Particle-in-Cell Simulations of Nonlinear Plasma Sheath Effects on Impedance of VLF Antenna Operating in the Magnetosphere

Abstract

A powerful coronal mass ejection or a high-altitude nuclear explosion (HANE) can produce an artificial radiation belt containing high-energy electrons (~1MeV) in the earth’s upper atmosphere that would populate its magnetosphere. Some of these high-energy electrons become trapped along the Earth’s magnetic field lines and would severely damage or destroy nearly all lower-earth orbit (LEO) satellites in just a few days. Over the years, it has been of much interest to devise a scheme that remediates these MeV electrons from the magnetosphere and reduces the amount of damage caused by them. A proposed technique is to use a space-borne high-voltage dipole antenna to inject very low frequency (VLF) whistler waves (3-30kHz) along the earth’s magnetic field lines to precipitate the electrons through pitch angle scattering. Because the magnetosphere is composed of plasma, a charged antenna will form a nonlinear plasma sheath around its surface. This sheath changes the input impedance of the antenna, reducing efficiency. This research uses a three-dimensional electrostatic curvilinear particle-in-cell (CPIC) code to simulate the antenna-sheath interaction to calculate the impedance induced by the sheath. We compare the numerical results to an existing analytical developed by Balmain et al. and Song et al. [1] [2] .