Ecton

Abstract: A new mechanism for the operation of a cathode spot in a vacuum arc, based on ecton processes, is proposed. An ecton is formed by the explosion of the tip of a jet of molten metal as it interacts with plasma. The time of ecton operation is assumed to be limited by the thermal conductivity of the liquid metal. For copper electrodes, the theoretical expressions are derived for the specific mass removal, ion erosion characteristics, current density, and the diameters of craters. The results agree well with the experimental data available.

Abstract: In this paper, we review the state of the art in studying the physical processes that occur in the cathode spots of vacuum arcs. The now available experimental data are interpreted in the context of the ecton mechanism of the operation of vacuum arc cathode spots. Central in this mechanism is the explosive electron emission, a phenomenon discovered by the author and his co-workers in the mid-1960s while studying high-voltage pulsed vacuum breakdown. In the light of the ecton mechanism, the cathode spot of a vacuum arc consists of individual cells which are explosive emission sites each emitting a portion of electrons termed an ecton. The cathode spot processes are cyclic in nature due to the finiteness of the ecton lifetime. It is shown that an arc is self-sustained due to the explosive emission processes initiated on the interaction of the cathode plasma either with nonmetal inclusions present in the cathode surface (first-type spots) or with liquid metal jets ejected from the zone of an active cathode spot (second-type spots). Attention is focused on the physical processes occurring during the operation of a cathode spot cell. A statistical model of a vacuum arc is used to interpret the effect of the spontaneous extinction of an arc. It is shown that an increase in the arc current is accompanied by a slight increase in the number of simultaneously operating ectons; therefore, as observed in the experiments, the parameters of a vacuum do not greatly depend on the current up to the kiloampere level.

Abstract: The autograph method was used to investigate the arc spot motion over a virgin tungsten cathode under a magnetic field of H=0.1-0.7 T in the current range 2-50 A. The cathode spot (CS) has been found to start dividing at a current of a few amperes. The current density measured at the moment of CS death is (1.2+or-0.5)*1011 A m-2 for a cold cathode and (3+or-1)*1010 A m-2 for a hot one. The CS lifetime is 25-50 ns for a cold cathode and it increases to 150-200 ns for a heated one. Neither the current density nor the CS lifetime depends on current. Estimates have shown that the erosion rate decreases with current and increases with temperature. The backflow electron current from the CS plasma is invoked to account for the experimental evidence.

Abstract: The paper presents a two dimensional (2-D) hydrodynamic model of vacuum arc emission center-"ecton"-which is an outgrowth of the one-dimensional problem that we have solved earlier. The numerical simulation was carried out for the initial stage of the operation of the cathode spot of a low-current vacuum arc on a copper cathode. It has been shown that, in terms of this model, the current flows in the main through the edges of the cathode spot. Based on a these data, a mechanism for the motion of a cathode spot has been proposed.