Electrostatic deflection aberrations revisited: Solution proposed to an old problem

Abstract

The deflection of charged particle beams into large angles is more often done with magnetic fields than with electric fields. One reason is that magnetic deflection aberrations are two to three times lower than electrostatic deflection aberrations. Electrostatic deflection aberrations have been re-examined in an attempt to design a 4 k by 5 k pixel cathode ray tube display suitable for digital mammography workstations. Using a novel ray trace program, it has been determined that electrostatic deflection aberrations can be reduced ten-fold by injecting the electron beam at an optimized offset position into a conventional deflection plate assembly. The surprising result is that the “sweet spot” is not near the center where it would be expected based upon looking at the fringe fields. The optimum injection position is offset almost halfway towards the attracting plate. This result has been confirmed in one test configuration. While the mammography application provided the initial motivation to reduce deflection aberrations, the technology may be useful in electron or ion beam lithography, especially so since the design readily accommodates four discrete beams.