Measurement of Ionization Coefficients in He/H₂O (95.4ppm) Mixture

Abstract

Measurements of the first and second ionization coefficients α and γ_T in He/H₂O (95.4 ppm) mixture are carried out using a steady state Townsend method. Observed ionized multiplication currents are analyzed by Nakamura's plot to determine both of the ionization coefficients. The obtained first ionization coefficient in the mixture is large compared with those of helium and water molecule in the range of the reduced electric field E/N≦1131 Td (E/p₀≦400 V/cm Torr) affected by Penning ionization between the metastable excited He atoms and H₂O molecules.
Therefore, it is validated that the Penning ionization is formed in the mixture and the related behaviors of the metastable excited He atoms He(2³S₁) and He(2¹S₀) are also discussed in this paper.