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This paper reviews the state-of-the-art study of the physical processes in the cathode spot of a vacuum arc. The most important experimental data are explained in terms of the ecton model of a cathode spot. The finite lifetime of an ecton is responsible for the cyclic character of the processes occurring in a cathode spot. It has been shown that the arc plasma is generated by microexplosions occurring at the cathode surface heated by the Joule mechanism due to the high-explosive emission current density. Up to kiloampere currents, the charge state of the arc plasma and directed velocities of the ions are governed by the operation of a cathode spot cell-an ecton.