Fundamental Processes of the Initiation of Electrical Discharges

The role of electrode and gas processes in the production of electrons which initiate spark discharges is investigated. The results for metal surfaces covered with thick (>or=10 -5 cm) oxide layers are consistent with the view that electrons may be liberated from sites of negative ions on the oxide. For metals covered with thin (similar 10 -7 cm) tarnish films the emission is also field dependent but in these cases involves the action of a surface charge of positive ions in setting up an intense field across the film causing tunnel effect emission: in both cases the macroscopic applied electric field was of the order of 10 5 v cm -1 . The influence of surface micro-geometry on the cold cathode emission processes is examined. These experiments in dry air, hydrogen and argon ( p similar 760 mm Hg) indicated that initial electron production by detachment processes and the quenching of metastable atoms does not play a significant part in the discharge initiation. The influence of moisture on these processes is examined. Recent work on breakdown of liquid dielectrics is discussed in the light of the present work.