Investigation of the character of cathode spot movement at vacuum pulse arc discharge

With the use of high-speed photo recording the character of cathode spots propagation from the initiation site of pulse discharge (radial movement) on a surface of Cu, Fe, Zr, Ni, Al, Mg, Zn, Sn with natural oxide film as well as on a surface cleaned by a discharge was studied. It was shown that in both cases a radial spot movement proceeds in a shape of expanding ring, consisting of first type spots on an oxidized surface and of separately located second type spots on a cleaned one. A rate of the radial spot movement and ring radius are significantly lower in the latter case. This process is accompanied by changes both in the number of spots and their linear density in a ring. A hydrodynamic mechanism of spots movement on the cleaned surface is discussed. As its base the "breastwork" mechanism of chaotic spot movement was used. Parameters gradients on the boundary of discharge zone were assumed to be the factors determining a radial spot movement.