Dynamics of cathode plasma speed in planar diode with explosive emission cathode

The research results of speed dynamics of explosive emission plasma expansion in the planar diode with the cathodes made of graphite and carbon fiber, of copper (solid and multi-edged) and with the multi-edged tungsten cathode are presented in the article. The plasma speed was determined by the volt-ampere characteristics of the diode with the time resolution of 0.2 ns. The experiments have been performed at the electron accelerator TEU-500 (350-450 kV, 100 ns, and 10 kA) in the matching mode of diode impedance and output resistance of nanosecond voltage generator. It was found out when the plasma formation at the cathode is completed and till the pulse ends the plasma speed is constant and equals 2±0.5 cm/μs for graphite and carbon fiber cathode, 3±0.5 cm/μs for tungsten cathode, 4±0.5 cm/μs for cathode made of copper. It is shown that the spread of explosive emission plasma is the principal tool determining its speed during the electron beam generation. The influence of the negative-charged layer by the cathode plasma surface (virtual cathode) on the additional acceleration of ions is insignificant and does not exceed 0.2-0.3 cm/μs.