Abstract
We present the design and beam dynamics analysis of a Transmission Electron Microscope illumination system. A LaB6 emitter is used as a cathode/source with an emissive surface area of diameter 50 μm generating fixed emission current of 5 mA which is biased by −300 V with Wehnelt electrode. The gun is comprised of five electrostatic lenses in-between the focusing and anode electrodes to accelerate and focus the beam with integrated energy of 160 keV in the post anode region with diameter around 228 μm. Finally, the beam is focused using the condensed electro-magnetic lenses of field strengths 183 mT and 331 mT, respectively to spot size 1.8 μm in the post-lens position. The obtained focal spots are largely symmetric along the two transverse directions. The illumination system geometry offers full beam collimation control. The study provides a theoretical basis for the structure and optics design of the Transmission Electron Microscope.
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