Mechanisms of electrical breakdown in mercury vapour

Abstract

Measurements have been made of breakdown potentials, primary ionization coefficients and formative time lags, under uniform field conditions in mercury vapour with a mercury pool as a cathode. Generalized secondary ionization coefficients (ω/α) were calculated as a function of E/p0 from the breakdown potentials and primary ionization coefficients. This curve is interpreted in the light of calculations made of the relative populations of atoms in the P states per ion pair and the application of Davidson's treatment of the temporal growth of ionization. It is concluded that the dominant secondary processes in mercury vapour for the pressure range 05-10 torr, when the cathode is a mercury pool, are collision-induced radiation from the destruction of metastables in the gas and positive-ion action at the cathode for values of E/p0 below 600 V cm⁻¹ torr⁻¹. At higher values of E/p0 the process is one of positive-ion action at the cathode alone, the ion acting by virtue of its potential energy.