Negative Corona in Freon-Air Mixtures

In order to gain information as to the importance of negative space charges in coronas, studies of negative corona in freon-air mixtures were undertaken. The mixtures used ranged from 10^-4 to 10² percent of freon-12 in dry air. The onset potentials of the intermittent corona region were constant in all mixtures, approximately 6 to 7 kv with X/p about 100; only in pure freon it changed to 12,600 volts with X/p about 200. Concentrations of freon up to one percent revealed corona characteristics very similar to those of air. From one to 20 percent mixtures showed rapidly decaying Trichel pulses. Upon analysis this seems due to the formation of Cl^- and F^-, which are shown to be still stable at values of X/p200. As a consequence, negative space charges will be stable in regions much closer to the corona point than in air and will, therefore, be more efficient in suppressing the discharge as is indicated by decaying pulse sizes. At still higher concentrations the more stable Cl^- and F^- formed heavier space charges, inhibiting the formation of large electron avalanches to such an extent that only incipient Trichel bursts were produced. Thus the range of potential of the intermittent corona region was extended to higher values, and the corona current vs. potential curves showed rapidly decreasing slopes with increasing amounts of freon.