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Title: Experimental study on thermal characteristics of positive leader discharges using Mach-Zehnder interferometry

Leader discharge is one of the main phases in long air gap breakdown, which is characterized by high temperature and high conductivity. It is of great importance to determine thermal characteristics of leader discharges. In this paper, a long-optical-path Mach-Zehnder interferometer was set up to measure the thermal parameters (thermal diameter, gas density, and gas temperature) of positive leader discharges in atmospheric air. IEC standard positive switching impulse voltages were applied to a near-one-meter point-plane air gap. Filamentary channels with high gas temperature and low density corresponding to leader discharges were observed as significant distortions in the interference fringe images. Typical diameters of the entire heated channel range from 1.5 mm to 3.5 mm with an average expansion velocity of 6.7 m/s. In contrast, typical diameters of the intensely heated region with a sharp gas density reduction range from 0.4 mm to 1.1 mm, about one third of the entire heated channel. The radial distribution of the gas density is calculated from the fringe displacements by performing an Abel inverse transform. The typical calculated gas density reduction in the center of a propagating leader channel is 80% to 90%, corresponding to a gas temperature of 1500 K to 3000 K based on the ideal gas law. Leadersmore » tend to terminate if the central temperature is below 1500 K.« less
Authors:
; ; ;  [1]
  1. Department of Electrical Engineering, Tsinghua University, Beijing 100084 (China)
Publication Date:
OSTI Identifier:
22410462
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AIR; BREAKDOWN; DENSITY; ELECTRIC DISCHARGES; ELECTRIC POTENTIAL; INTERFERENCE; MACH-ZEHNDER INTERFEROMETER; PLASMA EXPANSION; PULSES; SPATIAL DISTRIBUTION; TEMPERATURE RANGE 0400-1000 K; THERMODYNAMIC PROPERTIES