Anomalous Breakdown in Uniform Field Gaps in SF6

Experiments showing anomalously low breakdown voltages in uniform field gaps in SF6 are discussed. A generalized quantitative criterion suitable for computer calculations of breakdown voltages in known fields in SF6 and other strongly electronegative gases is described, and it is shown that the anomaly in the uniform field gap breakdown voltages can be satisfactorily accounted for. Similar anomalies can occur in other field geometries and in other gases; it is shown how to avoid such breakdowns.