[P-EM16] Space Plasma Physics: Theory and Simulation

[PEM16-03] Simulation study of the harmonic structure of lower hybrid wave due to energetic-ion injection under strong magnetic field

*Tsubasa Kotani¹, Mieko Toida², Toseo Moritaka², Satoshi Taguchi¹ (1.Graduate School of Science, Kyoto University, 2.National Institute for Fusion Science)

Keywords:harmonic lower hybrid wave, energetic-ion cyclotron wave, energetic-ion injection

Recently, it is reported that the harmonic structure of lower hybrid wave (referred to as harmonic LHW) is observed for the first time in the Earth’s magnetosphere. Here, the harmonic LHWs are characterized by their frequencies with ω = nω_LH where n is an integer and ω_LH is the lower hybrid resonance frequency. Although these harmonic LHWs are occasionally reported by some simulation studies, their excitation mechanism and influence on the surrounding plasma environment are not fully understood.
We investigate the excitation and non-linear development of the harmonic LHWs driven by ring-like energetic ions using one-dimensional, electromagnetic particle-in-cell simulations. To focus on the long-term evolution of the harmonic LHWs, we adopt an energetic-ion injection model in the simulations where the energetic ions are gradually injected into a plasma.
Our simulation results under strong magnetic field (ω_pe/Ω_ce = 0.25) show that the harmonic LHWs are excited by the non-linear interactions between the firstly excited LHWs with ω = nω_LH and the harmonics of energetic-ion cyclotron waves (ICWs) with frequencies near ω = nω_LH These results are also confirmed by bicoherence analysis which is widely used to diagnose the non-linear wave-wave coupling.