Plasma Impedance Tomography: A Noninvasive Plasma Imaging Diagnostic

Plasma impedance probes measuring the self-impedance of the antenna-plasma system have been shown to provide accurate measurements of electron plasma density for space and laboratory plasmas. Plasma impedance probes measuring the mutual-impedance between two antennas and a plasma dielectric have been successfully flown on sounding rockets and satellites to measure electron flows. At the US Naval Research Laboratory, we have recently developed a noninvasive method for generating real-time images of plasma density and magnetic field. The method consists of measurements of the complex self- and mutual-impedance between elements of an antenna array. The impedance spectra are collected after a short pulse has been applied to each element in sequence. These spectra provide path-dependent information about the plasma dielectric that are used to reconstruct images of plasma density and magnetic field. Numerical models have been developed to predict the expected antenna measurements from an arbitrary spatial dielectric map. These forward models are used to approximate the Jacobian of the system, which can be used in single step or iterative reconstruction methods. The goal of this project is to develop a system capable of providing tomographic reconstructions at a rate of approximately 1% of the peak plasma frequency of the system. The forward models, reconstruction algorithm, and antenna array construction will be presented as well as initial air and plasma experimental results.