High-current electron beam generation by a pulsed hollow cathode

Abstract

In this paper the parameters of a hollow-cathode electron source and the generated electron beam are presented. A gas puff valve is used to provide a sharp pressure gradient between the cathode cavity and the accelerating gap. To produce the plasma inside the hollow cathode we used a pulse forming network (10 kV, 5–10 μs, 5 Ω). Generation of a high-current electron beam was achieved under an accelerating voltage of 20-kV amplitude and 500-ns pulse duration. The parameters of the He gas and the plasma inside the cathode and the accelerating gap were studied by electrical and optical diagnostics for different gas pressures and discharge current amplitudes. It was found that the operation of the hollow cathode is characterized by a negative anode potential fall and that the plasma density and temperature inside the hollow cathode do not exceed 5×1012 cm−3 and 14 eV, respectively. The parameters of the electron beam were studied for different discharge current amplitudes and anode grid cell sizes. It was shown that efficient electron beam generation with a beam current amplitude of up to 300 A is achieved without significant increase of the plasma potential. Space-charge neutralization processes in the accelerating gap explain the excess of the electron current density above its space-charge-limited value, in agreement with the measured potential distribution in the accelerating gap. The results of computer simulations of the hollow-cathode operation are in satisfactory agreement with the obtained experimental data.