Effect of nitrogen pressure on the energy of runaway electrons generated in a gas diode

The energy spectra of runaway electrons generated in a gas diode under the action of voltage pulses with a front width of ∼300 ps and amplitude of ∼140 kV have been studied using a time-of-flight spectrometer at nitrogen pressures in a range of 0.1–760 Torr. The delay of runaway electron beam pulse relative to the driving voltage pulse has been determined. The electron energy depends in a complicated manner on the nitrogen pressure in the gas diode and on the cathode geometry. A minimum breakdown voltage for a gap between tubular cathode and flat anode has been observed at a nitrogen pressure of ∼100 Torr. A decrease in the nitrogen pressure below 100 Torr leads to an increase in the maximum of voltage drop on the gap and the energy of the main fraction of electrons.