Electron diffusion in self-consistent numerical experiments due to whistler-mode wave-particle interactions
Abstract
The diffusion of electrons in energy and pitch angle space by whistler mode waves is a cornerstone of our current theoretical framework of acceleration and loss in Earth's Outer Radiation Belt. The quasilinear theory of wave-particle interactions provides us with a tractable method to estimate the amount of diffusion that occurs for a range of wave and ambient plasma conditions. However, the whistler mode manifests in different ways throughout the outer belt: naturally generated chorus and hiss waves, and large amplitude nonlinear wave packets; artificially generated transmitter waves; and lightning generated whistler waves. It is likely that, formally speaking, the quasilinear theory is not applicable in all of these cases. In order to test the theory, we model the interactions between driven whistler-mode waves and ambient background plasma. Specifically, we propagate incoherent, broadband whistler-mode waves through conditions characteristic of equatorial magnetic latitudes in the plasma trough. We explore whether quasilinear diffusion is a reasonable description for different wave amplitudes. Using particle data directly extracted from the particle-in-cell simulation, we find that diffusive response of the plasma due to whistler-mode wave particle interactions is a strong function of phase-space. The mathematical description implicit in the underlying quasilinear theory, i.e. Einstein/classical diffusion such that variance(X)∝ (Δ t)a (with a=1 and for X either energy or pitch angle), is not borne out for all energies and pitch angles. We observe different regimes in phase space for which `super-diffusion' (a > 1), `sub-diffusion' (a
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..21..349A