Direct Radiation Resistance Measurement on a Loop Dipole Antenna from Excitation of Whistler Waves*

High energy electrons from either solar wind or from human activity may become trapped inside the Van Allen radiation belts or create an artificial radiation belt that can persist for long periods of time. Spacecraft flying through these belts may be susceptible to damage from these trapped electrons. Whistler waves are known to precipitate electrons into the atmosphere, so a proposed solution is using spacecraft to carry compact electron beams or antennas to remediate these trapped electrons. Results of a laboratory plasma experiment investigating the efficiency of exciting whistler waves by loop antenna are presented here. For the first time, the complex impedance on a loop antenna has been directly measured by measuring the voltage and current directly on the antenna loop. A significant decrease in the real part of the impedance is measured as the plasma density is decreased. Indicating a successful measurement of the radiation resistance, because as the density goes to zero, the whistler wave can no longer be excited, and coupling of the long wavelength light wave is extremely poor. Characterization of the loop’s complex impedance will help further understand the coupling efficiency for whistler waves in a magnetized plasma and allow us to test theories that have long waited on the shelf. (I.G Kondrat’ev et al, Radiation of whistler waves in magnetoactive plasma, 1992). The results from this experiment are pertinent to active space-based experiments on artificial whistler wave excitation because the results of the loop will be compared to that of an electric dipole in our future work to help determine the more efficient radiator of the purposes of radiation belt remediation.