The Electron Spectrometer is a variation of the spherical tophat electrostatic analyzer (Sablik et al, IEEE Trans. on Geosciences & Remote Sensing, Vol 28, No. 6, 1990, pp 1034 - 1048). The variation is the flattening of the first 17° of the inner spherical electrode and a corresponding flattening of the spherical cap to plate. Sablik et al 1990 optimized the spacings to achieve best focus. The end result is to improve the energy resolution by ~3.5 for a fixed set of plate radii without a large loss of geometric factor. No other variation of parameters for a pure spherical system can achieve this goal.
In addition, extensive effort has been taken to ensure a solar rejection of >10-13. This is accomplished by the inclusion of a light trap in the outer plate and a new form of copper black on all surfaces exposed to solar UV. Ray tracing indicates these techniques will meet this goal.
