The plasma sheet is a region of Earth's magnetosphere that lies within the magnetotail. Reconnection of magnetic field lines in the magnetotail compresses plasma, forming the plasma sheet. Particle energies in the plasma sheet increase through compression as the field lines approach Earth. The energetic particles begin to drift around Earth (ions to the west and electrons to the east), forming the outer radiation belt and extending the plasma sheet to the dayside magnetosphere. Some of the particles that cause auroras come from the plasma sheet. Auroral particles originating in the plasma sheet generally have energies in the 1 to 10 keV range, but can sometimes have energies as high as 100 keV.
Image courtesy the COMET and HAO programs at UCAR/NCAR.