Angular aberrations in a magnetic prism broaden the dispersive image of electrons with the same energy. We examine second-order correction after a 300 keV, 90° prism using an analytical exit map and finite-length, three-dimensional sextupole fields in SIMION. A single sextupole reduces the dominant vertical-angle contribution but leaves competing horizontal- and vertical-angle errors. Two independently powered sextupoles at different positions provide separate control of these contributions and cancel both angular-square coefficients in the second-order response model. For a uniform angular point source of radius 0.4 mrad, the centered geometric RMS width at a fixed detector decreases from 27.42 nm to 7.55 nm with one stage and 0.0864 nm with two. The field response and placement study explain how the two-stage arrangement produces this improvement.

electron energy-loss spectroscopy,magnetic prism,sextupole,second-order aberration,SIMION