Investigation of a parametric instability between ELF and VLF modes driven by antennas immersed in a cold, magnetized plasma

Abstract

We have studied the behavior of a VLF, ELF and combined ELF/VLF antenna immersed in a cold, magnetized plasma using a fully kinetic, three dimensional Particle-in-Cell simulation code called Large Scale Plasma (LSP). All the antennas are modeled as magnetic dipoles ($\rho_{ant}=0$) and are assigned a time varying current density within a finite sized current loop. The VLF antenna is driven at 10 Amps with a frequency ($\omega_{VLF}$) greater than the lower hybrid frequency ($\omega_{LH}$), while the ELF antenna is driven at 3 Amps with a frequency ($\omega_{ELF}$) less than $\omega_{LH}$. The combined ELF/VLF antenna (which we call a parametric antenna) includes both antennas driven simultaneously in the same simulation domain. We show that the parametric antenna non-linearly excites electromagnetic (EM) Whistler waves to a greater extent than the VLF antenna alone. We also show that the parametric excitation of EM Whistler waves leads to greater emitted EM power (measured in Watts) compared with a VLF antenna alone.