A determination of the L dependence of the radial diffusion coefficient for protons in Jupiter's inner magnetosphere

The technique proposed by Thomsen et al. (1977) to determine the radial diffusion coefficient in Jupiter's inner magnetosphere from observations of energetic particle phase space density profiles across the satellite orbits is extended to permit the unique identification of the parameters D₀ and n, where the diffusion coefficient is assumed to be of the form D = D₀Lⁿ. The derived value of D₀ depends directly on assumptions regarding the nature and the efficiency of the loss mechanism operating on the particles. The value of n, however, depends only on the assumed width of the loss region, and even that dependence is not strong. Application of the extended technique to University of Iowa Pioneer 11 proton (0.61 < E_p < 3.41 MeV) data leads to the values n ≃ 0 and D(6) ≃ 3 × 10^-8R_J² s^-1 when satellite sweepup losses are assumed to be the only loss operating on the protons. When strong pitch angle scattering losses are also assumed to be operating near Io's orbit, as was suggested by Thomsen et al. (1977), the results are n ≃ 2 and D(6) ≃ 6 × 10^-7 R_J² s^-1. For both assumed situations the large values of D(6) and, more importantly, the small values of n are strong evidence that the radial diffusion is driven by ionospheric winds rather than by fluctuations in the planetary magnetic field or convection electric field.