Chapter V the breakdown of dielectrics

Studies of the current build-up as a function of time after the application of voltage continue to be most fruitful in elucidating breakdown mechanisms in gases. Loeb¹, in a review article on formative time lags, emphasizes the differences between the initial threshold for onset of a current independent of the external supply of electrons (Townsend threshold) and later thresholds for transitions to various types of discharge governed largely by space charge distortion of the applied field. He suggests that future measurements should be concerned largely with the build-up of current in time and space as the discharge passes through the various transitions rather than with only the time to final, but unspecified, catastrophic breakdown. This attitude appears widespread and most of the papers on the subject this year have taken this approach.