Characterisation of Electron Beams Produced by Crossed-Field Secondary Emission Diodes

Abstract

The crossed-field secondary emission (CFSE) diode is a compact, simple and cheap source of tubular electron beams. The physical mechanism of current production is a self-sustained secondary electron emission. In this study, voltage-current, temporal and spatial characteristics of electron beams produced by axisymmetric and non-axisymmetric CFSE diodes have been investigated. The highest current obtained at the present stage of research is ∼240 A generated with a diode having a cathode diameter of 64 mm and operated with an applied voltage of ∼20 kV. The electron beams are characterised by extremely high temporal stability and narrow (∼1.4 mm) radial current density distributions. In axisymmetric diodes, the azimuthal current density distribution j(φ) is uniform but this is only achieved by careful adjustment of the cathode-anode assembly. In non-axisymmetric diodes, the j(φ) distributions are strongly non-uniform and depend not only on the magnitude but also on the direction of the magnetic field.