On the peculiarities of monopole and multipole focusing
Abstract: Magnetic dipoles can be used to focus electrons and they have very simple focusing properties, both in first order approximation and also in third order, where they have been found to have very small aberrations. These properties have been studied by analytical and digital methods. In view of the simplicity and the fact that dipoles only represent one facet of the whole spectrum of multipoles we have now looked closely at the properties of monopoles on the one hand and quadrupoles on the other. Perhaps it is no surprise, but these two members of the multipole family also display great simplicity and could also be used for focusing electrons.
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