Numerical simulation of plasma expansion at different rates of current rise in the spark stage of a vacuum arc

A kinetic numerical simulation of an expanding current-carrying plasma plume of the explosive-emission center in the vacuum breakdown was performed. It was found that at the current density rise less than about of 109 A/cm2/s the expansion of the plasma generally has a self-similar character. At the higher current density growth rate the plasma expansion has an essentially non-stationary character. The high density current leads first to the development of ion-acoustic instability and then to the development of Buneman instability. Strong current instability leads to the rupture of the plasma and the creation of conditions for the collective (anomalous) acceleration of ions to the cathode and the anode. Anomalously accelerated ions with energies up to 80 keV create an additional powerful heat flux to the cathode, which should facilitate the reproduction of the cathode spots in the spark stage of vacuum discharge.