A study of ionization coefficients and electrical breakdown in hydrogen

Abstract

Experimental measurements of the Townsend ionization coefficient α for hydrogen have been made from a study of pre-breakdown currents in uniform electric fields over a range of the parameter E/p from 15 to 40 V/cm mmHg. The results indicate that earlier measurements may be in error below E / p = 25 V/cm mmHg, and show good agreement with the theoretical calculations of Emeléus, Lunt & Meek (1936) which are based on a Maxwellian distribution of electron energies. Furthermore, measurements made at different gas pressures for the same value of the parameter E/p show that α/p is a function of E/p . The growth of pre-breakdown currents has been measured to within a small percentage of the sparking distance and is found to be well represented by the Townsend equation i = i 0 e αd /1- γ (e αd -1), showing the existence of a secondary ionization mechanism denoted by γ . The results are discussed in the light of existing theories of electrical breakdown, and it is concluded that the Townsend mechanism is sufficient to explain the initiation of breakdown in hydrogen up to a pd value of at least 2800 cm mmHg.