FAST OBSERVATIONS OF PREFERENTIALLY ACCELERATED HE-CYCLOTRON WAVES( IN ASSOCIATION WITH AURORAL ELECTROMAGNETIC ION)

The TEAMS instrument on the FAST satellite has detected events in whic h He+ ions are resonantly accelerated perpendicular to the magnetic fi eld to energies of several keV. The events occur in association with e lectromagnetic ion cyclotron (EMIC) waves and conic distributions of u p to a few hundred eV in H+ and a few keV in O+. Concentrations of Het can be significantly elevated during the events. Our interpretation i s that the He+ ions are accelerated through a cyclotron resonance with the waves. This acceleration is similar to a proposed mechanism for s elective ion acceleration in impulsive solar flares.