This experiment was flown to measure, throughout the orbit, the individual concentrations of
all thermal ion species in the mass range 1 to 72 atomic mass units (u) and in the ambient density range
from 5 to 5.E6 ions/cc. The mass range was normally scanned in 1.7 s, but the scan time per range could
be increased by command. Laboratory and inflight determination of spectrometer efficiency and mass
discrimination permitted direct conversion of measured ion currents to ambient concentrations. Correlation
of these measured data with the results from companion experiments, CEP (75-107A-01) and RPA (75-107A-04)
permitted individual ion concentrations to be determined with high accuracy. The experiment's four
primary mechanical components were guard ring and ion-analyzer tube, collector and preamplifier assembly,
vent, and main electronics housing. A three-stage Bennett tube with 7- to 5-cycle drift spaces was
flown; it was modified to permit ion concentration measurements to be obtained at low altitudes.
The balance between ion-current sensitivity and mass resolution in a Bennett spectrometer may be altered
by changing appropriate voltages. These voltage changes were controlled independently by ground command
for each one of the three mass ranges: 1 to 4, 2 to 18, and 8 to 72. More complete experiment details
can be found in H. C. Brinton et al., Radio Sci., v. 8, n. 4, p. 369, 1973.