Dynamics of subnanosecond electron beam formation in gas-filled and vacuum diodes

The dynamic characteristics of a subnanosecond pulsed electron beam formation in the accelerating gap of a gas-filled or evacuated diode have been studied at a time resolution ∼10−11 s. In the air-filled gap, the electron beam pulse with a current amplitude of several amperes is formed up to about one hundred picoseconds earlier than the analogous pulse under vacuum conditions, and the measured pulse duration (∼10−10 s) is close to the electron flight time across a diode gap in the continuous acceleration regime. It is shown that a nanosecond prepulse plays an important role by initiating the emission of electrons that are subsequently accelerated by the high-voltage pulse with a subnanosecond front.