Prebreakdown Process in Freon-Nitrogen Mixtures at Low Gas Pressures

Steady-state prebreakdown currents were measured under a uniform field in freon-nitrogen mixtures over the range 110¿ E/p¿240 (E = electric field in V.cm -1torr -1, and p = gas pressure in torr) and at pressures ranging from 1-20 torr for different concentrations of freon. From the measured currents, the values of ionization and attachment coefficients and the ratio of diffusion coefficients to mobility for electrons (mean energy), were determined. The addition of a small concentration of freon (¿10 percent) to nitrogen at high E/p values is found to increase the ionization rate considerably with a corresponding reduction in sparking potentials. A peak in the value of mean energy for electrons was also observed under this condition. This is attributed to a significant difference in the ionization potentials of freon and nitrogen molecules, which is capable of ionizing molecules.