Plasma Diagnostics Using Computed Tomography Method

Abstract

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.Index Terms-Equilibrium and non-equilibrium plasma sources, plasma diagnostics, plasma tomography, regularization method.

Bayesian Approach with Entropy Prior for Open Systems

“…Another form of prior, based on the entropy principle, was suggested by Jaynes [7][8][9]. Maximum-entropy (ME) approach has been successfully applied in the fields of X-ray-, radio-and gamma-astronomy, plasma tomography [10][11][12][13][14], but less in medicine tomography. Applied to radio-astronomical data, the maximum entropy algorithm reveals details not seen by conventional analysis, but which are known to exist.…”

Dielectric barrier discharge in air with a controllable spatial distribution—a tomographic investigation

“…In cases where the number of viewing angles is limited, by for example the windows of a vessel, or where a sufficiently high SNR cannot be obtained, specialized reconstruction methods using regularization theory are generally applied. Examples of such methods include the maximum entropy method [26][27][28][29] and the recently published method based on the minimization of a Mumford-Shah type functional [30]. In the present case however, operation of the discharge in open air allows in principle an arbitrary number of viewing angles and a sufficiently high SNR in the individual measurements is expected to successfully use FBP for reconstruction.…”

CO<inf>2</inf> dissociation using the versatile atmospheric dielectric barrier discharge experiment (VADER)

“…It is best to take measurements where this is not an issue, however it is often unavoidable. The solution often requires analytical reconstruction of the profile from an array of line integrated measurements, the most common methods include Abel inversion and tomography[104,113,[119][120][121]. A DBD consists of many very narrow streamers which have large gradients in temperature and density immediately outside of the discharge center.…”