From Switching Arcs to Ball Lightning to Curing Cancer!

Previous modelling of switching has been through calculation of reductions in temperature of the arc at "current zero". "Enthalpy density" as a function of temperature is found to be an important property. New calculations now include an account of non-equilibrium electron density as a function of time through current zero and it is found that electron attachment rates, which are very large for SF6, could be a dominant property. Modelling discharges is having other successes, for example in explaining "ball lightning" observations inside of houses and aircraft, which suddenly appear, usually at glass windows. Discharge modelling suggests these observations might be explained by the production of "singlet delta" metastable molecules of oxygen in electrical discharges in air. If metastable densities are sufficient, electrons can be produced from the detachment of negative ions to produce radiation and explain ball lightning. An exciting new development is that plasmas from electric corona in air have been found to reduce the size of cancer tumours. These excited oxygen molecules have also been proposed as having a role in this remarkable interchange between classical electrical engineering and medical science

Spectroscopic investigation of the high-current phase of a pulsed GMAW process

International audienceWhile metal vapours have an important impact on the efficiency of the pulsed gas metal arc welding process, only a few papers are focused on this effect. In this paper, methods based on emission spectroscopy are performed to improve the understanding of the physical phenomena occurring during the high-current pulse. Boltzmann plots applied to iron lines, the Stark broadening of the 696.5 nm argon line and composition calculations assuming local thermodynamic equilibrium are used to determine characteristic parameters of the plasma. It is observed that the central part of the arc is mainly composed of iron. The percentage of iron increases quickly at the beginning of the high-current pulse, and slowly decreases, when the central part broadens. During the high-current phase the temperature profile has a minimum value of around 8000 K at the axis of the arc while the argon envelope of the central part reaches temperatures of approximately 13.000 K. High percentage of iron and high radiation of the plasma at the centre can explain the measured shape of the temperature profile

3D static and time-dependent modelling of a dc transferred arc twin torch system

International audienceThe transferred arc plasma torch device consists of two electrodes generating a plasma arc sustained by means of an electric current flowing through the body of the discharge. Modeling works investigating of transferred electric arc discharges generated between two suspended metallic electrodes, in the so called twin torch configuration, are scarce. The discharge generated by this particular plasma source configuration is characterized by a complex shape and fluid dynamics and needs a 3D description in order to be realistically predicted. The extended discharge length that goes from the tungsten pencil cathode to the flat copper anode without any particular confinement wall and the fluid dynamics and magnetic forces acting on the arc may induce an unsteady behavior. In order to capture the dynamic behavior of a twin torch discharge, a 3D time dependent plasma arc model has been developed using a customized commercial code FLUENT form in both Local Thermodynamic Equilibrium (LTE) and non-LTE. A two temperature (2T) model has been developed taking into account only the thermal non-equilibrium effects in argon plasma. The main differences between LTE and 2T models results concern the increased extension of the horizontal section of the discharge and the predicted reduced (of about 60-80V) voltage drop between the electrodes when using a 2T model