The size of the emitting region and the current density at the cathode

The paper presents an experimental estimate of 10⁷ A/cm ² (lower estimate) for the current density in a vacuum arc cathode spot and a theoretical estimate of 10⁹ A/cm² (upper estimate) of this quantity. A criterion for the existence of an emission center (ecton) has been obtained which is the power flux required for an emission center to form, being a constant for a given cathode material. A hypothesis about the formation of current cells determining the internal structure of a cathode spot at the initial stage of a vacuum discharge has been put forward and discussed. It has been shown that this hypothesis does not contradict the available experimental data on the structure and dynamics of cathode spots