Improvement of the Resolving Power and Transmission of Electrostatic Spectrometers

Abstract

A method proposed by Delage for the calculation of electron energy distributions has previously been generalized and applied to various types of electrostatic spectrometers, that is, to toroidal‐type and mirror‐type spectrometers. Thus, it has been found that spectrometers with wide angular apertures yield an asymmetric energy distribution which may have an important tail on the high‐energy side. The analysis of a typical distribution shows that this tail is caused by the angular dispersion of the trajectories; because of the filtering action of slits and electrodes, the positive and negative angular components of the beam contribute unequally to the energy spectrum. By changing the way that the beam is filtered, it is possible to improve the energy distribution profile, without or with little loss of transmitted current. The improvement of the resolution may thus reach 30% or more, as the result of only a small displacement of the exit slit either on the exit equipotential, or toward the beam. Most of these results are new, principally in the case of the spectrometers of the toroidal type where the optimum deflection angle is greater than the focusing angle. Moreover, from Wollnik's conclusions about shielding from fringing field in toroidal spectrometers, supplementary calculations are performed to extend the validity of other results to more practical cases. Finally, results obtained for the cylindrical mirror are found in good agreement with conclusions presented before by Hafner, Kuyatt, and Simpson.