Generation of a Picosecond Runaway Electron Beam in a Gas Gap With a Nonuniform Field

The formation of a picosecond beam of runaway electrons in a gas-filled acceleration gap with a cold cathode and a strongly nonuniform electric field was investigated. The experimental data obtained were compared to those characteristic of the mode of generation and acceleration of electrons in vacuum. Voltage pulses of amplitudes up to -300 kV (in a traveling wave) whose minimum rise time and FWHM did not exceed 100-150 ps were applied to the cathode. The duration and amplitude of the current pulse of the picosecond runaway electron beam behind the anode foil were measured with high time resolution. The emission region of the beam in a gas-filled diode was determined experimentally. The time-of-flight method was used to investigate the acceleration mode of particles in the gap. Information about the part played by field emission in the initiation of the runaway electron beam has been obtained. It has been demonstrated that the point within the rise time of the accelerating voltage pulse at which the beam is injected into the gap correlates with the magnitude of the macroscopic electric field at the cathode emitting edge.