Time-Resolved Measurements of Plasma Electron Number Density and Electron-Neutral Collision Frequency Using a Microwave Diagnostic Method

Microwave interferometry is an established non-perturbing plasma diagnostic technique. Compared with other diagnostic techniques, it can be more robust and reliable in experimental applications. This thesis studies a simple and accurate microwave diagnostic method to characterize the electron number density and electron-neutral collision frequency, which are crucial to understanding the behavior and transport coefficients of plasma. This method is based on a modern vector network analyzer and measures the attenuation and phase shift of a microwave signal when propagating through a plasma layer. These measured quantities are related to the real and imaginary parts of the plasma index of refraction, which is described by Appleton’s equation and characterized by plasma parameters, including the electron number density and collision frequency. One can numerically derive these plasma parameters from the measured quantities by using Appleton’s equation. Since the electron number density and collision frequency can be calculated from measured quantities, one need not know the electron energy distribution function, the electron kinetic temperature, or the electron energy-dependent cross section for the collision process.

The experimental measurements focus on the time-averaged and time resolved parameters of commercial fluorescent lamp plasma and the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP^TM). The latter is an atmospheric pressure glow discharge developed at the UT Plasma Sciences Lab. Since the plasma properties should be periodic with the applied plasma driving frequency, 60 Hz for fluorescent lamp plasma and 2-10 KHz for OAUGDP^TM plasma, time-resolved measurements are taken to exhibit the variation of electron number density and collision frequency during one 60 Hz cycle of the fluorescent lamp plasma. This time-resolved measurement is achieved by applying the external trigger feature of the network analyzer.