Conduction currents in compressed methane

Conduction currents have been measured in compressed methane at pressures up to 12atm absolute. The standard Townsend method was used to determine Townsend´s first ionisation coefficient ¿ for values of E/p0 (electric stress/pressure corrected to 0°C) between 24.3 and 32.9 V/cm torr. This extends previous measurements to lower E/p0 and higher pressures. Field-emission currents were detected at the highest pressures, and an anomalous current, which does not follow a normal Townsend amplification law, was also observed following the electrical breakdown of the compressed gas. Suggestions for the origin of this anomalous current are given, and the contributions to breakdown of prebreakdown processes is discussed.