Electron Optics of Real Cylindrical Deflectors Loaded with High Current
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In this chapter monochromators are studied and optimised with the help of numerical simulations of trajectories in the presence of space charge. The advantage of monochromatisation in two (or more) steps is demonstrated. Since it is an advantage to produce a monochromatic beam via a stepwise monochromatisation, we present a numerical analysis of two types of monochromators in the following. In Sect. 5.1 we first discuss the result of computer simulations for the second stage of a two-step monochromator, which operates with the entrance and exit apertures at a potential equal to the average of the potentials of the inner and outer deflection plates. In Sect. 5.2 we present results relevant to pre-monochromators, where either a higher potential is applied to the entrance aperture, or a lower potential to the exit aperture. We have already encountered such retarding monochromators in Sect. 3.2, where the limiting case of a small current load was considered.
KeywordsSpace Charge Output Current Input Current Deflection Angle Energy Width
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