Electron Acceleration and Zebra Stripe Formation in Saturn's Radiation Belts

Abstract

This study uses the Versatile Electron Radiation Belt code to model Saturn's radiation belt environment, investigating electron acceleration, loss, and transport mechanisms. The simulations consider various physical processes, including convection particularly driven by a Volland-Stern (VS) electric field, radial diffusion, collisional energy loss, and local wave-particle diffusion driven by chorus and hiss waves. Starting from initial conditions derived from Cassini observations, our simulations successfully reproduce the characteristic “zebra stripes” pattern in spectrograms of Saturn's radiation belts. Our results suggest that radial diffusion and neutral-particle interactions have negligible effects on zebra stripe formation. However, the presence of a persistent VS electric field results in significant electron acceleration above the Corotation Drift Resonance energies in the MeV energy range, producing flux levels exceeding typical observations. Additional local wave-particle diffusion further enhances electron acceleration in this energy range. When the VS electric field pulse is treated as transient instead of constant to imitate dynamic conditions, the overestimation of MeV electron flux is reduced near $L\sim 5$ but remains elevated and further enhanced near $L\sim 8$. Despite these differences, the simulations underscore the critical role of the VS electric field and local diffusion in controlling electron acceleration and transport. Our results highlight the necessity of understanding the interplay between global electric fields and localized diffusion processes in shaping electron dynamics within Saturn's radiation belts.