THE FAST AURORAL SNAPSHOT (FAST) MISSION

The FAST satellite mission investigates plasma processes occurring in the low altitude auroral acceleration region, where magnetic field-ali gned currents couple global magnetospheric current systems to the high latitude ionosphere. In the transition region between the hot tenuous magnetospheric plasma and the cold, dense ionosphere, these currents give rise to parallel electric fields, particle beams, plasma heating, and a host of wave-particle interactions. FAST instruments provide ob servations of plasma particles and fields in this region, with excelle nt temporal and spatial resolution combined with high quantitative acc uracy. The spacecraft data system performs onboard evaluation of the m easurements to select data ''snapshots'' that are stored for later tra nsmission to the ground. New measurements from FAST show that upward a nd downward current regions in the auroral zone have complementary fie ld and particle features defined by upward and downward directed paral lel electric field structures and corresponding electron and ion beams . Direct measurements of wave particle interactions have led to severa l discoveries, including Debye-scale electric solitary waves associate d with the acceleration of upgoing electron beams and ion heating, and the identification of electrons modulated by ion cyclotron waves as t he source of flickering aurora. Detailed quantitative measurements of plasma density, plasma waves, and electron distributions associated wi th auroral kilometric radiation source regions yield a consistent expl anation for AKR wave generation.