Effects of electrode configuration and voltage polarity on the electrical breakdown of mercury vapour

Abstract

The electrical breakdown potential of mercury vapour is measured between mild steel coaxial concentric cylindrical electrodes. The mercury vapour pressure is varied over a range of almost five orders of magnitude and the ambient temperature of both the gas and the electrodes from 297–544°K. The breakdown potential values plotted against mercury vapour pressure exhibit the normal behaviour associated with Paschen breakdown curves. For a given mercury vapour pressure the positive wire breakdown value is lower than the corresponding negative breakdown value. The lower positive breakdown is observed over a wide pressure range, and is attributed to the large difference in the values of the total secondary electron emission when changing the role of the inner electrodes from being an anode to cathode. The total secondary electron emission is calculated over a wide range of E/p 0 values. The similarity theorem is obeyed for positive and negative wire breakdown, over a very wide range of mercury vapour pressure.