부산대학교 도서관

Recent study has demonstrated that electron cyclotron harmonic (ECH) waves can be excited by a low energy electron beam. Such waves propagate at moderately oblique wave normal angles ~70. The potential role of beam-driven ECH waves in affecting electron dynamics in Earth's plasma sheet is not known. Using two-dimensional Darwin particle-in-cell simulations with initial electron distributions that represent typical plasma conditions in the plasma sheet, we explore the excitation and saturation of such beam-driven ECH waves. Both ECH and whistler-mode waves are excited in the simulation and propagate at oblique wave normal angles. Compared with the whistler-mode waves, ECH waves grow much faster and have more intense saturation amplitudes. Cold, stationary electrons are first accelerated by ECH waves through cyclotron resonance and then accelerated in the parallel direction by both the ECH and whistler-mode waves through Landau resonance. Beam electrons, on the other hand, are decelerated in the parallel direction and scattered to larger pitch angles. The relaxation of the electron beam and the continuous heating of the cold electrons contribute to the saturation of ECH waves and suppress the excitation of whistler-mode waves. When the ratio of plasma to electron cyclotron frequency wpe/wce increases, the ECH wave amplitude increases while the whistler-mode wave amplitude decreases. Our work reveals the importance of ECH and whistler-mode waves in reshaping sub-thermal electron distributions and improves our understanding on the potential effects of wave-particle interactions in trapping ionospheric electron outflows and forming anisotropic (field-aligned) electron distributions in the plasma.