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Progress in Plasma Processing of Materials, 1999

ISBN Print: 1-56700-126-2



Conventional plasma torch designs lead to a circular cross-section of the emanating plasma jet. Consequently in surface treatment applications the plasma jet hits the substrate within a limited circular working area. Large scale work-pieces therefore have to be scanned resulting in a time-consuming procedure.
The innovative plasma torch system LARGE is characterized by the arrangement of the anode and the cathode opposite to each other on a common axis with a variable separation. The central body of the torch between the electrodes is divided into several electrically insulated cascade plates, each with a hole to house the arc. The plasma gas is injected perpendicular to the torch axis through an additional hole in each plate. Passing through the arc, the gas is transferred to the plasma state and leaves the torch laterally through a slit as a sheet-shaped plasma jet. Particularly in the case of high gas flows (depending on the plasma gas composition and the arc current), the arc tends to be considerably curved due to viscous forces. This bending can be avoided by a Lorentz force counteracting these viscous forces and resulting from the interaction of the arc current with a superimposed magnetic field generated by permanent magnets.
Shrouding the electrodes with an inert gas and feeding reactive gas mixtures as main plasma gas allow the torch to be used for plasma chemical reactions, too.
The plasma torch LARGE is investigated by electrical and magnetic diagnostics. A numerical simulation of the temperature and velocity fields in a cross-section of the arc chamber is carried out for a better understanding of the experimental results.
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