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Understanding the properties, origin and dynamics of energetic particles in the solar wind and magnetosphere is crucial for safe unmanned and manned space operations.  Therefore,  energetic particles have attracted attention from the space physics community for decades. However, different regions and energy ranges of energetic particles may have their own unique origin and role for magnetospheric dynamics, which have not been fully explored and deserve to be investigated case by case. For instance, MMS recently observed dispersionless micro-injections in the 30-300 keV electrons accompanied by strong anisotropic ion temperature at the high-latitude magnetospheric boundary layer in the vicinity of the exterior southern cusp.  Due to the different magnetic field geometry, these high-latitude microinjections could have a totally different origin than the typical low-latitude microinjections. Because this region is close to the radiation belts, ionosphere, and magnetosheath, these high-latitude microinjections could be the ~ tens to hundreds of keV seed population of the radiation belts,  as well as leak into the ionosphere or into the magnetosheath. This project will unravel the birth-mechanism of the source population of the Earth's radiation belts.