The Plasma Proton Environment within Saturn's F-G Ring Gap as Observed by the Cassini Plasma Spectrometer Ion Mass Spectrometer during Saturn Orbit Insertion

In analyzing the Cassini data between Saturn's, A-ring outer edge and Mimas' L shell numerous inconsistencies have been reported in estimates of total ionic charge and electron density which can be important with regard to estimating micron sized dust particle charge states. While investigating these inconsistencies we discovered protons between the F and G rings using Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) time-of-flight (TOF) composition measurements acquired during Saturn Orbit Insertion (SOI) outbound pass of this magnetospheric region. We also searched for H2+ ions but no such events were found. We will be presenting the latest results of our analysis of the proton measurements. During this period between the F and G rings the CAPS IMS was in a mode of reduced post-acceleration voltage at ±6 kV instead of the usual ±14.6 kV. All previous work for this region had not considered the TOF data. The new proton analysis was enabled by minimal scattering of 6 kV protons within the instrument's ultrathin carbon foils (CF), when compared to the larger scattering of the heavier ions such as for O⁺ and O₂⁺. In addition, we must deal with the background noise from penetrating radiation. We use a 3D Monte Carlo SIMION model of the CAPS IMS which includes the effects of energy straggling and scattering as the ions pass through the instrument's CFs. We also include the effects of ions scattered by the CFs which then strike the rings of the TOF Linear Electric Field (LEF) stack after which secondary electrons can be emitted which are then directed by the instrument's LEF electric fields to the CAPS IMS straight through ST microchannel plate detector. This will then allow us to remove the contamination of the heavy ions upon the proton energy spectra and allow us to determine the density, temperature and spacecraft potential of the protons; for this analysis we assume full corotation of the protons which are deep within Saturn's magnetosphere.