The Initiation of Electrical Discharges by Field Emission

The initiation of highly overvolted discharges produced in effectively ion-free gases by voltage impulses of short duration is shown to be independent of the gas between the electrodes, also of the pressure from one atmosphere down until the vacuum spark stage is reached. In asymmetrical fields values of the field intensity at the cathode required for initiation are the order of 5×${10}^5$ volts/cm, while at the anode the field for initiation is some 20 percent higher. Oscillograms showing the time lags and rates of fall of potentials of such highly overvolted discharges between spheres, and between points and planes have been obtained as well as those of an ordinary discharge for comparison. When the breakdown occurs because of high fields at the cathode, the initiation is readily explained by field emission of electrons. In the case of high fields at the anode it can be said that the initiation is determined by the character of its surface. When the discharge occurs the rate of fall of potential is greater than ordinary discharges in gases. Oscillograms of the wave fronts produced by 60-cycle discharges between magnesium electrodes, and the rate of fall of potential across such discharges have been obtained.