Using Hybrid Simulations to Investigate Nonlinear Processes in Electromagnetic Ion Cyclotron (EMIC) Wave Growth

Geomagnetic storms cause sharp changes in relativistic electron flux throughout the Van Allen Radiation belts. Over the course of a storm, the population of relativistic electrons spikes sharply followed by a fast partial loss and a slower decay down to normal levels. Ultra-low frequency (ULF) wave-particle interactions have been examined as a loss mechanism for relativistic electrons, mainly in relation to pitch angle scattering. EMIC waves are a type of ULF wave that contributes to electron scattering and are of particular interest as a candidate for the fast loss period. Simulations were carried out using a hybrid code, in which ions are considered as kinetic particles while electrons are treated as a massless fluid. We examined the formation of EMIC waves in a uniform plasma in 1- and 2D. Plasma with a temperature anisotropy and the accompanying instability led to the creation of EMIC waves. The results of the calculations were compared to theoretical descriptions of EMIC waves and agreed with previously determined results. Besides the primary mode, an electrostatic wave propagating parallel to the background field was generated in the nonlinear stage. EMIC wave formation in the presence of heavy ions was also investigated with multiple modes observed. Finally, it was found that heating of the background plasma during the wave generation process causes new behavior to emerge. Results showed evidence of nonlinear processes outside what can be described by traditional quasi-linear methods.