Double Pulse Effect in the Initiation of Runaway Electron Emission in an Air Gap

An experimental study was performed to analyze the emission of runaway electrons in atmospheric gaps in the presence of an advanced pulse, preceding the subnanosecond leading edge of the main voltage pulse, during which the electric field at the cathode reaches a strength sufficient for the occurrence of runaway electrons. The pulses of the runaway electron current vary due to the appearance and dynamics of the cathode plasma layer from the boundary of which the electrons run away. Plasma is generated by ionization of the gas by field emission electrons as early as during the advance pulse. It is shown that the characteristics of the runaway electron flow depend on the amplitude and duration of this pulse, as well as on the presence of an interval between it and the leading edge of the main voltage pulse.