Impedance measurement and optimization of Ferrite based antennas for launching whistler waves.*

Coupling power from a ferrite antenna in a magnetized plasma depends on the size, number of turns, and geometry of the ferrites. In this implementation we wind 1 to 5 turns on small ferrite cylinders having different aspect ratios. We experimentally investigate a number of different form factors to determine controlling factors for the impedance and radiation resistance. The impedance of the antenna in plasma is measured using a resistor divider network at the tip of the probe, which diminishes the importance of reliance on network parameters such as S₁₁. Parasitic capacitance in and around the tip complicate the interpretation, but can be mitigated by examining the difference in plasma vs. no-plasma measurements. An optimization to match the capabilities of an existing rf driver can then be performed to enable coupling the most power into the radiated wave.