Electron energy diffusion and advection due to non-linear electron-chorus wave interactions

Abstract

Non-linear plasma waves effects such as phase bunching and phase trapping can cause drastic changes (tens keVs) in the energies of electrons in the magnetosphere at the timescale of a few seconds. Previous studies of non-linear wave effects mainly focused on the energy changes of an electron passing through a plasma wave region, thus covering only a fraction of the electron's single-trip trajectory between its two mirror points. In this study, we use a test-particle method to study the cumulative non-linear wave effects over multiple electron bounce periods. From our simulation results and analyses, we find that non-linear wave-particle interactions are rather common with the presence of chorus waves. The non-linear wave effects take the form of energy advection, which can accelerate electrons rather efficiently. However, energy advection is often accompanied by electron pitch angle advection, causing electron pitch angles to decrease and constraining electron energy advection. The test particle approach we present here can be used to estimate nonlinear transport coefficients, which need to be incorporated into global radiation belt models.