Cassini Langmuir probe measurements in the inner magnetosphere of Saturn

In the inner magnetosphere of Saturn, the plasma density and drift velocity are high enough, and the photoelectron current low enough, for a Langmuir probe to produce useful data on ion parameters. Plasma density and velocity are found by analyzing the current due to collected ions and emitted photoelectrons for a negative probe potential. In order to correctly analyze the data, the current caused by photoelectrons emitted from the probe must be known. For a spherical probe at negative bias this should be a constant current, but for Cassini's probe it varies with attitude. A likely cause of this is a leakage current from the stub to the probe. The plasma drift velocities derived from Langmuir probe measurements did not agree with those found by the Cassini plasma spectrometer in the inner magnetosphere, but did so elsewhere. A possible solution to this is a two-component plasma where the components have different drift velocities.