A pre-breakdown phenomenon in the liquid dielectric hexane

Abstract

The paper describes the observation, recording, and interpretation of a pre-breakdown phenomenon occurring in the liquid dielectric hexane. The effect is seen as a region of changed refractive index, and an optical Schlieren system and a high speed streak camera have been constructed and used to investigate its nature and in particular its rates of growth and decay. From the results obtained a theory of breakdown of the point-plane electrode system is deduced and shown to explain the observed phenomena remarkably well. The region of disturbance itself is interpreted as a local heating which marks the extent of a weak plasma. This plasma forms at the point cathode, grows in size with time to span most of the electrode gap, and breakdown indicated by an arc finally ensues. From the plasma geometry it is estimated that the minimum field existing at the plasma boundary during breakdown is about five times greater than the mean applied field. Measurements of the rate of movement of the plasma boundary suggest that at these high fields electron mobilities are becoming field dependent and rising rapidly. The minimum breakdown field is estimated as about 620 kv cm-1 and the average electron mobility at this field is estimated as about 0.03 cm2 v-1 sec-1.