Investigation of metastable autonomous plasma formations from atmospheric discharges

Abstract

A 10 kV, 2 kW laboratory transformer was used to generate atmospheric discharges at spherical brass electrodes 15 mm in diameter and 8 mm long. After ignition, a moving electric arc generated an autonomous plasma formation. The lifetime of the autonomous plasma formations, measured from video frames of 40 ms in succession, depends approximately linearly on their geometrical size. By applying a cylindrical-symmetrical back projection transformation to the images of the autonomous plasma formations and computing the radiation intensity profiles, a vortexlike structure of the plasma formations was detected. Autonomous plasma vortices 2.5 cm in diameter showed lifetimes of about 120 ms. No significant influence of the ambient air temperature, ranging from 10°C to 30°C, was found, nor on the relative air humidity, ranging from 10% to 100%. The radiation temperature of the plasma vortices were estimated by fitting blackbody radiation curves to the measured intensities at four spectral wavelengths provided by optical-spectrum filters. The average radiation temperature of the autonomous plasma vortices was estimated at about 2000 K, having a temperature decay of about 300 K/ms. The reproducible formation of metastable autonomous plasma vortices as described in the literature can be verified at the laboratory scale. Its geometrical intensity profile and radiation temperature can be approximated and its lifetime measured. The described phenomenon could possibly be accounted as a physical explanation model for the occurrence of natural ball lightning. Further investigations should focus on experimental determination of the flow profile and to provide a self-consistent theoretical model for the description of the energy-storage and transfer mechanisms.