High-speed plasma measurements with a plasma impedance probe*

Plasma impedance probes (PIPs) are a type of RF probe that primarily measure electron density.  This work introduces two advancements to existing PIP techniques: a streamlined analytical model for interpreting PIP-monopole measurements and techniques for achieving $geq 1$ MHz time-resolved PIP measurements.  The model's improvements include introducing sheath thickness as a measurement and providing a more accurate method for measuring electron density and damping over a larger range of conditions.  The model is validated by a quasi-static numerical simulation which compares the simulation with measurements, identifies sources of error, and provides probe design criteria for minimizing uncertainty.  The improved time resolution is achieved by introducing higher-frequency hardware, updated analysis algorithms, and a more rigorous approach to RF calibration.  Finally, the new model and high-speed techniques are applied to two datasets: a 4 kHz plasma density oscillation resolved at 100 kHz with densities ranging between 2 x 10¹⁴ to 3 x 10¹⁵ m^-3 and a 150 kHz oscillation resolved at 4 MHz with densities ranging between 4 x 10¹⁴ to 6 x 10¹⁴ m^-3.