Multiple-element electrostatic lenses: II. A multiple disc lens

For pt.I see ibid., vol.1, no.8, p.738-46 (1990). The authors have constructed a cylindrical electrostatic lens using 31 discs, spaced at 0.1 diameter, mounted between two cylinders and have studied its focusing characteristics by both calculation and measurement. They apply potentials V₁ and V₃ to the cylinders, V₂ to a group of contiguous discs, and potentials intermediate between V₁ and V₂ and between V₂ and V₃, to the discs between the cylinders and the contiguous group. This potential distribution differs from that used in calculations by Read and the authors make a detailed comparison of the available ranges of magnification and the spherical aberration coefficients of these two lens systems. The problems of the practical operation of multi-element lenses of this type suggest that they have limited application.