Scattering Loss of Energetic Protons Due To Resonant Interactions With Ion Cyclotron Waves in Saturn's Magnetosphere

Abstract Ion cyclotron waves are frequently observed in Saturn's inner magnetosphere and play an important role in the dynamics of radiation belt electrons. Based on an empirical model of ion cyclotron waves, in this study we investigate the resonant interactions between ion cyclotron waves and energetic protons in Saturn's magnetosphere. By calculating the quasi‐linear bounce‐averaged diffusion coefficients of protons at L = 4–6, we find that ion cyclotron waves can result in efficient pitch angle scattering of <1 MeV protons, with the scattering efficiency significantly enhancing as the L ‐shell increases. At L ≥ 5, the pitch angle diffusion coefficients of 10–100 keV protons at equatorial pitch angles near the bounce loss cone can exceed the strong diffusion limit. Our simulations based on the Fokker‐Planck diffusion equation show that ion cyclotron waves can lead to efficient scattering loss of energetic protons. The corresponding loss timescale ranges from a few to tens of hours, depending strongly on proton energy and L ‐shell. Our results demonstrate the crucial role of ion cyclotron waves in the energetic proton dynamics in Saturn's magnetosphere.