Ionization Processes in a Long Discharge Tube with Application to Lightning Mechanism

Abstract

Properties of the progressive breakdown, occurring when an impulsive potential is applied to an electrode in one end of a discharge tube 14 cm in diameter and 12 meters long, have been investigated, principally by means of a high speed cathode-ray oscillograph. Potentials from 25 kv to 115 kv and pressures from 0.006 to 8.0 mm Hg were used, with dry air and hydrogen in the tube. Conditions in the discharge, when comparatively large over-voltages are impressed, have been discussed by several investigators, particularly with respect to impulses of positive polarity and in tubes of smaller diameter. These observations now have been extended to include the negative polarity. In addition, a low speed, low potential process has been obtained and its properties analyzed.A possible application of the lightning theory to such discharges is given. The low speed impulse resembles the hypothetical lightning pilot streamer as to speed and current, and the speed is of the order of magnitude of the drift speed of electrons in the tip field, as assumed for the pilot streamer. The high speed processes are more similar to the lightning dart leaders. It is pointed out that conditions in the tube are such that propagation in this case may be controlled more by the presence of photo-electrons ahead of the tip than by a preliminary ionizing leader.