Abstract
In this article, we propose a compact 10–20 keV electron gun based on a simple magnetic focusing of a dense array of field-emissive microtips. The properties of this magnetic focusing system have been investigated with the view to providing a homogeneous electron beam on a target with a predefined cross section (10 μm×1 mm). The gun focusing performance has been estimated through an analytical calculation based on aberration optics. Because of the large aperture angle of the microtips, the system magnification is mainly due to spherical aberrations. Then, with an experimental setup immersed in a 0.046 T uniform magnetic field, an 80 μm×1 mm beam spot was obtained on a 5.5 kV-biased anode from a 10 μm×1 mm microtip array, located 15 mm from the anode. The 0.6 mA peak emitted current brought the power density to 4 kW/cm2, with a spot size larger than expected from the calculations. An adjustable magnetic field setup has made it possible to get a good understanding of the focusing mechanism. The limited focusing performance obtained in this experiment was attributed to the electric-field nonuniformity inside the vacuum chamber.
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