FLUCTUATIONS IN ATMOSPHERIC PRESSURE ARC PLASMA DEVICES: A THEORETICAL INVESTIGATION SUPPORTED WITH EXPERIMENTS

摘要

Fluctuations in atmospheric pressure arc plasma devices play important role in plasma processing applications. A number of experimental investigations are reported in literature to characterize dynamic behavior of such systems. Recently, experimental works by the authors established existence of chaotic behavior in such systems. Investigation, presented in the paper, addresses possible theoretical explanation of the behavior observed experimentally. Starting from the basic governing equations, a third order nonlinear amplitude equation is obtained through systematic development for dynamic evolution of such systems. Coefficients of this equation depend on thermo-physical properties of the system that in tern depend on plasma temperature, arc current and flow rate of plasma gas. System has been found to follow period doubling route to chaos under change in value of control parameter in agreement with that observed experimentally. For higher value of control parameter, system is found to exhibit catastrophic behavior in terms of sudden extinction of arc. A number of interesting facts about the dynamics are obtained through study of coefficients that matches with experimental observations. The developed theory for fluctuation is fairly general to explain dynamic behavior of atmospheric pressure arc plasma devices. Outcome of the theory has been compared with reported experiments performed by the authors in terms of time series, power spectra, Lyapunov exponents, fractal dimension, phase portrait and response under variation in control parameters. Nice match is observed between experiment and theory in all cases. The theory has also been applied to explain observed behavior in most of the important experiments on fluctuation reported in literature performed by various experimentalists. The theory reproduces observed behavior to a reasonably good extent in all the cases. Details of these results are reviewed in this paper. Possible impacts of the obtained results are also discussed.