Basic Processes in Spark Breakdown
The basic phenomenon of any discharge, including a spark, is the ionization of gas atoms and molecules by electron impact. Experimental data available on spark breakdown in long gaps exclude the possibility for a long, streamer-type cold channel to develop in air. The problem of gas temperature in a developing spark is of great importance for the understanding of spark breakdown, especially in air gaps, which have always been of primary interest to researchers. The chapter begins with the concepts of ionization wave and streamer. The most effective mechanism of streamer expansion is that of ionization. The streamer parameters calculated in terms of a simple theory are quite reasonable and agree with both measurements and calculations from more sophisticated problem formulations. According to the generally accepted, mostly speculative, views and scarce experimental data, initial electrons arise in front of an ionized streamer head due to the absorption of energetic photons emitted by the plasma.