Spatial characteristics of electron beams from symmetric and nonsymmetric crossed-field secondary emission sources

The crossed-field secondary emission (CFSE) diode is a cold electron source based on a self-sustained secondary electron emission. The output electron beams are tubular and could be generated in a wide range of currents up to several hundred amperes. In this study, radial and azimuthal current density distributions of electron beams produced by symmetric and nonsymmetric CFSE diodes have been investigated. The electron beams are characterized by extremely high temporal stability. The wall thickness of the tubular beam with a current of > 10(2) A from the diode with a 5 mm anode-cathode gap was measured to be as small as 1.4+/-0.2 mm. In axisymmetric diodes, the azimuthal current distribution j(phi) is uniform but this is only achieved by careful adjustment of the; cathode-anode assembly. In nonaxisymmetric diodes, the j(phi) distributions are strongly nonuniform and depend not only on the magnitude but also on the direction of the magnetic field. Results of the present research show that the CFSE electron sources are patent candidates for incorporation into medium and high power microwave devices.