Using Driven Particle-In-Cell Simulations to Examine Electron Diffusion by Whistler-Mode Waves

Electron diffusion in energy and pitch angle space due to wave-particle interactions with whistler-mode waves is an important component of radiation belt modelling. Whistler-mode waves manifest in a number of different forms, each with different spectral forms and wave amplitudes: chorus, hiss, transmitter and lightning-generated whistler. Electron diffusion coefficients are typically derived for each of these forms using quasilinear theory, and then implemented into numerical diffusion codes. It is expected that the quasilinear approach will have limited success in particular circumstances, and this ultimately motivates our investigation. We report on novel numerical experiments that are somewhat analogous to an active experiment in space, and offer the chance to critically examine the efficacy of predictions by quasilinear theory for a given wave mode and ambient background plasma condition. The approach is to utilize quasi-static boundary-value-problem kinetic numerical experiments, for which whistler-mode waves are excited by using perturbative methods. For different background plasma conditions and wave excitations, diffusion coefficients and other characteristics are directly extracted from particles within the domain, and compared to predictions using quasilinear theory.