Arc root dynamics in high power plasma torches — Evidence of chaotic behavior

Abstract

Although plasma torches have been commercially available for about 50 years, areas such as plasma gun design, process efficiency, reproducibility, plasma stability, torch lives etc. have remained mostly unattended. Recent torch developments have been focusing on the basic understanding of the plasma column and its dynamics inside the plasma torch, the interaction of plasma jet and the powders, the interaction of the plasma jet with surroundings and the impingement of the jet on the substrate. Two of the major causes of erratic and poor performance of a variety of thermal plasma processes are currently identified as the fluctuations arising out of the arc root movement on the electrodes inside the plasma torch and the fluid dynamic instabilities arising out of entrainment of the air into the plasma jet. This paper reviews the current state of understanding of these fluctuations as well as the dynamics of arc root movement in plasma torches. The work done at the author's laboratory on studying the fluctuations in arc voltage, arc current, acoustic emissions and optical emissions are also presented. These fluctuations are observed to be chaotic and interrelated. Real time monitoring and controlling the arc instabilities through chaos characterization parameters can greatly contribute to the understanding of electrode erosion as well as improvement of plasma torch lifetime.

Decomposition of Naphthalene by dc Gliding Arc Gas Discharge

“…Arc root is arc attachment on the electrode, which is also the joint of arc column and electrode. 34 The highest arc voltage (the lowest arc current) corresponds to the breakdown voltage (current) of the starting point. The arc voltage variation behavior is contrary to that of arc current.…”

Resonant Excitation of Boundary Layer Instability of DC Arc Plasma Jet by Current Modulation

“…Instabilities of a shear layer on the boundary between high velocity plasma jet and steady cold gas, which are produced due to high velocity and density gradients in the shear layer, are sources of jet instability with characteristic frequency controlled by plasma flow velocity, density and jet diameter. The arc attachment fluctuations and shear layer instability were recognized as main sources of plasma jet instability in [12,13]. Possibility of control of jet fluctuations by applied external magnetic field was studied in [14].…”

“…The jet instability connected with the arc attachment movement is considered as main component of jet oscillations by many authors [1][2][3][4][5]13]. The second frequently recognized instability is related to the gas dynamic phenomena in the shear layer of the jet.…”

Dynamic behaviour of dc double anode plasma torch at atmospheric pressure

“…Different arc fluctuation modes have been observed in relation to the thickness of the cold boundary layer between the arc column and the anode wall: 'restrike mode' with a sawtooth shape profile and high voltage fluctuation, 'takeover mode' with a more or less sinusoidal voltage waveform and relative small voltage fluctuation and 'steady mode' with very low mean voltage and weak fluctuation due to the balance between the drag force of the plasma gas and the electromagnetic forces acting on the arc attachment. Recent works published by Maheu et al [10] and Das [11] have been devoted to the investigation of chaotic behaviour in middle and high power plasma torch. They used specific tools developed in the frame of nonlinear system theory as phase space construction to study and control the arc dynamics.…”