Filamentation and self-focusing of electron beams in vacuum and gas diodes

In this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the interaction of electrons with the anode are shown to develop in vacuum and gas diodes at nanosecond and subnanosecond durations of a beam current pulse and a decrease in the interelectrode gap. The average electron energy in filamentation and self-focusing of an electron beam in a vacuum diode of an accelerator at a current of $\sim$2 kA and a no-load voltage of $\sim$400 kV was established to be 50–100 keV while the energy density was 10$^9$–10$^{10}$ J/cm$^3$. It is confirmed that the beam current density in a gas diode can exceed 1 kA/cm$^2$. It is hypothesized that superdense electron beams in vacuum and gas diodes are formed as a result of avalanche multiplication of runaway electrons in the cathode–anode gap plasma.