Conduction phenomena in gases

THE CENTRAL problem in understanding the conduction of electricity through gases is that of finding the means by which a body of gas initially containing mainly neutral particles is converted into one with a high density of charged particles and maintained that way. It is the motion of charged particles under the influence of an electric field that constitutes the flow of electricity through a gas, exactly as in a metal conductor. In a metal conductor there is always a copious supply of electrons free to move whenever a field is applied. In the gas there is normally no such supply, only a few electrons and ions caused by the action of cosmic rays. The problem confronting the physicist is to find the mechanisms by which these few electrons and ions can be multiplied by an applied electric field to a much larger number. When such amultiplication has been effected, the gas changes its state from that of an insulator to that of a conductor, and breakdown is said to have occurred.