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25 September 1995 Fringe-field-induced 12-pole component of magnetic quadrupole lenses
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Energetic ions or electron beams can be focused to very small diameters by the use of electrostatic or magnetic quadrupole lenses or by combinations thereof. In all cases the fringing fields cause image aberrations of third and fifth order that are many times larger than the corresponding aberrations caused by the main field. Though the 12-pole component in the fringing field only influences the fifth order image aberrations their magnitude can be relatively large. For this reason we have investigated the 3D fringing-field distribution for differently cutoff ends of the electrodes or pole faces. It can be shown that by this method the effects of the 12-pole component of the fringing field can be reduced drastically or even be adjusted to compensate corresponding effects of the main field region.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
B. Pfreundtner and Hermann Wollnik "Fringe-field-induced 12-pole component of magnetic quadrupole lenses", Proc. SPIE 2522, Electron-Beam Sources and Charged-Particle Optics, (25 September 1995);

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