The steady state growth of current in a prebreakdown discharge in the presence of Penning ionization

Publisher Website
Google Scholar
Abstract
A theoretical formulation of the effect of Penning ionization on electron and metastable particle densities in a prebreakdown discharge is proposed. The corresponding effect on the spatial growth of ionization, including surface secondary emission by metastable particle impact at the cathode, is determined and discussed. It is found that the form of the electron density is more complex than the Townsend form due to the Penning secondary ionization of impurities occurring in the gas volume. The model confirms that the effect of Penning ionization on the spatial growth of current is to reduce the breakdown voltage and give an apparent increase in the Townsend primary ionization coefficient alpha . When Penning ionization is the sole secondary process, breakdown will still occur but only for a limited range of impurity concentrations. On saturation of Penning ionization the apparent alpha converges to the sum of the ionization coefficient alpha and the excitation coefficient alpha m of the metastable state responsible for the Penning ionization. The theory indicates that the luminous flux method, or other methods involving analysis of the spatial growth of current assuming a traditional Townsend form, will determine the apparent primary ionization coefficient alpha eff when there is Penning ionization present. Calculations indicate that for neon gas with 5 PPM argon impurity, there is a 4% error in the determination of alpha if the traditional Townsend growth is assumed.