Near-field characteristics of electric dipole antennas in the inner magnetosphere

Electric dipole antennas are commonly used in space plasmas with applications that range from radio frequency probing of the magnetosphere to plasma diagnostics. With the recent interest in the in-situ injection of ELF/VLF waves for the study of magnetospheric wave-particle interactions, the characterization of the antenna-plasma coupling behavior in this regime is of primary importance. The coupling considered in this dissertation occurs in an operating environment that corresponds to magnetospheric conditions found between L=2 and L=3 in the geomagnetic equatorial plane.; The near field of the antenna consists of a plasma sheath which directly affects the terminal impedance properties. Inside the sheath region, the plasma dynamics are highly nonlinear and must be solved numerically. In order to optimally inject VLF waves and thereby maximize the antenna-plasma coupling response, it is necessary to determine the characteristics of electric dipole antennas operating within this region of space. This dissertation addresses the efficacy of using electric dipole antennas as in-situ wave injection instruments and focuses on the near-field coupling of these antennas to the environment in which they are immersed.; A two-tiered hydrodynamic approach has been developed to solve for the plasma dynamics in the region surrounding the antenna. First, a three-dimensional full wave solution of Maxwell's equations is implemented to simulate the current distribution and input impedance of an electric dipole antenna operating in a cold magnetoplasma at VLF. It is shown that the current distribution for antennas with length <100 m is approximately triangular for magnetospheric conditions considered herein. Calculated variations of input impedance as a function of drive frequency are presented for two case studies and compared with predictions of existing analytical work.; This model is then extended to include finite temperature effects allowing for the determination of the sheath characteristics as a function of drive frequency and voltage. The primary assumptions underlying the closure mechanisms for the infinite set of fluid moments are examined through theoretical observations and simulated comparisons of the various truncation schemes. Results from these two models allow for the complete characterization of the near-field properties of electric dipole antennas operating in this highly anisotropic environment.