A Survey of Time Lag of Sparkover in a Uniform Field

Abstract

An original instrument for measuring time lag of sparkover has been developed. This is capable of measuring lags over a range from one one-hundred-thousandth of a second up to any longer values. This entire time range is available for any individual measurement without readjustments and independently of the method or wave shape of voltage application. Spark lags are found to fall into three distinct domains. First, long initiatory lags (${10}^{+1}$ to ${10}^{\ensuremath{-}3}$ second or less) of random distribution spent in awaiting a favorable fortuitous space and time arrangement of the somewhat insufficient supply of initiatory electrons. Second, intermediate formative lags (of the order ${10}^{\ensuremath{-}4}$ second) distributed about a definite peak value of the order of time required for a positive ion to cross the gap and assist in building up a space charge gradient. Third, short formative lags (of the order ${10}^{\ensuremath{-}7}$ second) distributed about a definite peak value of the order of time required for an electron to cross the gap. A picture of the mechanism of sparkover in an initially uniform field is presented accounting for the existence of these three domains. The available experimental reports are correlated and shown to be consistent with each other and with the proposed explanation.