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

The gyroresonant interaction between electromagnetic ion cyclotron (EMIC) waves and energetic particles was studied in a multi-ion (H+, He+, and O+) plasma. The minimum resonant energy Emin, resonant wave frequency ω, and pitch angle diffusion coefficient Dαα were calculated at the center location of the symmetrical ring current: r ∼ 3.5RE with RE the Earth's radius. Emin is found to decrease rapidly from 10 MeV to a few keV with the increase in Ω in three bands: H+-band, He+-band and O+-band. Moreover, EMIC waves have substantial potential to scatter energetic (∼100 keV) ions (mainly H+ and He+) into the loss cone and yield precipitation loss, suggesting that wave-particle interactions contribute to ring current decay. (astrophysics and space plasma)