Bounce-averaged Pitch-angle Diffusion by Electromagnetic Ion Cyclotron Waves in Multi-ion Plasmas

Abstract

We present a study on the gyroresonant interaction between electromagnetic ion cyclotron waves and ring current particles in multi-ion (H+, He+, and O+) plasmas. We provide a first evaluation of the bounce-averaged pitch angle diffusion coefficient (Dαα) for three typical energies of 50, 100 and 150 keV at L ≈ 3.5, the heart of the symmetrical ring current. We show that in the H+-band and He+-band, (Dαα) can approach ∼ 10−4 s−1 for ion H+, and ∼ 5 × 10−5 s−1 for ion He+; meanwhile, in the O+-band, (Dαα) can reach ∼ 10−5 s−1 for ions He+ and O+. The results above show that the EMIC wave can efficiently produce precipitation loss of energetic (∼ 100 keV) ions (H+, He+ and even O+), and such a wave tends to be a serious candidate responsible for the ring current decay.