Ionization processes in spark discharge plasmas

The dominant mechanisms of electron generation and loss during different phases of spark discharge are considered. The focus is on spark formation in long non-uniform-field air gaps through leader and streamer processes. The streamer development in dry air and the effects of humidity, temperature and density on the properties of a long positive streamer in air are discussed. The ionization kinetics in the leader channel in long air gaps is described. The ionization mechanisms which lead to the re-breakdown within a post-arc air channel and to the streamer breakdown in undisturbed air and in Ar are presented.