Plasma Acceleration in the High-latitude Magnetosphere: On the Macro-and Microphysics of the Energetic Electron Microinjections

Magnetic reconnection can create large-scale diamagnetic cavities in the high-latitude magnetosphere where particles can be accelerated to 100s of keV in the reconnection quasi-potential. The acceleration mechanism creates strongly perpendicular pitch angle distributions for ions and electrons, likely contributing to the source for the ion temperature anisotropy in the high-latitude magnetosphere. Recently, 4 MMS spacecraft flew through a dusk-sector southern hemispheric diamagnetic cavity observing strong ULF wave activity, driven by the drift-mirror instability, at the edge of the cavity. The high-energy electrons within these wave field depressions showed counter-streaming pitch angle distributions while ions remained trapped. The ULF waves also contained strong higher frequency plasma wave activity. In this talk we discuss the nature and microphysics of these high-frequency plasma waves observed during energetic electron microinjection events. Furthermore, we discuss the potential importance of these microinjections for contributing to the seed population of the Earth's radiation belts.