The study of primary and secondary charge carriers in nanosecond pulse irradiated liquid dielectrics using a resonant microwave cavity

Abstract

A microwave resonant cavity technique for studying changes in conductivity of pulse irradiated dielectric liquids is presented. The sensitivity of the method is such that transient changes in conductivity of 5 × 10−9 ohm cm−1 can be measured with a signal to noise ratio of 10 and a response time of approximately 10 ns. The use of the technique is illustrated by a study of primary (excess electron, hole) and secondary (molecular ions derived from solutes) charge carriers in the saturated hydrocarbon liquid trans-decalin. The temperature dependences of the mobilities of the excess electron and hole are found to be described quite well by μ(−) = 25 exp(−4500/RT) cm2 V−1 s−1 and μ(+) = 4.0 × 10−3 exp (500/RT). The mobility of the hole is found to exceed that of the electron below approximately 10 °C. The sum of the mobilities of the secondary ions at 22 °C in a 5 × 10−3 M SF6 plus 10−2 M benzene solution is 5.2 × 10−4 cm2 V−1 s−1. In order to determine the mobilities of even the primary charge carriers consideration had to be given to the presence of geminate ion pairs on the time scale of the observations. The way in which corrections for geminate ion pairs were carried out is fully discussed.