ADVANCED THOMSON SCATTERING DIAGNOSTICS FOR VARIOUS APPLICATIONS

Controlled nuclear fusion has been pursued as an ideal form of renewable energy for decades and the study of fusion plasma is fueling an increased demand for diagnostic capability. Furthermore, with the increasing applications of plasma in industry and medicine, it has become essential to characterize plasma dynamics and properties. Laser Thomson scattering diagnostics are considered to be the most reliable plasma diagnostic approaches for measuring electron temperature and electron density, the two most important parameters of a plasma. Four advanced Thomson scattering systems are discussed in this work to respectively address four different limitations or difficulties commonly encountered in conventional Thomson scattering based plasma diagnostic scenarios.

The background of this study is discussed in Chapter One. Chapter Two discusses the solution for lifting the limitation of spatial resolution of Thomson scattering diagnostics. A multi-point Thomson scattering system has been implemented for an electrothermal arc source to test its diagnostic capability. A high-speed Thomson scattering system is demonstrated in Chapter Three as a solution to the low temporal resolution in the conventional setup. This chapter presents the development of a high-repetition-rate Thomson scattering system to greatly increase the temporal resolution of measurements while maintaining a high rate of data acquisition. Chapter Four identifies a challenge in low-temperature plasma, especially in a weakly ionized gas discharge, that the probing laser of a Thomson scattering system could also induce rotational Raman scattering. A new approach presented in this chapter bypasses the necessity of making the estimation of gas temperature and seek to resolve this problem directly with a forward scattering approach. Chapter Five demonstrates a preliminary study on a compressed sensing-based enhanced data acquisition technique for future planar laser-based 2D Thomson scattering diagnostic. The work presented in this chapter demonstrates a compressed single-shot hyperspectral imaging system. And lastly, Chapter Six summarizes all works in the four tasks and discusses unaddressed problems, potential upgrades and future works.