FDTD Simulation Study of Brillouin Scattering Emission Lines Stimulated by High Frequency Radio Waves in the Ionospheric Plasmas

Abstract

A high-power electromagnetic (EM) wave can decay into an ion acoustic wave and a scattered EM wave in a plasma through a process called Stimulated Brillouin Scattering (SBS). A one-dimensional fully electromagnetic Finite-Difference Time-Domain (FDTD) method is used in a magnetized plasma with an increasing density ramp to simulate the propagation of a linearly polarized high-frequency (HF) radio wave traveling through the plasma along magnetic field lines. The study shows that the plasma splits the linearly polarized EM wave into two separate counter-rotating circularly polarized waves: the X-mode and the O-mode waves. The specific cutoff points for each of these circularly polarized waves are illustrated, with the X-mode reflecting at lower frequencies compared to the O-mode. As the radio wave approaches the cutoff frequency, it decays into a scattered high-frequency EM wave and a low-frequency wave. By analyzing the frequency spectrum of the scattered wave and the excited electrostatic low-frequency wave, the electrostatic wave is identified as an ion-acoustic (IA) mode, thus confirming the process as SBS. The growth rate of the excited longitudinal electrostatic wave is studied by calculating the excited longitudinal wave energy. The evolution of energy transfer and conversion from the HF wave to IA wave, as well as electron and ion kinetic energy, is investigated. The results indicate that electron and ion density perturbations experience similar fluctuations.