Numerical study of the feasibility of runaway electron generation in an emerging cathode layer of a self-sustained high-pressure space discharge

The formation of the cathode layer of a self-sustained high-pressure space discharge with preliminary ionization of a gas medium, excited by nano- and subnanosecond voltage pulses, is calculated. It is shown that, at pressures of $\sim$1 atm, at the final stage of cathode layer formation, conditions for runaway electron generation are created. Runaway electrons from the electric field amplification region in front of the leading edge of a plasma (streamer) channel, originating from the top of the cathode micronib, is considered. It is shown that, at pressures of $\sim$10 atm, conditions are created for the runaway of electrons immediately after their emission from the top of the micronib in its amplification zone; the runaway electrons thus obtained, in turn, can create preliminary ionization of the gas medium and ensure the formation of the initial phase of space discharge in systems without illumination.