In this thesis, a simple model of the stretched magnetic field lines in the nightside magnetotail was created. The nightside magnetosphere model contains four main regions: plasmasphere, plasma sheet, magnetic lobes, and low latitude boundary layers. The plasma sheet is split into three regions based on the shape of the closed field lines present: dipole plasma sheet, transition plasma sheet, and stretched plasma sheet (SPS). The SPS, the focus of this thesis, is split into two regions: disruption zones (DZs) and a central neutral sheet (NS). The shape of the stretched field lines contain four inflection points. The convex curvature regions form the DZs and the central concave curvature region forms the NS. The NS is split into two regions: outer neutral sheet (ONS) and inner neutral sheet (INS). Due to the reversal of the x-component of the magnetic field at the center line of the NS, the protons are magnetized in the ONS and "unmagnetized" in the INS. There are two main current systems in the SPS. The first is a double vortex current system consisting of eastward current in the DZs that closes westward in the NS. The second system is the NS field-aligned current (FAC) system. It is generated in the INS mainly by the earthward convective drift of the electrons while the "unmagnetized" protons have little convective drift and remain tailward of the electrons. This FAC system produces the pre-onset electron auroral arc during the growth phase of the substorm. A simple model of the stretched magnetic field lines was created in order to calculate the current systems present in the SPS. The simple model was based entirely upon the shape of the stretched field lines. It passed two physical tests, divergence of the magnetic field and limits at infinity, so it was used to calculate currents. The total current using Ampere's law and the curvature current was found. Both results agreed with the double vortex current system.

This thesis presents a study of the inner plasma disk of Saturn. The results are derived from measurements by the instruments on board the Cassini spacecraft, mainly the Cassini Langmuir probe (LP), which has been in orbit around Saturn since 2004. One of the great discoveries of the Cassini spacecraft is that the Saturnian moon Enceladus, located at 3.95 Saturn radii (1 RS = 60,268 km), constantly expels water vapor and condensed water from ridges and troughs located in its south polar region. Impact ionization and photoionization of the water molecules, and subsequent transport, creates a plasma disk around the orbit of Enceladus. The plasma disk ion components are mainly hydrogen ions H+ and water group ions W+ (O+, OH+, H2O+, and H3O+). The Cassini LP is used to measure the properties of the plasma. A new method to derive ion density and ion velocity from Langmuir probe measurements has been developed. The estimated LP statistics are used to derive the extension of the plasma disk, which show plasma densities above ~20 cm-3 in between 2.7 and 8.8 RS. The densities also show a very variable plasma disk, varying with one order of magnitude at the inner part of the disk. We show that the density variation could partly be explained by a dayside/nightside asymmetry in both equatorial ion densities and azimuthal ion velocities. The asymmetry is suggested to be due to the particle orbits being shifted towards the Sun that in turn would cause the whole plasma disk to be shifted. We also investigate the ion loss processes of the inner plasma disk and conclude that loss by transport dominates loss by recombination in the entire region. However, loss by recombination is still important in the region closest to Enceladus (~±0.5 RS) where it differs with only a factor of two from ion transport loss.