A new model for plasma transport and chemistry at Saturn

Abstract

A model of plasma transport and chemistry is described which calculates the evolution of a plasma population in latitude and radial distance. The integrated quantity NL² is used in the diffusion equation to calculate plasma transport, then the density of each ion species in radial distance‐latitude space is calculated to determine changes in the plasma due to chemistry. This model can use as input arbitrary neutral density and ion source profiles and correctly handles the effects of anisotropies and the ambipolar electric field. This model is applied to the magnetosphere of Saturn, where it is used to fit the density profile of the heavy ions assuming both satellite and ring sources of plasma. Use of an extended source region is found to significantly alter the resulting plasma profile. Water ions cannot fit the observed density profile inside L=6 even with a large ring source. Oxygen ions can fit the density profile throughout the region inside L=12 given a suitable profile of neutral hydrogen; a suitable profile contains up to 5 H cm−3 outside L=4 with the number increasing inside this. Preferred values of K are 1‐3×10−10 Rs²s−1, but any value K less than 10−9 RS²s−1 can be accommodated. The temperature profile is shown to favor models invoking in situ plasma formation and loss as opposed to models where transport is important.