Gyroresonance Between Electromagnetic Ion Cyclotron Waves and Particles in a Multi-ion Plasma

<正> The gyroresonant interaction between electromagnetic ion cyclotron （EMIC） wavesand energetic particles was studied in a multi-ion （H+, He+, and O+） plasma. The minimumresonant energy Emin, resonant wave frequency ω, and pitch angle diffusion coefficient Dαα werecalculated at the center location of the symmetrical ring current: r 3.5RE with RE the Earth'sradius. Emin is found to decrease rapidly from 10 MeV to a few keV with the increase in ω in threebands: H+-band, He+-band and O+-band. Moreover, EMIC waves have substantial potential toscatter energetic （～100 keV） ions （mainly H+ and He+） into the loss cone and yield precipitationloss, suggesting that wave-particle interactions contribute to ring current decay.