Numerical Analysis on Electric Field Antennas in Space Plasma Environment via Electromagnetic Particle-In-Cell Simulation

For the sophisticated use of electric field antennas for electric field measurements or some active experiments in future magnetospheric missions, we need the precise knowledge of the antenna behavior in space plasma environment. For example, antenna characteristics such as impedance and effective length are essential parameters for determining transfer functions used in the plasma wave data calibration. For the investigation of such antenna behaviors, inhomogeneous plasma environment resulting from plasma-antenna interactions should be taken into consideration in the analyses. However, the analysis of the antenna immersed in space plasma is generally complex because the plasma is a dispersive and anisotropic medium, and thus it is too difficult to include the effects of the inhomogeneous plasma distribution near the spacecraft in antenna analyses using analytic approaches. To conquer the difficulties, we investigated the characteristics of electric field antennas by making the most use of the electromagnetic Particle-In-Cell (EM-PIC) simulations. The PIC simulation enables us to include the kinetic effects of antenna-plasma interactions in the antenna analysis in a self-consistent manner. The present EM-PIC tool is capable of simulating both transmitting and receiving antenna behaviors. In the receiving antenna simulation, we set up external waves in a simulation region and receive them with the antenna placed in the simulation region. By using this method, we evaluated the effective length of antennas onboard scientific spacecrafts. We have also started the investigation of the behavior of antennas that transmit waves with large amplitude. Such high-power antenna behavior will be important for some experiments as the control of high- energy particle flux by wave emissions from the antenna in Earth's radiation belts. We will report the present status of the EM-PIC simulation tool and the preliminary results obtained in the investigations described above.