Boltzmann equation analyses of electron swarm parameters in Hg vapour: effect of metastable Hg atoms

Abstract

A Boltzmann equation, in which the generation of secondary electrons through cumulative ionisation and collisions between two metastable atoms (electron-concentration-dependent processes) is taken properly into consideration, is presented for the first time. This equation is applied to an analysis of the steady-state electron swarm parameters in Hg vapour. The ratio of the Townsend first ionisation coefficient to the electric field strength, alpha /E, for E/N values from 50 to 1412 Td is compared with experimental values. The effect of metastable Hg atoms on the swarm parameters is discussed. It is found that secondary electrons generated through collisions between two metastable Hg atoms are much larger than those generated through cumulative ionisation in a low range of electron concentrations such as is given in Townsend discharges.