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1191 |
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Fluctuations in one-cathode plasma torches: characterization and modeling |
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Jose-Luis Marques* / Institute for Plasma Technology and Mathematics,
University of the Federal Armed Forces Munich, Germany Mathias Fuchs / Institute for Plasma Technology and Mathematics, University of the Federal Armed Forces Munich, Germany Sebastian Lange/ Institute for Plasma Technology and Mathematics, University of the Federal Armed Forces Munich, Germany Jochen Schein/ Institute for Plasma Technology and Mathematics, University of the Federal Armed Forces Munich, Germany |
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An increasing erosion in the anode wall of an one-cathode F4 torch changes the fluctuation pattern of the plasma jet. Trajectories and temperature history of particles injected into the plasma become accordingly modified. In this work such fluctuations are characterised through spectral analysis of the torch voltage as well as of the light intensity of the jet outside the torch. Instead of considering the evolution of the main peaks in the frequency spectrum for both voltage and optical signals, the change with wear of the spectrum?s high frequency fraction is focused on. The evolution of the noise fractal dimension in this high frequency range displays a reliable correlation with the erosion of the anode wall. This is further confirmed by the developing of a simple stochastic model for the motion of the arc root along the anode wall. This model yields, depending on the gradual suppression in the freedom of the arc root jumps, a fractal dimension and an evolution just within the range observed in the measurements. Additionally, the separated tracking of the fluctuations at different locations outside the torch enables the separation of those fluctuations specifically produced by the turbulent entrainment of cold air into the plasma jet. |