Pinch effect in vacuum arc plasma sources under moderate discharge currents

An analysis of a wide set of events, which have been observed in cathode plasma jet of vacuum arcs and sparks, is presented. In particular, they are (i) the substantial decrease of cross-section of cathode jet in a steady-state vacuum arc far from the cathode, (ii) the appearance of high charge states of ions under discharge current increase and pulse duration decrease and (iii) the significant enhancement of the energy of ions in cathode plasma jet with increase of the current rise rate and of the interelectrode gap length. We concluded that these effects, revealed within a wide range of discharge parameters, are similar in nature and could be explained by cathode plasma jet pinching out of the near-cathode region. This qualitative conclusion was supported by quantitative estimation of magnetic compression influence on plasma properties. Such estimations were obtained from theoretical models which have been developed to describe both the steady-state jet and a jet with increasing current.