Plasma Diagnostics Using Computed Tomography Method

In the last decade, the range of applications of various low-temperature plasma sources has steadily grown. New applications require development of advanced diagnostic methods to control plasma parameters. Computed tomography is a powerful method which can provide much useful information on the plasma structure and its evolution in time. From a mathematical point of view, tomographic reconstruction is an ill-posed problem, which should be solved by using the regularization (in the large sense of the word) method. In this paper, we discuss a "technology" of tomographic study of plasma objects. It has been shown that numerical testing is a necessary component of the tomographic technology of plasma sources, particularly in situations with limited number of views and with ordinary discontinuities or high-gradient source functions. We are focused on a comparative analysis of the tomographic technology in equilibrium and nonequilibrium plasma sources. The analysis has been made using some examples from our practical diagnostics. The analyzed objects were as follows: nonequilibrium plasma of high-frequency low-pressure inductive discharge, equilibrium arc plasma of high-intensity discharge lamp, and methane plasma evolution in plasma-chemical reactor. We have concluded that the tomographic reconstruction in equilibrium plasma sources is the standard technology at present. The tomographic technology of nonequilibrium plasma sources is a developing approach, which has a great potential at making a contribution to understanding the fundamental processes and phenomena going on in the plasma.