Electric Breakdown in CO2 from Low Pressures to the Liquid State

Abstract

The electric breakdown in CO2 has been investigated from low pressures through the critical point into the liquid state. Paschen's similarity law is verified for low pressures. At high pressures small departures are observed for long gap-lengths and large departures for small gap-lengths. Simultaneously the scatter of the breakdown voltage becomes independent of illumination and the breakdown strength dependent on the cathode material; this appears due to the onset of field emission. Measurements of prebreakdown currents have yielded values for Townsend's first coefficient as well as for the field emission constants. For small gap-lengths the prebreakdown currents are higher than the normal field emission equation predicts, indicating some new process effective at short gap-lengths. The transition from the gaseous to the liquid state does not produce a discontinuous change of the breakdown voltage.