Propagation of individual plasma spots on cathode surface by high-current discharge process

In this Letter, plasma distribution on a carbon-fiber-aluminum (CFA) cathode powered by a ∼450 kV, ∼350 ns, ∼50ΩHV pulse generator is investigated by time-and-space-resolved electrical and optical diagnostics. A quasi stationary behavior of cathode plasma expansion into the vacuum gap was observed during the main pulse. The cathode plasma distribution is characterized by individual plasma spots. It was shown by optical and X-ray measurements that the uniformity of the extracted electron beam is satisfactory in spite of the individual plasma spots. A mechanism for this phenomenon is suggested. Relativistic electron beams, with the current densities up to 340 A/cm2, were obtained. This class of CFA cathode may offer the promising prospect of high-current electron beam sources.