SUPERCONDUCTING LENS FOR ELECTRON MICROSCOPY

Abstract
Arrangements of superconducting materials have been investigated to obtain objective lenses with the lowest possible spherical aberration coefficient (Cs) for the electron microscope. Various configurations of Nb3Sn in ferromagnetic containers giving current loops of small radii which produce axially symmetric magnetic fields with high peak intensities and narrow halfwidths were studied. The axial field distributions were measured (bismuth probe) and optical parameters and spherical aberration coefficients were calculated. Available superconducting materials appear to set a limit of Cs ≃ 0.4 mm and Cs ≃ 1.8 mm for 100 kV and 1000 kV electrons, respectively (bore diam, 5 mm).

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