Two-Color Heterodyne Interferometry for PI3 Line-Averaged Plasma Density Measurements

Abstract

This thesis investigates two-color heterodyne interferometry, which is a technique used for plasma density diagnostics in fusion experiments. Funded through a Mitacs Accelerate internship, this work focused on improving vibration compensation of the existing multi-chord interferometer used at General Fusion for line averaged plasma density measurements on the Plasma Injector 3 system. This thesis starts with a brief history of fusion confinement techniques as well as a review of plasma diagnostic methods, then outlines the theoretical background in plasma physics and optics necessary to understand the two-color, vibration-compensated, heterodyne interferometry being done at General Fusion. Various interferometer configuration upgrades were considered when working on this problem. Limitations of the existing system includes mismatched beam diameters along the probe beam's optical path as well as the single-pass configuration of the interferometer which limited the strength of the interference signal. To address this, various refined optical layouts were designed and tested alongside the existing system. Experimental results from the new optical layouts were then analyzed and compared in performance and spectral characteristics to that of the old system. These results show improved vibration compensation from the system with RMS phase error of 3.01 degrees and phase resolution of 0.3 degrees. This refined optical layout also helped inform the optical design of the interferometer system implemented in General Fusion's plasma compression experiments.