25 September 1997 Electrostatic deflection aberrations studied with ray tracing: a surprising and simple solution proposed
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Magnetic rather than electric fields are usually used to deflect charged particle streams into large angles primarily because electrostatic deflection aberrations are 2 - 3 times larger. This very mature subject has been reexamined using a ray trace program. Traditionally, beams are injected centered between deflection plates to avoid the fringe fields and scanned symmetrically. Analysis produced a simple and surprising result. Injecting the beam asymmetrically significantly reduces aberrations. This very far-off-axis solution is only effective if the beam is deflected toward the near plate. Electrostatic deflection aberrations can be reduced over 10-fold by (1) injecting the beam into the deflection plate gap with a specific off-center displacement located at the inflection point of the beam landing at the target versus injection offset curve, (2) asymmetrical scan, and (3) quadrupole upstream. These results have been partially confirmed. One application has been studied -- a 4000 by 5000 pixel CRT for digital mammography workstations. By dynamically adjusting the injection offset, the beam can be scanned 61.0 degrees with undetectable (greater than 13 fold reduction) deflection aberrations. With static offset, (offset 42% toward the attracting plate) the beam can be scanned 38.1 degrees toward and 9.5 degrees away from the near plate. Multiple discrete beams are possible.
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Michael W. Retsky, Michael W. Retsky, "Electrostatic deflection aberrations studied with ray tracing: a surprising and simple solution proposed", Proc. SPIE 3155, Charged Particle Optics III, (25 September 1997); doi: 10.1117/12.279402; https://doi.org/10.1117/12.279402

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