Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere

Abstract

Voyager low energy charged particle (LECP) ion phase space densities at constant first and second adiabatic invariants have been used to place limits on the rate of radial diffusion of energetic ions (30 keV to 1 MeV) in Saturn's inner magnetosphere. Upper and lower limits to the radial diffusion coefficient, DLL, are deduced from physical requirements on the rates of diffusion and loss. Lower limits to DLL are obtained between L = 4 and L = 9 by requiring the rate of inward diffusion to be just large enough to balance satellite sweeping losses. An approximate upper limit on DLL is obtained by requiring the rate of inward diffusion not to be so large as to predict observable ultraviolet aurora on plasma torus L shells. Both methods make no assumption about the functional form of DLL. An independent upper limit to DLL is obtained by assuming various functional forms for DLL and requiring the inferred loss rate of energetic ions to be less than the strong diffusion rate. If DLL is near the lower limit found in this work, then satellite sweeping accounts for a large fraction of the total ion losses. If DLL is near the upper limit, then ion losses can approach 10% of the strong diffusion rate. In this case, ion losses are dominated by wave‐particle interactions, and sweeping losses are relatively unimportant.