Energetic electron populations effect on HF wave propagation in plasmas and modes driven by temperature anisotropy.

The propagation of high-frequency (HF) waves through a magnetized plasma with nonuniform density in the presence of energetic electron populations is studied. A Fully electromagnetic particle-in-cell method is employed to simulate the interaction between a high-power left-hand circularly polarized HF wave and the plasma. The energetic electron population and its anisotropy are modeled using a bi-kappa distribution, while the cold background electrons and ions follow Maxwellian distributions. The presence of energetic electrons influences the plasma by creating non-equilibrium velocity distributions. The energetic electrons are considered to have anisotropy in momentum. Simulation results show that energetic electrons characterized by an excess of perpendicular momentum, induce strong coupling between the HF wave and plasma, exciting strong plasma waves. The interaction of HF wave with the excited plasma modes generates higher-frequency HF components. Furthermore, whistler turbulence-driven by momentum anisotropy-couples efficiently to the HF wave, attenuating the incident HF signal while amplifying the whistler mode. The nonlinear interaction between the whistler wave and excited plasma modes additionally generates higher-frequency whistler emissions. Conversely, energetic electron populations with an excess of parallel momentum have no significant influence on HF radio wave propagation. Energy and spectrum analysis are conducted to reveal the nature of these transverse and longitudinal modes and the mechanisms by which they are generated in the plasma. These results enable optimized wave-based technologies such as space communication systems resilient to anisotropic plasmas, high-precision remote sensing, and advanced plasma diagnostics.