Threshold conditions for vortex-stabilized electrical discharges in the atmosphere

Laboratory experiments with vortex-stabilized arcs show that any effect the vortex may have in decreasing the deionization rate between pulses of power to the arc was too small to be measured with available apparatus. The major function of the vortex is to keep the plasma in contact with the electrodes, and a secondary function is to hold the plasma column on the shortest spacing between the electrodes. The concentration of the plasma by centrifugal action of the vortex gives only a 13% reduction in arc threshold power at the expense of a threefold increase in vortex kinetic energy. This effect is less important than previous experiments have indicated. The threshold power density of the arc is essentially a constant at 52 watts/cm3 and does not change appreciably over a threefold change in vortex kinetic energy. Tests with hard sparks did not show any preference for the axis of the vortex, but sparks occurring in rapid succession, say 10 to 20 per second, tend to restrike in the same channel more often in the vortex than elsewhere. Multistroke cloud-to-ground lightning discharges may not show preference for a tornado axis, since, owing to the absence of electrodes, the vortex will not play the same role as in the laboratory experiments.