The Cassini Ion Mass Spectrometer: Performance Metrics and Techniques

The Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) uses a unique electric field configuration coupled with precise sub-nanosecond timing to produce a high mass-resolution plasma analyzer with both broad energy an mass ranges. The IMS maintains a spectrographic mass resolution (m/Δm) of ≥50 over a mass range of 1 to 40amu for singly charged positive ions in the energy range of 0.001 to 15ke V. Ions having energies between 15 and 50keV are measured with a lower mass resolution of ∼7.5 as are ions below 15keV which are neutralized or negatively ionized by passage through thin carbon foils at the entrance to the mass analysis section. Bot high and medium mass resolution measurements are made simultaneously on incoming ions of all masses. The total angular acceptance is 11° × 160° and areal acceptance is ∼1cm 2 per pixel. An overview of the design and results of the laboratory testing of the IMS are presented here.