Electron beams formation in helium-filled diode under atmospheric pressure

The formation of a beam of runaway electrons in a diode filled with helium at a pressure from 0.1 to 760 Torr was studied under conditions of a pulsed (4 ns) high (200 kV) voltage applied to the discharge gap. The experimental data results indicate that the electron beam is generated either at a large strength of electric field, when the fraction of runaway electrons is large, or in the field of low strength, where intensive electron multiplication takes place. In the latter case, cathode plasma propagates to anode at high velocity, at that with electrical field distribution in gas diode area the critical value of E/p is reached either due to geometric quotient leading to formation of nanosecond and subnanosecond electron beams. The electron beams obtained in the helium-filled diode had the current amplitude of up to 200 A (corresponding to the current density above 20 A/cm(2)) at electron energy of similar to130 keV.