Counter-Streaming Interaction between Fast Magnetosonic Wave and Radiation Belt Electrons

Fast magnetosonic (MS) waves have been suggested to be able to effectively accelerate radiation belt electrons. We present gyro-averaged test-particle simulations to investigate counter-streaming interaction between MS wave and radiation belt electrons. It is found that an MS wave can significantly scatter counter-streaming electrons through a non-resonant process. The corresponding energy diffusion coefficients for counter-streaming interaction are always comparable to those for co-streaming interaction, independent of wave normal angle. The pitch-angle and cross diffusion coefficients of counter-streaming interaction are much smaller than those of co-streaming interaction for small normal angles, while they become comparable for large normal angles. Moreover, the bounce-averaged diffusion coefficients exhibit quite different distribution from those for co-streaming or counter-streaming alone in the pitch-angle-energy space. These results suggest that the non-resonant effect associated with counter-streaming interaction is indispensable for the acceleration processes driven by an MS wave.