Spatial and time characteristics of high current, high voltage pseudospark discharges

During the early phase of the discharge (ignition), fast ionization waves are observed propagating with a velocity of 10/sup 6/ m/s from cathode to anode. During this transient phase, a first peak of an energetic electron beam develops. Simultaneously, a moderate radial expansion of the axially concentrated background plasma (produced from beam electrons) is observed, but the plasma parameter remains still smaller than the borehole diameter (equal to 3 mm). The transition into the high current phase is characterized by further continuous radial expansion of background plasma, which is interrupted by a sudden and rapid radial expansion of plasma into the last two or three gaps in front of the anode. One reasonable explanation is based upon a kind of plasma blow-up by the field of the space charge accumulated there. Part of the beam electrons, extracted from the hollow cathode and adjacent gaps, are apparently deflected or even reflected in this high local electric field. Parallel with increasing total current, the internal resistance of the system drops dramatically, synonymous with the energy of the beam electrons, too. Characteristic for the development of the hollow-cathode plasma is a stepwise expansion. The plasma itself develops a hollow structure, and the diameter of it is still larger than the borehole diameter. During the high-current phase, the diameter of this characteristic hollow structure increases rapidly to the wall, indicating the end of the first current half-wave.