Beaded Discharges Formed under Pulsed Breakdowns of Air and Nitrogen
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TEMPERATURE PLASMA
Beaded Discharges Formed under Pulsed Breakdowns of Air and Nitrogen D. V. Beloplotova, A. M. Boichenkoa, and V. F. Tarasenkoa,* a
Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: [email protected] Received July 14, 2018; revised October 14, 2018; accepted October 25, 2018
Abstract—The mode of a pulsed discharge in a nonuniform electric field is investigated at which bright plasma bunches with a beaded structure are generated in atmospheric-pressure air. Using an ICCD camera, it is found that, at centimeter gap lengths and a voltage pulse duration of ≈300 ns, the beaded structure can be observed with a probability close to 100% within time intervals from a few nanoseconds to several tens of nanoseconds. The beaded structure can also be observed in the time-integrated photographs of the discharge gap, but with a low probability. It is shown that individual beads arise in the point-to-plane gap after the diffuse stage of the discharge and start from the electrode with a small curvature radius. It is established that the spark channel bridges the gap by passing through the formed beads. The glowing beads are again observed in the final stage of the discharge, when the discharge current and, accordingly, the intensity of spark emission decrease. DOI: 10.1134/S1063780X19030012
1. INTRODUCTION In resent years, interest has arisen in studying different types of atmospheric-air discharges (see, e.g., [1–5]). This is related to the improvement of recording equipment, observation performed from aircraft and the International Space Station, and development of advanced numerical codes for simulation of discharge processes. One of the least studied types of atmospheric discharges is bead lightning (see [6–10]). Attempts to investigate bead lightning using highspeed cameras did not meet with success due to its rare and unpredictable occurrence under natural conditions. Among recent publications, there were only several works dedicated to observations of bead lightning under natural conditions [11, 12]. The most interesting results illustrated by photographs were given in [11], where bead lightnings observed in an artificially initiated atmospheric discharge were described. In [11], the initiated lightning was photographed with a frame exposure of 1 ms. At the beginning of a sequence of 14 frames (frames 3, 4, 5 in Fig. 1 from [11]), a relatively brightly glowing channel homogeneous along its length is observed. In frame 6, as well as in frames 7 and 8, it can be seen that individual beads connected to one another arise in the channel. In the subsequent frames (9–13), the intensity of lightning radiation decreases and dark areas appear between individual beads. The length of an individual bead under these conditions was about 50 cm. Further (frame 14), during the return stroke
(the development of the opposite leader), a relatively uniform glow with a higher intensity is again observed over the entire channel length. Analysis of these data in
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