Formation of 1.4-MeV Runaway Electrons Flow in Air

Delay stage of pulsed breakdown in air gap lasts longer than the time of electron free acceleration from the cathode to anode. When the voltage rise time in the gap is comparable with this time interval and electric field strength is sufficiently high, one can expect formation the flow of runaway electrons (RE) with a relativistic energy approaching to that determined by the amplitude of the voltage pulse. The train of serially connected gyromagnetic nonlinear transmission lines at the solid-state modulator S-500 output was used to form -860-kV travelling voltage pulse possessing a maximum rate of the voltage rise of 10 MV/ ns at a 100-ps-long front. Due to breakdown delay stage, the pulse amplitude was doubled at the cathode of 2-cm-long air gap in an open-end regime. As a result, RE energy of at least 1.4 MeV was achieved at the anode of the gap. Temporal-and energetic structure of REs pulse is considered.