-mail: [email protected] Received September 4, 2017
Abstract—The initial stage of a nanosecond discharge in gaps with a high electric field at a cathode is studied by laser methods (interferometric, shadow, schlieren methods). The studies are performed in air at atmospheric pressure. Prominence is given to studying the evolution (appearance and growth) of the plasma channels at an anode and to estimating their parameters. DOI: 10.1134/S1063776118030160
1. INTRODUCTION The variety of the processes that occur at various stages of a pulsed gas discharge makes it impossible to create a general picture to describe both the initial and subsequent stages of the discharge. This is mainly true of the prebreakdown stage (before the beginning of a sharp increase in the current through a discharge gap), when the plasma parameters in a discharge gap change very fast (from several hundreds of picoseconds to several nanoseconds) on extremely small spatial scales (from a micron to several tens of microns) [1–3]. The processes that take place during an air discharge at the surface of a cathode point and result in a dense (higher than 1017 cm–3) plasma have been studied better than the anode processes. First of all, they include micropoint explosions and shunting breakdowns on the cathode surface because of the presence of dielectric inclusions or films on the surface [4, 5]. To record such fast small-scale processes, researchers should have diagnostic techniques that have a high spatial and time resolution. The required spatial and time resolution can be achieved using laser probing techniques [6]. In [7], we used laser interferometry, shadow, and schlieren methods to investigate the cathode plasma formation and showed that a dense plasma object, which had a transverse size of several tens of microns and an electron density higher than 1019 cm–3 and was elongated toward the anode, formed near the cathode tip at the prebreakdown stage of discharge. We also detected plasma objects at the anode, where the electric field is lower than that at the cathode by 2–3 orders of magnitude. However, the
details of the appearance and evolution of plasma objects and other parameters were not discussed. The purpose of this work is to study the formation and growth of plasma objects (plasma channels, filaments, etc.) at the anode and to estimate their parameters. 2. EXPERIMENTAL STAND, DIAGNOSTICS, AND IMAGE PROCESSING All experiments were carried out on the setup described i
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