This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Multipole lenses normally need many power supplies, especially for those used for aberration correctors. For instance, in the quadrupole–octupole correctors presented by Krivanek et al [1], each quadrupole layer of the corrector needed four current supplies, including one for its ‘‘normal’’ quadrupole, one for ‘‘skew’’ quadrupole, two for its X and Y dipoles, respecitaly, and there were 12 quadrupoles totally. Each quadrupole–octupole layer needed five supplies and there were three quadrupole–octupole layers totally. Therefore, the corrector needed 63 power supplies.

[1] Krivanek OL, Corbin GJ, Dellby N, Elston BF, Keyse RJ, Murfitt MF, Own CS, Szilagyi ZS, Woodruff JW. An electron microscope for the aberration-corrected era, Ultramicroscopy, 108 (2008) 179–195.