Current density distributions of electron beams produced by CFSE diodes

The crossed-field secondary emission (CFSE) diode is a compact, simple and cheap source of tubular electron beams. It is of a magnetron type with smooth cylindrical electrodes and an axial applied magnetic field. The physical mechanism of current production is a self-sustained secondary electron emission which thus effectively makes the CFSE diode a cold electron source. The electron beam from the CFSE diode could be generated in a wide range of output currents from ~10 A to several hundreds of amperes. The highest current obtained at the present stage of research is ~240 A generated with the diode of ~60 mm cathode diameter at ~20 kV of applied diode voltage. Our previous study revealed that the thickness of the electron beam wall is ~1 mm as evident from imprints of the electron beam on metal targets in the beam collector region. Such a small beam thickness combined with an extremely high temporal stability is of great importance for various applications including primarily devices for microwave generation. It is therefore an important task to investigate in detail the radial current density distribution of the electron beam produced by the CFSE electron source. Uniformity of the electron beam around a cathode circumference is also an important characteristic from the viewpoint of potential applications. The investigation on radial and azimuthal current density distributions of the CFSE output electron beam is a major goal of the research described in this paper