Effective ionization rate in nitrogen–oxygen mixtures

The effective Townsend ionization coefficient in nitrogen–oxygen mixtures at various pressures is determined. In addition to the commonly accepted difference of the ionization and the attachment coefficients, α and η, respectively, the electron detachment from the negative ions created by the avalanche itself is taken into account. This leads to non-zero effective ionization rate below the threshold field corresponding to α − η = 0.