The current column contraction and ion charge increase induced by the current build-up in a pulsed vacuum discharge

Abstract

It is shown that three current build-up regimes may be realized in a pulsed vacuum discharge, depending on the relationship between the pulse duration τ and the characteristic times of the plasma flow (τL) and the cathode spot spreading (τS). For a rapid build-up (τ τS), the contraction becomes insignificant. The first two cases give rise to additional nonequilibrium ionization in the current column, which leads to the ion charge increasing with the current. The third case is characterized by a “frozen” ion composition corresponding to the plasma parameters in the near-cathode region.