Scattering mean free path of energetic protons in the Heliosphere

Abstract

The effect of magnetic field fluctuations on charged particle propagation is investigated. Quasi-linear theory is used to deduce the diffusion coefficient of energetic particles from magnetic field data measured by Ulysses at high heliographic latitude. The λQLT scattering mean free path of 1 MeV protons is determined along one complete off-ecliptic orbit of Ulysses. It is shown that the difference between the fluctuations in the high and in the low speed solar wind results smaller λQLT in the polar regions than near the ecliptic. The mean free path increases by the R radial distance from the Sun, which can be approximated by the power function λQLT ∼ R1.3.