Some features of imaging of the processes occurring in an extended arc discharge in atmospheric-pressure air
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Some Features of Imaging of the Processes Occurring in an Extended Arc Discharge in AtmosphericPressure Air V. O. German, A. P. Glinov, A. P. Golovin, P. V. Kozlov, and G. A. Lyubimov Institute of Mechanics, Moscow State University, Michurinskii pr. 1, Moscow, 119192 Russia email: [email protected] Received July 20, 2012
Abstract—Processes occurring in the lowtemperature plasma of extended quasistationary arc discharges in air between graphite electrodes are investigated. Along with the conventional (constricted) discharge geom etry, other discharge modes—diffuse (distributed) and diffuse–constricted—are studied. Contraction, strat ification, and shunting processes are considered. Current oscillation modes are revealed that are caused by the interaction between the cathode and anode jets and the origination of plasma jets and solid particles from the locally overheated anode surface. DOI: 10.1134/S1063780X13070131
INTRODUCTION Electric arcs were traditionally (V. Petrov, 1903; Davy and Ritter, 1908) [1] studied experimentally in air on graphite (or carbon) electrodes, which are the cheapest and do not pollute the discharge space with a liquid phase that appears in discharges operating between metal electrodes. A common representation of such arcs consists in the following: its current chan nel is narrow (constricted) as compared to the inter electrode spacing and slightly deviates from the short est anode–cathode path [1, 2]. However, as was noted and shown in [3], the cur rent channel can have a complex geometry, and its length can manifold exceed the interelectrode spacing lie. When exceeding the threshold current, counter 1
streaming plasma originates from electrode spots, i.e., cathode and anode jets (flames), and the dis charge pattern becomes very complicated [3, 4]. The influence of the electrode material, the current inten sity, the air composition, and the physical and spectral parameters of such discharges on the current channel geometry is studied in [5–7]. In this work, we focus on an experimental study of an extended (lie ~ 30–50 mm) quasistationary current of up to 300 A in atmosphericpressure air on graphite electrodes. The purpose of the study is to precisely examine the current pattern and to investigate differ ent inhomogeneities of the spatial structure of the interelectrode medium. This can be of interest for practical use of arc discharges, e.g., in plasmatrons and arc treatment sets [3]. 1 The
use of graphite electrodes with standard atmospheric pres sure excludes the presence of the liquid phase in the electrode spots
The main attention is paid to imaging of processes related to the current flowing using highspeed (1200– 60000 frame/s) shooting with a short exposure in the visible wavelength range 0.4–0.8 μm. In addition, the shooting was carried out in the IR range 0.9–4.8 μm. As a result, the joint analysis of images made in differ ent wavelength ranges, as well as current and voltage oscillograms provide for a pattern of the discharge geometry evol
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