Pre-breakdown Ionization in Hydrogen at Low Pressures

Detailed studies of pre-breakdown ionization in hydrogen gas at low pressures have been made in the presence of uniform electric fields and appropriate analytical methods and experimental procedures suitable for similar studies in crossed electric and magnetic fields have been established. The factors influencing determinations of the first Townsend ionization coefficient α/ p 0 from pre-breakdown ionization measurements are discussed and an observed pressure dependence of α/ p 0 at E / p 0 = 350 is shown to be due to the presence of vapour impurities which can give rise to the large values of α/ p 0 recently reported. Values of α/ p 0 have been measured for the range of values of E / p 0 from 50 to 450 v cm -1 (mm Hg) -1 .