Control over plasma distribution on explosive emission cathodes

Distributions of emission centers (ECs) on planar explosive emission dielectric (velvet) cathodes at moderate electric fields of 30-70 kV/cm and pulse durations of /spl sim/2 /spl mu/s with the use of a fast framing camera have been investigated. The experimental results suggest a link between the ECs distribution and current conduction paths through which the electron current is supplied to the cathode plasma. On bare velvets, the surrounding metal electrode was shown not to be of primary importance for the current conduction, instead, the current is supplied to explosive emission plasma mainly through the base of the velvet fabric. A development of a circle of brighter and larger ECs along the perimeter of the cathode was normally observed shortly after the beginning of the high voltage pulse. These ECs were found to be a major factor in the diode perveance growth and instability. Domination of the ECs on the cathode periphery has been suppressed by adding a pattern of well-defined current conduction points, e.g. perforations of the velvet fabric, to the cathode design.