The Earth's outer radiation belt is a dynamic and spatially extended radiation environment within the Earth's inner magnetosphere, composed of energetic plasma that is trapped by the Geomagnetic field. Whilst the lifetime of some individual energetic particles can be long (~years), orders of magnitude changes in the particle flux can occur on much shorter timescales (~hours). Whilst we know that the radiation belt environment is ultimately driven by the solar wind and the pre-existing state of the magnetosphere, it is very challenging to accurately predict, or model, fluxes within the radiation belt; a pressing concern given the hundreds of satellites that orbit within this hazardous environment.

Decades of research into particle dynamics within the belt have revealed the importance of wave-particle interactions for both bulk (radial) and 'local' (energy and pitch angle) diffusion. Most physics-based computer models of particle dynamics in the radiation belts rely upon a specific version of the 'quasilinear diffusion theory', that is used to aggregate the effects of these interactions. This approach is founded upon a number of physical assumptions that are now known not to always hold in the radiation belt. By processing data from novel boundary-value-problem particle-in-cell numerical experiments (using the Warwick EPOCH code!), we try to test the applicability of the quasilinear theory.