ESIC measures the 3D distribution functions of the major ion species, H, He+, He++, and O+. It consists of a
retarding-potential analyzer (RPA), followed by a toroidal energy-per-charge (E/q) analyzer with disk-shaped field of view,
followed by a 20 kV post-acceleration into a time-of-flight (ToF) analysis section. Without RPA operation, the E/q range is
15 eV to 40 keV, otherwise it starts at essentially zero volts. To accommodate the large dynamic range in ion fluxes, the
instrument has split the 360 degrees FoV into two 180 degree sections whose sensitivities differ by a factor 100. Moments
of the distributions of all 4 ion species are computed on board and are available every 4 spins, i.e., every 6 seconds.
The instrument is identical to the CODIF portion of the CIS instrument on CLUSTER.