Numerical modeling of linear and non-linear plasma waves due to antennas immersed in a space plasma

To meet the objectives of SF241-0016 SBIR solicitation (Numerical Simulation of VLF Antennas in Space Plasma), Tech-X has assembled a team of experts in computational plasma physics and ionospheric physics with significant experience in analytic modeling, numerical simulation, and algorithmic development to model the next generation of spaceborne VLF antennas. In this proposal, we will discuss novel methods of designing space-based antennas that can efficiently generate electromagnetic whistler waves in earth's space environment. One reason for generating these waves is to remove high-energy electrons, which are known to damage spacecraft, from earth's radiation belts. EM whistler waves can be efficiently excited by spaceborne antennas either directly, or via a parametric beat-wave instability between two linear modes in the VLF and ELF range, and in this proposal we describe methods for modeling the dipole and loop antennas which generate these different wave modes. The linear behavior of these modes, both in near-field and far-field limits, must be well-characterized to ensure efficient mode excitation and (for cases with non-linear wave beating) that the generated modes satisfy the conditions required for parametric instability onset. Numerical simulation tools capable of simultaneously resolving detailed features of the antenna hardware (e.g.~ 5 cm thick, 20 m diameter loop antenna), accurately capturing the physics of plasma sheath formation near antenna surfaces, and characterizing kilometer-scale far-field linear wave modes will be demonstrated. These simulation tools, which are based on finite-difference time-domain (FDTD) methods, exercise novel numerical techniques (variable grid generation, semi-implicit/stenciled time-advance algorithms) and hardware optimization schemes (GPU acceleration) that enable both far-field linear modes and local, near-field physics adjacent to the antenna to be captured by the simulations. Modifications to the linear mode spectrum induced by sheath formation and local power deposition near the antenna will also be considered. In addition, we will carry out non-linear simulations using a hybrid model (with fluid electrons and kinetic ions) to explore and characterize the EM whistler modes which are excited in the near-field as linear modes couple to produce non-linear beat wave modes. Using this hybrid model, we will estimate the role of near-field plasma heating in the sheath on the efficiency of this process.